Playing with a ferrite rod at VLF

Just for amusement, but with a slight hope it might work, I tried resonating a LW ferrite rod coil (about 3.5mH) at 8.97kHz to see how it might perform as a miniature portable receiving loop in my earth-mode tests.

To test other antennas and VLF preamps, I first connect my 8.97kHz 5W transmitter into a resistive dummy load and check that I can detect the signal strongly some distance away locally (about 10m away only). The emissions from the cables are such that this gives me around 30-40dB S/N on Spectran with the usual settings on my 80cm loop. Switching over to the ferrite rod RX antenna it was hard to tell if a signal was there at all.

So, that's one experiment I'll close and report as a failure. Had it worked, even 10s of dB down, it might have made a magnetic field antenna that could have been deployed mobile. You may recall I tried /M on 8.97kHz a few months ago with my 80cm loop strapped behind the car, until someone pointed out this probably would have invalidated my car insurance and I stopped.  I had vague ideas of dropping the VLF resonated ferrite rod close to the ground behind, somehow fixed from the rear bumper.

Ho hum, another idea bites the dust.

Shortwave Radio Archive

Just spotted on the Southgate site that K4SWL is creating a website to archive shortwave broadcast  recordings before these disappear. Already many SW BC stations have closed at least parts of their services. The HF broadcast bands are nothing like they were even 20 years ago. See http://shortwavearchive.com/ . 

My shortwave radio experience started over 50 years ago listening to SW broadcast stations on a simple crystal set in my bedroom. As much as I hated the propaganda from the communist broadcasters like Radio Moscow and Radio Sofia, Bulgaria, I do miss them and their evocative interval signals.

See also https://sites.google.com/site/g3xbmqrp3/hf/interval and take a nostalgic trip down memory lane.

Good results with new VLF earth-mode RX system

Today I carried out a test with my new simpler RX system for VLF/LF earth-mode "through the ground" communications, testing with a 5W TX into 20m spaced earth electrodes at 8.976kHz.

The new preamp is just a single MPF102 impedance converter feeding into a small,low cost, external USB sound card (£3) that feeds my baby Asus X101CH netbook (£172) running Spectran software to display the received QRSS3 signal. The external soundcard was only needed as I didn't have a 4-pin jack to use the audio-in socket on the Asus.

Tests were carried out at the usual test sites at 1.6, 3.6 and 6km as well as one further (unsuccessful) test at 6.2km.

In all locations, decent signals were copied, even at 6km. The little Asus netbook has an SD card running Readyboost and behaved perfectly well during the tests. Now, the whole system is very simple to deploy in the field to take measurements. The preamp is only tuned by the loop and its resonating capacitors (a capacitance decade box), so the very same preamp can be used right across the VLF and LF spectrum with a suitable receiver.

Today the weather was dry and has been for around a week now. I believe signals by earth-mode are stronger after a period of dry weather as the soil conductivity is lower. Results are as good, or better, than I have ever experienced before with earth-mode at 8.976kHz.

The next test will be to repeat this test at around 1kHz and possibly lower frequencies.I also want to try WSPR and repeat the tests at much higher LF frequencies around 72-73kHz. For the latter test, I need to build a simple down converter to audio.

YouKits TJ2B SSB handheld kits on eBay

The TJ2B 4-band SSB HF handheld is available direct from China for around £176 as a kit with all the SMA components already mounted on the PCBs. See eBay item number 271195721443.

Hamshop.cz

Although I have not used them myself (yet), www.hamshop.cz has a range of interesting and useful parts and kits available for purchase by PayPal. They ship worldwide too. Check out the page in English. As far as I can see, the prices are quite reasonable too.

Cloudbounce and scatter optical and IR tests

This morning I read a most interesting article about French cloudbounce and scatter optical tests using lasers. The article is some years old but makes a fascinating read. My own experience with clear air forward scatter at optical frequencies using relatively low powered red LEDs makes me believe that a LOT more is possible in this area. It is a bit like people saying, "UHF is only line-of-sight". Rubbish! With decent, easily built kit it is possible to copy QRP amateur signals over the horizon even at IR and visible optical frequencies.

See http://sd-1.archive-host.com/membres/up/22679775843705539/CBVUK.pdf

First Icom IC7100 review on eHam.net

http://www.icomamerica.com

This evening I noticed that the first user review of the Icom IC7100 has appeared on eHam.net. YB1FWO bought a unit in Japan and give it a 5 out of 5 score. I've not heard if this radio has appeared in the USA or European dealers. It was not priced a few days ago but I gather the UK price is just below £2000, so not a low cost product although it is a neat, multi-band (including 4m), multi-mode 100W radio.

6m WSPR and the transatlantic path by Es

6m spots - note the drift

 There seem to be more people trying WSPR on 6m than in previous years. Prompted by Nick G4IKZ this evening I have moved from 10m to 6m and have spotted CN8LI (2113km) and been spotted myself by a few G stations. On 6m the Doppler shift on signals can be quite fierce and setting the FT817 accurately on frequency is a little more tricky: I have to set the FT817 to 50.29260 rather than 50.2930kHz to get the correct frequency spots. I assume my 12 year old reference oscillator in the rig is a bit off. On inter-G signals I suspect that the Doppler is a result of aircraft reflection. On more distant DX stations I assume it is as a result of E layer clouds moving around.

Doppler on transatlantic 6m multi-hop Es signals might be a killer - I can imagine reflection points moving around in the E layer  - but if not, then WSPR would be a great way to check for transatlantic openings.

I'll leave the 2W WSPR to the co-linear vertical running overnight tonight and on a few further nights through June and July. We just need LOTS more USA and Canadian stations both monitoring and RXing on 6m WSPR.

More VLF earth mode tests

Tomorrow morning, all being well, I hope to do a further test on VLF earth mode at 8.97kHz using my new Asus X101ch netbook using Spectran software and a simpler loop preamp on RX. Initially I'll test locally to check results are as expected before venturing further with the new (simpler and smaller) RX system.

Also, I want later to try TXing with a large, single turn, horizontal loop on the ground around the garden rather than the earth electrodes. On the basis that I am coupling into the ground and utilities, a horizontal loop might be as effective at coupling as the earth electrode antenna. A straight comparison of one against the other will be worth trying.

I also want to try WSPR at VLF using both my PCs.

2m UKAC contest

The few stations worked this evening on 2m SSB

Just for a bit of fun I went on the 2m UKAC contest this evening with the FT817 to the vertical colinear from home, not the most ideal of antennas when everyone is running horizontal beams. Nonetheless, I managed 6 QSOs in just over an hour of operating. No great DX - the best QSO was just 47km tonight - but a bit of fun. The better stations were exchanging serial numbers in the 70s (at least) and I was hearing stations working GM, GW and F. The map shows my (meagre!) QSOs. Maybe in a month's time I'll erect that big wheel here at this QTH and we can compare results v. the vertical antenna.