600m WSPR at "Thor's Hammer"

Since I visited the QTH of OZ9QV last month I have been monitoring the WSPR reception there.

The WSPR receiver is of course the same as the one for QRSS, with WSPR running concurrently on the PC.

With the tiny indoor tuned multi turn loop (diameter 22cm) the following stations have now been received successfully on 600m .

PA0A, PA0O, G3XIZ, PE1GRL and EI0CF being 1225km from there.

For such a simple setup I am quite happy with the results, even though I know that improvements are certainly possible.

Grabber : "Thor's Hammer" at OZ9QV : updates

During a holiday (and being there for other reasons) in Denmark I have made an update to the "Thor's Hammer" QRSS grabber. More will happen later at another visit.

The grabber can, as usual be found at :
Thor's Hammer

The grabber now works on two bands, a more stable receiver (old TRX with defective TX) has been installed for 10 MHz and the viewable frequency range reduced. Still using an older low powered PC

10 MHz Grabber :
RX range : 10139.880 - 10140.120 kHz
SpectrumLab set for display of 3 stripes of consecutive periods
Antenna : indoor dipole

500kHz Grabber :
RX range : 502.700 - 505.500 kHz - some noticeable frequency drift, but acceptable
SpectrumLab set for 3 strips as above
Antenna : indoor multi turn tuned loop

The 500kHz RX seems to have some problems with receiving WSPR, only once or twice the WSPR signals from PA0A and PA0O have been received.
The signal from (I think) G3XIZ was visible, but no decodes.

All in all I am fine with the improvements, but more is needed. I would like to add more bands, e.g 80m, 40 and 20m, possibly 136kHz but things do take time to get running, and new antennas will be necessary.

I may experiment with a wide band active loop antenna (H-probe) or an E-probe (short active whip).

Update IC-703 500kHz

After having made a study of the IC-703 manual I see that there is a high pass filter in the TX path , cutting off at 1.6 MHz.
This is most probably for avoiding the IF frequency (455kHz) reaching the TX output.

A switch - switching in a 500kHz bandpass filter (alt 136kHz filter for LW) or bypassing the filter - would probably be possible, but the *tiny* SMD components at this place in the radio makes me think twice about making the attempt.

It *may* be possible to tap the signal out to an external amplifier, but then there is still 30mW out of the TX at 500kHz, so that could as easily be used.

Conclusion : 500kHz looks possible with the 703, but I doubt the internal filter mod is worth the risk of ruining a perfectly good TRX.

Modifying the IC-703 - - and 500kHz

Ham radio manufacturers are funny (funny-strange, I mean).

They make 100 W radios needing lots of cooling, yet the PA's work through.

On the other hand, making QRP radios, PA transistors go KAPUT, drivers go KAPUT (FT-817 and IC-703 respectively)

SInce I have a FT-817 with a PA that died, I know it is just a matter of time before it happens again, unless the correct mods are made.

This week end ( with temperatures up around 30 C) I got to do the necessary mods for the IC-703

1) Driver modification. This one is not too bad, a matter of cutting a single PCB track and rerouting a piece of wire on the accessible side of the PCB, no need to remove the PCB. When at it, I adjusted the bias to the driver down to the recommended .5V, so the driver should be safe even with high temperatures now. In the original IC-703 the driver is connected directly to the full supply voltage, now it is connected to the 8V supply line.

2) CW Keyer input. For some obscure reason the keyer jack is grounded through a choke, giving rise to RF making it impossible to release the TX key. The solution, connecting the keyer jack ground directly to RF ground can be made provisionally outside the radio, but the more elegant solution requires the main board PCB to be lifted from the housing. Not too tricky, but beware of the flat cables (connectors).

3) 500 kHz TX option. This one required moving a *tiny* SMD diode. I managed to do it with a "normal" small solder tip, but the result is not that pretty.
The mod does open for TX on 500 kHz, but max output is about 40mW, and it looks like something is heating up, because the output reduces a bit after key-up, then stabilizes. I would probably not try to use the max output, but reduce it a bit, them make a power amp.

All in all not too bad for a hot summer's week end.

A bit of 500kHz experimentation

The new cardboard box frame antenna with better wire turns out to be a bit better. A few dB increase of S/N has been gained.

The loop was at first connected to the HF-3 receiver, and gave some WSPR spots from local stations like PA0A, PA3EGO (also seen with QRSS) and PA3FNY, with relatively good signals if considerably lower than Joachim gets with his Octaplumb. Also G4JNT during night time and one or two other spots from G stations. All in all not very impressive, but not too bad for an antenna inside the noise field of the apartment. Also every night DI2AM with QRSS, and occasionally a good signal from OK0EMW.

A test with the ATS909 receiver, using just the built-in ferrite antenna gave surprisingly good results, almost as good as the cardboard loop with the HF-3, with DI2AM in every evening.

Test with the FT-817 gave a marginal improvement over the HF-3, maybe 1 - 2 dB.

Test with a FRG-100 receiver showed that the receiver is considerably more sensitive than the FT-817, but due to "antenna noise" (apartment noise) the improvement was again marginal, 1 - 2 dB.

The antenna has now been moved upstairs, still indoors, and another 1 - 2 dB has been gained. interesting to see how much signals will come from the G stations now.

An improved loop for outdoor mounting, like Joachim's Octaplumb will be built here, and some tests with larger transmit antennas are in the plans. Well, and a TX, too, probably beginning with some 50 - 100 mW, so ERP will be in the microwatt range.

This week I am having a visit from a friend staying over, so not much time for building activities, but after that it should go on.

