Re: LF: 137.5kHz WSPR success

[Roger Lapthorn <rogerlapthorn@gmail.com>]

The loop area is perhaps 70m sq, but irregular in shape. If the weather is good tomorrow I will try to take a photo of it to share here.

Now I have the WSPR transverter working I need to run some tests using the earth electrode antenna again with people like G3XIZ to compare gain, but initial tests on QRSS3 suggest there is maybe 6dB improvement with the "in the air" loop on 136kHz. I have still to do the local test where I go out to the nearby carpark 1.6km away and measure signal levels directly.

838Hz tests are on hold whilst I play with 136kHz, but I hope to return to these soon. There are too few days in the week ...and I am retired, HI.

Yes, I could run 20-25V with my existing PSU, so that is the easiest way to increase ERP Stefan.

73s
Roger g3XBM

2010/9/18 Stefan Schäfer <schaefer@iup.uni-heidelberg.de>

Roger,

This sound very hopefully and enthusiastic :-) What is the area of your loop? And what is the "gain" compared to the earth antenna? Will you give up the earth antenna project? And what about your ULF (838 Hz) tests?

For the IRF510 you can allow 20...25 V supply voltage, if well matched, so if the voltage is now 12...13.8 V you can double the voltage and get 6 dB more power, so maybe twice the distance :-)

73 and keep us informated!

Stefan/DK7FC


Am 18.09.2010 20:06, schrieb Roger Lapthorn:

Hi Stefan (et al),

Still using the single IRF510 but driving it with a better square wave now. I hope to change the design tomorrow to run from a higher supply rail and realise another 3-4dB or so of ERP. The other simple change I can make (later) is with my loop antenna, which is made from wire only 1mm diameter. Increasing this to 4-5mm wire should reduce the losses another 3dB or more. I can also try running the lower part nearer the ground thereby increasing the loop area by another 20%. However this may introduce other losses.

So far I am pleased with the results: with only around 4-5W from the PA, a very simple loop antenna with thin wire, tuned with a simple ATU on the bedroom table using just a standard capacitance decade box, a simple 3C90 step-down transformer and a current meter, I've now been heard/seen by 4 different stations in SE England and the WSPR reports already suggest further is possible.

This autumn is going to be a bundle of fun!

73s
Roger G3XBM

2010/9/18 Stefan Schäfer <schaefer@iup.uni-heidelberg.de>

Hello Roger,

Congrats to that distance and to the PA :-) Which FET is in use now? And how is the driver realised?

73 and GL,

Stefan/DK7FC

Am 18.09.2010 12:54, schrieb Roger Lapthorn:

Some success this morning with my second ever 137kHz WSPR report, this time from G3XIZ who got me up to -23dB S/N during the morning. According to the WSPR database the distance is 46km. BTW, the PA is running about 5W RF out (ERP about 10-20uW) in class-E with a nice cool heatsink. Next steps will be to increase the power and ERP.

2010-09-18 08:50

G3XBM

0.137534

-23

-1

JO02dg

0.001

G3XIZ

IO92ub

46

240

Many thanks Chris, and everyone else please keep looking!

73s
Roger G3XBM

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088

-- 
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088