I’ve managed to miss every pass of AO-91 either due schedule conflicts or incompetence on my part. I finally set an alarm to go off before a 41 degree high pass today starting at 16:54 UTC.
At first I was concerned that I had programmed SATPC32 incorrectly, as I didn’t hear anything until about 16:58 UTC, at which point the satellite was 18 degrees overhead. Even then there were long & deep fades.
At 17:02 I had my first contact with Rich WB3CSY in PA (FN10). Mike WB3JVD in WV (FM19) followed at 17:04, then Paul N8HM in DC (FM18), and at 17:05 Peter W2JV in NY (FN30).
Shortly after speaking with W2JV the bird faded out, when I was showing about 12 degrees above the horizon. I’m only using egg beaters here, and was only able to work about 3-4 minutes when the satellite was close to overhead.
The contest ended at 11 AM local time, so it’s in the bag. I finished with 302 contacts (only 17 DX contacts). I was on for 5.75 hours on Friday and 5.25 hours on Saturday, so 11 total. Probably spent 2 hours of that deep searching the 1830-1835 segment for DX. I ran S&P the entire time (with one brief exception, explained below). On Friday the contest fit in 60 KHz of the band. Last night it was more like 90 KHz. I was surprised that there were many new (to me) stations on last night.
Anyway I uploaded my log to LotW when I got off the air last night, and immediately saw 5 confirmations. By this morning the count was more like 45. No doubt many logs will come in the next couple of days (only 5 days to submit the log!)
With the objective of adding to WAS and DXCC, I already have to a tiny extent: two more countries confirmed and one more state. Maybe a couple of more in each category by the time folks upload their logs. Signals were good enough that I should, in theory, be able to work all the 48 states, and I should be able to get DXCC between Central & South America plus Western Europe & the Caribbean. I faintly heard, below the noise floor, a KL7, but I would need another 6 dB at least to be able to copy, and of course that doesn’t mean he could hear me. Of the lower 48 states I heard all but ID, KS, NB, ND, NV, UT, and WY. I only failed to work MS, who I heard in S&P mode too. I even tried to set up a few KHz higher and call CQ, hoping he would come back to my call, but that didn’t work).
So much fun!
I’m only noodling around, running S&P mostly to find new states or countries. Band noise floor is about -110 dBm, which is pretty quiet. A few signals are 70 dB above that. Most are 35 dB above the noise floor. Band is pretty full from 1800 to 1860 KHz. (Ed: Sat/Sun the contest spanned from 1800 to 1880 KHz.)
A good friend of mine, John WA1ABI, is responsible for planting the FMT bug in my head. I’ve been admiring his results in the ARRL FMTs for years — he is constantly an outstanding performer. John graciously suggested that we spend about an hour today having a mini-local FMT on four AM stations plus CHU. We would each measure/divine the frequency from data collected over a two minute period, shifting to a different spot ever 5 minutes.
Our results were amazingly close, especially with two stations that are known to be high accuracy/stable: WBZ when in IBOC mode, and CHU. In fact we were amazingly close on all measurements except for 920 KHz — I probably messed something up.
Anyway, here is the result table.
||Freq in Hz
WBZ and CHU were within 1 milliHertz (1 ppb). WPRO and WARV were within 5 milliHertz (3 ppb). My oddball was WHJJ which was 36 milliHertz different (39 ppb).
(ED 12/4: John and I captured the audio data from each run and swapped those files for processing on a later date. He informed me the next day that he analyzed my audio file and would have called the frequency 919999.863 — in other words he thinks my gear was doing fine, but I likely jotted down an incorrect reading. I wouldn’t be surprised! When I get a chance I’ll run the audio file through Spectrum Labs and see if I come up with something different than I initially reported.)
