LF/MF antenna change

Today I changed the earth electrode antenna by raising the height of the connecting wires to form a (part) loop in the air as well as in the ground. The loop part in the air has an area of >100 sq metres.  This should increase the effective loop area by a factor of at least 2, thereby improving the ERP. Later I'll repeat the tests with just the loop in the air only, so I have 3 different sets of results to compare. On 500kHz WSPR my signal with M0BMU (69km) was 6dB stronger than before with the earth electrode antenna. At the moment I am QRSS3 beaconing on 137.675kHz and seeking reports.

136kHz WSPR - first report received

Well, it is no great DX at 3km away in the next village, but I've now received my first WSPR report on 136kHz from G6ALB. He gave me -21dB S/N when I was running 20uW ERP from the earth electrode antenna.

WSPRing on 137.5kHz at last

136kHz TX transverter

Having got the TX part of the 136kHz transverter going today I am, for the first time, putting out a WSPR signal on 137.5kHz. Power from the PA is around 4W and the ERP from the earth electrode antenna is around 20uW. I am hopeful that Chris G3XIZ in Biggleswade may be able to decode the signal, possibly others not too far away. In the picture the transverting bit (from the 10MHz band) is on the right and the PA in the top left with low pass filter visible using the T106-2 toroid. Note the heatsink for the IRF510 - a couple of crock clips being all I could find in the junk box!

My 20uW ERP QRSS3 signal as received by G3XIZ

This was the signal G3XIZ got today 48km away on QRSS3 from me on 137.675kHz.  It is somewhat stronger than earlier in the week, confirming the few dB extra ERP.

136kHz TX transverter almost ready (5W from PA)

Today I should complete the first breadboard version of my QRP TX transverter for 136kHz. It mixes down from 10MHz in a similar arrangement to my 500kHz unit, which transverted down from 28MHz. ERP on the original 137.675kHz QRSS3 beacon has been increased by 3dB to 20uW. The ERP from the transverter into the earth electrode "antenna" will be about the same level initially. I'll run WSPR tests for the first time on 136kHz this weekend.

Another report on the 136kHz QRPp beacon

G3XIZ has sent me a nice screenshot of my 10uW ERP 136kHz beacon as received in Biggleswade, about 35km away. Chris believes I'd be perfect copy with QRSS10 (10 second dots).

62km with QRPp and earth electrodes on 137.675kHz

Today I ran an earth electrode transmission test with Mike G3XDV in Welwyn Garden City 62km away. I put my QRSS3 8-10uW ERP beacon on and Mike took regular screen shots through the day until mid afternoon. Although unable to copy the message in QRSS3, when using QRSS30 speed for reception the start and end of the message sequences (9 mins 7 seconds apart) could clearly be seen. He was able to precisely detect when the beacon was turned off. Mike estimates another 6-10dB should allow him to read the message properly. Signals were weaker later, possibly because of rain here altering the effective loop size within the ground.

136kHz RX loop calibration

Today I attempted to calibrate my 136kHz 80cm loop antenna by measuring the signal strength of DCF39 in Germany on 138.83kHz. I'm told that the field strength of this signal in daytime in this area is around 1mV/m. The level of DCF39 was -4.5dB on the Spectran screen with the settings I used. So, by extrapolation 0dB on the screen should be close to 1.7mV/m.

I then measured the signal level of my QRSS3 beacon on 137.675kHz  to see how much lower the level was at the same point about 1.5km away from the home QTH. My QRSS3 beacon was measuring -42dB approximately, corresponding to a field strength level of 12uV/m at 1.5km.

To work back to my ERP from the earth electrode antenna I used the formula ERP = (E * d)^2 /49 and this gives a result of 6.3uW and an antenna "loss" factor of 56dB (power in to RF out).

There are several sources of error:

• loop orientation +/-3dB
• loop Q/tuning +/-3dB
• measurement accuracy +/-2dB

So, the ERP could be as high as 40uW or as low as 1uW.

Chinese SSB and CW transceiver kits/built

YouKits of China is advertising a new 6 band HF SSB transceiver, the TJ6A that is available both in kit form and ready built. Prices look very attractive for a 10W transceiver. Well worth a look at their website.  This last year we have begun to see Chinese ham products appearing. It is only a matter of time before a Chinese manufacturer will produce quality transceivers to seriously rival Icom and Yaesu, and at unbelievable prices.

Pakistan Floods

This map appeared on the Oxfam site today and gives a graphic indication of how much land is affected by the floods in Pakistan when overlaid on a map of the UK.  It must be truly awful for the poor people there affected by this with crops, homes and businesses in ruin. Just imagine if this happened here (see map) and think how we would like the rest of the world's governments and peoples to help.

Help here: http://www.oxfam.org.uk/get_involved/campaign/actions/pakistan_response.html

ICQ Podcast: LF/VLF and QRP stuff

Last week Martin M1MRB interviewed me by Skype for an ICQ Podcast mainly about LF/VLF and QRP . My contribution starts about half way through the podcast. Thankfully Martin edited out many of the "ums" and "errs" that littered the piece!