WISPY-10 schematic (draft A)

OK, I promised to show the schematic of WISPY-10 (there may be versions for lower bands later) today so here it is. I have breadboarded and tested the TX and the RX parts on-air and both work well. In the transceiver I have used the oscillator with an additional buffer (x2) stage on TX and this has still to be tested but I don't expect any issues at all. Also shown is the TX-RX change-over using the back-to-back diodes in the middle of a series tuned circuit on the RX input. On TX the diodes conduct and the capacitor forms part of the output low pass filter.

Updated schematic (an error spotted by G3TFX)

At the moment I am not planning any further work as I want to crack on with the 472kHz work but I expect to return to this in a few weeks' time.

Click on the schematic for a larger, more readable, version. Please let me know if you spot any obvious errors (e.g. where I have put grossly wrong values of components in) so I can update the schematic.

Please feel free to use this as a starting point for your own version. All in, I doubt the components would cost more than £5 (7 euros or 8 dollars) even if all the parts were obtained new.

The 2N3866 runs quite hot in class A and I want to change this biasing in the final version. I may also susbstitute the 2N3866 for a couple of paralleled 2N3904s to save further cost.

The same circuit will work well on PSK31 (pull the crystal to the right frequency of course) but both with WSPR and PSK31 do not over drive the PA. This is a DSB transmitter and there will be splatter either side of the carrier for tens of kHz if driven too hard. Adjust the drive so the output from the PA is a clean, DSB signal free from obvious audio distortion.

WISPY now transmitting!

Breadboard of WISPY TX - 50mW pep WSPR (100mW DSB)

Very pleased with my little 3 transistor DSB 28MHz WSPR transmitter. Since turning it on at 11.34am I've received around 30 reports from stations in Europe despite the power being just 50mW pep ...and as I write my first spot from Africa: -14dB S/N (a good report) from EA8FF in the Canary Islands!

Schematic to follow tomorrow. OK, I know - there is no low pass filter on the breadboard. As the circuit is linear throughout and there is filtering on both stages the output is pretty clean, but I will add a 3-section LPF on the final transceiver version.

This is a very simple, all discrete parts, design using 2 x 2N3904s, 1 x 2N3866 (may be overkill) and a couple of 1N4148 diodes in the mixer.  Again, I use a cheap 14.060MHz crystal, pulled a bit and  doubled, as the LO.

FLEX-6700R hype?

Just read this on a UK supplier's website:

The FLEX-6700R™ Signature Series receiver is based on a new hardware architecture and SmartSDR™ software platform.  This hardware uses Digital Down Conversion (DDC) to convert from RF to digital.  The FLEX-6700R uses two Spectral Capture Units™ (SCU) for the RF to digital conversion and an ultra high performance on-board signal processing and control system to perform demodulation, filtering, and audio stream management.  The result is incredible receiver dynamic range and received signal clarity.

The FLEX-6700R model receiver utilizes two SCUs for reception from 0.33 to 77 MHz plus 135 to 165 MHz and the ability to create up to 8 full featured independent SLICE RECEIVERS.  Optimized preselector filters can be selected for the ham bands for greater out of band rejection.

SmartSDR is the “ecosystem” of the radio platform.  It organizes all the signal processing power in the radios into an advanced radio fabric.  SmartSDR understands the capabilities of each SCU and how to harness its power.  It also comprises of the “presentation layer” or GUI client that the user interacts with.  The FLEX-6700 utilizes an Ethernet connection for high-speed “driverless” access to the graphical user interface (GUI).

Now I know there are people around with too much money and there are some applications when a very good receiver may be of benefit, but would YOU spend £4799.94 on one? This is just the receiver remember! No thanks. I'll continue to build simple rigs for a few pounds and accept their limitations.