My go to ham rig is my K3s, which includes the KTCXO3-1 Temperature Compensated Crystal Oscillator, a device specified to maintain 0.5 to 1 PPM, One might think that in a reasonably controlled environment that the K3s could be used in CW mode coupled with an audio spectrum analyzer like Spectrum Labs to participate in the ARRL Frequency Measuring Tests.
While it is useful for ham purposes, the reality of the K3s/KTCXO3 is that the frequency will vary considerably even within a few minutes as oscillator frequency is adjusted by the radio’s firmware. This is NOT a temperature related thing.
Below is a screen capture from Spectrum Labs showing variability in the the received audio tone (CW mode, pitch 300 Hz) tuned to a Rubidium 10.0 MHz source. The rig had been powered on for more than five hours in a room that was temperature controlled to 71.5 degrees +/- 0.8 degrees.
The audio tone shown below over an interval of 45 minutes, wobbles from a low of 299.65 Hertz to a high of 300.56 Hertz. While certainly capable of measuring a frequency to within 1 Hz, it isn’t capable of getting “Green Band <0.1 Hz” FMT results.
The upper half of the waterfall shows the K3s in CW mode detecting a 10.0000 MHz rubidium source. The detected audio wobbles significantly.
The bottom half of the waterfall shows the K3s in AM mode detecting a 10.0003 plus 10.0000 MHz signal, which create a precise 300 Hz beat-tone. This indicates that Spectrum Labs and the soundcard in the K3s are rock solid in that mode, recording a signal of 300.000000 Hz for hours.
I am starting my journey into the world of Frequency Measuring Tests. I decided to use my receiver in AM mode and compare the unknown frequency to a known frequency obtained from a HP3335A (locked to a Rubidium source) that is set to produce a beat note around 300 Hz.
That AM beat-tone approach takes out any impact of the receiver in the process. However the soundcard being used to measure the audio frequency (with Spectrum Labs software) is subject to error. In my case a precise 300 Hz tone was reading low by about 39.7 ppm. Not horrible for a standard crystal source, but still a source of error. After adjusting the 48000 sample per second rate to 48001.904 sps, the audio frequency was spot on.
The source of the precise 300 Hz tone was another AM beat-tone. I used the 10 MHz output of the Rb source fed through 80 dB of attenuation to a BNC-T on my radio. The other side of the T was connected to my HP3335A set to 10.000300 000 MHz at a level of -80 dBm. Those two carriers produce a very precise 300 Hz frequency.
I turned the PC and rig off overnight, and rechecked things immediately following power on the next day. The worst case error was less than 50 microhertz (300.000 050) and it improved over time.
I’ve been spending a little time with a young neighbor, introducing him to Amateur Radio. I try to mix a little on-air activity with some theory. It’s amazing how comfortable he is with solving equations in his head.
This past Friday, I decided to give a satellite contact a go. Because of the time of day (mid to late afternoon), there weren’t a bunch of options, just a 20 degree elevation pass of CAS-4B, which I had never used before. My assistant waited patiently as I surfed the web for information needed to update my SATPC32 files (satellite names, Doppler offsets, etc.). The good news was our patience paid off, and after the satellite was about 5 degrees above the horizon we started hearing the CW Telemetry Beacon.
Ryan Listens to Satellite CAS4B
After listening to the beacon for a bit (Morse Code is still in our to-do jar), we tuned around a bit to find a ham to contact. After hearing no one, we called CQ and easily adjusted the downlink correction. Our own SSB signal was S9. A KE4A– called us faintly. Sadly this was right at the end of the pass so we weren’t able to make a contact.
Still a good day, I think.
After cleaning the synthesizer inside and out, I replaced multiple screws that were missing from the internal metal frame, and bolted down the power supply, which was obviously replaced in the past (without putting it back in properly). Despite the TLC, the reset issue continues.
While I am quite sure the caps in the PS need replacing, I took the +5 regulator out of the equation by supplying it with my bench power supply, so the input to that regulator is now rock solid (per scope measurement) That hasn’t impacted the reset problem. Other power supplies are still questionable, like the -8 VDC unregulated supply which has a low frequency ripple on it that is about 1 Vpp.