I still have some experimentation on the Rockmites and a Warbler, so more than enough to do here.

Also some experiments with the TL592 amplifier for active antennas (LF,MF,HF) is in the thoughts here, such as variations on the antenna from this site

DI2AM reception on 505 kHz

The 500 kHz grabber is now set to two narrow frequency ranges, the "WSPR segment" and 100Hz around the frequency of DI2AM.

DI2AM reception seems to be there essentially all the time after sunset, albeit with some (expected) QSB, and WSPR signals coming and going.





Nice result with a "cheapo" frame antenna wound on a cardboard box 35x40 cm small.

A new somewhat bigger frame antenna (more than 70x70cm) will be made some time, but that will have to wait.

In the week end the construction of the 500 kHz TX should begin

500 kHz transmit permit

Today I received a permit for experimental transmissions on the 500 kHz band, 501.000 - 504.000 kHz.

Now I will need to build a transmitter, I will most probably go the way Joachim proposed, using a 27 MHz crystal on the fundamental frequency (9 MHz), then dividing by 9 with a 4017, then by 2 with a flip-flop, followed by a "buffer amplifier" , and later an IRF510 as power amplifier.

The hard part will be the antenna, it needs to be compact, so a "magnetic loop" is probably the only way to go here.

Better antennas for LF/MF

In order to make loop/frame antennas with higher Q for the low bands (160m, 600m, 2.2km) I have ordered some Litz Wire from across the "pond".

It will be interesting to see how much improvement I can get from this.

"eBay" , of course. It can be a dangerous place, but it is our last, best hope for strange raw materials.

TVEPG up and running from The Netherlands

I got the TVEPG set up with the HF-3 and the 500 kHz antenna, you can find it at here

The grabber is running on an Acer Aspire One 110, the old model with 8 GB SSD, under Linux, running SpectrumLab under Wine and an upload shell script originally written by Allan OZ5AR.

The frequency range is set to 503.5 - 505.5 at the moment, but I do have another setting for the 500 kHz WSPR band.

Update :
New setting for the 500 kHz Grabber : split screen with WSPR segment and a wider segment shown together.

500kHz antenna connected to the HF-3

The antenna is now connected to the HF-3 and receiving there. DI2AM is visible, if not too strong. Some WSPR signals are easily visible, with the WSPR program they should decode nicely.

For now I will leave it running, and in the week end the 500 kHz system could come on the TVEPG grabber page. no time now, and tomorrow some non-radio activity.

Still the signals are not all too strong, so a better antenna is required here.

The noise levels, however seem very low here.

"Progress" report 500kHz RX antenna

Well - let us say - the antenna tunes down to 500 kHz, but the output looks lower than I get from the ferrite antenna of the ATS-909. The S/N, however sounds like it is better.

The source of the lower output ? I am not sure, but suspect the small size of the loop contributes, and perhaps the coupling winding is not enough with a single turn. further tests are needed.

OK - this antenna is rather small and uses standard hookup wire, so the highest efficiency is not to be expected. a somewhat larger antenna, say 1x1 m made from Litz wire should provide substantially better results.

The first test was with a "dual gang" variable capacitor, but with only one plate set used. of course the hand capacity detunes the antenna so it is essentially untuneable.

SO the second test was with both plate sets, and now we are getting there. because the hand is at the center of the capacitor, no detuning or hand capacity effect is noticeable.

With the 25 windings, the antenna tunes down to just under 500 kHz, so the antenna is a qualified success.

The ATS 909 seems to have a rather good sensitivity on MW, so it is a bit difficult to fully judge the efficiency and usability of the antenna.

The tuning is not *very* sharp, but with a decent maximum at resonance.

The next test should be connecting the antenna to the HF-3 RX which should have a very high sensitivity on 500 kHz. Oh, now for soldering another connector to the cable and see what it will do.

Another solution to the low output could be to build an amplifier, but that sort of defeats the purpose of a 'simple antenna'.

More room for experimentation.

500 kHz Receiving Antenna in the Make.

I have been looking into the options for receiving amateur signals on the 600m band (500 kHz). Since I live in an apartment size does matter, so looking for a small sized antenna I looked around and found this article from VK2ZAY , showing a simple 'frame antenna' made with a cardboard box.

Being close to all kinds of noise sources I think the loop is probably the best option for a receiving antenna on such a low frequency.

Since I intend to use the antenna indoors the support material does not matter much.

The box measures are on the small side - 35x40 cm (14x16 inches if you like) - but as a proof of concept I have put 25 windings with taps at 15 and 20 windings, as well as a single winding coupling loop.

Now I will be looking in my junk box to find a suitable variable capacitor to complete the project (this may take some time).

If this works out to my satisfaction I will try out frame antennas for 80m, 160m and 2.2km as well, at some time.

Since there seems to be an experimental license available here in The Netherlands I may even try to put out a 600m signal, yes, I am considering joining the experimental group. The decision, however, has to be made soon before the opportunity expires.

600m test for the TVEPG

I tried this afternoon, the first identifiable Amateur radio signal comes from DI2AM, a museum ship in Rostock. The signal has a nice S/N of about 20dB, and given the distance of somewhere between 150 and 200km it is not very surprising to receive it.



Not bad for a very portable setup : EeePC, Sony SW-100 RX and a wire of about 20m length.

Update :

Just tested with the built-in ferrite antenna of the RX : The signal is now just visible and barely readable. The wire antenna does its work. Back to the wire antenna.


The Very Experimental Portable Grabber has been om 600m.


Tests with frame antennas and external ferrite antennas could become interesting.