Sunday, November 28, 2010

Recently at KCUR

Even though I haven't been posting as much of late, I'm still active at KCUR. Two weeks ago Robin and I installed a fix to the HD transmitter to prevent RF interference from the power supply. I'll note that Robin never mentioned noticing any kind of RF interference coming from the HD transmitter, but it's still a good precautionary measure to take.

This fix involved putting a ferrite choke around an internal power cable1. The linked article discusses chokes in depth, but basically the point of a choke is to present a high impedance to RF currents. Any such currents that are generated along the cable will either be reflected up the cable or will be absorbed by the ferrite choke and dissipated as a negligible amount of heat. Also, we attached a grounding strap (a braided strip of wire) to the outside of the crossover pipe (rigid coax - where the generated RF signal comes out). Since the outside of the crossover pipe acts as a shield, I think this means that any stray currents on the outside of the pipe will be shorted to ground and won't get outside the transmitter cabinet.

This whole business took something like 15 - 20 minutes. The rest of the day was spent helping Robin out with various things around the station, including installing a T-1 surge protector in the TOC. Last week I did the same thing at the transmitter.

1 Looking at the manual, the purpose of the cable is "current share", and I'm not sure what that means. If there's the potential for RF interference, I think it must have AC on it.

Monday, October 11, 2010

Setting up a little SMTP server to interface to another

I'd say, "Look, a non-radio post!", but this post is an elaboration of a reply I made to someone on Pubtech, so... :)

By way of background, someone on Pubtech was asking a Nautel rep when their VS Series transmitters would support SMTP servers that require login. I replied that until such a time, you could set up your own little SMTP server and use the server that requires login as a smarthost. Here's how you do it:

Step 1: get yourself a Linux box of some sort. Since this is (presumably) going to live at a transmitter site, and it would sure be nice if you could just "set it and forget it", as it were, I would recommend something like EMAC's Server-in-a-Box (SiB). With the SiB, It's not clear from their website whether or not it an SMTP server included in the Linux distribution it ships with, so contact the manufacturer to make sure. If it doesn't, I'm certain they can install the requisite software.

Step 2: configure the SiB's SMTP server to log in to your other SMTP server. There are a variety of SMTP server software packages out there, and I can't cover them all. I'm going to use Postfix for this example; if you need another example, comment on this post and I'll see what I can do.

This example is based heavily on the example posted here. Whenever you see, you should replace it with the host name of the mail server that requires login. Replace myusername with the username to log in to the SMTP server, and myPassword with the password associated with that username.

Create a text file on your server called "/etc/postfix/password". This file should look like so:

# server username:password myusername:myPassword

Now, execute the following commands (note the '#' is used to indicate a command prompt):

# chown root:root /etc/postfix/password
# chmod 0600 /etc/postfix/password
# postmap hash:/etc/postfix/password

Then append the following lines to /etc/postfix/

relayhost =
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/password
smtp_sasl_security_options =

Finally, restart postfix:

# /etc/init.d/postfix reload

Give the SiB a static IP address (how this is done is outside the scope of this post), connect it to the network, rack it up, and give the Nautel the SiB's IP address for a mail server.

EDIT: The original poster on Pubtech replied that he couldn't have an open SMTP relay floating around. I'm not sure that I'd have my transmitter with a publicly (or semi-publicly) accessible IP, but then again, I'm not sure that I wouldn't. There are benefits and drawbacks to each, but that's a topic for another post. In his situation, I would lock down Postfix to only relay from the Nautel's IP. To do this, add these line to /etc/postfix/

mynetworks =
smtpd_client_restrictions = permit_mynetworks, reject

Substitute with the IP of the Nautel, of course. Reload Postfix again when you've added those lines.

And then

Saturday, October 9, 2010

Trail of Tears Broadcast Dry Run

Through KCUR, I have been retained to engineer KKFI's broadcast of the Trail of Tears discussion panel at the United Minority Media Association's Midwest/Southeast Regional Conference. As the barnraising was the first time I had engineered any live broadcast, I thought it prudent to do a dry run today. Especially since I was using unfamiliar equipment (a TieLine Commander G1).

Earlier in the week, I collected the equipment from KCUR. Today was the first chance I had to actually set up the equipment. I thought I might need a second pair of hands for this, so I asked my friend Aubry to help. To begin with, we went over to KKFI to hook up the studio unit (the TieLine equipment is a pair of codecs, a studio unit and a field unit) in the studio. This was very straightforward - all we had to do was hook up an analog phone line and run it into the board.

