Radio Nederland and shortwave broadcasts

One of my favorite shortwave broadcast stations back in the 1960s was Radio Netherlands . I still have my QSL card from them somewhere. When testing my shortwave crystal set today I noticed a strong transmission of the Dutch language service today in the 31m band. Little did I realise (until tonight) that this is the very last day ever of transmissions in their worldwide Dutch language service.

The HF broadcast scene is quite a lot different from when I last seriously listened some years ago: there are far fewer English language services to be heard. I guess these days people who want to find out about different countries listen to broadcasts on the internet.

Also, the CW maritime services, which could be perfectly copied sometimes on a crystal set as a result of cross-modulation (the CW sounded like a raspy hiss keyed) are long gone. One of my interests some years ago was seeing how many HF marine coast radio stations I could positively ID on a simple crystal set: the answer was quite a few around western Europe.

In fact SWLing on HF is rather a dying scene I think, although devotees will no doubt disagree.

Crystal set sensitivity experiments

This afternoon I had a little play with a simple crystal set to see what sort of minimum discernible signal (MDS) was possible. My previous experiments with single germanium detectors had yielded an MDS of around -55 to -57dBm in the 5-30MHz range with a high impedance crystal earpiece.

Today I tried the same test with both germanium diodes and a hot carrier diode (HP2835) with and without some bias applied to the diode(s). Best results were with the HP2835 and with about 0.11V forward bias applied. Only a few uA are needed so battery drain is next to nothing. MDS was around -62dBm for a well modulated AM signal. For the tuned circuit I used a T50-6 toroid with around 20 turns with an antenna link winding adjusted for best sensitivity/selectivity and a 365pF variable capacitor .

Incidentally, forward bias for the diode could be obtained by rectifying other signals available on the antenna such as MW/LW broadcasters using a separate tuned circuit, rectifier and reservoir capacitor. I must give this a try sometime. Several hundreds of mV DC should be possible.

Then I tried switching the diode with a second signal generator at a power of between 1-10mW to see what sort of sensitivity could be obtained on a CW signal. MDS improved by around 25dB to around -86dBm i.e. I could just hear down to around 10uV. This would be a just usable level as a basic HF SSB/CW receiver.

I also tried the same tests with a pair of high sensitivity ST-3 headphones that Michael AA1TJ kindly managed to find for me. These are much lower impedance than the crystal earpiece so I experimented with antenna match and the match of the diode to the tuned circuit, expecting a better performance at the best settings. Disappointingly, the results were several dB worse than with the crystal earpiece.

Now, the results with the crystal earpiece are very close to those (without bias) that I obtained some years ago, so I don't think my hearing (at 63 years old) has changed much for the worse. So, Michael must have incredibly sensitive ears as there is no way I was able to hear down to the levels he could with his passive receivers.

At the moment I am playing with the AM crystal set with -62dBm sensitivity listening to shortwave broadcasters. Fun.

Six continents on 10m WSPR

This afternoon I exchanged WSPR reports with RI1ANF in the South Shetland Is in Antarctica on 10m. This now means I've had reports this year from every continent on the 10m band using 5W or less with the wire halo antenna.

PA1B's power attenuator calculator (see link below)

As this is all getting rather too easy (!) maybe I need to follow Bert PA1B's advice and build a switchable attenuator so I can repeat the challenge with much lower powers. See his power attenuator design page for details of how to make suitable RF attenuators to reduce QRP rig output powers to milliwatts.

50MHz, 432MHz and 481THz this evening

Well, this was an interesting evening. Just after teatime I noticed 50MHz was open with some strong Es signals from Europe. A few stations were worked on QRP SSB using the newly erected halo antenna (S52NR, S53OQ and OE5FIN). Heard, but not worked, on 50MHz were CT8/K0RUI in HM68 (Azores Is) and 4X4DK in KM72. Both DX stations were good solid signals on the halo.

Stations worked on 432MHz this evening (5W/4el)

Later I went out portable with my FT817 (5W) and my small "coat hanger" 4 element yagi for the RSGB 432MHz activity contest and worked 14 stations in just over an hour before closing as it was dark and I could not see the logbook very well. Best DX 155km although I did hear, but not work, F8BRK in IN99.

Finally, for the very first time, I have detected GB3CAM on 481THz (red light beacon) at a distance of 32km from the Nine Mile Hill site where I was active in the UHF contest. Signal was weak with lots of scintillation, no doubt caused by the rain that started up just as I began listening with my 100mm optical receiver (KA7OEI/K3PGP hybrid). If I can find another 6dB sensitivity I think the signal will be solid in low haze/clear conditions over this LOS path. GB3CAM is a very low power light source, so copying it is a big challenge.

Monday nights at 8pm on 144.575MHz FM

Every Monday evening a number of East Cambridgeshire locals get together on 144.575MHz FM for an hour between 8-9pm clock time. The usual stations on the net are G6ALB, G3KKD, G4NUA, M3YPZ and G3XBM.

