Still Fighting ...

But is it a good fight?  Ahhh ...

The fight with VHF repeater continues.  On April 11, 2018,  the RC-210 controller was removed from the repeater (that's why there is no courtesy tone).  There are actually two auxiliary receivers connected to that controller and while it was unlikely that this was injecting the interfering signal into the system, it was easy enough to remove it to test.  Removing the controller was not expected to magically fix everything, and it didn't, but it did give us some more data - in the interval between a mobile unit unkeying and the repeater's transmitter dropping, the "other" signal was apparent.  That's the good news.  The bad news is that the signal is probably the repeater's transmitter on 147.0600 MHz.

The duplexer (not diplexer) is the filter that is supposed to keep the repeater's receiver from hearing its own transmitter.  This is no small trick given that there is a 25-W signal on 147.0600 MHz and the repeater is trying to listen for signals 600 kHz away (147.6600 MHz) that are in the microvolt range ... at the same time ... on the same feedline and antenna.

Miraculously (or maybe not if you know N5MS), Mike had a duplexer "in stock".  The unit was tuned up on "66/06" (that's how hams 40 years ago described a repeater - input/output) and placed in service today by N5HZR and N5UWY.  If this "cures" the problem then the next steps are pretty clear.  Note that in the repeater rehabilitation work that the Technical Committee has done over the past several years, the duplexer was the only component not replaced.

Unfortunately, in order to install the temporary duplexer, the NORMAN digipeater (on the APRS frequency of 144.3900 MHz) was removed from service.  The digipeater shares the VHF repeater's antenna and feedline by use of a multi-coupler (similar to a duplexer - a tight filter that keeps 147.0600 MHz RF away from 144.3900 MHz).  This is unfortunate for a couple reasons - 1) APRS users are deprived of a high-site digipeater and 2) it's possible that the digipeater itself was an issue (it's not at all clear that it was).

Time will tell if this is the "cure."


Repeater Site Expedition Report - 2018-01-27

A number of us visited the county yard on Friday the 26th (N5UWY, KD5UGO, N5HZR, W5HLG, WE5Z, WB5ULK, AG5DB, AG5LB, KB5LSB).  We looked only at the VHF system and not the UHF system.

A couple of numbers for posterity:

  • Squelch opens at 0.2 μV.
  • Full quieting is reached at 1.0 μV
  • Modulation  bandwidth is 9 kHz
  • Deviation of repeated stations is 3.5-4 kHz
  • Transmitter frequency error +30 Hz
  • Power output is 20 W
  • 70 dB reject on transmit.

KD5UGO provided several tons of test equipment and knowledge to operate it.  We looked at the parameters quantified above.

We listened to the input frequency through the duplexers as well as straight from the antenna and we were looking at it on the spectrum analyzer at the same time; No unusual signals were heard or seen, only the signal of the HT (or the service monitor) we were using to key the repeater. 

We "swept" the Bp (Tx) and Br (Rx) sides of the duplexer and found no anomalies.  Yes, we wiggled wires and tapped on connectors while watching signals, none of which had any effect.  We checked their tuning and were able to coerce another 2 dB of rejection from the receive side (I do not have the initial or resulting values, only the 2 dB difference).  We saw no evidence that the transmitter on 147.06 was being heard by the receiver on 147.66 via the antenna system.

Bottom line:  No Trouble Found.

Clearly, there is a signal from somewhere mixing with the signal being received from stations trying to use the repeater.  None of the tests we did yesterday revealed the source of that signal. In fact, we saw no evidence of another signal. But it's there because we heard it on repeated stations within an hour of our visit.  It's real, we just have yet to find it.


Callsign Cobwebs From The Mental Attic

Heard some chitterchatter recently on one of the repeaters regarding callsign structures. I thought I'd clear out some of the stuff in my mental attic, so here goes:
  • By international treaty, the USA is allocated W, K, N, and AA-AL, technically WAA-WZZ, KAA-KZZ, NAA-NZZ, AAA-ALZ (AMA-AZZ being allocated to other nations).
  • Internally, the FCC decides how to break up those allocations into the various services.  
  • Way back in the day, when their were true regional offices for the Department of Commerce (before the Federal Radio Commission or the Federal Communications Commission), each district office had a number. Oklahoma's licenses were handled out of the New Orleans office, which was #5. You see where this is going.
  • Initially, US hams got a number (corresponding to the issuing office) and then letters assigned in sequence starting at AA. When they got to WZ, they started again at AAA (because for a while, if the first letter after the number was X, Y, or Z, it had a special meaning). There was also a period when some stations, usually a portable station operated by an amateur away from his usual address, that had 4 letters after the digit.
  • After one of the international radio conferences, c.1923, everyone agreed that all callsigns should start with the letters that had already been assigned, so US hams all grew Ws ahead of the digit.  
Skipping LOTS of trivia ...
  • For about 40 years now, more or less, in the Amateur Radio Service, callsigns have been grouped. Amateur Extra Class licensees were assigned calls from Group A, 1x2 or 2x1 starting with W (e.g., WE5Z, W5TC) . When those ran out (and in the 5th district they ran out about 1992 or so) they "refreshed" the group with calls starting at AA5AA. Advanced Class licensees (none issued since 2000) got calls from Group B, 2x2 starting with K (e.g., KK5IO). Technicians and Generals got assigned calls from Group C, 1x3 calls starting with N (e.g., N5ZZM). Remember, until 1987, the only difference between the test or Tech and General was the Morse code, so they got calls in the same group - the written exam was the same and if you passed the 13-WPM test, you got General, if not, you got Technician. Group C was exhausted in our district about 1992 as well (N5ZZM just squeaked in!) Novices (none issued since 2000) got calls from Group D, which were 2x3 calls starting with K. Once Group C was exhausted, instead of "refreshing" it with some other pool, the FCC started pulling from Group D, which is why all new Tech and Generals get 2x3 calls.
  • Now, then. When it comes to vanity calls, you are still restricted to the group that corresponds to your license class. So Technicians and Generals can get any available 1x3 callsign (starting with an N, K, or W) or any available 2x3 call (starting with WA-WZ, KA-KZ, NA-NZ, or AA-AL) with some restrictions. To get a 1x2, a 2x1, or a 2x2, you have to hold an Amateur Extra license.


Edit: Looks like Group A in the 5th District was exhausted on 1987-06-02 from looking at QRZ's 1993 database causing the FCC to start at AA5AA after WZ5Z was issued.