We then went over to the Bruce R. Watkins Cultural Center to set up there. This was a bit more complicated as we weren't exactly sure where the event was going to be held. So we set up in the Great Hall, figuring that to be the most likely place (we later found out that we should have set up in their "broadcast room" at the Cultural Center. ah well.) We connected up the loaner mics from KKFI and I got a feel for how loud they were. Then we found an analog phone line and tried dialing in to the studio unit at KKFI. Unfortunately, while the field unit said we were connected, the studio unit said we weren't, and there was no sound on the board at KKFI. So it was pretty clear that we weren't connected. I went back to KKFI to try and diagnose things there (leaving Aubry to watch the equipment) but had no luck.

To test KKFI's lines, I dialed the TieLine test number with the studio unit. I connected successfully at 21.6 kbps and got some cheery music. I then took the studio unit back over to the Cultural Center and was able to connect there at a slightly faster speed. So KKFI's lines and the Cultural Center's lines both appeared to be good, and yet I wasn't able to get the two units to connect. I called the studio unit from my cell phone, and the unit picked up, so it was certainly answering calls. So I'm a little perplexed, but I have a plan for further testing. The next step is to take both units to KKFI and see if the one unit will connect to the other there (KKFI has multiple analog telephone lines).

Friday, October 8, 2010

Watching the KCUR TX

Day 3 of the barnraising will come in due course, but I want to talk about something more recent first.

Recently, Robin took a well-deserved vacation - in fact, he went on vacation at the same time as I was at the barn raising, though he was gone for longer. At any rate, while he was gone (and I was in town) I got to take care of the transmitter. This involved putting my number as the first one in the transmitter remote's call list, getting the password to the remote control, and a set of keys. I also received a spreadsheet of what monitors were connected to the individual channels on the remote (a Burk ARC-16), so that I knew which channels did what.

In the time that Robin was gone, the transmitter did not blow up, and KCUR did not go off the air. Thus I am counting my first time as being the person in charge of the transmitter a success. However, I could have done a fair sight better, I think, and I plan to do better next time. First of all, voltage. A couple of times I got calls from the transmitter saying that the voltage was low. I cleared the alarm, and figured that since the transmitter didn't call me again after I cleared the alarm, the problem was transient and nothing to worry about. In fact, it was not a transient problem, and when Robin got back he had to call KCP&L to get the voltage back to where it should be. Additionally, this low voltage situation was causing the transmitter to operate inefficiently, causing the room to be overly warm. There was also a problem with the HVAC - the air conditioning wasn't blowing cold air. I got calls from the transmitter once or twice warning that the temperature was above the set level, but again, since the transmitter didn't call again after I had cleared the alarm, I figured it was a transient problem. Ultimately, it was an error in my thinking: these "transient" problems were still problems that warranted investigation.

I also went over to the TX last Saturday, while Robin was gone, to try and get VINA, an organization that leases a 92kHz subcarrier from KCUR, back on the air. They had sent a box of equipment to the station for us to install at the transmitter in place of the equipment they had been using. During the week I had been out to the TX to replace the satellite (they get their signal via a Ku band satellite downlink) receiver they were using, but that wasn't enough to get them back on-air, so I went to replace the LNB on the satellite dish located on the roof of the transmitter hut. I got the LNB replaced, and I got some signal on the air, but it wasn't very strong, and it sounded distorted. It wasn't until this past Monday, when Robin came back, that we were able to get VINA on the air properly. I ended up having to rotate the LNB almost 50° from the 0° mark on the bracket, and there was some damaged wiring that needed replaced as well.

So all in all, I'm treating my first time watching the transmitter as a lesson in proper thinking. As Robin says, you do all you can do until the job is done. If you can't do it, there's no shame in calling another engineer to assist. I'll remember that next time.

Barnraising: Day 2

(Posted *way* late. Sorry, I got busy. *g*)

Day 2 of the barnraising began with me trying to find all the web streaming equipment that had been scavenged to do the stream from the Cannonball Room. This did not go very quickly, so the streaming for some of the workshops got started late. The streaming happened, though, so I must count that as a success. :)

By the time I'd finished getting all the streaming going, I'd missed most of the morning workshop session, so I didn't get to finish the tiny transmitter I'd been working on the day before. That's all right, though - I can build my own when I get home. I bet I can even adapt the design to broadcast on ham frequencies - maybe have my own little 70-centimeter or 2-meter transceiver.

I was going to go over to the station and help out there after the morning workshop session. Instead I spent some time checking on the web streaming. When I went in to check on the streaming in the workshop about recruiting volunteers and preventing burnout, I was immediately handed a slip of paper informing me that I was an octogenerian stockbroker who loved to dance. This was a role-playing exercise, you see, where some of us were potential volunteers and some of us were people trying to recruit volunteers. I played along, stayed for a bit of discussion, then wandered off to see what else was going on.

