137kHz WSPR RX

At some point I intend to take a look at 137kHz WSPR. At present I can only receive and not transmit. Also, my RX is deaf and my antenna poor. Still, "nothing ventured, nothing gained" as they say. In other words, it is worth a go. If I copy anything on LF, that would be a bonus! I might copy the stronger  stations. Maybe later this week?

I should also try my coax outer, used as my antenna on 630m, on other bands.  I can TX on any HF band.

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 .

And STILL they wait....zzzzz

In the USA the FCC has still not released 137 and 472kHz to radio amateurs!! Frankly this is almost unbelievable. The FCC seems so unbelievably S L O W. At this rate many potential users will be dead i.e. those over 30 years old before these bands are released.😟 

I suspect most at the FCC know absolutely nothing about radio. This is demonstrable by the time taken to make radio related decisions. Come on FCC - get a grip!!!

I am losing all faith in the USA. First you elect Donald, seen by many in the world as a bad joke, and your main radio regulator appears useless to many of us in the rest of the world.

See http://www.arrl.org/news/band-plan-proposed-for-eventual-472-479-khz-use .

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.

137 and 472kHz bands in the USA

My conclusion is the FCC is a bunch of morons and pen pushers. I may be wrong and this is my personal view. To others, they may be wonderful.

According to Southgate News, these bands are still not available in the USA years and years after these bands were released in the rest of the world. As my own experiments on both bands with very low ERPs show, great ranges can still be achieved. I just don't understand their reasons for delays. OK, I know some utilities pump RF over cables in this frequency range in the USA, but if there is any harmful interference just instruct the station to go QRT or reduce power. With a low ERP limit initially I very much doubt there would be any problems.

FCC - get your fingers out and release these bands! To the rest of the world you appear a bunch of idiots incapable of making any decisions. Does anyone there understand RF? Wake up!

137kHz

It is some years since I tried this band, but I really ought to give it a go again. The last time was QRSS3 (I think) when I went looking for the signal with a mag-mounted E-field probe on the car roof, my deaf FT817 and a PC. After 24km I gave up as I was still getting decent copy despite the very low ERP.

Although I am pretty sure I have given this link several times before, you may be interested if you are starting out on that band.

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

137kHz transverter

Click circuit to enlarge

It is some time since I tried 137kHz. In fact, I have not tried this band at this QTH. The last time I used this band was at the QTH we moved from in summer 2013, shortly before my stroke. I need to try this band from this QTH.

If you are starting up on the band you may want to look at my TX transverter. With my 20m spaced earth-electrode "antenna" in the ground this was regularly copied by G8HUH some 250km away on WSPR. The ERP with this "antenna" is only about 30uW.  Sadly, the FT817 is deaf at 137kHz.

As you will see, it is very similar to my 472kHz design although this is a transmit only design. It is designed to be used with the FT817 at 500mW.

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

FCC - so so S L O W .....wake me!

It is hard to believe just how slow the FCC is being over the release of the 137kHz and 472kHz bands in the USA.  Years have passed and neither band is released. The FCC is worried about interference to utilities. For goodness sake! Surely they could release both bands with a tight ERP level initially on a "non interference" basis? I moan about OFCOM but the FCC seems far far worse!

This is from the ARRL site...

"Meanwhile, the Amateur Radio community continues to await action on ET Dockets 12-338 and 15-99 that would spell out service rules for the new 2200 and 630 meter Amateur Radio bands. The FCC was expected to issue a Report and Order last fall. That subsequently got moved back to the first quarter of 2016, which also has slipped.
Regulatory provisions under consideration have included a possible notification requirement by some radio amateurs to utilities that operate PLC systems in that region of the spectrum, prior to their starting operation on either new band. Utilities use unlicensed PLC systems to control parts of the electrical power grid.
Earlier this year, the ARRL has asked the Commission not to adopt overly broad requirements to notify utilities in advance of intended Amateur Radio operation on the pending bands. The Amateur Service would gain access to 135.7-137.8 kHz (2200 meters) and 472-479 kHz (630 meters). Both bands have been used by numerous Experimental (Part 5) licensees, and the ARRL’s WD2XSH 600 Meter Experiment continues."

