Category: tech stuff

Harris FM25-K

Old blue, I like to call them, the Harris 1980s model transmitters with black faces, white cabinets, and blue trim. I have yet to find one that I really like, the FM 25-K is, well okay. Sort of like that 200,000-mile jeep that works, most of the time, and it’s paid for.
This particular FM-25K transmitter is located at WIZN in Charlotte, VT.

Harris FM25-K transmitter

This transmitter was new in 1987.  It had a bad day yesterday, deciding to throw a temper tantrum and trip the HV power supply breaker.  Fortunately, the station has a backup transmitter.  When we arrived, we found the HV power supply feed through the insulator at E1 arced over and broken.  Again, fortunately, this station’s management believes in stocking spare parts and a replacement was on hand.

Harris FM25K HV power supply feed through insulator

This is part of the RF filter for the HV power supply. This happened once before, about two months ago. The replacement insulator then was used, so that might be a factor. Two months ago, both capacitors in the Pi filter and the HV power supply cable (RG-8 coax) were replaced all the way back to the rectifier stacks.

The FM25-K can produce spontaneous high-frequency oscillations if not tuned properly.  We looked at the transmitter output with a Rode Schwartz spectrum analyzer and found it to be clean.  Exactly why it blew out another feed-through insulator is a bit of a mystery.  Since the first replacement was a used part, we surmise that it may have been cracked.  If this replacement insulator arcs, there needs to be a full investigation.

As I said in the beginning, I have found these transmitters to be okay, not the best, not the worst.  Most of the problems I have encountered with the K series FM transmitters had to do with the controller cards.  There are two, one analog and one digital.  That’s what Harris calls them anyway.  Like the SX transmitter, and the MW transmitter to a certain extent, the control circuits are way over complicated and full of +/- 5 volt CMOS logic.   Having that type of control logic connected to a radio tower (e.g. lightning rod) is asking for trouble.

How do you listen to streaming audio on an Android smart phone?

Update:There is a better way: www.engineeringradio.us/blog/2011/03/tunein-radio/

Ahh, since I posted about my android, a few readers have emailed me and would like to know. If you have tried to stream audio using a smartphone web browser, you have found out that it simply doesn’t work.  The web browser is unable to decode the radio station stream because most of them are in AAC, AAC+, HeAACv1 or some other codec.  At this point, most people give up on the idea and move on. I, on the other hand, determined that it should be doable.

First, I attempted to down load a few apps, but they either crashed or didn’t do what I wanted or weren’t in the right language, or something.

Clear Channel has something called iHeartRadio, which is a clearing house for mobile users that want to listen to Clear Channel radio streams on their iPhones.  I don’t know, once you have heard one Kiss-FM station, you’ve heard them all as far as I am concerned.  Most other Clear Channel programming is boring and uninspired.

What I finally ended up doing was going to Moodio and reading up on a few things.  Here is a good step by step way to use Moodio to listen to radio station web streams on any mobile device.

  1. Be aware that not all data plans are the same.  ATT, Sprint, and others now cap data transfer and charge extra if a subscriber goes over.  Know your plan.
  2. On a regular computer, go to Moodio (http://www.yourmuze.fm/)
  3. Set up a user account
  4. Select from there list, the stations you want to listen to.  They have many US stations as well as many from Europe.  If the station you are looking for is not there, you can request that it be added.
  5. Select the default data rate.  Since I have unlimited data, I chose the highest rate for the best sounding audio.  Others may want lower data rates so as not to exceed data caps.
  6. Point your mobile device web browser to www.m.yourmuze.fm
  7. Log into your account
  8. The stations on your listen list will be displayed.

That is a lot of steps to take.  Somebody has to be very into radio or a radio station to do something like that.  A forward thinking radio station or group will be writing or paying somebody to write mobile streaming apps for their stream(s).  A forward thinking radio station or group would then feature links to these apps prominently on their web pages.  Very prominently if they are in a PPM market.  Ahem, very prominently if they are in a PPM market.

That is what a forward thinking radio station would be doing…

Satellite dish wasp fade

More bee-related RF stories. This happens often this time of year, the paper wasps have worked hard all spring to build their nests up in size, and during July, they become large enough to block the aperture of the antenna mounted on a satellite dish. As the nest fills up with eggs and larvae, it becomes denser and blocks more RF from the antenna. Soon, the signal on the satellite receiver drops, and audio dropouts occur.

I have noticed that the newer generation satellite receivers are not as good as the older Starguide III and II units.  The Starguide receivers were pretty light-duty when compared to the Scientific Atlanta 7300 or 2300 series units.  Those things were built like tanks, took up a lot of rack space, and so long as one replaced the power supply capacitors every so often, never failed.  The newer satellite receivers are very intolerant of phase shifts or carrier disruptions.  Many times, the signal strength might look to be above the dropout threshold (usually 4.5 to 5 dB), but the audio still occasionally cuts out.  That symptom is almost always bees in the feed horn.

3.2 meter comtech dish
3.2 meter COMTECH satellite dish

This dish is mounted up high above the roof of the building on 6-inch well casing.  In order to service the feed horn, one has to either rent a cherry picker or loosen the azimuth bolts and spin the entire dish around so the feed horn is over the roof area.  Then an eight-foot step ladder is a need to get to the feed horn.  Luckily, it is a flat roof.  Needless to say, I made sure the feed horn had the proper cover over it so that no bees could get in.

satellite feed horn with insect cover
Satellite dish feed horn with insect cover installed

Bee fade is best cured with a can of Raid Hornet and wasp spray.  The culprits are almost always paper wasps, which, I can tell you from experience, have a nasty sting.  Once the nest is cleaned out of the antenna aperture, a proper cover must be installed.  If one finds that they don’t have a proper cover, I have found that a top from a spray paint can work as a temporary cover until a proper one can be installed.  I would not call a spray paint can cap a permanent solution because the sun will eventually degrade the plastic and it will fall apart.

Ready for CAP? (AKA Common Alert Protocol)

Like any good government agency, the FCC in conjunction with FEMA is working on upgrading the acronym-heavy EAS system with CAP, which stands for Common Alert Protocol. CAP includes something that  FEMA has been working on something called IPAWS, which stands for Integrated Public Alert Warning System.

The FCC is still in the comment/response process (FCC Docket 04-296) which can get long and drawn out.  I would not expect to see any NPRM until late fall 2010 with any changes taking effect in early 2011 or so.

Basically, CAP looks like this:

An EAS to CAP converter monitors a CAP source (think e-mail server) and when a CAP message is received, it converts it to EAS protocol and sends it to an input source of an EAS encoder/decoder.  The EAS encoder/decoder then passes that information through and broadcasts it.   Of course, the EAS encoder/decoder can still be programmed to pass through specific types of messages for specific areas and ignore all others.

Thus far, several manufacturers have designed CAP converters for use with existing EAS units:

Implementation would look something like this:

EAS CAP converter diagram

For a TFT-2008 system.  Others such as SAGE and Trilithic are integrated into the EAS encoder/decoder units.  Basically, the CAP part of the EAS system needs an ethernet port with access to an IP gateway to receive messages from the CAP server located off site.  That is the weak link in the system, as far as I am concerned.

It is not like some of our so-called trading partners have been trying to tinker with the inner tubes or anything.  It is also not like that same trading partner makes most of the cheap ethernet switches and routers found in many radio stations, hardware that can be easily configured remotely.  Configured to redirect certain IP addresses to new, exciting, and exotic locations such as Iran or Pakistan.

Perhaps I am paranoid, or not.  It falls back to my time in the military when somebody said “It’s good to be a little paranoid if everyone is out to get you.”