While chatting locally on 2m FM I suddenly noticed that my 10m FT8 monitor showed a spot from Puerto Rico. This is very early for a sporadic E opening, so I wonder what the propagation mode(s) is/are.
All in all from about 2200Z to 2300Z stations came in from:
Caribbean:
KP4JRS, J69HZ and J69DS
South America:
PU5BOY, YY1ALE, YY5YAM, HK3GJ, HK4GSO, HC1DAZ
Though I tried to call several of them, no QSO could be made by me. Best signal strength was +1dB by one of the HK stations. He was detected sending RR73, then disappeared. Maybe he went QRT, maybe propagation disappeared in his direction.
6m was not tested, there may have been some reports on that band by others, I do not know.
2020-04-16
Pixie tests with VXO and Ceramic Resonators.
Quick test today using ceramic resonators.
40m model:
Even with a 5 - 60pF variable capacitor the frequency could be pulled down to under 7.000MHz, with a ceramic resonator for 7160kHz. The stability, however, was not sufficient with the Pixie. The tuning was fiddly, and the TX signal had a significant chirp, and the receive frequency was drifting too much for my taste. Well, it was clearly audible ...
Further, the RX offset of the oscillator, when using a crystal in series with the variable capacitor, was insufficient at the lowest frequency, even when it was set to maximum, i.e. the RX local oscillator (BFO) was too close to zero beat.
The 80m version did not fare much better. Yes, it was a bit better, but still had chirp on the TX and some drifting on the RX the RX could not be pulled down to the band edge, either, but did have a sufficient range to have been useful.
More experiments with an inductor added to the VXO (crystal) should be an interesting experiment. It might provide for a better stability, and somewhat better offset. This needs to be tested.
It may be possible to use one Pixie as RX and another as TX, providing a "spot" function, but I doubt the stability will be sufficient with the ceramic resonators.
Because VK3YE has tested oscillators and even regenerative receivers with ceramic resonators, and achieved sufficient stability for CW operation, I would consider the Pixie as too simple for good results as a frequency agile CW transceiver. It would be quite suitable for simple fixed frequency operation, e.g. as a monitor receiver for FT8. Crystals for such a receiver (20m and 40m) should arrive in about a week, if not delayed by the corona virus situation. A test of the Pixie as a simple QRSS RX should be another simple experiment.
40m model:
Even with a 5 - 60pF variable capacitor the frequency could be pulled down to under 7.000MHz, with a ceramic resonator for 7160kHz. The stability, however, was not sufficient with the Pixie. The tuning was fiddly, and the TX signal had a significant chirp, and the receive frequency was drifting too much for my taste. Well, it was clearly audible ...
Further, the RX offset of the oscillator, when using a crystal in series with the variable capacitor, was insufficient at the lowest frequency, even when it was set to maximum, i.e. the RX local oscillator (BFO) was too close to zero beat.
The 80m version did not fare much better. Yes, it was a bit better, but still had chirp on the TX and some drifting on the RX the RX could not be pulled down to the band edge, either, but did have a sufficient range to have been useful.
More experiments with an inductor added to the VXO (crystal) should be an interesting experiment. It might provide for a better stability, and somewhat better offset. This needs to be tested.
It may be possible to use one Pixie as RX and another as TX, providing a "spot" function, but I doubt the stability will be sufficient with the ceramic resonators.
Because VK3YE has tested oscillators and even regenerative receivers with ceramic resonators, and achieved sufficient stability for CW operation, I would consider the Pixie as too simple for good results as a frequency agile CW transceiver. It would be quite suitable for simple fixed frequency operation, e.g. as a monitor receiver for FT8. Crystals for such a receiver (20m and 40m) should arrive in about a week, if not delayed by the corona virus situation. A test of the Pixie as a simple QRSS RX should be another simple experiment.
2020-04-12
Pixie Transceiver Kit Building and Mods.
Over the pas year or two I have eBay'ed quite a few kits of the simple Pixie CW transceiver. Now was the time to build and test a few, one as the original and one modified.
All those kits are so cheap from Chinese eBay'ers that I can buy 3, sometimes 4 kits for the tax free limit to Denmark (about 12 - 13 USD). I purchased a few, then another few. For that low price the kits are excellent for experimenting.
More modified will be built, for all the lower bands, but here is the first impressions:
Kit #1: 40m CW on 7023kHz:
The kit is easy enough to assemble. I made good use of my PCB holder for stability.
Resistor marking was good old standard. Some markings were missing on capacitors, so they were checked. The inductors were checked, as well, as I was not sure of the colour coding for those.
First impressions of the finished kit. It was expected to be tricky making contacts with such a low power device only capable of operating on a single TX frequency.
Power output, measured with a SWR/power meter is estimated to be just over 300mW. A trim-potmeter varies the oscillator frequency for receiving, so a decent "side tone" can be achieved. For receiving an old speaker was connected. A low hiss was audible, but the audio level was too low for comfortable operation. Further, some odd noises and distortion were heard (more about that later).
The first test was done with a local friend and my low hanging HF dipole, at the massive distance of 3km (about 2 miles) ;) Reports received were 599 (yes, for real), but I could only give 539, most likely due to the low audio level.