FCC - the world looks on and is amazed!! Wake up!! One cannot help thinking that the FCC is a pile of bureaucrats who do not understand radio. Please, release these bands in the USA.

Worldwide 136/137kHz grabbers + a simple 2200m RX (kit or ready built)

This link to a very useful list of 2200m grabbers worldwide was found on the website of Yuki JA5FP.   If you are interested in 136/137kHz this list of grabbers may be very useful.  A grabber is a receiver that uploads what it receives to the internet, usually as a spectrograph.

For how to make your own grabber, see how I did it. My grabber is usually only active when I do experiments. See https://sites.google.com/site/sub9khz/vlf-grabbers/vlf-grabber-creation . I used a public folder in Dropbox and pointed my grabber website to this location. In my case I was monitoring 8.97kHz VLF,  or thereabouts, but the same idea will work at any frequency. I used Spectrum Lab or Spectran software to do the actual "grabbing". Other methods are equally valid.

Also on Yuri's site are details of his 136/137kHz receiver. See http://icas.to/lineup/idc-136ii-kit-eng.htm .  This simple, but very effective, receiver uses a divided down HF crystal to give a very stable LO frequency of 130kHz. The output feeds a PC using Spectrum Lab or Spectran software. The receiver is available as a kit or ready built. Ready built the cost (with enclosure and shipped to Europe) is currently $110.  I have no idea if duty is payable.  Kits (less enclosure) is $75 shipped to Europe.

137kHz E-field probe on my website

This afternoon I put a new page on my www.g3xbm.co.uk website describing the 137kHz E-field probe antenna used in my recent "drive around" tests in the local area out to 25km. You may recall I put my 6uW ERP QRSS3 beacon on and went out into the Cambridge countryside trying to see how strong it was in various locations.

The whole unit is fixed to a car mag-mount antenna and works very well indeed.

137kHz 30-40W TX transverter schematic

As promised, here is the schematic of the current 30-40W TX transverter for 137kHz. I have used a 10MHz crystal but a lower local oscillator frequency would be slightly better from a stability viewpoint when using narrowband modes like QRSS30 or WSP15. One choice is to use a low cost 1.843kHz crystal mixing with the driver transmitter's output at 1.979kHz. When a stable external LO source is possible e.g. a GPS disciplined oscillator, remove C7 and feed the LO into the double balanced mixer. Although an SBL-1 mixer was used an alternative, available from eBay is the ADE-1. As balance is not super critical, a home made double balanced mixer would also be possible.

For PA heatsink I just used a couple of small TO220 heatsinks in the prototype. With optimal PA matching into 50 ohms there is little heat from the PA device. A larger heatsink could prevent overheating when the antenna is mismatched. My output network was optimised for my slightly higher than 50 ohms output load presented by my earth electrode antenna.

ERP is around 30uW with my earth-electrode antenna.

Some may prefer to use capacitive coupling into the FET gate. If TR3 failed open circuit, the gate voltage would rise leading to the IRF640 failing. Hasn't been a problem so far though.

137.766kHz ERP - now measured at 6.6uW

So, today I repeated my field measurements to establish the ERP of my 8W 137.766kHz beacon feeding my earth-electrode antenna. This time I did the measurement correctly. Here's how.

1. Travel 2km from the home QTH with E-field probe, FT817 and PC running Spectran.
2. Choose a location in the best direction for the "loop in the ground" so the measured signal strength is close to the maximum possible i.e. not off the sides of the loop.
3. Set up FT817 so the RF gain is adjustable and turned well back and the AGC is inactive.
4. Tune in my LF beacon and adjust the RF gain to the lowest possible detection level.
5. Measure the S/N of my signal with Spectran and note reading.
6. Retune to DCF39 (138.830kHz) and, without adjusting the RF gain at all, measure the S/N with Spectran.
7. Repeat these measurements 5 times.
8. Calculate the difference in dB between my signal and DCF39 (in my case 41.3dB)
9. Using the assumption that DCF39 has a field strength of 1mV/m, work out my own field strength (in my case 9uV/m)
10. Using the formula ERP = (E^2 * d^2)/49 work out the ERP.

