More loop experiments at 500 and 136kHz

Today I converted my earth electrode antenna with elevated feed wires into a full "in the air" loop for both 500kHz and 136kHz. As might be expected, tuning is now very sharp as there is no longer a 50 ohm earth resistance in circuit dampening the Q. At first I found matching and tuning impossible until I decided to match the loop with a step-down transformer (3.5:1 on a 3C90 core) and separately do the tuning. This works a treat and it is now a simple matter to tune the loop either for 500kHz or 136/137kHz.

First reports on 136kHz with the QRSS3 beacon suggest the signal is about 6dB stronger, which is a great result. The loop is wound with quite thin wire (1-2mm diameter), so a higher efficiency is possible with thicker wire, but with even sharper tuning.

LATER: Attracting any attention is turning out to be a serious issue with real QRP on 136kHz. Even with alerts on my blog, the LF-reflector and the GQRP Yahoo groups it's hard to get that many people taking a listen/look. With uW ERPs I'm beginning to think that I'm never going to be able to get much further than my present best DX of 62km.

Last days on 56MHz (5m) - lost recording?

Many years ago Jack Hum G5UM attended the Cambridge club and talked about VHF. During the talk he mentioned a gramaphone disc being made recording the very last night of operation on 56MHz in the London area in the 1940s. Does anyone know what happened to this most historic recording?  This would be a wonderful item of ham history if it could be located.

More results on 137kHz and a better ERP calculation

Today I managed, I believe, for the first time to accurately measure the ERP of my QRPp system on 137kHz. This is the method used:

• Using the E-field probe, FT817 (AGC off, gain backed off as far as possible and a 10dB pad between the EFP and the FT817) and Spectran I went to my usual test site 1.5km away from the QTH, 45 degrees off the main lobe of the TX loop/earth electrode antenna.
• Measured the signal level of DCF39 on 138.83kHz
• Measured the signal level of G3XBM on 137.675kHz
• Repeated this three times to reduce errors.
• Noted the difference in FS level.

Difference in signal level = 44dB . I feel pretty confident this is an accurate figure now and not effected by AGC and overload. Assuming DCF39 is 1mV/m here (info from Alan Melia)  then my FS at the test site is 6.4uV/m.  Using the formula ERP = (E*d)^2/49 where E = 6.4*10E-6 and d=1.5*10E3 gives an ERP = 1.9uW giving an antenna efficiency of -63dB using the earth electrode antenna with the elevated feed and 4W from the PA. 

The test site is about 45 degrees off the main line of fire of the antenna, so in the best direction it could be 10dB (?) stronger, i.e. 20uW ERP giving an antenna efficiency of -53dB in the best directions. Frankly I'm amazed that anyone can copy this signal at any distance, so full marks to G3XIZ (48km) and G3XDV (62km).

Mike G3XDV sent me another screenshot of my signals this morning during the tests. if you look carefully you can just make out "G3X..." in QRSS3.

Solar activity progress

See http://solarscience.msfc.nasa.gov/images/ssn_predict_l.gif

Sunspot cycle 24 does, at last, show signs of gathering some momentum. Despite the ups and downs in the sunspot count, there is an inexorable climb now towards the next maximum, probably on 2012 or 2013. This autumn we should start to get the regular 10m transatlantic openings again which, to me, are a sign that the new cycle is here and "good" for several years. In the press there's been some alarmist headlines about solar storms around the sunspot maximum knocking out swathes of the power systems and satellites around the world. Certainly the danger exists, but surely it is a manageable risk with planning and contingencies in place? See news.com.au on this subject.

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.