A More Expensive, But Not That Expensive, Portable Receiver.

On Ebay I purchased the Tecsun PL-660 portable radio receiver.

The PL-660 covers long wave (LW), medium wave (MW, AM band),  short wave (SW) up to 30MHz, the FM broadcast band (76 - 108MHz)  and the 118 - 136MHz air band (using AM). The receiver is also capable of AM synchronous demodulation and SSB  reception.

The receiver has a digital signal processing demodulator at the IF, and provides two bandwidths on AM reception, and that is a very useful feature, I found.

The receiver has an antenna input jack, specified to work on SW and the FM band. A test shows that it sooks like working in the air band as well. An external (active) antenna for air band reception should provide useful,  an FM antenna should be interesting, too.

The receiver uses 4 AA size cells for it power supply. These can be 1.5V (alkaline) or 1.2V rechargeable cells. I used a set of Eneloop (NiMH) cells, and when fully charged, they showed "battery full" on the indicator, and also tells that I was using NiMH batteries. It stayed like that throughout the testing of the radio.

The air band would have been perfect for my propagation monitoring if the VOR band 108 - 188MHz were included, but I reckon that I could use a low cost SDR for that, if need be.

A quick test showed that the sensitivity of the receiver is quite good on MW,SW and FM, as well as the lower part of the air band. The higher part of the air band seemed to lack gain, maybe due to bad tracking of the input filter.

Speaker quality sounds quite good for its size.

To me, however, it sounds like the DSP (demodulator/IF filter) could be improved, I detected some distortion, especially with somewhat noisy signals, that I never noticed on a fully analog receiver, or with my Icom IC-7300 and similar SDR/DSP heavy radios. OK, I guess that I got what I payed for ;)

I do think that this could be improved in later models. I suspect that it is not possible, or at least not easy, to update the firmware of the PL-660.

The accompanying power adapter, however was a bit of a disappointment. The adapter from US plug to EU plug did not fit into a mains socket, and just bent completely out of shape, no matter how carefully I tried to insert the plug(adapter). So I could simply not test the power adapter. I should probably try to find a suitable adapter, or simply cut the cord with the plug for the radio and make my own 6V power supply for this receiver.

All in all it is a nice and usable addition to my receiver park, I like monitoring a lot of frequencies simultaneously, to get an idea of the radio propagation conditions, be it on LW,MW,SW or VHF/UHF/Microwaves. The previously purchased "cheap" receiver is no more than just a toy, unlike this one. 

Maybe I should make another post or a few, about the setup I use for propagation monitoring. I think, however, that this should be at a later stage when I have completed more of the system.

Local Tropo and Other Propagation on 2m.

 In August we had some beautiful sunny weather, providing some excellent tropo propagation on 2m, and, as reported by others, also on the higher bands. Now we are back to the classical Danish weather, a little bit of sunshine, some heavy rain, even cloud bursts.

A few evenings the local FM channel had S9 signals from distances between 100 and 200km (60 - 120 miles). I refer to this kind of propagation as "Local Tropo", mostly because running SSB/CW regularly provides longer distances than this. 

Don't get me wrong, "Local Tropo" is quite fun, but I prefer working the longer distances, using SSB/CW, and sometimes the weak signal modes, like FT8. 

Mind you, on 2m FT8 is an excellent addition to the arsenal in tropo openings, but for sporadic E the fading in and out is often too fast for finishing a QSO, whereas with SSB or CW the signals can be quite strong for a very short period, then disappear forever, but in that time a QSO can be easily worked with CW or SSB. If the sporadic E lasts longer, the signals are often quite strong for a long time, and it is not necessary to use FT8. 

While this is true for Sporadic E, there might be some longer lasting scatter-like propagation making contacts possible with FT8, that could not be made otherwise, so I cannot totally discard it as being useful. As an example, some weak, slightly longer lasting sporadic E or some scatter mode, extended by tropo propagation just might provide some possibilities for 3-5000km distances for a station location like mine, not particularly suited for long haul tropo (-scatter). Yes I am not located close to an ocean, where really long sea ducts can occur.

Portable Radio on the Cheap.

I have tested the Retekess radio. All analog. Price about 20 GBP on amazon UK. I wanted to play a bit with a modern cheap radio with short wave.

Power supply is a single 18650 cell, rechargeable in the radio via a micro USB connector. I like that. The cell can, of course, be replaced. 

The radio covers FM 88 - 108MHz, SW 8 - 18MHz and MW 530 - 1710kHz.

FM works mostly nicely, tuning is OK, a little fiddly, but doable. Good sensitivity.

MW tuning quite fiddly, sensitivity poor to mediocre. Probably due to a small ferrite antenna.

SW: One band 8 - 18MHz. practically impossible to tune to a station. Sensitivity barely sufficient with the built-in telescopic antenna.

Very nice sound from the speakers, surprisingly good for such a small radio, will probably be in use.

The radio, as it is, is unsuitable for short wave reception, it is essentially impossible to tune it to a single station, mostly due to backlash in the tuning system, and due to covering 8 - 18MHz in a single band. It is essentially just a toy for SW reception.

I might be possible to make it tuneable on SW with a fine tune addition, but the modification might not be fit into the casing.

All in all a somewhat decent portable FM receiver with a medium wave performance only sensitive enough for local reception of strong transmitters.

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.

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 ;)

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.

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.