2020-07-12

Interesting Propagation on 6m Today. Update.

Today's FT8 monitoring of 6m had some interesting results. Propagation into North America.

While this takes place in the sporadic E season I still do not think this is classical multi-hop Es, but a different mode. Because it appears in the Es season it is correlated, for sure, but what causes this propagation is not really understood.

Between 1617 and 1847 UTC signals were detected from KP4. K8, N3, N5 and XE. First time I have detected a signal from Mexico, albeit in the Northern part near Texas, there the N5 was located.

This is where a digital weak signal mode makes things interesting. We discover propagation that we could not see before because the signals were too weak to be detected reliably in SSB or CW.

The strongest signal detected was the XE with -10dB S/N, and that could probably have been detected in the CW mode. The others were much weaker, and would have been non-detectable with my setup.

Now, my setup is **very simple**: I am using the IC-7600 transceiver with a vertical triband antenna for 70cm, 2m and 6m, the Diamond V-2000. With a beam antenna, even a small one, I am sure that I could have heard more.

Of course, all this happened while I was away from the radio, but OK, I detected the propagation.

Update, Monday July 13th:
Many stations seen this afternoon, from Texas, Minnesota, Georgia, South Carolina, a host of North-Eastern states, and one Canadian station: VA3DX.

Also, I noticed that, as opposed to May and June, in July there are more openings to Northern Scandinavia. I seem to recall that this has been the case in previous years. If anyone has more data on this I would appreciate some information.

2020-07-08

Revival of Old Sealed Lead-Acid Batteries.

I now have some more solar panels, but not enough batteries to match them.

Enter an amateur radio friend of mine. He has a large solar array at his house, and he has a bunch of old dis-used 12V/48Ah batteries. Only trouble is that they have all but died.

He told me that it is possible to bring them back to life, probably not with full capacity, but also warned that it could take quite some time, sometimes a month or so, to bring them into a useful state.
The trick is to provide a voltage of 14.2 to 14.4V to the batteries, and if there is any current, even a few mA, it should be possible to revive the batteries. 
I got 4 batteries to try out.

Talking about this on the radio I may have found a second source of (used) batteries, we shall see how that goes.

For that purpose I got myself some modules from China:
- a 24V/14A switch mode power supply
- a few adjustable DC/DC buck converters with voltage as well as current limitation, both adjustable.

Now the DC/DC converters can be set to 5 - 23V, the current limit to 0 - 5A. That is the specification, but I intend to limit the current to considerably less for the revival process.

Having the modules connected, the process has now started.
After a week or so, the first (best initial voltage) battery does draw more than 1A current with 14.2V, but because a cell might be bad I have set the current limitation to 300mA. The voltage is now slowly - very slowly - increasing, and has reached 9.7V. Yes, there is still a long way to go, so we shall see how it goes, and how long it takes.

The second battery was connected a few days ago, and is now drawing about 100mA at 14.2V. It is slowly increasing, in the beginning the current draw was just about 5mA.

It may be a good idea to mount the two regulator modules in a box, at the moment they are just loosely attached to a shelf - or maybe make it wall mounted, with the 24V supply at the back of the shelf.

The two other batteries had an extremely low initial voltage, so I doubt that they can be revived. They may truly be dead, and if so they will go to scrap metal.

Apart from the radio activities there are some interesting times ahead.
The battery revival does not claim too much time, just some monitoring a few times a day, so other activities can slowly re-start. The electronics workbench/test-bench is still quite messy after starting the reference oscillator activities as well as the battery revival equipment. 
I see a lot of tidying and organizing  in my future ;)

2020-07-02

Receiving FT8 With a Pixie.

After a long wait I received some crystals for the FT8, JS8Call and WSPR/QRSS frequencies on 40m and 20m, ordered some time in March.
The Ebay seller was not at fault, I suspect that the COVID-19 situation had left the package stranded somewhere on the way, for a long while. Other packages from the USA have not arrived yet, either, but who knows, they may appear one sunny day.
One set of crystals has 3 crystals per band:
7074kHz (FT8)
7078kHz (JS8Call)
7038.6kHz (WSPR/QRSS)

14074kHz (FT8)
14078kHz (JS8Call)
14095.6kHz (WSPR/QRSS)

In previous posts I have written about some experiments with the Pixie kits, and now is the opportunity to continue with that
The original 7023kHz crystal was unsoldered and a 7074kHz crystal soldered in. I am leaving the long leads at the crystal, as I think I will use it for a different receiver (or, maybe a transceiver). The frequency was adjusted to 7074.00kHz, so the test could begin. During the day not too many signals were heard, but in the evening the signals are coming in very nicely.
The antenna is a low hanging 10-15-20-40-80m dipole, so not the best, but this is excellent for the test.
Connecting the Pixie to the antenna and a set of computer speakers, FT8 signals were heard, immediately.
A quick test with a laptop, using its microphone, yielded immediate FT8 spots. A USB sound interface was found and connected in place of the speaker/microphone, and the spots poured down the screen. In the span of less than 2 hours spots were seen from North and South America, Europe, Africa and Asia. 
The system is actually working.
I left the system running over night, and in the morning I could add Oceania to the list (Indonesia). No Australia or New Zealand, but that was to be expected at this time of the year.