One interesting feature of the barnraising was the interview booth. The idea is that two people go into the booth and one of them interviews the other. The other then returns the favor. A volunteer staffer is also in the booth, and they record the interview, along with a couple of station ID's, for later broadcast. So I and a pretty girl named Meghan went in, and she interviewed me. I talked about why I'd come to the barnraising, and how I was trying to move away from IT and into broadcast engineering, and what got me into radio in the first place (a subject that I should perhaps elaborate upon in another post). I even briefly mentioned my days as Uncle Squishy, the host of the WEFT children's music show. (Uncle Squishy later reappeared as the occasional host of one of my WEFT overnight shows).

What with one thing and another, I didn't get over to the station until after lunch. I helped Sakura from Prometheus set the levels on the board, hung out while a carpenter was drilling holes for cables, and helped design a set of shelves to hold equipment until such time as a rack was obtained for said equipment.

Let me briefly describe the way we set the levels on the board. This may well not be industry standard, but once WGXC goes on the air, they can always adjust them again.

To start with, all the faders on the board were set to the same point. The reason we did that was to try and make sure that two given pieces of equipment would have roughly the same perceived volume when the faders on their respective channels were at the same point. When you've got a radio station, you don't want to have to remember that having the fader, say, halfway up on the CD player is fine, but having the fader halfway up on a microphone is *way* too quiet.

Using a Behringer cable tester, we generated a test signal. This signal could be set at three preset levels (i.e. volume) - one for microphones, one for consumer-grade equipment, and one for professional-grade equipment. For each channel on the board, then, we chose the appropriate level and ran it into the board. We then adjusted the trim pots - which are these tiny potentiometers (i.e. a variable resistor, often used to control volume) that you use to adjust the levels on a particular channel. Remember what I said above about having all the equipment being at the same volume for the same fader position? The trim pots are what you use to make that happen. In the case of the six (there are three physical mic modules, but each module on that board takes an "A" and a "B" input that you can switch between) microphone channels on the board, we only adjusted one pot each, because microphones are mono devices. For everything else, we adjusted the left and right pots separately. We set each channel so that with the fader about a quarter of the way up, the VU meter was near +11.

I left for dinner, and when I came back, I made a couple of XLR cables and helped run wiring in the studio. I really like the way their board does things - it's an Arrakis MARC-15. The neat thing about the MARC-15 is that the A & B inputs on each channel are RJ45. They're not Ethernet, though - it's not an IP console. Instead, the pins on the RJ45 are wired such that you can fit two balanced audio channels and a contact closure relay (a dingus that shorts two electrical wires, often used for start/stop control of attached audio devices) onto one jack. I like this idea. If you do it right - only have the wires going to your connectors be a few inches long, and the rest of the wires be contained in the Cat5 sleeve - it keeps the wiring very clean and compact. I'm on a plane right now, otherwise I'd post a picture.

Once things wrapped up at the studio, I made my way back to St. Mary's Academy and helped clean up, then went back to the Youth Center to sleep.

1 A VU meter (VU for "Volume Unit") is a thing on a console that tells you, effectively, how loud your broadcast is. It's an analog thing with a needle. The ranges vary from meter to meter, I expect, but I think the one on the WGXC board went from -10 to +3. That's probably a logarithmic scale.

Friday, September 24, 2010

Barnraising: Day 1

I got up this morning around 0700, hit the shower, and went to "Debbie's Lil' Restaurant" in Hudson for breakfast with a couple of other barnraising folks. One of them grew up in the Champaign-Urbana area - a place I spent several years - which was pretty cool. He was a WEFTie for several years - another connection we share.

After breakfast I volunteered to help out with the web streaming of the various workshops. There are four web streaming kits, but they don't all have the same hardware. Three of them are using Behringer UB1202 mixers and a PC or Mac laptop to stream to an Icecast (or Live365 in one case) server. One of them is using a Marantz digital recorder where the line out goes to a PC streaming to the Icecast server. Every session was recorded with a single condenser mic.

The barnraising is largely a DIY thing when it comes to equipment. People bring what they have. So it's only to be expected that there will be a serious diversity of equipment. That doesn't make it easy, though. I had to run around to try and find 1/8" to 1/4" headphone adapters that I could plug into the headphone output of the board, for example, as none were supplied. Later, I realized that it was better to start up the media player on each laptop - that way whoever was monitoring could hear the audio as a listener would hear. Of course, it ended up that no-one was monitoring, because there was only me to do it, but it's good practice for tomorrow's and Sunday's sessions.

