LF - 137kHz

In all the time I have been at this QTH (now over 4 years) I have never once used 137kHz. At the old QTH I did use the band occasionally. At various times I used a 137kHz QRSS beacon and WSPR using the TX transverter shown here. Best TX range was 250km. On RX I copied Sweden.

See https://sites.google.com/site/g3xbmqrp3/mflf/137khz_tvrtr .

137kHz E-field probe mag-mount RX antenna

Some years ago I did some tests (in the car) looking to see where I could copy my low uW ERP 137kHz signal from home. Results surprised me, even with my deaf FT817.  I gave up on the far side of Cambridge (approximately 24km) with S/N still respectable.

This is all that you need to receive on the LF bands.

See https://sites.google.com/site/g3xbmqrp3/antennas/137efp.

Failed 136kHz QRSS3 test

Well, I optimised my 136kHz QRSS3 beacon match into my earth electrode "antenna" used on 472kHz and tested it in the house and right outside. All looked promising, so I headed for my local car-park about 1.8km  away. I was quite confident that with an E-field probe on the car I'd get a decent result. From the old QTH I got to the far side of Cambridge before I gave up as copy was so good!

Not a dicky bird - nothing at all, indeed I only got copy again when I entered our close at a range of a few hundred metres. As at VLF, the earth electrode "antenna" at this QTH is useless.

Not only that but at the end of the test I realise how poorly I still must be as I was totally exhausted. In my fitter days this test would have been totally trivial, but not any more. I think my trees and short baseline make this "antenna" totally out of the question at this QTH at LF. I need a better antenna for LF and MF use.

So, 136kHz was bad. A poor result and quite a lot worse than I was expecting. I was hoping for an encouraging result, but none was to be had.

136kHz test?

Between tomorrow and Sunday I have 2 major aims.

Firstly I need to test my 40,30,20 and 15m K1 rig as someone wants to buy it. It should be fine. I have not used it at this QTH but has worked some good DX on all bands in the past. As "surplus to requirements" I shall be really pleased that someone else will enjoy using it.

Secondly, I want to try my QRSS3 136kHz beacon using my E-field probe on the car on RX. I have managed to get the E-field probe back together again and will test things on RX in the lounge first using the EFP, FT817 and PC.  I have still to match my beacon to the earth-electrode "antenna" on TX but this should be easy.

136kHz QRSS3 test

Well, I have found most of the bits needed for my 136kHz QRSS3 test including the E-field probe (EFP) to mount on the car roof. I need to solder 1 short BNC to free end coax in the E-field probe and charge up a PP3 battery (for the EFP) and the FT817.  I also need to match the beacon to the earth electrode "antenna" at 136kHz.  I shall start copying the beacon in the lounge first before venturing out in the field.

Although I now have a preamp for the (deaf) FT817 thanks to a very very kind person, I'll not use this as I did not use one on the last test 2 years ago from the old QTH.

A few years ago this would have been so easy to do. Now it is a major exercise! Life is so much harder now since the stroke, but I remain determined to get better. Given time (maybe a lot more time) I hope things get back to more as they once were.

136kHz QRSS3 field test maybe?

If I can manage it (health worries) I want to try a test with my 136kHz QRSS3 beacon and earth-electrode antenna from my current QTH. Last time, several years ago, from the old QTH, I managed to copy my signals quite well on the far side of Cambridge using an E-field probe on the car roof. This time my aims are far more modest: I just want to see if I can copy the signal at all in my usual carpark test site about 1.8km away. If I can copy the signal, I might ask others to take a look. It is so long since I used this kit I have forgotten what is inside the box!

My biggest challenge will be reassembling the RX kit as I am still very wobbly. 15-20 minutes and I am normally "done in", especially if this involves physical or mental effort. I wish so much I was fit and well again.

I know I have to be patient, but at the same time I need to get the most from my body as it is now. Although I still get tired, I seem to regain a more normal  state more quickly than I did, which is hopeful.

Although I am hopeful of a full recovery, given more time, I am beginning to think I shall always have some level of disability. I need to know my absolute limits. If this is the end of field work it will be a very sad day.

My ERP on 137.766kHz is.......

Thanks to G4FEV, I've just realised that I made a fundamental mistake measuring my field strength, forgetting to turn off the AGC when taking the measurements of my signal relative to DCF39. Whereas my initial measurements indicated the ERP was in the low mW region, in reality my signal is much, much weaker. For example, G4FEV reckons my signal is some 70-80dB weaker than DCF39 where he is, if not more! So, tomorrow I shall have to try the test again and see if I can get a sensible figure with AGC turned OFF.

G3XDV's screenshot of my QRSS3 LF signal this afternoon.

Mike G3XDV (61km) has just sent me a very comprehensive report with 178 screenshots of my QRPp signal over the last 30 hours. Copy was remarkably good considering everything. Again, I am amazed how well this works.

New frequency for LF QRSS3 beacon : 137.766kHz

Using the strong German commercial station DCF39 on 138.830kHz (it is S9+ with me) as an accurate frequency reference, I have checked the frequency of my QRSS3 QRP beacon and it is running higher up the band than I thought due to the way the crystal is loaded. 

Frequency to look is 137.766kHz   +/- . It should be within 1Hz of this frequency. 

Reports and screenshots (looking now in the right place) would be very much appreciated. I shall leave the beacon running all today at QRSS3 speed.

137.675kHz QRSS3 beacon report

The <20uW ERP 137.675kHz beacon was copied again by G3XIZ 48km to the west of me last night. I'm pleased with this report as the power from the PA was less than it was a week or so ago, yet he still managed to copy me. Work is now progressing on the class-E PA based WSPR beacon which should run about 10W from the PA (ERP around 20-50uW).

137.675kHz QRSS3 beacon back on

This evening I restarted beaconing with my sub-20uW ERP beacon on 137.675kHz having fixed the blown FET PA. The current design is stable and seems to be working very reliably with around 4-5W from the PA. All being well the latest version of the 137.5kHz WSPR beacon will be ready and on-air this weekend. The design of this is a class-E PA and should run around 10W from the PA with an ERP of up to 50uW.

Encouraging QRPp results on 136kHz tonight

This evening I had a good report and screenshot from Chris G3XIZ 48km away. This is my best report in terms of S/N and distance yet, with very clear images on the Argo screen.  I was going to try WSPR on 137.5kHz but had problems with the PA so QRSS3 beaconed instead. ERP was less than 20uW.

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.

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.

136kHz QRP QRSS3 beacon video

This is a video showing the 2W QRP beacon for QRSS3 on 136.93kHz. Using a 20m spaced earth electrode transmit "antenna" it has been copied 8.6km away using an E-field probe antenna.