31 Jul 2012

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.

27 Jul 2012

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.

26 Jul 2012

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.

25 Jul 2012

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

21 Jul 2012

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.

472/500kHz transceive transverter

Rev C Transverter (one correction: o/p LPF cap 6n8, not 100n)

Armed with the sensitivity data in the last post I have now modified my MF transverter to add the receive parts, without a preamp. I used the same scheme adopted in my old transverter to automatically switch through the 500kHz (or 472kHz) signal on receive directly to the FT817. Only 4 additional parts were needed to make it into a TX/RX transverter.  As proof that the RX part is working I have just copied PA0WMR with a huge signal on OPERA Op4 with the signal passing through the transverter.

How deaf is the FT817 at 136, 472 and 500kHz?

You may have read that the FT817 is deaf below 160m. This matters if you want to use the rig "as is" without preamps as a receiver for 136, 472 or 500kHz. So I decided to measure the performance using a signal generator. I measured the MDS on CW (the level at which I could just still hear a  CW tone without additional filtering), the level for S1, S5 and S9 on the FT817's meter. I also checked whether having the IPO switched in or out made a difference

These were my results:

136kHz (best results with IPO on)  DEAF!
MDS -103dBm
S1 -72dBm
S5 -68dBm
S9 -48dBm

472kHz (best results with IPO off)    SLIGHTLY DEAF
MDS  -120dBm
S1  -84dBm
S5 -81dBm
S9 -60dBm

500kHz (best results with IPO off)    A BIT DEAF

MDS  -124dBm
S1 -85dBm
S5 -82dBm
S9 -60dBm

What conclusions can be drawn? Well, the FT817 is definitely very deaf on 136kHz and needs a preamp to be usefully sensitive. On 472/500kHz, although the MDS is worse than at 1.8MHz, the sensitivity is arguably OK without a preamp. Yes, a small amount of high dynamic range gain with good filtering to stop overload from adjacent broadcast stations may give you a slightly better sensitivity, but the question is whether this matters when external noise may be the limitation. I have used to FT817 on 500kHz for several years and heard most of what was going, including transatlantic stations. At 472kHz it is slightly worse but still useable I think.

20 Jul 2012

GQRP Component Data Book

Tony Fishpool G4WIF, G4CCQ, G3OOU and others have created an on-line, downloadable, GQRP Data Book which has the pin-outs of a number of devices commonly used in QRP designs featured in SPRAT and elsewhere. It is just what I need to stop me having to look up parts on the internet every time. This is "a work in progress" as they say with updates and additions coming frequently.

Finally, why not join the GQRP Club? Its quarterly magazine SPRAT is still the best amateur magazine in the world and remarkable value at £6 UK, 12 euros or $18 US. Details at http://www.gqrp.com/join.htm .  As well as very interesting constructional projects, the magazine has operating news, useful adverts from QRP suppliers as well as adverts for GQRP club sales which supplies members with useful QRP parts (semiconductors, crystals, DVDs of SPRAT back issues, etc) at very reasonable prices. The GQRP club represents the spirit and ethos of amateur radio at its best.

472/500kHz TX transverter - first schematic

10W 472/500kHz TX Transverter (CW, WSPR, OPERA, QRSS)
OK, here is the first schematic (subject to corrections, changes and improvements) of my simple TX transverter for 472 or 500kHz. This one needs no expensive parts and went together painlessly. The PA filter parts used the GW3UEP approach of winding thickish copper wire (1mm in my case) onto 22mm white PVC drain pipe pieces. The mixer, LO and squarer stage all use ubiquitous 2N3904 transistors (my favorite!) and the PA a cheap IRF510 FET that produces 10W RF without even getting warm.

Next stage is to add the RX preamp and filter and sort out RX-TX switching. I also want to try to go for a higher PA output power which will require changes to the output network.

15 Jul 2012

500kHz tranverter (Mk 2) breadboarding

This weekend I've made considerable progress with the new transverter for 472 and 500kHz and fully breadboarded a 10W TX transverter.

My objectives are to make the design simpler than the original 2010 design  (no expensive SBL1 double balanced mixer!), produce more power and improve the RX performance. Also I want to reduce the need for special parts such as toroids.

