Walford Kits "Fivehead" SSB transceiver

A friend of mine is building a Walford Kit "Fivehead" SSB transceiver. He has got the kit, but was surprised to find the parts placement was not silk screened on the PCB; I guess this is a cost saving measure.

Although there is a not-to-scale layout, a clear colour photo from above of the assembled board from the component side would help him a lot. He's asking Tim if he has one he could email, but does anyone already have one they could email me please?

XBM80-2: a 2-way QSO and report

This morning I worked M0DRK using my tiny 60mW XBM80-2 transceiver I designed last week. It uses just 13 parts plus the crystal, earpiece and optional frequency offset switch. My report for Derek was 599 and he gave me 599+40dB. Derek is in the same village. Also monitoring was G4LHI in Huntingdon 32kms away and he reported my signal was as strong as Derek who was running 5W.  In fact 60mW is only going to be about 3 S points down on 5W. I also heard GM3JUD when listening on the XBM80-2 on 3.560, but was unable to raise him.

Shortwave in the 1960s - interval signals montage

Yesterday I found this wonderful link which is a montage of 40 different old shortwave interval signals from almost 50 years ago. Get a coffee, sit back and listen.  Imagine you are listening on your one valve radio in your bedroom in 1964.  It brings back such happy memories that I am almost tearful with nostalgia.

http://garlinger.com/QSL/montage.mp3

G3ZJO in QRSS3 on 500kHz

G3ZJO has a QRSS3 beacon sending in FSK built in Altoids tins and running QRPp power. This is is a screenshot (from Spectran) of his signal this afternoon. I have superimposed his callsign, which is clearly visible on the upper line. The first dash of the G in his call is missing in my capture.

Simple 80m CW transceiver

Want to try something really simple?  I am now waiting to have a QSO on 80m CW using my XBM80-2 transceiver that I put together in the week. Pout is 60mW. The only switching between TX and RX is by the morse key. Additional offset can be had with the switch in series with the crystal. Skeds with local stations are being arranged.

ERP on 500kHz (part 2)

Yesterday I did a recalculation of the G3XBM ERP based on the classic formula and re-measurements of my antenna current. My antenna is a 5m long vertical with a spiral top hat of about 7 turns about 1.5m x 1.5m. Not being clear how to model the top hat I assumed effective heights of 5, 4 or 3m. The measured antenna current is 0.12A. My results are as follows:

Assumed effective height 5m     ERP = 1.53mW
Assumed effective height 4m     ERP = 0.98mW
Assumed effective height 3m     ERP = 0.55mW

So, I believe my 1mW ERP previously calculated is not a bad estimate, and it may indeed be lower than this figure.

Rik ON7YD (OR7T) has just sent me this email:

"I simulated the antenna based on your description (with MMANA) and the current through the vertical wire seems to be quite constant. So the tophat works well and the effective height will be more or less the physical height. The simulation gives a radiation resistance of 0.074 Ohm, so with 0.12 A a radiated power just over 1mW EMRP (1.75mW ERP). In the real world it will be some dB's less (as Jim stated recently), probably something like 0,5 to 1mW ERP.  Very impressive that it covers over 1200km."

JT4A mode on 500kHz

The next (operational) project is emerging from the mists..... Several people have started to experiment with JT4A WSJT mode on 500kHz. This allows basic EME/MS style QSO exchanges so should allow me some 2-way contacts on the band with my low ERP. Still to work out how to run the software though: when I tried the other night I could see strong traces but no decodes. Getting this sorted will be half the fun. Then I might try to mode on VHF too. JT4A uses a bandwidth of 17.5Hz with tone spacings of 4.375Hz and can decode down to -23dB S/N. This is somewhat less sensitive than WSPR but would still allow QSOs with quite a large number of the stations who've heard me on WSPR.

QRP Books

International QRP Collection is a new book bringing together articles from magazines around the world on QRP (low power) radio. There are articles on commercial equipment, homebrew ideas, test equipment and operating on bands from 160m to microwaves plus much more. A friend who is not too familiar with QRP thinks it is a good introduction, but I must admit I was disappointed: the collection seems disjointed and, in my view, a better set of articles could have been put together. As an example, the intriguing transceiver on the cover does not appear in the articles inside! Overall, I'd give this one 6 out of 10. The book is available from the RSGB. 

QRP Basics by G.Dobbs G3RJV is a much better book and worth buying.

The Pixie Files

The Pixie and Micro80 are  well known simple transceivers for any HF bands. I've built both in the past and they do work well considering their lack of complexity. The main limitation is the receiver which uses the TX PA as a simple mixer. For those wanting more information on the Pixie and its derivatives check out The Pixie Files which is a collection of articles from SPRAT.

ERP calculation on 500kHz

I've recalculated my ERP based on a better measurement of antenna current. I was using a dust iron core for my current transformer, so swapped this for an FT37 ferrite toroid today and got a lot more current measured now. My antenna current is actually around 0.12A. My antenna is 5m long with a small spiral top so the effective height must be <5m. Even putting in 5m into the classic formula I cannot make my ERP exceed 1mW. I make it more like 600uW. Interestingly this is 20dB more than the original estimate from M0BMU and since then I'd increased the ERP, I believe, by around 20dB which would also make it 600uW. Of course the margins of error must be large.