472kHz transverter

A few years ago my design for a simple 472kHz transverter was published in the ARRL journal QST. It is also on my website. Several derivatives have been constructed including a version using SMD parts.

Although simple and low power, it has been copied as far north as Norway on WSPR. Although the transverter produces 10-15W output, the ERP from the earth-electrode "antenna" is a measured 10mW.

Now is the time to get ready for "the season" which tends to start in the autumn. In the summer months quite a few stations desert the band. This transverter and a simple earth-electrode "antenna" in the ground are all that are needed to get on the band.

Certainly with more power and a "real" antenna and ground system better results can be expected, but this "KISS" approach you can get over 1000km on WSPR on winter nights.

4m transverter

Some years ago at the old QTH (2012?)  I designed and built this transverter for 4m (70MHz). As I recall I erected a wire dipole for the band just before a contest and worked a few stations on CW.

At the present QTH, I have never been on 4m.

Many years ago (1968?) I recall working ZB2VHF via Es one summer from university with 4W of AM on 70.26MHz. I can't recall the 4m antenna we used, but it was at best a small yagi.

As I recall, this QRP transverter put out 1-2W on the band, but could probably produce a bit more with some optimisation.

These days there are quite a number of countries on the band. This was not the case back in the 1960s when it was mainly a UK allocation and only 70.2-70.4MHz. Maybe I should give the band another go? As I recall it is quite an effective Es band in the Es season, and with a few watts much of the UK can be covered.

472kHz transverter video

The video I made many years ago of my 472kHz transverter was not on my YouTube G3XBM channel, not sure why. It now is. It is also here.

Out with the soldering iron

Well, it was harder than it used to be and I got tired easily, but this morning I mended my 630m transverter using my soldering iron.  Assuming the mod worked, I'll try 630m TX this evening.

My antenna will have to be the coax up to my 2m big-wheel via an ATU and a mains earth as my brother managed to cut through my earth-electrode "antenna" when gardening earlier in the year! I could mend this later.

4m QRP transverter

It is some years since I was active on 4m.  Several years ago now, I designed and built this transverter as I had no gear for this band. I worked a few stations in a 4m contest with it and just a wire dipole.

Of course, these days the IC7300 from ICOM covers 4m.  These days there are lots of EU countries on the band, so it can be good in the Es season.

Years before I recall working ZB2VHF with 4W of AM in my university days by Es.

At some point I intend to get on 4m again.

See https://sites.google.com/site/g3xbmqrp3/vuhf/4m_tvtr .

472kHz band

In the autumn and winter, this is one of my favourite bands.

For several seasons now I have been on 472kHz WSPR transceive with my earth-electrode "antenna" in the ground. Despite the very low ERP (around 5mW!) it has been spotted well over 1000km away several times. My transverter which appeared in QST magazine about a year ago produces 10-15W, so with a decent antenna it could do well.

As far as I know, the USA is still awaiting access to this band. This is a fascinating band, well suited to WSPR.

See https://sites.google.com/site/g3xbmqrp3/mflf/472khz_tvtr

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 .

Not a bad session on 472kHz WSPR

Overnight, I was spotted in 5 countries by 11 unique stations on 472kHz WSPR. As usual, I get a measured 5mW ERP on TX from my earth-electrode "antenna". The power from the transverter is about 12W into 50 ohms.

Just about anyone could get on this band with WSPR with a similar set-up. Big antennas and great earth systems are nice, but are not a prerequisite to get started on the band.

472kHz homebrew transverter

Uniques on 472kHz WSPR overnight on TX (5mW ERP)

630m Transverter

A reminder that there was a 4 page article in Sept QST on the design of my simple transverter for 630m. This is also on my main website at www.g3xbm.co.uk. I use it with my FT817, but other rigs could be used.

630m is a good band and the transverter puts out 10-15W into 50 ohms. Even with my earth-electrode "antenna" it has spanned most of western Europe on TX with a measured ERP of about 5mW on WSPR.

Flattered? 472kHz TX transverter kit

An anonymous comment in my last post brought to my attention that there is now a kit based on my 472kHz transverter. I see the kit uses toroids whereas I used homemade coils wound on PVC pipe pieces. Flattered!

