2020-05-30

First Baby Steps in the Solar Power Department.

A little while ago I received a 50W solar panel from a friend, and waited for a controller, so I could use it safely with a battery.
The quick setup has been done now, the wire feeding the panel's power to the controller and battery, mounted indoors.

At the moment it is just charging, so now I will have to decide what the power can be used for. I think I will go for some simple receivers used for monitoring fixed frequencies. Low power consumption, so they can run 24/7. One example is a simple receiver for the international beacon network frequency on 10m - 28.200MHz. I can probably keep the power consumption down to about 25mA for that one Very simple superhet with a 19.2MHz oscillator and therefore 9MHz IF. More on that later.

I had the idea of running a QRSS grabber with a Raspberry Pi, so I did a quick calculation for running it 24/7. I was surprised that the 50W panel with a good sized battery was only close to fulfil the requirements for full off grid operation. I will have to test the power consumption of the Raspberry Pi running the grabber software, in order to see if my estimate is too high (or, maybe, too low). The calculation includes some redundancy for several days without sunshine, buffering with the battery. Yes, the sunshine hours can be very unreliable in Denmark.

I do have some small, very low power solar panels that I will experiment with, with very low power requirement equipment, such as low powered receivers or active receiving antennas. I expect the battery used here  to be Li-Ion cells, with 3 for 11V or 4 for 14V supply voltage.

More on solar experiments later.  

2020-05-29

More Signs of the Es Season on 2m.

While I was away doing other stuff, there was an opening on 2m, signals from I, IS0, F, EA, EA6 coming in via FT8. No spectacularly strong signals, mostly in the -10dB range.

This may be FAI (Field Aligned Irregularities), some kind of scatter signals, I think. The openings lasted about 2 hours, maybe more. Of course, 6 and 4m had openings, more typical Es type signals, and for longer.

I hope to make it to 2m sporadic E this year, it's been a while.

Edit 2130UTC: Later in the evening: Many stations have been received on 6m in EA8, CT3, CU3, CN and S01WS, plus very weak signals from across the Atlantic: KP4. - and, of course, most of Europe, East and West.
Signals from EA1 coming in on 4m right now. We shall see if I can make a QSO.

2020-05-27

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.

2020-05-16

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?

2020-05-08

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".

2020-05-06

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.

2020-04-27

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.