WISPY progress (TX side)

Despite promising to finish off the 472kHz transverter properly first, I decided to have a go at the TX side of the 10m DSB WSPR and PSK transceiver (WISPY). Starting with the PA and working back to the drivers I breadboarded a simple linear amp based on a couple of 2N3904s and a 2N3866. Power out is around 1.2W pep. I also added the osc/doubler and single balanced mixer later but have not optimised the overall strip. This phone image shows the breadboard I was working on - not a pretty sight. If time allows tomorrow I'll continue this and maybe get to hook it up to an antenna and a PC on TX.

Moonbounce with WSJT and MAP65

At a recent EME conference in Cambridge John Regnault, G4SWX demonstrated EME using WSJT by remotely operating his 1kW EME station (using the call GB2EME) located on the east coast of the UK. They worked well over 100 DX stations off the moon during the conference (which I did not attend). Joe Taylor W1JT who invented WSJT and MAP65 (and WSPR!) was there.

Although I'm an engineer who enjoys doing "a lot with a little", one has to be impressed by the dedication and sheer hard work some amateurs put into the hobby. Recently G4BAO demonstrated to me his 10/24GHz station which has software controlled rotators, mast top RF sections and GPS locked SDR receivers. He was able to make state of the art 10/24GHz narrow-band operation look easy, when in reality it was the culmination of a lot of very hard work over very many years. Of course, the effort goes on and on.  

Energy harvesting wireless bus bell push

The latest edition of Land Mobile Magazine (a magazine for professionals in the mobile radio business) has an interesting column showing how London Eco-Routemaster buses are being fitted with a novel sort of bell push (the kind you push to ask the bus driver to stop) which harvests energy from the action of pushing the bell to send a wireless signal through the bus to the driver. The bell push uses an energy harvesting chip from EnOcean a company that specialises in such devices.

The EnOcean evaluation kit (for professional developers) as shown on their website

This is the first time that I've seen a very practical use for energy harvesting. I assume that the device "harvests" kinetic energy (from the pushing action) and thermal energy (from the finger tips) but it must generate a few uWatts for this to work.  So, no batteries, no wires, wireless comms and good for 300k presses. There has to be a QRP application!

For more on this read the article on line at Land Mobile magazine. 

On with the projects.....

Back home now, so it is on with the autumn projects list.

Several people have been contacting me about the latest 472/500kHz 10W transverter. Someone in OK-land is designing a PCB and I hear a "dead bug" version has been successfully built in the USA - not sure whether an exact copy or "based on" - but it has already been used on MF WSPR with a report from over 2000km up the USA east coast. So, I will continue with refining this design first and then get on with the "WIPSY" 28MHz simple WSPR transceiver next.

The non line-of-sight optical beaconing tests will resume a little later when the evenings start to draw in. I want to set up a more powerful, semi-fixed 481THz optical beacon so that I can do a series of DX tests under various degrees of cloud cover. Tests last winter suggest much further will be possible than the 9km NLOS ranges achieved with clear air scatter when signals were audible by ear. By using much lower sub-carrier frequencies the optical detector sensitivity will be very much greater allowing even weaker signals to be detected on QRSS3 and QRSS30.

DXTV challenge?

Sorry for the absence of postings last week but we've been on holiday. No ham gear with me, but I did spot several nice HF and VHF yagis on my travels.

Several of my blog readers were DXTV enthusiasts (like me a long time ago), so I wonder who will be the first to identify where we were on holiday by this testcard copied at 4am this morning on the hotel TV? No prizes for giving me the country, but interested to know how many out there know the answer and whether or not this card has ever been copied in the UK on Band 1 TV. This was on 625 line UHF.

A plug for my son's MS concert in Oxford, Oct 7th

My son Tim Lapthorn, who is a professional jazz pianist, is holding a concert in Oxford on Sunday Oct 7th to promote his new album. All proceeds will be donated to the MS Society. You are most welcome to attend and enjoy.

Tickets may be obtained from http://www.oxfordplayhouse.com/ticketsoxford/?event=17386. The lunchtime concert is in the Jacqueline du Pre Music Building, Oxford starting at 1pm.