After I had the web streaming set up, I went to Pete Tridish's workshop on building tiny transmitters. The transmitters were based on the designs of Tetsuo Kogawa. There weren't enough materials to go around, so I worked with a group of two other folks. We got as far as getting the resistors soldered on. :)

After dinner I went over to the Cannonball Factory to hear the spoken word performers. There was a Finnish girl there who read a poem entitled "The Brothers-in-Law". The poem itself I don't remember enough of to comment on. However, she read it first in Swedish (she's a member of the Finnnish minority who are native Swedophones) and I was struck by the almost musical quality of the words.

There were two sets of spoken word performers. I left in the middle of the second set and walked over to the station to see if they needed any help over there. They were wrapping up for the night, so I went into the studio to hang out for a bit. At first I thought I was hearing some weird experimental music, but in fact it was the feed from the Cannonball Factory - the third set was a set of hip-hop performers, and the volume levels were considerably higher than the previous sets. This caused the broadcast (well, webcast) to sound like shit, so I went back and turned down the gain on the streaming PC.

After that, I went back to the crash space and went to sleep.

Thursday, September 23, 2010

Barnraising: Day 0

I got into Hudson about noon and met up with Chuck, a fellow barnraising attendee who was raised in KC, but now lives in San Antonio. Chuck and I waited around a while, and eventually someone from WGXC came and took us from the Albany airport to Hudson. This someone was an engineer, in fact, and he gave me a few salient facts:

WGXC will be transitioning from an LPFM station to a 3.3 kW ERP FM. They have an Energyonics 1.5 kW transmitter and a pair of log-periodic antennas. Not a whole lot of ERP, but it's a start.

At any rate, when I got to Hudson, I got a brief tour of the studio then went over to St. Mary's Academy, where a lot of the workshops are being held. I helped out with a couple of things, including setting up the stage for the speakers, then got assigned to KP duty. ;)

I think that I will not be sleeping out at the farm where I had arranged a couch surf. Instead I will stay in Hudson. I think I'll get more of the experience this way.

Wednesday, September 22, 2010

Off to the barn raising!

That's right, Dear Readers, I'm going to the WGXC barnraising! I'll try and post some from the event itself. I'm really looking forward to it!

Saturday, August 21, 2010


I've decided to branch out and do some art. And not something small. Inspired by a local artist (whose name escapes me) who made angels out of aluminum cans and bits from the junk yard, I've decided to make an angel from found objects and things I have laying around.

The wings are constructed from parts of four shipping pallets. The spine is a wooden post (as Marco d'Eramo says in The Pig and the Skyscraper, we're a nation very fond of wood) that I found at the site of the former DAV Thrift Store on Southwest Blvd. They are attached to the spine by a two-by-four, also from one of the pallets. I'll use a piece of wood that I found in my basement (once the wood dries out, anyway) as an additional wing brace.

For the angel's breast, I'll use the old gas tank from my first motorcycle, Arcadia. I'll add a halo (once I discover the head piece) that is the old rear sprocket off my current motorcycle.

I'm going to have to find a way to make the angel stand up on its own. Perhaps I'll add a simple base; I don't think I want to try making legs.

Anyways, I'll post more about the angel as she takes shape. And of course, more adventures in radio. Stay tuned, true believer!

Sunday, August 8, 2010

Channel 37

So I was reading the latest SBE newsletter and there was an op-ed by the SBE's General Counsel. I'm not going to talk about that op-ed because I don't know enough about the issues he mentions. What I do want to talk about is something mentioned in passing in that op-ed, TV channel 37.

Channel 37 is a channel that "has never been used by any over-the-air television station in Canada or the United States" ( Think about this for a minute. In all the umpteen million TV stations in the U.S. and Canada, nobody has ever used this channel. Why is this?

Turns out that channel 37 - or rather the frequency band from 608 MHz to 614 MHz - is very important to radio astronomy. Since radio astronomy deals with very weak signals - on the order of 10-18 watts - any activity on this channel has the potential of causing significant interference to those sorts of measurements ( It's also used in Very Long Baseline Interferometry (VLBI), another technique used in radio astronomy and a subject I know nothing about. :)

So there's a bit of randomness for you. Reporting from the Channel 37 News Desk, I'm Kit Peters.

Saturday, July 31, 2010

Sending equipment out for repair

Periodically, Robin sends various pieces of equipment out for repair. Each piece has its own particular procedure for getting sent out, but there's something that he does for every piece:

  1. Puts a KCUR sticker in a prominent place on the chassis

  2. Tapes his KCUR business card to the bottom

  3. Attaches a form letter with model number, serial number, and problem description

This helps to make sure that we get the same equipment back that we sent, we get the problem we complained about fixed, and that the problem gets fixed in a fairly timely manner.