The Controller card in the 3335A is quite old, obviously (the design dates to 1976). It is based on a Motorola 6800 CPU (privately labeled for HP at the time). Since resetting was the issue, I dug into the service manual and schematic, to discover that there is a power-on reset circuit on the card intended to hold the CPU in reset until the power supplied have stabilized long enough for the processor to start executing code. It is based on a 74LS123 multivibrator and a opamp used as a voltage detector (driven from +5 regulated and -8 unregulated supplies). The schematic is shown below:
The Q’ (the ‘ means NOT, as in Q-not) output of U12B above is the RESET’ signal that goes to the CPU on the controller card and (HORRORS) travels unbuffered off the card through multiple feet of unshielded cables to the HP-IB card on the rear of the instrument. (ED: Whoever designed the Controller card for HP back in 1976 certainly wasn’t well informed as to noise issues with NMOS inputs — a fact attested to by the layout as well.) U21 forms a voltage detector circuit which presents a ‘0’ to the B input of U12B when the voltage is stable. The other half of U12A is fed from a 2 MHz off-card source and is used to guarantee that the RESET’ signal meets the minimum low time for a valid reset.
The good news is that by pulling the B input of U12B low the reset issue goes away. So it isn’t noise on the RESET’ line itself, but is coming from the valid power detector. The root cause is either noise on the +5 regulated supply or the -8 unregulated supply. Replacing the ancient Caps (about $150 worth) should resolve the issue.
Posted in FMT, Gear, Testing
I’ve always been sort of a time nut, but that’s pretty closely related to frequency. The ARRL helps to sponsor a periodic Frequency Measurement Test, usually held in April and November. A good friend of mine, John WA1ABI, always participates and usually has outstanding accuracy. I’ve always been fascinated by that, so I went looking for some surplus gear.
My plan was to us a milliHertz resolution frequency synthesizer to generate a carrier of known frequency that was manually adjusted to be within a few hundred Hertz below the unknown signal. A RX in AM mode would produce a heterodyne audio beat note equal to the frequency difference. Add the audio frequency to the known frequency and the unknown will be revealed.
I put my sites on a HP 3335A signal generator. This is a massive beast that is about 40 years old (would have been new when I started my first engineering job in the late 1970s). They are fairly common on eBay, and can be found in various states of disrepair. I happened to locate one locally from someone who had worked on closing a capacitor factory in Massachusetts. The good news was it was inexpensive. The bad news it was sort of working and absolutely filthy.
After several hours of scrubbing the covers, they now are no longer sticky to the touch and dirty, but they show 40 years worth of wear and tear. The unit powers up and generates a fantastically stable/repeatable signal (the internal 10 MHz source, once warmed up for an hour, is within 44 milliHertz of spot on — that’s 4.4 parts per BILLION). It is pretty amazing to be able to change any of the 10 digits by one and see that exact change show up in the output.
But there is a significant problem. The unit randomly resets itself every 30 – 300 seconds. At that point the frequency is reset to 1.0 MHz, and the output level drops down below -80 dBm. The reference oscillator remains running, and within a fraction of a second of entering the frequency and amplitude via the keypad, it is up and running again.
After going through the service manual and schematics, it appears the only reason this would happen is if there were a voltage issue with the internal 5 volt supply. That could cause the 6800 CPU to reset. The 3335A never really powers off fully. The unregulated supplies are always on as long as the power cord is plugged in. It is highly likely that 40 years of this has fried the large power supply caps, and that would make the 5 volt supply unstable. We shall see!
Posted in FMT, Gear, Testing
Many other projects (like teaching another set of Technician’s) reduce the amount of time I have on air, but DX progress continues slowly. My confirmed country count hasn’t changed (262), but the DX Challenge count has creeped up to 1250. No endorsement until 1500, which may be years away at this rate