28 Feb 2015

40m Pixie - bench test went well

Well, it took a super-human effort on my part as a result of my extreme fatigue (brain bleed issue) but today I bench tested the little 40m Pixie kit I managed to build earlier this week. It is hard to explain just how exhausting this simple task was for me currently. I now need to recover my energy!

On receive a 1uV signal was perfectly readable and I could detect carrier on/off down to at least below 0.5uV. On TX it was putting out about 250mW into a 50 ohm load. On my antenna it was suffering some AM breakthrough, but less than I was expecting. I was using standard Walkman stereo headphones and a rechargeable 12V sealed lead acid battery. On a small 9V battery I'd expect about 100mW RF out, although this was not tried.

Overall, these results exceeded my expectations: it is more sensitive than I was expecting and the breakthrough of AM broadcasters is certainly OK in the day time. This is of course with no casing at all and no ATU. Using the fitted pot and fitted 1N4001 as a varicap it is easy to get the TX frequency and RX frequency to correspond, often an issue with very simple QRP rigs.

Next stage will be some on-air tests, but it most definitely works. Working the locals should certainly be possible. Sked with G6ALB (3km) arranged for 1000z Sunday on 7.023MHz CW.

UPDATE 2120z:  There is a contest in full swing and several Russians and Asiatic Russians copied on the little 40m Pixie. I did not stay on long but there was no apparent BC interference noticeable. So, on a quiet night I should able to use the rig in the evenings. The main issue on RX seems to be the lack of AF filtering, so one has to use "the filter that is between the ears" i.e.the brain.


John J said...

Brilliant news, well done - I'll be listening out for G3XBM on 40!

Roger G3XBM said...

7.023MHz - not the ideal frequency, but this was the crystal it came with. OK for "listen and pounce" operations. Not expecting miracles!

Bert, PA1B said...

Hello Roger, in the evening it must be possible to work loud stations with 250 mW.
I worked with a 7 MHz transceiver with 500 mW and an Inverted Vee for about 10 years on 40m.
The 40 m band will show activity with signals over S9 when the propagation is good. GL, 73, Bert

Dave said...



Roger G3XBM said...

Have an on-air sked with local G6ALB(3km) at 1000z tomorrow (Sunday, March 1st). Thank you everyone for the encouragement.

gj7rwt said...

Perfect Roger! Good luck with the sked tomorrow.

De Andy

G1KQH said...

It looks like you beat me to the build, I won't get started this week, too much on.. But enjoy using yours.

73 Steve