Internet at the TX

Robin is thinking about getting wireless 4G out at the TX for Internet access. Clear is offering "business-class" service for $75/month, which is fairly cheap, all things considered. This would allow us to have IP-based remote telemetry of the equipment that supports it (I don't think our main transmitter (BE FM30B) does, but I bet our HD equipment will). It will also allow us to stream RDS (the text that shows up on some radios with song information and the like) from the studio. On the down side, that's more equipment that needs to be examined and protected from a security standpoint. But I can help with that. :)

We would also need to get an external antenna hooked up and run outside the transmitter building, as that building eats microwaves. Perhaps all the RF equipment causes interference as well, but if that were the case, I would expect that interference to be just as great immediately outside the building. Then again, the GPS antenna is outside the building and it works just fine (when it hasn't been struck by lightning, that is).

So, Dear Readers, have any of you in the radio business (are there any of you in the radio business?) done this? If you have, what have your experiences been?

KCUR audio link down

Apologies for the lack of updates lately, Dear Readers. I'll make up for it with a bunch of posts all in a row. :)

Two weeks ago (18 July) our T-1 audio link between the transmitter and the studio went down. Robin got a call from the monitoring hardware at 0345, then switched over to our backup link. Robin called me the following Monday to say he'd had "an eventful weekend", and rather than meeting him at the transmitter, I ought to meet him at the station. When I got there, he was calmly updating the EAS logs. This may strike you, Dear Reader, as odd, so allow me to explain Robin's philosophy of "important" vs. "pressing".

When I first met Robin, he explained that a given engineering issue can be thought of in two dimensions, "important" and "pressing". An "important" issue directly affects the running of the station - in this case, the audio link between the station and the transmitter going down. A "pressing" issue is an issue that needs to be addressed immediately. The audio link falls into this category as well. However, once Robin had switched to the backup link, the issue continued to be important - after all, with the primary link down, the station was running "without a net", if you will - but the backup link would serve well enough through the weekend, so it was no longer pressing.

Anyway, after he was done with the EAS logs, Robin decided to call AT&T and register a trouble ticket as he was pretty sure it was a telco issue. He got an ETA for the AT&T technician of "soon" and we headed out to the TX to meet the tech. When we got there, the tech hadn't arrived yet, so I set about taking the readings as usual. Everything looked normal on the readings except (of course) the T-1, which was showing an alarm.

When the AT&T guy finally got there, he determined that the problem was a bad pair, and set about finding a good one. It's curious to me, Dear Reader, how much trouble two little copper wires can cause. Somebody can break them with a backhoe. Water can (conceivably) get in and corrode the wires and/or cause a short. Or, as the AT&T tech surmised in our case, lightning can strike and fry the wires and the card attached to those wires.

Once the AT&T guy had found a good pair and replaced the T-1 card, we were good to go again. If we'd had a microwave STL, this wouldn't have happened. However, microwave STL's have their own set of potential problems, I'm certain.

Saturday, July 17, 2010

Going to the barnraising!

Thanks to a generous donation, I have managed to cover registration costs for the WGXC barnraising. I'm trying to arrange housing via I still need to cover travel expenses and food while I'm there, so I'm still looking for donations. Locals, I'm also willing to work in exchange for a donation to the cause - just let me know what you need done.

WGXC Barnraising!

I heard about this on pubtech. They're putting up a full-power FM community radio station the last weekend in September. I totally want to go to this, but the registration alone is $100 at minimum (it's a sliding scale type of thing). Still, that's valuable experience, and I've got a couple of months to make arrangements...

Friday, July 9, 2010

Recently at and around KCUR

Sorry that I haven't updated. I've been busy with my Real Job™

Since Monday was a holiday, I went to the transmitter on Tuesday. I took the logs as I have been doing, then Robin and I changed the air filters on all the equipment. Our BE FM703i (HD transmitter) has washable air filters, which is cool. Our BE FM30B (analog FM transmitter) does not have washable air filters, but its air intake is half the size of the air filters Robin buys. When it's time to change the filter, he flips the filter that's in there upside down, allowing one filter to serve two duty cycles (a couple of months, IIRC).

Wednesday I met Robin over at the studio for some DAD hands-on training. Except it wasn't quite hands-on, more "look at the way we have DAD set up." And that's good, but to really get a feel for DAD I'm going to need to fiddle with it myself. Maybe Enco has an academic version or something, or maybe Robin will let me play with "MOM", our backup DAD installation.