As the publicity says:

"Benefit concert for Multiple Sclerosis Society. Tim Lapthorn and his trio will play material from the forthcoming album, Transport (Pathway Records) which includes brand new original material. The group will also play reworkings of jazz/folk standards. Please come along to this very special event to help support a great cause!"

See also http://www.st-hildas.ox.ac.uk/jdpevent/tim-lapthorn-trio-ms-fundraising-concert

Progress on the WISPY transmitter

This afternoon I managed to do a little more work on the WSPR transceiver for 10m, building the oscillator/x2 multiplier stage and the balanced mixer for the TX part using a couple of 1N4148 diodes and a T50-6 tuned circuit. Carrier suppression is around 30dB without much effort. Next stages will be to add a linear amplifier to bring the DSB output to around 1W (500mW pep SSB carrier). Although I could combine the same mixer on RX and TX, I may stick with the Polyakov RX mixer as this is working so well. 

I should have added that with a linear PA, the WISPY transceiver should also be perfect for PSK31 as the 14.060MHz crystal (when doubled) will certainly pull to the PSK31 10m sub-band.

New ICOM all-band multimode

Icom have announced that they will be introducing a new multi-mode, multi-band radio called the IC7100 which includes 70MHz at 50W on some versions. This is, to my knowledge, the first time one of the big manufacturers has properly included 4m in the design. I know at least one Yaesu rig was capable of working on the band, albeit with some compromises. The new Icom rig has a separated control head with a sloping front, which is ideal for desktop operation and mobile.  It will be interesting to see the price and when it is likely to be launched. Also, whether or not they intend to do a 10W version (like the IC703) which was very popular with QRP enthusiasts.

A bit further with the WISPY RX

Although not in the best of shape today, I spotted CX1BP (11131km) and EA8FF on 10m WSPR today.  Not bad for a handful of cheap parts.

I had a bit of trouble today with the SE602 I was using for the TX part of WISPY (it may have been faulty but I was unable to get a clean DSB signal out of mine), so when I get back on the project after a week of interruptions coming up I'm going to go for the simple 2 diode single balanced mixer instead on TX. I know this works well and is less expensive.  The TX part can be simpler than the RX I believe.

Spots with WISPY RX

FR1GZ and others coming through just fine

This is the PC screen capture using WISPY as the 10m receiver for WSPR in the last hour or so. It is working just fine.

WISPY Schematic (more clearly)

For some reason when I put multiple images on a post it is not easily possible to see them clearly when clicked (at least with Firefox). So here is the schematic again. Clicking this image should bring up the full sized image clearly.

Hum fixed on the 28MHz WISPY WSPR RX

Rev B 28MHz WSPR receiver

Adding more audio decoupling around the oscillator and adding a common base FET RF preamp has totally fixed the common mode hum issues with my Polyakov mixer based DC receiver (WISPY) for 28MHz WSPR. Even running from a mains PSU I am getting good sensitivity and no hum. The board is working on the bench with no attempt at screening and appears totally fine. The oscillator buffer appears redundant, so has been removed.

Wispy Rev B (built using MeSquares)

One possible further mod is to make the input to the RF amp a series tuned circuit. This would be needed when the full transceiver version is made (back-to-back diodes would short the cap to ground on TX).  For now, I will leave the little RX running to see what I spot.

WISPY (Polyakov RX) - 1st spot

I rebuilt my 10m WSPR RX today (the rig has to be called Wispy) onto a tidier, smaller board using MeSquares and took a few steps to reduce the 50Hz common mode hum pickup, although there is still too much there and more work is needed. Someone suggested it was radiation of the 28MHz 2nd harmonic of the oscillator mixing with 50Hz in nearby PSUs being re-radiated and detected. Still unsure of the mechanism but there are lots of things to overcome this.

EA8FF on the Polyakov RX (note the 50Hz and harmonics lines locally generated)

However, the good news. The RX, even without a preamp, can detect down to an amazing -127dBm MDS, possibly lower but this is as low as my signal generator will allow and I did not try with an attenuator. My first reception of a WSPR signal was EA8FF at -18dB S/N. Remember this is a DSB RX so the noise figure is actually 3dB worse as it is picking up noise from both sidebands.

