SixBox QSO 3 - sensitivity testing

This evening I had a third QSO with G6ALB using the SixBox 6m 50mW AM transceiver. The main aim was to test the receiver sensitivity since fixing an issue last evening. Andrew first called me using his FT817 on the lowest AM power setting and he was good copy. He then switched over to a modulated AM signal generator at 7dBm level (5mW). This was easily copied on the superregen RX. Even with a 10dB pad in at my end I could still copy the signal i.e. at an equivalent of 0.5mW from Andrew 2 miles away. So, without accurate test equipment I can safely assume the RX is detecting low uV level signals. I must work out the path loss.

Having got the SixBox working pretty well it now remains to see how far it can reach. I am really pleased with this simple project. It is very satisfying to work people on AM using really simple homemade equipment built with minimal test equipment and using parts which cost very little.

The current TX frequency is 51.125MHz. I need to buy a crystal for the 6m AM working frequency (50.57MHz in the UK or 50.4MHz in the USA).

Sunspots creeping up

Noticed the sunspot numbers trend recently? Whereas a few months ago there were weeks and weeks without a spot, now there are spots on a high proportion of days and the general level of active cycle 24 spots is creeping upwards. All this bodes well for this autumn when I hope we'll see some F2 transatlantic propagation on 10m again on many days, with plenty of US and Canadian stations workable with QRP - a sure sign that the old sun is waking up.

6m Sixbox AM QSO No 2

RS59 from G6ALB this evening with the SixBox 50mW AM transceiver. In putting the transceiver in its box and adding the RX tuning I inadvertently removed the coupling cap between the RF and and detector stage so the RX was a little bit deaf. I will add this back tomorrow and expect sensitivity to be back to low uVs level. Even without it, I could hear signals of 2-3mW out from Andrew.

Next week I am in Devon on holiday, so will be looking for some 50MHz AM QSOs with the SixBox from clifftop highspots. I will set up some 6m AM skeds using the local VHF and UHF repeaters.

10m AM Net in S.London (Wednesdays)

A 10m AM net has been started in South London, UK by Gary G7IRG. It meets on 29.05MHz (AM mode) on Wednesdays at 9pm local time. Last week the net had 3 people on: G7IRG, G0KRT and M0GPG. If you live in this area, or indeed anywhere, why not see if you can hear the net and give them a call?

When 10m is wide open, as it will be in a couple of years time, the band between 29.00 and 29.1 MHz will be filled with AM stations from around the world.

6m when the band is quiet

6m is a band ripe for exploitation when there is no DX around. When there is sporadic-E or F2 DX about, people use the band in thousands and some have worked DXCC. However, when conditions are not good, it is left to a few dedicated enthusiasts to work random MS and tropo and ionospheric scatter mode QSOs using QRO with modes like JT6m. The amount of LOCAL 6m activity, at least here in the UK, is very low indeed.

We have 2MHz of band in the UK (4MHz in the USA) and it is a pity more use is not made of this fine band for local QSOs using simple QRP homebrewed equipment. It is an ideal band for QSOs up to around 20 miles or so and much quieter than 160m or 80m, which can be very noisy these days.

3 transistor SSB transceiver

http://www.intio.or.jp/jf10zl/3trssb.htm

The website of Kazuhiro Sunamura JF1OZL is magic and contains some superb ideas for QRP enthusiasts. Every time I return to this site I find something to enjoy and to inspire me. Take for instance the 3 transistor 6m transceiver he describes: it is wonderful. Kazuhiro San, if you read this THANK YOU for your great ideas.

10m or 6m QRP DSB ideas

Having finished my SixBox 6m AM transceiver, my mind is now turning to ideas for either a 10m or 6m QRP DSB transceiver. I have already breadboarded a 10m version in separate sections (RX based on the Neophyte RX, a DSB TX based on a single balanced diode mixer), but I have still to breadboard a mixer-VFO based on the NE602 which would be useful for either band. Actually a fundamental crystal x2 would give around 25-30kHz shift on 28MHz and around 50kHz on 50MHz, so this may be a simpler, and adaquate, route. However crystals "to order" are expensive these days, although the spec (temperature, cut frequency accuracy, etc) would be very low.

Today I noticed another 6m DSB schematic from a Japanese ham. There are plenty of good ideas from JA land where, despite commercial rigs, homebrewing is still in strong. See http://www6.plala.or.jp/jr8dag/micro6dsb/mi6dsb02.htm for JR8DAG's schematic. In my view, this is a rather complex schematic and I am sure it could be simplified.

SixBox 6m AM QRP rig now boxed

Today I complete this project and put the 50mW AM transceiver into a small diecast aluminium box. Using a 9V battery inside the box the rig puts out about 20mW. From an external supply it is about 50mW. The polyvaricon tuning capacitor works very well and the RX tunes from around 45MHz to 70MHz. Already it has been useful as an indicator of Band 1 activity.

Overall, I am pleased with this little transceiver. It was all done with the most basic of test equipment and is a circuit that should be easy to copy. Now to try to get some local 6m AM activity going! It would be very nice to make a PCB for this project. I'm thinking about it....

My next project is either the long intended 10m DSB rig or a DSB version of this 6m AM rig. However, to be useful this would need VXO control and a 3rd overtone xtal will not pull very far.

SixBox QRP 6m AM rig closer to completion

Today I did a full rebuild of the 6m QRP AM transceiver on a much smaller (dead bug style) board so that it will fit in a small diecast (or aluminium) box. In the course of the rebuild I tried out the RX varicap tuning idea which works, but I was unable to move the frequency more than 1-2MHz before the superregen stopped oscillating. I tried a 1N4007 and the collector-base junction of a 2N3904 as varicaps. In the end I decided to use a low cost polyvaricon tuning cap in series with 22pF and this covered 6m plus a few MHz either side. I also ran the PA stage in class C and this seems to improve the modulation. Here is a picture of the SixBox after rebuilding, but before I started the testing. Because of family commitments I shall not be able to finish this now for a few weeks but I am looking forward to some local "DXing" with this around the Cambridge area. It is funny but working local stations with this is (almost) as much fun as working real DX with a proper radio!

SixBox 6m AM QSO

A solid QSO this evening with G6ALB (2 miles away) on 6m AM using the 50mW SixBox rig with vertical antennas at each end. In the other direction, using the super-regen RX at my end, we did some sensitivity tests with Andrew putting a signal generator on and gradually dropping his AM modulated carrier. I was able to copy his signal when it was reduced to 0.5mW.

I also tried to receive a 7dBm carrier from Andy on 70.26MHz AM using the retuned super-regen RX, but was unable to hear it, although we were both using 6m antennas which were not resonant on 4m.

Currently I am putting a rebuilt SixBox in a real box. Later, I will make a breadboarded DSB version.

More details on the SixBox page of my website.