The experiment is a success, so now I consider the next step:

- setting the same receiver up with a raspberry Pi running headless, but using VNC, or
- inserting the 7038.6kHz crystal and setting up with a Raspberry Pi for QRSS, and maybe also WSPR.

If I just set the Pixie up for QRSS with an older Raspberry Pi, this could make for a low power, solar powered QRSS grabber system, so that is a tempting option.

Further steps could be a low power DSB or phasing SSB transceiver for FT8 or JS8Call, at first for 40m, later for 20m.

Now, if I could find a corresponding set of crystals for 60m or 80m, that could be interesting, too. On 80m, however, I could possibly use a ceramic resonator and tune it to the FT8 frequency (3573kHz). For the JS8Call a standard NTSC colour crystal (3579kHz) could be used, re-tuned to 3578kHz. It *may* be possible to use a Super-VXO (2 or more crystals in parallel) type oscillator for generating the 3573kHz signal.  

As always, too many ideas, but it is never boring.

2020-06-05

Test of OCXO and Rubidium Standard. And Building a Bit.

I wanted to test some 10MHz OCXOs so I needed some stable reference. I have a surplus rubidium 10MHz standard, and tried it for the first time.
In the first instance I want to get my very old, but otherwise frequency counter up and running again. The counter did have a reference oscillator locked to the old transmitter frequency of the national long wave station of 245kHz, which moved to 243kHz in order to comply with the new frequency grid. The reference frequency of the counter is 1MHz, generated by a crystal oscillator, which cannot now be locked to the standard. A new reference oscillator is therefore needed. The counter does have an input for an external 1MHz reference.
When I last tested the counter, the frequency adjustment range of the oscillator had deteriorated, so it could not be adjusted to the correct frequency, so I decided  to generate an external frequency.

The intention is to use a oven controlled crystal oscillator (OCXO) which can then be calibrated occasionally with the Rubidium standard, or maybe later, with a GPSDO reference.

In order to test the OCXO an even better reference is needed. so I found my surplus rubidium  (Rb)standard and tested it for the first time. I do not know its exact frequency (well 10MHz), but I could see the classic frequency sweep for some minutes, and after some cycles it locked into place.
So now I have a stable 10MHz reference, which should probably be calibrated, but I will use it as it is for now.

The first OCXO needs a 5V supply, and the Rb but at the test bench I had only one variable supply and a fixed 13.8V supply. I then built a quick 5 and 9V supply, using two DC/DC buck converters. All went into a small plastic box, normally used for interconnections in electric installations. The voltage into the converters can be from 12 - 30V, so I connected it to the 13.8V supply, the variable lab Power supply was then available to provide power for the Rb standard-

In order to compare the frequency I connected the two oscillators to my 2 channel scope, triggered by the Rb standard (Ch1) and connected the OCXO to Ch2, after letting them warm up for an hour or two.
Of course, the signal from the OCXO will then move across the screen, because its frequency is different from the Rb standard. The trick is then to change the control voltage of the OCXO until the signal moves as slowly as possible across the screen.
I managed to adjust it to move across one period, taking 3min:40sec (220sec). This corresponds to a frequency difference of less than 5mHz (yes, *milli*Hertz), but it was still drifting a bit.
However, this is quite acceptable, because the OCXO was just lying on the test bench, and not even insulated. A well insulated OCXO should be sufficiently stable for my amateur use (when placed indoors), even up to 10GHz equipment.

What next? I think I should build one of the OCXOs into a box (w/insulation), then add some buffering for the 10MHz signal, so a few output signals can be generated, as well as a "converter" for generating a 25MHx signal for control of an LNB, and finally a divider for generating a 1MHz signal.

The intention for the 25MHz signal is using a divide-by-two (5MHz), then extract the 5th harmonic, and voilá ... 25MHz. A square-wave conversion circuit followed by a good filter is probably a good idea.

Oh!, and testing the other OCXOs need to be done, too

All in all this was a few productive days, getting more test equipment up and running. Always enough projects to do here.

2020-05-31

Finally: 2m Sporadic E QSO, the First After I Moved Back to OZ.

Hooray !
After a few false starts, first receiving FT8 signals while away from the radio, and hearing sporadic (sic!) signals on 2m, I made my first QSO via 2m sporadic E, since I moved back to Denmark.
This is probably my first sporadic E on 2m since I moved to The Netherlands in late 1989.

Before this, today I heard a few signals, was calling EB1A, close, but no QSO. I was told that he had heard me, but we could not complete.
Then hearing a local, OZ6OL, working into HA, I could hear the HA, but no.
Then, after a bit of quiet, I worked YU7ACO in KN05rd. The MUF was clearly hig in some other places, but at least I got started.

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.