Next stage is to add a small preamp to see if this helps reduce the common mode 50Hz pick-up and increase the sensitivity another few dB.

Polyakov mixer and 50Hz hum

There is something strange about my Polyakov mixer based direct conversion receiver for 28.1246MHz WSPR at the moment.

On the bench, when connected to a 50 ohm signal generator or sitting on the bench without an antenna connected, the background noise is a quiet hiss. With an earpiece in a quiet room I can just hear a -125dBm signal, even without an RF preamp: it is a good, sensitive and simple design.

However, the moment I connect my outside halo antenna via a coax to the (unscreened) breadboard RX the 50Hz hum level is quite high, certainly some 40dB higher audio than the MDS signal. This is with the RX run from a small sealed lead acid battery. With a mains supply I might expect some hum, but what is going on? Why the high hum pickup?

My coax antenna feed passes through the loft and then outside passing plenty of mains cables, so I must be inducing some 50Hz pick-up on the coax outer which is coupling into the copper laminate breadboard ground plane. A tidy rebuild will be needed before I could put the RX into a screened box.

I do not recall having a similar problem with other DC designs I have tried (single balance diode pair, NE602, SBL1 etc.) when used in a similar lash-up breadboard.

Anyone any suggestions?

KX3 leadtimes shortening

The KX3 image on the Elecraft site

The Elecraft website now shows "New Order Lead Time: 60 days" for the KX3 10W transceiver. At one time this was around 120 days, so they are working hard to get products out more quickly now that any initial teething troubles have been addressed. www.eham.net still shows a satisfaction rating of 5 from 25 reviews, which is excellent.  A 2 month lead-time would put delivery around the end of October when DX on HF is likely to be at its best for many years.  I have to admit that I'm very tempted, but it is a lot of money.

The second 472kHz transverter (with MeSquares)

Partially built 472kHz transverter using MeSquare islands

This afternoon I started the build of my second 472kHz 10W transverter to confirm repeatability of the design. This time I'm using MeSquares from www.qrpme.com as islands to aid construction. The build is about 75% complete so I thought I'd take a photo to show the technique before the board gets too crowded. With some care the results can be almost as neat as a PCB.

MySquares and MyPads arrive

My order from www.qrpme.com arrived today by airmail from the USA. The PCB stick-down island pads look just the job and my plan is to build a second sample of my 472/500kHz transverter using these on a piece of copper laminate. There is no doubt that these pads will be a big improvement on my own rough-cut homebrew pads. I especially like the islands for SO8,  DIL8 and DIL14 ICs as fixing these with Manhattan construction has always been a real pain.

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?

Another country on 472-479kHz

Lubos OK2BVG reports that he has been granted access to the new 630m MF band and is already working stations.  Gradually more countries are gaining access although I doubt UK amateurs will be allowed access to the band before January 2013.

A few years ago I was extremely excited when Lubos managed to copy my 2mW ERP 500kHz WSPR beacon at over 1000km for the first time. Since then the beacon has reached Finland at almost 1800km. 

It is good to hear that several German stations are now active in the new band with conventional CW QSOs being quite common.

RX performance comparisons (and the KX3)

http://www.sherweng.com/table.html

Sherwood carry out comprehensive tests on various amateur products. See the full list in the link above to get an idea how good the Elecraft KX3 is. Sometimes ultimate performance is unimportant but it does indicate which products are the very good ones when it matters .

Simple 28MHz Polyakov Mixer WSPR RX

As the first part of my WSPR transceiver project for 28MHz, I breadboarded a Polyakov harmonic mixer based, crystal controlled, direct conversion receiver this afternoon. It was a great success!