Originally this started as a regular session between G6ALB and G3XBM on 144.55MHz AM. We managed to engage in some sort of QRP related experiment most weeks. We've worked each other on all bands from 1.8-432MHz with extreme QRP and had 1-way contacts on 8.97kHz, 136kHz and 500kHz QRP too. We are 3km apart, which is an ideal distance to try all sorts of things from listening to each other on crystal sets to trying to see how weak a signal can be copied on each band: you may be surprised how little signal can be copied at this range: it is no wonder we suffer from so much interference on HF these days as nanowatts go a long way.

These days the net conversations cover all manner of subjects but, sadly, Andrew G6ALB and I don't get to do experiments so often: this is a drawback of a larger net. At some point I think Andrew and I will find another spot to do experiments on another evening whilst letting the Monday net continue as it is. It is fun to simply chat.

Let me share a pearl from this evening:  Alex M3YPZ, who has a truly fascinating background going back to working on radar in WW2 and research in Cambridge University, mentioned he had a book on how to improve his memory.  He lent it to someone   ....but could not remember who.  The joys of getting a bit older!

If you are the area feel free to call in to the net.

10m across the pond

Late this afternoon I was very surprised when my 5W to the halo was spotted on 10m WSPR by K9AN 6505km west of me. It is unusual, I think, to get 10m transatlantic propagation at this time of the year by F2, so wonder if this was Es propagation? There were quite strong PY stations coming through earlier, so it could be F2 back-scatter. Incidentally, 4X1RF and I seem to have a pipe between us on 10m: we WSPR spot each other most days and I often copy him when his beacon is running 50mW.

Further to my earlier post, WSPR allows one to do "gentleman's DXing": you can see how far your signal is reaching whilst running QRP and a simple antenna and still do other things in the shack at the same time. Perfect.

DX Chasing (no thanks)

Chasing DX is just not my thing any more. For example, on 10m CW this afternoon there was one heck of a pileup of stations trying to work 7O6T in Yemen. This is a rare country but those who get through tend to be the stations with the BIG beams, high power and who call and call. Occasionally, a QRP station with good skills can manage it. On rare occasions I have found DX before the pileups or the DX cluster shows it's there and then a QSO is possible.

But basically I am past this stage in the hobby now. I prefer to explore new things, experiment and have fun. I know that if I had 400W+  and a big beam up high I could work the world if I was patient, but having amassed well over 100 countries worked with 5W SSB/CW it matters not to me that I don't work that rare DX.

On VHF and UHF it can still be fun though, and counting squares is still my answer to train spotting, HI.

AM lightbeaming down the street

With my wife manning the TX this afternoon and pointing it out of the landing window we managed a daylight speech test today with 100mm optics at both ends at 0.3km using the v.simple AM lightbeam TX described in the previous post. The LED was run with an 80mA standing current. Biggest problem was aligning the TX beam and the lack of talkback, but I managed to get 59+ copy of my wife saying, "I'm bored with this. Come home and have some tea" when I was aligned on the TX beam.

There is no doubt the simple circuit can be refined to improve audio quality when clipping, but it works. The RX is far more sensitive at night too.  I am now finding a way of replacing the XYL for these tests by using another source of speech such as a radio receiver or MP3 player. She is good at cooking and other things, but not at doing optical tests!

Later this week I'll begin experiments with a simple single LED AM 481THz transceiver.

481THz AM transmitter

This morning I took a step further towards making a complete 481THz lightbeam transceiver by breadboarding and testing a simple AM transmitter for use with a high brightness red LED. The circuit could hardly be simpler but works very well. The bias on TR2 is adjusted to give around mid-rail so the LED has a standing bias before audio is applied. Listening (without optics) on my modified KA7OEI receiver head and looking on a scope, the modulation looks good with around 150mA current into the LED.

Dual band 10m/6m halo erected

10m and 6m nested wire halos on the mast

The Homebase-10 halo is now a Homebase-10/6 with a second dipole within the first covering the lower part of 50MHz. After just minor adjustment both bands have a near unity VSWR over the parts of the bands where there is CW/DATA/SSB activity.

Since making the changes I have exchanged 5W WSPR reports with FR1GZ  on 10m, and got -19dB S/N on 10m WSPR from CX2ABP (11127km), so that is still working as before. I have yet to work something on 6m to be able to judge the omni-directivity of the 6m halo.

Dimensions for the inner 6m dipole were simply scaled down from the values at 10m: the outer sections are 564mm long and the folded dipole inner section 873mm long (these are the dimensions each side of the feed point). A single 50 ohm RG58 coax feeds both 10m and 6m sections.

Details of the original Homebase-10 were in my Practical Wireless article a few years ago and also on my webpage at https://sites.google.com/site/g3xbmqrp/Home/homebase10 .