The design evolving is, like all my designs, a mixture of my own ideas and the best from other people. When the design is ready I will put it here and on my main website. I've moved away from 28MHz IF (too high, too much start-up drift) and instead gone to 3.7MHz using a 3.2MHz crystal available from GQRP inexpensively. The TX mixer (none is needed on RX as it is uses the FT817 in split mode receiving directly on MF) is a simple bipolar stage followed by a low pass filter. For the PA I have largely copied GW3UEP's excellent designs for a 25 (and later 100W) amplifier. Initially I am using an IRF510 from 13.8V and getting around 10W RF out. The next stage is to look at the RX front end. I want a little gain ahead of the FT817 but with good large signal handling and decent filtering. The FT817 works OK at 500kHz but is a little deaf.

So, a satisfying few hours building.

13 Jul 2012

QRP semiconductor pin-out sheet?

Is it just me or do you also have to search the web quite frequently to confirm the pin-outs of devices you've used time and time again?  I need to do this for LM386, 2N3819, IRF510 and the 2N3904/6 almost every time I get them out of the drawers just to be sure. "Senior moments" I hear you say!

Does anyone know of a simple (all in one place) "crib sheet" that I could download giving the pin-outs of the common devices we frequently use in QRP projects?

500kHz WSPR

I left my 500kHz WSPR station running overnight last evening to see what reports I got. People are now generally using 500kHz USB dial for WSPR so that simultaneous monitoring on RX of both OPERA and WSPR is possible. Personally I can't tell much difference.
500kHz WSPR reports earlier (20mW ERP)
Anyway, my best reports were from F59706 (560km) and F5NWK (559km) when I was running around 15-20mW ERP from my current transverter and antenna.

11 Jul 2012

My first ever website - 1996

Looking on the internet today I found an old link to my first ever website that I created in 1996. I'd forgotten the URL, so I put it into the Wayback Machine to see if it had been crawled and stored. It had. Created in Nov 1996, this was a snapshot of the site in 1997. See http://web.archive.org/web/19970328203144/http://www.lapr.demon.co.uk/ .  Actually, for the tools available then, it wasn't a bad effort as I think the page was created in raw HTML.

9 Jul 2012

FT817 speech processor - English translation

Dave G3YMC kindly did an approximate translation of the German instructions for the Funk Amateur speech processor that I built at the weekend. This may be of use to others building this kit. Dave says this is not a precise translation and does not want to be held responsible if he has made any mistakes!

Incidentally on a local SSB contact with G3KKD this evening I switched from "processor out" to "processor in" and Ian said it nearly blew his head off, so it works, HI.

8 Jul 2012

G3XBM Shack - 1977 style

My shack in 1977. I still use the same Morse key.
Just came across this picture of my shack in 1977. On the left is the Eddystone EC10 receiver. Next to it is a crystal controlled CW transmitter for 28MHz and a down-converter to 4-6MHz IF, tuned on the EC10. On the far right is the Belcom Liner-2 2m SSB transceiver, a state-of-the-art rig at the time. The boy in the chair is my son aged 2 at the time. These days he is a successful professional jazz musician. I never did interest him or his younger brother in amateur radio.

More countries on 472kHz

Last night I left my 472kHz WSPR system running through the night and was very pleased to receive SM6BHZ and DF6NM at good S/N at times.
477kHz WSPR DX last night

FT817 speech processor built and working - brilliantly!

DYC-8x7 speech processor tucked under the FT817
This morning I built the Funk Amateur DYC-8x7 speech processor kit that came last week. Total assembly time, taking it slowly, was just 30 minutes with no problems at all. Testing and set-up was easy in the end and the results so far are spectacular.

VHF NFD is running - I'd forgotten this - so this is an ideal time to test the rig with the processor in circuit. Using just my 10m halo - feeder loss is such that it is a good match, if not an efficient antenna, on both 2m and 70cm! - I went on and gave a few points away on 2m and 70cms. Whereas before I would be struggling, contacts came easily. The little speech processor makes a LOT of difference and is an excellent product.