28MHz Polyakov mixer based WSPR RX

The circuit shows the idea implemented. A low cost GQRP club 14.060MHz crystal is pulled to 14.0623MHz in the oscillator/buffer stage. This is then injected into the back to back diode "Polyakov" harmonic mixer which switches at 2x injection frequency i.e. 28.1246MHz, the WSPR USB dial frequency. The 28MHz input from the antenna is filtered and directly applied (no RF amp) to the diode harmonic mixer with the audio output amplified and filtered in the 2 stages of audio gain. The output then goes to the PC sound card. I may improve the audio filtering and add a 600ohm line transformer between the audio output and the PC mic or line input.

Minimum discernable signal (MDS) is around -124dBm, possibly a shade better. AM rejection was tested by injecting a 100% AM modulated carrier at 28MHz. An input of -53dBm was needed before the AM signal was detected, so 70dB AM rejection, which I think is very good.

More bench work to do, then I'll try looking for 10m WSPR signals on-air with the RX, but for about an hour of work, a very fine result. Once the RX is air-test proven, the TX part will be added to make a complete WSPR transceiver.

Autumn project list

My wife often calls me a "fireside fusilier" as I am always gunner (going to) do this or gunner do that.

Well here is my current projects ideas list, some of which I hope to address in the coming weeks and months. How many will be replaced with other ideas first?

1. Finish the 472kHz transverter and write this up.
2. Simple 28MHz QRP WSPR transceiver to use with a netbook.
3. Stand alone 137kHz receiver (for use with PC).
4. Semi-permanent E-field probe antenna and on-line 137kHz/472kHz grabbers
5. More non line-of-sight light beam experiments (get better distances).
6. Semi-permanent 481THz QRSS beacon for NLOS light beam tests.
7. Alternative HF antennas - maybe re-erect my Par Electronics 40/20/10 end-fed.
8. Further earth-mode (ground conduction) experiments - tests at around 30 and 73kHz as well as more tests at VLF aiming to improve best though ground DX (currently 6km with 5W).
9. Experiment with horizontal loop antenna on TX at VLF (maximising coupling into ground).
10. Build some better LF/MF test gear such as resistive SWR bridge, 50W dummy load and a noise bridge.

I'll give you all a progress update in about 6 weeks time!

PC based LF/MF receivers

There are some very neat ideas for simple LF receivers around that make use of programs like Spectran or Argo effectively as the second IF and detector stages.

DK7FC's simple 137kHz receiver

DK7FC recently posted his schematic for his 137kHz receiver which used a 4MHz crystal divided down to 125kHz using a 4060 IC with the IF at 12kHz (corresponding to 137kHz) being fed straight into the PC software. With programs like Argo the scale can be offset so that the correct frequency is displayed. Of course, there needs to be some front end filtering to remove the image, in this case at 113kHz. Using this approach one can make a very simple "stand alone" LF receiver for 137kHz weak signal reception. Such an approach is ideal for grabbers which are permanently connected to a PC anyway, uploading the received signals to the internet.

Baofeng UV-3R very inexpensive VHF/UHF handheld

You may or may not have seen the adverts on eBay for the Baofeng UV-3R handheld transceiver. These are available in several colour versions (including the yellow version shown here) for prices between £25-40 including shipping. For example Solidradio of Hong Kong have these available for just £29.90. Reports suggest these are not bad rigs at all.

What I've just noticed is that, the same supplier shows there is a 3 year UK SquareTrade (no matter what) warranty available for £8.49. So, for less than £40 you can buy a dual band VHF/UHF handheld with a decent warranty for 3 full years.  I've heard of some deals, but this takes some beating.

QRP 10m WSPR

As I cannot access my "lab" currently (kitchen refit materials are everywhere!) I am restricted to operating from my shack, so this morning I've been trying out 28MHz WSPR with 500mW out to the halo in anticipation of my QRP WSPR transceiver design coming soon. This will be DSB, so I will need 1W RF out to get the equivalent of 500mW on the WSPR frequencies.