Answer? My measured ERP on 137.766kHz is 6.6uW

Caveats:

1. If DCF39 is not approx 1mV/m then the ERP needs to be adjusted up or down proportionally.
2. Measurement error is +/- 2dB.
3. The ERP is the figure measured in close to the best direction. Off the sides of the loop the ERP will be much lower.

Conclusions:

1. Stations able to detect the QRSS3 signal at any distance are doing well as the signal is very weak indeed.
2. Using my proposed WSPR transverter at 32W, for example as a reasonable target output, would give me 6dB more ERP at around 25uW.
3. Based on results with QRSS3, I should be able to be copied using WSPR-2 at up to 100km on ground wave. At night with sky wave, considerably further is possible. 
4. Using WSPR-15 and 32W my ground wave range should be up to around 200km, possibly a little more. 

The QRSS3 beacon is still running over the weekend and more reports would be welcomed

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.

G4FEV reports my QRSS3 LF signal at 56.7km

Path between G4FEV and G3XBM

This afternoon I was out and about with my E-field probe checking signal levels of my little 137.766kHz QRPp QRSS3 beacon at various locations around the Cambridge area. The furthermost point I tried was near Comberton, 21.5km WSW of the home QTH in Burwell. I have taken a lot of measurements, including the level of DCF39 at the same locations so that later I can work out my field strength and thence ERP.

G4FEV's screen shot of my QRPp QRSS3 137.766kHz beacon at 56.7km

When I arrived home I had an email from Dave G4FEV 56.7km due west of me to say he had copied my signal and had sent a good clear screenshot. Signals with Dave looked quite good, suggesting the signal due west may be stronger than signals in the Cambridge direction (SW - WSW). The earth-electrode antenna has directivity but, aside from a zero copy at one location orthogonal to the "loop" I have still to work out exactly which directions have the strongest signals. Based on the above I think it is close to W-E.

New 137kHz Transverter thoughts

IRF640 FET

This evening, I've ordered a reasonable sized heatsink to use with the new 137kHz transverter. I am aiming for a power from the transverter of at least 30W and want to be sure that with mismatch the PA is able to survive quite hard abuse. The IRF640 looks a good choice for the PA, maybe a pair, as it is rated at a high voltage (200V) and high current (18A) so I can run the PA from a 30V (or even 50V) supply to get more out. Even with 30W RF, the ERP will still be in very low milliwatts.

As I want to ensure the 10MHz LO signal is very stable so I can use it with WSPR-15 and QRSS30 modes, I may put this in a separate insulated enclosure and pipe the injection signal in via coax.

What I am most concerned about is the lack of activity on the 137kHz band: the last time I gave it a go with WSPR the biggest issue was the very few people actually monitoring WSPR on the band. At the moment, the new 472kHz band is very much the focus of attention with up to 50 WSPR users monitoring and/or TXing on any evening. On 137kHz however the number of WSPR users is often just 3 in the world with no-one on in Europe at all.

Still, I am convinced that with WSPR-15 I should be able to reach near Europe even with my 20m earth-electrode antenna if I can get the power up to around 30W from the transverter. It may even be possible, just, with WSPR-2.This is worth a go, before getting back onto other projects ...like finishing off the Tenbox transceiver!

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.

E-field probe mag-mount now built

This morning I decided that it would be better to build the E-field probe for 137kHz RX at the base of the whip directly on the mag-mount base rather than inside the vehicle and having to tune out the cable capacitance. This way,  the cable capacitance is no longer an issue. I built the E-field probe into a small plastic box and arranged it so the whole unit attaches to the mag-mount using a PL259 plug in the bottom of the unit. Radio 4 on 198kHz is an S9+ signal with the mag-mount sitting on the bedroom window-sill with around 10 inches of whip. It appears to be working well.

