M0BMU receiving DK7FC's 8.97kHz signal 10dB S/N

Jim reports that Stefan's DK7FC's 8.97kHz test signal is visible at 10dB S/N in Tring UK this morning. He is also visible on other grabbers in Europe. This is an excellent report and further encouragement for those of us taking our first (QRP) steps on the 33km band.

7th new reporter on 137.5kHz WSPR

M0BMU copied my 137.5kHz QRP WSPR signal today giving me -19/-20dB S/N, which is quite a good report. Distance is 69kms. This is now the 7th unique station reporting my WSPR beacon. I'm still hoping for a report from outside of the UK soon, but suspect I'll have to increase the ERP beyond the current 20uW level to achieve this. The consistent signal report from Jim should allow me to calculate ERP based on field strength at a good distance. This will allow me to check the accuracy of my ERP measurements much nearer to home.

M0BMU's latest complete 8.97kHz Portable Receiver

Jim Moritz M0BMU has updated his loop/preamp circuit for 8.97kHz turning it into a complete direct conversion receiver for 8.97kHz. He posted this on the LF reflector in the last few days. I have added this to my sub-9kHz website (scroll down for Jim's description and schematic on the webpage. See http://sites.google.com/site/g3xbmqrp/Home/10khz

Receiver for 8.97kHz DX experiments

Jim M0BMU successfully copied signals from DK7FC on 8.97kHz VLF last weekend using a small loop antenna and preamp feeding into a Spectrum Lab soundcard VLF receiver. I've put a copy of Jim's latest preamp on my 9kHz page on my website. Others have tried voltage probe antennas.

9kHz band receiver front-end (M0BMU)

Jim M0BMU has produced a neat loop/preamp design suitable for listening on the 9kHz band for which we hope NoVs will be available shortly in the UK. His design has sufficiently low noise to provide a state-of-the-art receiver for this band when used with the many excellent software based VLF receivers such as Winrad and Spectrum Lab. This circuit was posted on the LF Reflector this evening.

New 500kHz ERP calculation

Some weeks ago Jim Moritz M0BMU made an estimate of my 500kHz ERP based on received signal strength levels at his QTH 69kms away. As I've recently increased my ERP, I asked Jim if he would kindly do a recalculation. These are his latest estimates.

Well, repeating the original calculation, taking your "best" signal level as -12dB on a noise level estimated at 3uV/m in 2.5kHz, your received field strength at my QTH is 0.75uV/m. At a distance of 69km, and assuming only "geometric spreading" propagation losses (i.e. an inverse relation between FS and distance), your ERP is

ERP = (Ed)^2 / 49 , with E = 0.75u, d = 69000, ERP = 55uW

Then we have to consider what additional propagation losses exist; originally I suggested 3dB, which would increase the ERP to 110uW. However, looking at G4FGQ's grndwav4 program, and the ground resistivity around this area, the "ground type" in the program might be 6 - 8, making the ground wave propagation losses between 4.2 and 8.5dB. This would make the ERP between about 140uW and 390uW.

Obviously there is a lot of uncertainty in this kind of estimate - the two main things are the possible variability in noise levels between when I estimated the noise level and now, and the propagation losses. Both these could contribute several dB variation, so the ERP estimate should only be regarded as "order of magnitude" accuracy.

Still, your signal is certainly much stronger now - one of my nearer-term projects is to make some more accurate FS measurements by injecting a calibration WSPR signal into the loop antenna, which should give a more direct and accurate measurement of the signal levels.

Cheers, Jim Moritz
73 de M0BMU

136kHz band WSPR reception

Jim M0BMU was firing up his transmitter on 137kHz today using WSPR. Managed very good reception of his 200mW ERP here at 69kms range. See screenshot - he is the yellow dashes. He was clearly audible by ear too, so a 12 wpm CW signal would have been copied well.

500kHz WSPR screenshot from G3XVL

Chris, G3XVL, in Ipswich has just sent me a screenshot of my 500kHz WSPR signal this morning when I transmitted at 100% for about 30 minutes. It clearly shows the drift when I go on TX continuously. The drift is about 40-50Hz worst case. I now suspect this is drift in the FT817's reference oscillator as the box heats up and NOT drift in the transverter. I may try using the IC703 as this has a larger mass and should drift less.

The very strong signal is M0BMU and the one towards the top is G7NKS. No new reporters overnight, so it remains at 4 reporters with best DX 69kms when using less than 1mW ERP.

More QRPpp success on 500kHz

My tiny 500kHz WSPR TX station was heard 69kms away at dawn today with a report from Jim M0BMU who spotted me several times. I also had a lot more reports from G3XVL (61kms) , some 10dB stronger than his first report last night, as well as more from G6ALB (3kms).

The picture shows my 500kHz ATU on the bedroom dressing table. This is the ONLY thing between the 700mW QRP TX and the 15m of wire dangling down the back garden - no big loading coils etc. The small toroid is a 1:50 current transformer so I can measure antenna current with a multimeter. I tune up by getting the best received signal by ear adjusting tap points used, then carefully peaking the series capacitor for maximum antenna current, which barely shows anything!

Next step is to convert the transverter to full transceive which should only need the addition of a couple of relays and an RF-sensed changeover.

WOLF weak signal mode success

After a frustrating evening of not decoding a WOLF signal, I was told how to calibrate my PC's sound card. Then I retried decoding M0BMU's signal and met with immediate success:

2009-09-10 21:15:29 >WOLF10 -r 8100.257 -f 1000 -t 1 -w 0.0000
t: 24 f:-0.339 a:-1.5 dp: 85.6 ci: 7 cj:272 M0BMU IO91VR 2W -

It seems this mode is more critical than WSPR but offers the prospect of decoding even weaker signals on the LF bands. The calibration is easily done using the 198kHz Radio 2 signal and takes only a couple of seconds.

136kHz WSPR on an active antenna

Just tried a PA0RDT designed active antenna (but just used an MPF102 and 2N3904 instead as these devices were to hand) with 1m of wire, later just a small piece of copper laminate (see picture), indoors taped to the window and have just spotted M0BMU running 200mW ERP on 137.45kHz WSPR. Amazing that this can work so well. The antenna looks useful for VLF through to low HF. See also
http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna.html and http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna-continued.html

SM6BHZ on 500kHz WSPR

Just received my first WSPR signal on 500kHz - from SM6BHZ running 1W erp. Signal first appeared at 1916z and was decoded 6 minutes later. This is a screen shot of his signals. Several other stations are also copying Gus if you look on the WSPR database and maps tonight. Later in the evening he was so strong he could have been copied with just 2mW ERP.

I also copied another 500kHz WSPR signal, this time from G4WGT who was -23dB S/N with 500mW ERP from IO83 at 248kms. The map shows stations active on TX or listening and shows I've received SM6BHZ and G4WGT. Very clever database this!

Later still copied M0BMU and G4WGT again on 500kHz WSPR.