Conclusion: at 34 euros delivered to the UK this represents excellent value for such an effective product.

7 Jul 2012

FT817 speech compressor kit arrives

My Funkamateur BX-8x7 audio speech compressor kit (also known as the DYC-8x7) has now arrived. I was impressed by the speed of delivery and the packaging. The kit looks ideal and straightforward to build. One problem with this design was the RJ45 connector lead, but the latest version has 2 RJ45 sockets already fitted on the module and a ready made lead (with plugs on) to connect between the unit and the FT817. The MH-31 mic simply plugs into the other socket. The actual building should only take about 20-30 minutes.

My only difficulty is in the instructions which is a copy of the original Funk Amateur article  in German. I am hoping someone can translate this for me, or give me a precis with setting up instructions.

Ceramic filters on 472-479kHz?

An eBay seller from Hong Kong has 100 off 472kHz DIP ceramic filters on sale for £5.31 delivered to the UK. See item number 400305093888.

Some filters similar to this have useful bandpass characteristics and acceptably low insertion loss (around 3dB), so may be seriously useful for 472-479kHz rigs and transverters. For example, as a roofing filter to protect a RX after a small gain stage, or as a filter to clean up the output of a transverter at low level before applying a signal to a driver and PA. I guess they must also be useful in a ceramic stabilised oscillator.  Anyone used these in similar applications?

6 Jul 2012

WSPR on the new 472-479kHz band

For the first time I've been monitoring 477kHz USB dial for WSPR signals, hoping to copy some of the Germans now allocated the band. SM6BHZ is on too, but not yet seen.

At 2058z DF0WD was copied at -27dB S/N for my first German WSPR signal on 477kHz at a distance of 556km. I have also heard a couple of other stations from elsewhere in W.Europe who appear to be testing at very low power before the band is officially released in their countries.

1 Jul 2012

500kHz WSPR and OPERA compared

Today I've been comparing OPERA OP4 and WSPR performance by running my QRP beacon in daylight in both modes for several hours each on 500kHz. Theoretically OP4 should outperform WSPR by a few dB, but I am getting roughly similar reports from stations 126 and 210 km away in both modes.

Personally I prefer WSPR because of the neater on-line reporting system and user interface, shorter TX period (2 mins rather than 4 mins) and the fact that more data is being transmitted (call, power, location). Unfortunately only a couple of UK stations have been looking for my 500kHz WSPR signals, so the test is a bit limited.

SAQ VLF tests today

SAQ, the very old alternator TX on 17.2kHz VLF, was transmitting today and was copied as far away a North America. Here are some recordings made in Germany by Stefan DK7FC.
Dear VLF group,

Today the S/N of SAQ was much weaker here in Heidelberg/JN49IK, probably due to the high QRN levels.

I extracted a wav file containing the full message and tests. Can be used for reprocessing if of interest for someone: https://dl.dropbox.com/u/19882028/VLF/SAQ/SAQ_afternoon01Jul2012.WAV (117 MB)

And here is a mp3 file for listening in a normal player (first 2/3 is a test procedure, then the mesage comes): https://dl.dropbox.com/u/19882028/VLF/SAQ/SAQ_afternoon01Jul2012.mp3 (24 MB)

73, Stefan/DK7FC

MF bands and local comms

This morning with my 20mW ERP on 500kHz I worked G3XIZ around 45km away on CW. Chris gave me 569 (on his meter) when using his loop antenna on RX. He was a very good signal here. Earlier I copied the other stations in his net M0JXM and G3DXZ. Yesterday G3KEV was a good CW signal and PA0A was copied later today.
500kHz QRP transverter with ferrite rod ATU on bench
The new 472-479kHz will be an ideal band for local area CW nets: as my far less than ideal set-up here proves, one can work up to around 45-50km without any problem even with very low ERPs. Running 6dB more power from the PA (I currently have just 5W out) will help further.

This afternoon my 500kHz OPERA has reached yet another new station: G8ALS in Coventry 126km away. My maximum daytime range on OPERA OP4 mode seems to be around 220km, although a few more stations reporting may increase this.