500mW 10m WSPR reports today

Not unexpectedly, there are loads of reports on the screen when I last looked from all over Europe. The best report so far today is +8dB S/N which suggests just 500uW would have been sufficient to be spotted. I know that others have achieved similar, indeed very much better, success when the band is open. What is also intriguing are that I have been spotted within the UK at over 300km, presumably by Es or backscatter, although maybe by tropo?

I have still to finish off the 472/500kHz transverter and write this up before starting on the 10m WSPR rig, but should have the latter done quite soon. It will be fun to have a stand-alone 10m WSPR transceiver running with a little netbook.

Lack of recent posts

My apologies for lack of recent content, but we've been away from the home QTH whilst our kitchen is being refitted. The local builder, a good and reliable person, advised us to go away and avoid the chaos, so we have been exploring Kent and East Sussex from our son's home near Canterbury. No ham gear with me, just the iPod Touch 4g.

Update Aug11th: we have now returned home (PW awaiting me) to find the kitchen almost finished - 2 more days work - and looking good. Problem is access to my "lab" is impossible because of boxes and builders tools. With luck all should be clear by Wednesday when ham radio building can resume.

CW from Mars

The latest NASA rover "Curiosity" apparently imprints JPL in CW on the Martian surface as a result of its tyre pattern. See http://www.tyrepress.com/News/OFFBEAT/25967.html . If I recall correctly my callsign is on a microchip on "Curiosity" (see post last autumn).

MePADS and MeSQUARES

MeSQUARES

MePADs

As a fan of sticking small bits of cut-up PCB material to a solid piece of copper laminate ground plane in most of my projects I get through a LOT of bits of copper laminate. Getting lazy in my old age, I've just ordered some MePADS and MeSQUARES from www.qrpme.com in the USA. These are arrays of pads or IC footprints for dead bug or Manhattan style construction that can be snapped out and glued to the main ground plane making a neat layout possible without a real PCB.

Finally RIP Heathkit

It was a long time finally dying after the last Heathkit amateur radio product was made by this once fine company, but I read today on the Southgate Amateur Radio News page that what was left of the company has now filed for bankruptcy.  Latterly it had been involved in educational systems but funding was drying up.

VE6CN's fine line-up of Heathkit products

Founded in 1926, Heathkit was famous for its kits in the 1950s, 60s and 70s. They were the Elecraft of their day with sound designs and clear step-by-step building instructions.  My first introduction into electronics and radio was with a kit for Christmas 1961. I never looked back thanks to that wonderful product.

I hope VE6CN wont mind me linking to his picture showing his fine line-up of Heathkit products. For a lot more pictures of Heathkit amateur radio products see http://www.ultrawebb.com/OHP/gallery.htm .

Sub-harmonic mixer based 10m WSPR transceiver

My favourite HF band is 28MHz and I often put my FT817 on and run WSPR in the background whilst getting on with other things in the shack. You may be surprised how often good DX reports are received. This ties up the FT817 so I have been rethinking how to make a very simple WSPR transceiver for 28.1246MHz.

One neat idea is to use a 14.060MHz crystal (cheap from GQRP) pulled up to 14.0623MHz (it is possible) and use this to drive a Polyakov sub-harmonic mixer, which needs half frequency drive, in a simple direct conversion receiver feeding a PC sound card via an isolating transformer. The same oscillator, doubled would be fed into a single balanced DSB modulator and a small QRP PA stage. The resulting WSPR signal would appear as a DSB signal , not SSB, so half the power would be wasted but who cares with milliwatts?

The resulting full WSPR transceiver would be extremely small and simple, need no VFO or VXO and could be left running almost continuously when the PC is switched on. This would be ideal with a small netbook PC.

The idea is not new: see for example http://www.qsl.net/d/dl1gsj/html/qrssrx30.html .

Sounds like this is my next project......

Elecraft KX3 user satisfaction poll

A few weeks ago I ran a poll on the Elecraft KX3 Yahoo group asking owners how satisfied they were with the KX3 QRP radio released earlier this year. I don't own one of these radios, but do covet one. Poll results can be interpreted in a number of ways, but I think this is a fair summary:

• 65% of respondents found the KX3 exceeded or far exceeded their expectations.
• 24% of respondents found it met their expectations
• 9% were to some extent disappointed with the product

This is a very high level of satisfaction. Not sure why the total doesn't add up to 100%.