The strange noises were identified, the LM386 did oscillate, apparently triggered by strong signals received. Not good.
An Internet search revealed that this is a general problem with the LM386 in this configuration when connected to a low impedance (8ohm) speaker. A test with connecting the to a set of active computer speakers showed no oscillations or distortion at all. So much for the simplicity of the kit.
With the extra gain of the computer speakers the receiver is more lively, too.
Kit #2: 80m CW on 3560kHz:
Components from the original (2nd) kit, and some components from a third kit were used like this:
the values of the capacitors and inductors in the RF part of the circuit were doubled in value. The inductors from the 2 kits were connected in series, and the capacitors in the oscillator resonant circuit and the low pass filter were coupled in parallel. Interesting enough, it was quite easy to fit the parallel capacitors in the mounting holes.
That was all. Connected to the computer speakers the receiver sprang to life, and the sensitivity seemed OK, the noise level increased a bit when the antenna was connected.
My friend was not available at the first test, so no test QSO was made (yet)
Power output of the modified 80m was close to 500mW at 9V power supply. A bit more than the 40m version, but not surprising.
Running a CW transceiver at low power, and at single frequencies is, of course an exercise in frustration, so the next test will be modification of both kits for some frequency agility.
For the 80m version the first test will be replacing the crystal with a ceramic resonator and a variable capacitor. This should provide coverage of a good part of the 80m CW band.
The 40m version is a bit more tricky The resonator available is a 7159 version, and might not be capable of covering the CW band portion of 40m. I do have a 7.02MHz ceramic filter, and that might cover a part of the 40m CW band. Otherwise a VXO with some switched crystals available will be sufficient. Crystals available to me are 7.000, 7.015, 7.030 and 7.040MHz. With those I would expect to cover most of the 40m CW band.
It should be possible to make versions for the 6m, 160m and 630m bands, with other modifications. I should have the necessary replacement components available, but that is for later.
Update: The 80m version was tested today, and provided a 599+10 report from my local friend. It works, most definitely.
All those kits are so cheap from Chinese eBay'ers that I can buy 3, sometimes 4 kits for the tax free limit to Denmark (about 12 - 13 USD). I purchased a few, then another few. For that low price the kits are excellent for experimenting.
More modified will be built, for all the lower bands, but here is the first impressions:
Kit #1: 40m CW on 7023kHz:
The kit is easy enough to assemble. I made good use of my PCB holder for stability.
Resistor marking was good old standard. Some markings were missing on capacitors, so they were checked. The inductors were checked, as well, as I was not sure of the colour coding for those.
First impressions of the finished kit. It was expected to be tricky making contacts with such a low power device only capable of operating on a single TX frequency.
Power output, measured with a SWR/power meter is estimated to be just over 300mW. A trim-potmeter varies the oscillator frequency for receiving, so a decent "side tone" can be achieved. For receiving an old speaker was connected. A low hiss was audible, but the audio level was too low for comfortable operation. Further, some odd noises and distortion were heard (more about that later).
The first test was done with a local friend and my low hanging HF dipole, at the massive distance of 3km (about 2 miles) ;) Reports received were 599 (yes, for real), but I could only give 539, most likely due to the low audio level.
The strange noises were identified, the LM386 did oscillate, apparently triggered by strong signals received. Not good.
An Internet search revealed that this is a general problem with the LM386 in this configuration when connected to a low impedance (8ohm) speaker. A test with connecting the to a set of active computer speakers showed no oscillations or distortion at all. So much for the simplicity of the kit.
With the extra gain of the computer speakers the receiver is more lively, too.
Kit #2: 80m CW on 3560kHz:
Components from the original (2nd) kit, and some components from a third kit were used like this:
the values of the capacitors and inductors in the RF part of the circuit were doubled in value. The inductors from the 2 kits were connected in series, and the capacitors in the oscillator resonant circuit and the low pass filter were coupled in parallel. Interesting enough, it was quite easy to fit the parallel capacitors in the mounting holes.
That was all. Connected to the computer speakers the receiver sprang to life, and the sensitivity seemed OK, the noise level increased a bit when the antenna was connected.
My friend was not available at the first test, so no test QSO was made (yet)
Power output of the modified 80m was close to 500mW at 9V power supply. A bit more than the 40m version, but not surprising.
Running a CW transceiver at low power, and at single frequencies is, of course an exercise in frustration, so the next test will be modification of both kits for some frequency agility.
For the 80m version the first test will be replacing the crystal with a ceramic resonator and a variable capacitor. This should provide coverage of a good part of the 80m CW band.
The 40m version is a bit more tricky The resonator available is a 7159 version, and might not be capable of covering the CW band portion of 40m. I do have a 7.02MHz ceramic filter, and that might cover a part of the 40m CW band. Otherwise a VXO with some switched crystals available will be sufficient. Crystals available to me are 7.000, 7.015, 7.030 and 7.040MHz. With those I would expect to cover most of the 40m CW band.
It should be possible to make versions for the 6m, 160m and 630m bands, with other modifications. I should have the necessary replacement components available, but that is for later.
Update: The 80m version was tested today, and provided a 599+10 report from my local friend. It works, most definitely.
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