The present design is a poor man's PA0RDT probe but using an MPF102 and a 2N3904 rather than the better devices used in Rodolph's high IP2/3 design. I may put a tuned circuit in the FET drain to increase the gain at 137kHz and reduce the gain outside the band. I will experiment with this before going out in the car.

Currently it is snowing continuously here, so road testing the EFP and checking coverage of my QRP 137kHz CW and QRSS3/30 beacon will now have to wait until later in the week.

UPDATE: I have modified the EFP so that the FET output comes from the drain with a drain tuned circuit tuned to 137kHz. I have the source resistor not decoupled initially but will consider adding this if I need a little more overall gain as the barefoot FT817 is very deaf on 137kHz.

Back on 137kHz TX

QRSS and CW beacon TX for 137.685 kHz

Today I went into the shack with the intention of making a new transverter for 137kHz based on my recent design for 472kHz.

Instead, I ended up building a new CW, QRSS3 and QRSS30 8W beacon transmitter using an IRF640 PA device. This evening and overnight the beacon will run QRSS3 on approximately 137.685kHz and I have requested reports and screenshots.

The antenna being used is my 20m spaced earth-electrode pair set-up used very successfully on 472kHz last weekend. On 137kHz signals are much weaker than on 472kHz, so I await reports with interest.

The whole unit runs quite cool when housed in a plastic box. Switches on the front of the boxed unit allow up to 7 pre-programmed messages to be beaconed at varying speeds. As normal, I use the K1EL beacon chip for the beacon message generation. The signal source is a 3.579MHz crystal in a divide by 26 circuit implemented in a PIC like device and kindly supplied to me by a French amateur Francis F6HSI a few years ago.

Thoughts turning to 136kHz again

After a few weeks on the new 472-479kHz band, my thoughts are again turning to 136kHz, a band that I experimented with a year or more ago now. This band is MUCH harder work than 472 or 500kHz with around 20-30dB more of everything (!) needed.  By this I mean that for the same power, the "effort" to get a contact or report seems to be about 20-30dB more. This is partly because the short antennas I use have a very low radiation resistance at 136kHz so losses become more significant. Also, noise can be even more of an issue.  Despite all of this, I plan to make a 136kHz version of the transverter I did for 472kHz, but maybe with a bit more RF output (in the 20-30W region). Most of the design is ready done (in my head) so it should only take a few days to do. The plan is to TX using my earth-electrode antenna.

On 136/137kHz there are fewer stations using WSPR, so I will probably use QRSS more. In the past I have made QRSS crystal controlled beacons for this band, but with a transverter and my FT817 I will be able to generate a QRSS signal wherever I want in the band and also be able to have QRSS QSOs.

Does anyone have recommendations for SIMPLE PC program that will allow me to generate QRSS (various speeds) as an audio tone? 

This way I can use my SignaLink USB interface and VOX to send QRSS (or DFCW) using audio tones. Please don't suggest Spectrum Lab unless you can give me a "Noddy guide" on how to use it for QRSS! This is a very good program, but to a simple soul like me it seems like you need a PhD to drive it. In the past I've used it for VLF reception, but it took me weeks to work out how to drive it and every time I go back to it I need to learn it all again. I just want a simple QRSS tone generator.

LF/MF Loop antennas on transmit

For the last few winters I've used a wire loop antenna on 136 and 500kHz transmit with moderately successful results. Well, considering the extremely low ERP it is better to say excellent results. My wire is not that thick: around 1mm PVC covered multistrand wire and the loop area around 80m square, with the lower part of the wire either very close to, or actually on, the ground.  Using the TX loop calculator at http://www.66pacific.com/calculators/small_tx_loop_calc.aspx the efficiency is around -30dB at 500kHz, so that 5W from the PA would result in around 5mW ERP radiated. My calculations and measurements, with less than ideal loop geometry, suggest the ERP is some 3dB lower at around 2-3mW. At 137kHz the loop is considerably less efficient at around -50dB.

For a small plot with nearby trees I am not sure how well this compares with a small Marconi with a short vertical section (around 6m max) and a horizontal section of around 6m. Anyone know the answer?