Thursday I went to my first SBE (Society of Broadcast Engineers) meeting. At said meeting, it was moved that the dill pickle be adopted as the official pickle of our chapter (I think it was some kind of running gag). The motion carried with nearly unanimous support. We adjourned shortly after that to watch a presentation about the coolest things (at least according to Broadcast Engineering magazine) at this year's NAB show. Most notable were a couple of things that looked like their sole purpose was to allow a station to be run with fewer people. Automation, and the desire to reduce headcount, are everywhere.

I was also introduced to a couple of contract engineers. Robin wants me to try and go out on calls with them so that I can see more transmitters. I think that's a fine idea. I also want to visit WSMI, the radio station in my home town, and maybe some of the Spanish-language AM stations here in town. The more the better, after all.

Monday, July 5, 2010


Friday at the transmitter, Robin gave me a homework assignment:

Assume a radio station that receives network programming over a satellite link. Assume that the receiver for this link uses a dry contact closure to signal an automation system to play local content. Set up this scenario in ENCO DAD (Digital Audio Delivery).

To begin with, I'll need to reference the DAD manual at .

At first, I thought it might be under Switchers. It looks like this is only for equipment controlled via serial connection, though.

Next, I found DAD's General Purpose Interface. This looks promising: "The General Purpose Interface allows DAD to control external devices via relay outputs [GPO], and enables DAD to receive external command signals (inputs) [GPI] from devices such as a satellite controller, a master clock or a manual push button from a Console". I think we have a winner.

So, to begin with, I'll assume that there is a GPI card (or a USB GPI interface, but I'm just going to call it a "card") of some sort installed in the machine running DAD. I'll further assume that the GPI card has been installed in the DAD machine and set up according to the instructions. I'll assume that the length of the break in network programming is precisely known, rather than the satellite system signalling at the start of the break and at the end of the break. I'll assume that local content is live.

I'll use input #0 on my hypothetical GPI card for the satellite receiver. I'll use output #0 to control the switch from live to satellite. Assuming no other inputs connected to the card, my GPI file (I'll call it 'DAD.GPI') should look something like this:


Note that "<x>" here is the length of the pause in satellite output, in seconds.

I'm not certain this is exactly what Robin had in mind. I'll give it to him and post his comments.

UPDATE: Robin's comments: "You are on the right track. You have the basics but it will take a little more to make it work."

Wednesday, June 30, 2010

Monday at the TX, and installing new coax

Note: "TX" is shorthand for "transmitter". Also Texas.

Monday I took the readings at the KCUR transmitter. I remembered where almost everything was except for the bits about the T1 (the studio is connected to the TX via a dedicated T1. I didn't ask if it was fractional or full.) Robin had turned off the HD transmitter hardware (I'll be doing a post about terminology shortly, don't worry) the night before because it had overheated. This was due to the air conditioning being unable to cope with the level of heat in the transmitter building, as it had been beastly hot that weekend. Turning off the HD transmitter hardware allowed the building to cool down to normal levels.

It's worth noting here that the transmitter building is not properly air conditioned, according to Robin. It's not that the AC is underpowered. Rather, the AC is apparently placed wrong - it's set up to keep the building cool in the areas where humans would move around (i.e. it's blowing from the top), rather than where the air intakes for all the equipment are (i.e. near the floor). I always thought that cold air sank, though, so I'm not sure why blowing from the top is such a big problem. Maybe it's that the AC is blowing across the top of the equipment, effectively cooling the warm air that the equipment exhausts, rather than cooling the air going into the equipment.

Robin told me that there are a few big names in transmitter hardware. Broadcast Electronics is what we use, and they're apparently pretty popular, as I was easily able to find a video about their FM30B transmitter (by which I mean the big metal box that you connect to the broadcast antenna). There's also Harris, who apparently do all sorts of things besides make transmitters. Now, Robin tells me that both BE and Harris are out of Quincy, IL, but Harris' web site says they're based in Florida. A bit of Googling suggests that maybe their broadcast equipment division is in Quincy, or at least the broadcast equipment factory.

BE and Harris, along with Nautel (based in Nova Scotia), Continental Electronics (out of Dallas), and several Italian manufacturers make tetrode-based transmitters. A couple of other manufacturers, QEI, and CCA (now defunct, link goes to a guy who sells CCA replacement parts) use triodes. Both of these are ginormous vacuum tubes (yes, vacuum tubes aren't just for audiophiles and people restoring antique radios - they're apparently very popular for all sorts of RF applications) used to amplify the signal coming from the studio.

After getting the readings done, I had to run to the airport to pick up a friend, so Robin and I didn't do much more talking that day. The next day, however, or rather the next evening, I got to help Robin replace the feed line from our BE FM30B to the broadcast antenna. And this requires a description of this feed line. The transmitter is connected to the antenna via a coaxial line. But this isn't the regular RG59 that connects your TV to the wall. This is some high-grade stuff here.