See http://njdtechnologies.net/wp-content/uploads/2015/07/MF-Solution-Flyer-2015.jpg .

Four metres

Four metres (70MHz) is now quite widely allocated in Europe and a few other countries.  At one time this was only allocated in the UK and some UK territories. A few years ago I wanted a way of getting on 4m as this was one of the few bands not covered by my rigs. A simple transverter was called for. The following design fitted the bill. There are very few commercial rigs for the 4m band, among them being the IC7100 from Icom.

It is possible this design has appeared here before.

At the current QTH I have no antennas (even dipoles) for 4m, but I worked some decent distances on an fixed indoor dipole at the old QTH. It should certainly be possible to work Es DX with this transverter although I have not tried. I need to erect a 4m antenna!

See https://sites.google.com/site/g3xbmqrp3/vuhf/4m_tvtr .

472kHz (630m)

This is a fascinating MF band. I am truly amazed how slow the FCC has been releasing this band and the 136kHz band in the USA. Do they sleep all day?

Simple, small, 472kHz transverter

Even with just 5mW ERP from a just a short baseline earth electrode antenna (earths 12m apart) I have been copied on WSPR more than 1000km away. Copy at shorter range is very easy. I use my transverter with the FT817. The ARRL was due to publish the circuit over 2 years ago, but are still waiting for the FCC release. For goodness sake wake up FCC! You look total fools to the rest of the world!

See https://sites.google.com/site/g3xbmqrp3/mflf/472khz_tvtr .

472kHz transverter

Over the winter I have been using my simple, small transverter for the 630m band on WSPR with my earth-electrode "antenna". It has been widely copied with best DX on TX being over 1000km. 630m is an interesting band.

See my website for more details: http://www.g3xbm.co.uk  (lots of QRP stuff) and specifically  https://sites.google.com/site/g3xbmqrp3/mflf/472khz_tvtr.

Australian 472kHz transverter

See http://www.vk3xdk.net46.net/89_31_600M-472Khz-479Khz-Transverter-V2.html . This is a 472kHz, mostly SMA parts, tranverter which is available from Australia for 180 Oz dollars ready built and tested. That is around £90, but this does not include shipping or duty. The transverter uses a 28MHz packaged oscillator. My own design (see www.g3xbm.co.uk website) is built "dead bug" style. Both the VK3XDK and G3XBM designs put out about 12W into a 50 ohm load. 472kHz is a fascinating band and even very compromised antennas work.  I have nothing special WRT antennas. I tune up the feeders to my V2000 vertical and Par end-fed and use a mains earth. This far from ideal arrangement gets out ( best DX is 896km with 5mW ERP and best RX DX is 1190km so far this season).

Recommendation: give 472kHz a go.

472kHz transverter

It is always very satisfying to see when someone has taken one of my designs and taken it on to the next stage. In the case of M1GEO, he has made a PCB for a design based on my transverter. It looks so much better than my original! Dead bug build style is fine for "one offs" mind you.

See http://www.george-smart.co.uk/wiki/472_kHz_Transverter

It is quite a while since I was last on 472kHz. I really should try loading up  the feeder to my 2m/70cm antenna to see how this performs.

472kHz TX

Yesterday I wound a loading coil on a 110mm drainpipe for the 472kHz band which should allow me to transmit on the band using my homebrew transverter. The only thing stopping me is fatigue: I get SO tired doing the simplest of things because of my recent illness. With luck, I shall try this later this week.

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.

Website working again

The main www.g3xbm.co.uk website is now working properly. I contacted my domain providers last night who confirmed they'd updated some systems that screwed up web forwarding. If you spot any more problems, typos or link errors please let me know.

Currently I am drawing out the schematic of my 30W 137kHz TX transverter. This should be on the website tomorrow. Still deciding whether to box it, and add the RX preamp section, or stop at this stage.

SMA version of the G3XBM 472kHz transverter

In an email,  John G4BAO tells me he has built an SMA version of my 472kHz transverter. At present, he is getting 5W RF out using standard SMA parts and a different FET.  If you wish to enquire about this version please contact John and NOT me!

G4BAO's SMA version of the G3XBM 472kHz transverter