Sporadic E on 2 Meters

Yesterday and today I experienced Es on 2m for the first time this year.

In the morning of yesterday I detected an opening, but only after looking at my FT8 PSK-reporter map.

There was a solid signal from the Ukraine and a weak one from UA6, just East of the Black Sea.

Then, today the following appeared, almost while I looked at WSJT-X:

1016 RT3G   KO92up

1028 RK2T   KO93ad

Both were in the -15 - -20dB range, so quite weak, but they were there, none the less.

The past week there have been substantial Es openings on 28, 50 and 70MHz, but I did not detect anything on 2m until yesterday. Also, today Russian FM stations were there aplenty on 70MHz.

A few days ago I detected signals on 50MHz from Japan. No North America on 6m yet.

The season has really started. Interesting to see what this year's season will provide.

Build of a Small PCB Based Oscilloscope - and Another Oops.

A little while ago I purchased a kit for a small, very simple oscilloscope.
This is the JYE Tech DSO138, a kit with SMD components soldered, so only through-hole components need to be mounted.
The scope is a single channel device with a bandwidth of 200kHz, using a sample rate of 1Ms/s, and has a small, but readable 2.4" screen, if I recall correctly.
The kit went together all right, even if soldering was tricky, even with a quite hot soldering iron. The tip had trouble heating up the PCB pads, probably because they had a very narrow edge around the through-holes.
Otherwise, when I finally found the assembly instructions for the correct version of the board, the check/test went well, and after adjustments the screen shows a relative good square wave, using the built-in test generator.
This test was done with a USB cable connecting a 5V power supply to the scope.

Now came the test with the "normal" power (only) connector on the analog board (with all the switches etc). I found a battery and a red/black wire set mounted on the connector, got it connected, and - <snif> <snif> - something gets hot, and nothing on the screen.
A check revealed that the connector had reverse polarity .... Oops.

A correctly connected cable was found, and phew! The screen showed something. But not all was good.
I checked the voltages on the board, and the -5V voltage was essentially absent - a few 100s mV. Not good. I disconnected the output of the ICL7660 DC/DC converter IC, still no negative voltage output.
The 7660 has definitely gone to the eternal IC fields. The quad OP-amp could also be defective, so I have ordered spares of both.
The arrival of the spare parts is expected in a few weeks, so the project is now on hold. Not a huge problem, it is not a critical item that I need right now, and I have more than enough other projects to get to.

So, what can we learn from this? Oh, yes, when building kits and/or connecting power  to kits or modules, check, then double check the polarity of the power supply leads, and the polarity on the PCBs.
A pity that there is no standard for this, but what can we expect from stuff coming from different parts of the world?

Ha ! My Pixie Test Mistake. You May Laugh ;)

OOPS!

Looking at my radio desk I found out that I had not connected the 80m Pixie modified for transmission only, to the SWR-meter and the antenna. There was another BNC-BNC cable on the radio desk.

The stability and frequency offset was still not good, but the output was there. Also, the erratic behaviour of the frequency when keying the TX was gone. It was most likely due to RF floating all around.

The 472kHz version is still not good. No oscillation I can detect. Some experimentation with the oscillator circuit will probably provide oscillation, and some RF output from that version of the Pixie.

Laughing is allowed, I did chuckle when I saw the mistake.

Now I need to see if I can make a receiver version with sufficient stability. Otherwise I will have to go for some "real home brew".

Quick Pixie Updates: Ceramic Resonators for TX.

After some more experiments with the Pixie kits I am suspending the Pixie for a while.

Versions of the Pixie modified for transmit only, 80m version and 630m version with modified inductors and capacitors in the frequency dependent circuits, and the components specific to the receive mode have been omitted. For example, the diode and switch for RX oscillator offset has been removed. Further, a variable capacitor ("Polyvaricon") has been connected from the crystal to ground, in place of the diode offset "capacitor")

80m:
The oscillator does oscillate in the "RX mode", and the frequency range is about 3500 - 3600kHz. When keying, however the oscillator frequency still changes frequency, sometimes in an unpredictable way (sometimes up, sometimes down).
I suspect 2 reasons:
- the oscillator voltage is not stabilised
- the load of the oscillator changes when switching to "TX" mode.
Further, the output of the transmitter with the ceramic resonator in the circuit is too low to register on the SWR/PWR meter. Not exactly a resounding success. This could be due to a lower Q of the ceramic resonators, resulting in a lower oscillator output.

630m:
I could not register any output from the oscillator. There can be several reasons:
- the oscillator may be more loaded by the buffer stage
- the capacitive load of the oscillator capacitors may be too high
- the frequency determining capacitors may have a low Q
- the Q of the ceramic resonator may be too low for solid oscillator loop gain
- the capacitor ratio in the feedback loop may result in a loop gain below 1.

My conclusion is that the basic design of the Pixie is too simple for a wide range (ceramic resonator controlled) transmitter, though it may be brought to work OK with a crystal, with some VXO functionality. A few switched crystals may provide some coverage, especially in the 40m band. I have crystals resonating on 7000, 7015, 7023, 7030 and 7040kHz, possibly 7035kHz. From box73,de 7005, 7010, 7020, 7035, 7050, 7052, 7055 and 7070 are available This should provide some coverage of the 40m CW band, so I might try that and see how much of the band can be covered with such a setup.
I see that several Xtal frequencies for the 10MHz band are available at box73.de , so a 10MHz version of the switched Xtal TX may be feasible. Frequencies available from there:
10105, 10106, 10115, 10116, 10120, 10135 and 10145kHz. This should provide good coverage of the 10MHz band with a VXO circuit.
Also from Box73.de :
80m : 3530, 3540, 3550, 3555, 3560 and 3570kHz. Generally available is also 3579kHz Partial coverage of 80m looks possible.
160m: 1800 and 1820 available from box73.de. Generally available: 1843kHz. I do have a crystal for 1963kHz.

Experiments with crystal control of the Pixie should therefore be available to me on the following bands:
- 160m
- 80m
- 40m
- 30m

While I do have crystals for higher bands (14,18,21,24 and 28MHz) I consider that the Pixie is probably not suitable for those bands. I could do a test on 28MHz, just to see what the kit does, but I do not expect good results. It may possibly work with better transistors, and with lower power.

I am still looking for crystals in the 5250 - 5450 kHz band.

Receiver experiments, with the offset diode circuit removed, should prove interesting enough. For a receiver a stabilised voltage supply can easily be arranged

Other experiments have been suggested by VK3YE on his page :
The Pixie Hack Challenge

I may try out a few of those at a later stage.

As you can see, there are still many experiments/hacks possible with the Pixie kits. That is why I purchased quite a few before starting the experimentation.

I may have a pause in the Pixie play now. Many other projects I want to do. We shall see.

10m Openings to South America and the Caribbean.

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.

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.

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.