Regular coax has a center conductor, an inner insulator, a braided wire shield, and an outer insulator. Wikipedia explains it better than I can, but basically the wire shield keeps the radio signal inside the cable, and the outer insulator keeps anything metal from touching the wire braid and screwing up its electrical characteristics somehow. The coax we use runs along the same principle, with a couple of minor differences.

First of all, the stuff we use is big. Regular coax has a diameter of maybe half an inch. The stuff we use is something like 4 1/2 inches in diameter. The inner conductor is hollow and about an inch and a half in diameter. There's no dielectric (the stuff between the inner conductor and the outer conductor). Instead, every so often there are Kevlar spacers to keep the inner conductor in the center of the outer conductor. The inner conductor is hollow, too - skin effect. The outer conductor is just a hollow copper cylinder, rather than braided wire. Both the inner conductor and outer conductor are rigid - to bend them, you've got to connect them to an elbow like you would a water pipe. And, like a water pipe (ok, some water pipes), there's no insulation on the outside. It doesn't seem to be a problem for the outer conductor to touch other conductive things, though - the feed line from the transmitter to the antenna relay (which in turn connects to the antenna) is supported by metal straps hanging from the ceiling. Maybe it's OK 'cos the straps aren't grounded.

I'm sure you can order this stuff cut to any length you want. That gets expensive pretty quick, though, I'll bet. At KCUR, we just have these huge (~ 15 ft) lengths of the stuff that you have to cut yourself with a hacksaw or a cutting disc. Precision is not required, though - using the elbows and such you've got a little bit of wiggle room.

So when I got to the transmitter last night, the first thing to do was to switch over to the backup transmitter, which is an Armstrong unit. It's about 1/3 the size of our main transmitter setup, and doesn't do HD at all. I think it's lower power, too. Anyway, to do that, Robin took the power down on the BE FM30B, warmed up the Armstrong, then switched from the BE to the Armstrong. I think we may have been briefly off-air, but I'm not sure.

Once the BE was down, and we were sure that the Armstrong was operating properly, we measured the distance from the harmonic filter on top of the BE to the elbow coming out of the antenna relay. 18.5", give or take. (Remember what I said about wiggle room). Anyway, after we had the run measured, Robin and I took the ginormous length of coax outside and set it on top of one of the AC units. We figured that would make a good solid base for sawing on. I measured 18.5 inches, then Robin said we needed to take an inch and a half off of that. I misunderstood him to mean that the length of both inner and outer conductor (the inner is inside the outer) needed to be 17". In fact, the inner conductor needed to be 17". IIRC, the inner conductor in the elbow sticks out past the outer. Anyway, because I misunderstood him, I cut both pieces to 17", which was too short. Because I am not good with a hacksaw, and because the hacksaw we have at the transmitter is kinda crap, I cut the copper at too much of an angle. So we had to cut a new piece, but we should clean the piece we did cut up first. No sense in letting it go to waste, after all.

Cleaning up a piece of coax basically means filing down all the sharp edges left over from the hacksaw. If you don't do this, you end up with places where the current collects, and that could heat up the copper and potentially burn a hole in one or both of your conductors. Bad times. But this piece not only had burrs (sharp bits) from being cut with a hacksaw; it was cut at an angle too far off from the vertical to be within that "wiggle room" I mentioned earlier. Getting that piece down closer to square with just a file sounded like a long and arduous task to me, so I suggested we take a bench grinder to it. Robin just happened to have one at his house, so off we went. An hour and various assaults with file, bench grinder, and cutting disc later, we had a reasonably square piece about 16.5 inches long. :) We still needed that 18.5" piece, though, so back to the transmitter we went with Robin's considerably nicer hacksaw.

Once the piece of correct length had been cut and filed, it was time to install it. This is not exactly easy. Getting the elbow or the flange on to the outer conductor isn't bad. It's just a press-fit type affair that you tighten up with a hose clamp. And connecting the flanges isn't bad - you just bolt them together. No, the real trick of it is getting the inner conductors to connect. The inner conductors are joined by these things called "bullets" - metal dinguses slightly smaller than the inner conductor with a stopper ring in the middle. But these bullets aren't solid - they're hollow, and they have "fingers". The last thing you want is for those fingers to split, so you put a thingy in the middle of all the fingers (I wish I could find pictures, 'cos I can't explain this properly) to keep that from happening. These things always fall out, requiring you to stick them back in before you try to get your inner conductor over the fingers, which also never works. But eventually, with much manhandling and bumping of your head (because the building is cramped), things get connected and bolted together.