So, will I buy one? Not sure. What is certain is that if I ordered one today I'd be unlikely to see one in my hands much before Christmas such is the backlog and demand.

Updated MF transverter schematic

The current Rev D version of the 10W MF (472/500kHz) transverter is shown below. There are a few changes around the PA and output filter.

Revised 10W transverter schematic (27.7.12)

The Lesser Chirpy 10m CW transceiver

SPRAT 151 had my article on Chirpy, an ultra-simple, very basic crystal controlled CW transceiver for 28MHz. This does work and has even managed a few decent QSOs but, boy, does it chirp! So, today I followed up on an idea I had to reduce the chirp by FSKing the oscillator when on TX. The schematic is attached.

The basic idea is to switch to TX by closing S1 (increases the oscillator output to around 150mW) then key a capacitor in series with the crystal. As the oscillator is on at full power with the key off or on (FSK shift) the chirp goes. There are a couple of disadvantages (a) the rig is no longer full break-in, and (b) when the key is up there is the "opposite" morse about 1kHz up the band, which is wasteful of power and may confuse. Still, this is a "for fun" rig and, with virtually no chirp, a much better radio. As before, a small low pass filter on the output is advisable unless your ATU provides this.

I also adjusted the turns on the main collector inductor finding that a tap 3t from the cold end worked better. You will almost certainly have to experiment with the values of capacitance around the crystal and key to get the right amount of TX-RX offset.

UPDATE 29.7.12: corrected the circuit diagram (crystal going to wrong place!)

472/500kHz video

There is now a short video describing the 472/500kHz 10W transverter on my YouTube channel. This shows the transverter working on WSPR with the associated simple ATU and antenna current meter, all on the operating bench.

472/500kHz antenna improvements needed

For the last month whilst testing my 472/500kHz transverter I've been using a highly compromised antenna. Essentially it is a very short Marconi tuned against my central heating system ground. The first 6-7m is a coax cable running next to pipes in the loft horizontally. Eventually the coax runs outside and up 5-6m to my 6m/10m halos. The coax inner and outer are strapped together when used on 500kHz. In the last week we have had a new central heating boiler fitted, this time in the loft, so there are even more copper pipes and wires running close to the coax. Reports appear to be a few dB worse on 500kHz as a result.

The time has now come to design a "no compromise" 500kHz Marconi! Looking at the geometry of my garden I should be able to erect a 5-6m vertical away from the house with some 10m of horizontal top loading. I can add some inductance near the top of the vertical section and tune it all against a reasonably decent ground (4 x 1m long earth spikes, a couple of radials and the central heating copper).  Not sure how soon I can work on this but I would hope the ERP increase could be up to 6dB. At least with WSPR (and OPERA) one can do a series of tests over several days with each antenna and compare results. It will be easy to measure antenna current which gives a good indication of ERP when the antenna effective height is calculable.

New MF transverter ready for testing

472/500kHz transverter built more presentably

Being satisfied with the latest 10W version of my 472/500kHz transverter breadboard, I have now rebuilt it more tidily so it will fit in a small plastic or diecast box. This uses my normal "dead bug" construction using a piece of copper laminate as ground plane with small PCB pad islands to join some components. It will be tested tomorrow, but I am not expecting any issues.

UPDATE 26.7.12
Tested the transverter above on-air this evening and getting reports from several stations on WSPR.

WSPR reports so far this evening on 500kHz

Results with the new 500kHz transverter

WSPR reports received this evening (40mW ERP)

A decent evening testing the new 472/500kHz transverter with WSPR reports from 6 different stations (best DX 440km) and copying 3 different stations on OPERA Op4 mode. There is still a slight PA instability that needs to be fixed (probably decoupling changes), so there is a bit more optimisation to do.