Once everything was back together, Robin shut down the Armstrong (or possibly shifted it into the dummy load and then shut it down, I'm not sure) and brought the FM30B back up. Everything came back up properly, and we went to our respective homes. It was 0100 or so. :)

Oh, I also got to see Robin's ham (radio) shack and meet his cat, which was cool. :)

Sunday, June 27, 2010

Friday at the KCUR Transmitter

Friday was largely uneventful at the transmitter. Robin and I talked about a few things, including how he could reduce the actual power going into the transmitter if he could get it up a bit higher. He also told me that he had a site survey done to see if it was feasible for us to set up a wireless data link between the studio and the transmitter. The result of the survey? We would need to put the studio antenna at a height of 75 or 100 feet for it to work, which would require putting up a tower on the roof of the studio. As the studio is a University building, University regulations would require contractors, insurance, and a host of other things that would make the job much more expensive than if were being done at somebody's home. Which is a pity, as I was really looking forward to building such a beast. Maybe I'll spec it out anyway as an exercise. Robin also told me that he got the conductor he ordered in (it's replacing a line going from the transmitter hardware in the equipment building to the transmitter hardware on the tower), so maybe this coming week I'll be helping him install that. I hope so. :)

Later that day I went to help set up the ARRL Field Day activities being hosted by the Raytown Amateur Radio Club. I helped put up a big antenna mast with three horizontal antennas on it (Like the one on the right in this photo. I don't know what sort of antenna it was and didn't think to ask.) and someone's satellite antenna. I was surprised to find that the satellite antenna was this sort of V-shaped affair, rather than a dish.

Saturday I went to the field day proper, but it wasn't exactly clear what there was for me to do. People seemed to be intent upon their own business, and as I don't yet have a license, I didn't think I was allowed to ask, "Hey, can I try to transmit on this equipment?" As it turns out, there was a GOTA (Get On The Air) trailer set up, but it wasn't clear that was what it was. I realize that I could have asked, and I probably should have asked. But I let my timidity get the better of me. I also could have come back later, but by that point I was feeling ill and in no condition to go anywhere. Next year, perhaps.

So it occurs to me that all I've been talking about is KCUR and radio stuff. That's not all I'm interested in. I'm also interested in motorcycle maintenance, as I think I've stated previously on this blog. I'm at a bit of an impasse there, however. To learn more about motorcycle maintenance requires having a motorcycle in need of maintenance, and my motorcycle, thankfully, is not in need of the maintenance type things I want to learn more about - mostly engine stuff. I can do an oil change, replace turn signals, and replace a chain. I feel confident that I could do my fork seals if I needed to. I can replace my own brake pads, and rebuild my brake calipers. I can replace my own spark plugs and coil wires. But I've never dipped my carburetors. I've never adjusted my valves. I've never been inside the guts of an engine, and that's something I want to learn about. I asked if I could work some hours at Blue Star Motorcycles in exchange for wrenching lessons, but Don (my friend who's the GM of the shop) said he didn't have enough work coming in for that. Maybe I should see if I can just hang around and pester the mechanics with questions.

Wednesday, June 23, 2010

And we're back!

It's a new day here at KCD, and I've decided to take this blog in a new direction. I've decided to start pursuing other career options besides IT, and more broadly I'm going to start pursuing the things that interest me. It's my goal in life to be as competent as possible in as many areas as possible.

One of those areas is radio. I've long been fascinated by radio. I can remember as a child staring at microwave towers. There was also a radio transmitter (my parents called it a booster station, I'm not sure if that was accurate or not) by my house; I always wondered what was in the little attached shack.

Having recently become unemployed, I found myself with a lot of time on my hands. In an effort to fill up some of that time in pursuing interesting things, I decided to call up KCUR's chief engineer, Robin Cross, and ask him if I could help out around the station in exchange for learning about radio engineering. He said yes. :)

To start with, I've been meeting Robin on Mondays and Fridays at the KCUR transmitter. This past Monday, Robin let me take the readings for the maintenance log. He handed me the clipboard and told me to have at it, and to come to him with any questions. The maintenance log is laid out very straightforwardly, so it wasn't difficult, but it was still cool.

Like many radio stations, KCUR uses RDS to transmit information about what's currently playing. This is handled by a dedicated PC at the transmitter running software that interfaces with the RDS transmitter. If we had a dedicated data (i.e. TCP/IP) link from the station to the transmitter, we could let the on-air people edit the RDS via a computer in the studio. We do not have such a link at the moment, but I have an idea for one: set up a point-to-point 802.11g link between the station and the transmitter. This will require a specialized antenna, as the station and the transmitter are roughly 7 miles apart from one another as the crow flies, but I think we can do it. It will certainly be fun to try.