At long last I have completed my 70Mhz transverter, which I first wrote about here. Since I took that video I have rebuilt the transmit stages using Manhatten style construction. I have also replaced the tx/rx switching circuit with a much simpler arrangement.
Whilst it is probably not the most sensitive receiver around I am proud of the fact that I built it from scratch. It is the design by EI9GQ published in Radcom in June & July 2009.
The transmit output is now 100mW. To bring this up to a level to drive my Pye A200 amplifier I bought a ready constructed amplifier from SP2DMB For 100mW input this gives 8W output. Using this to drive the A200 gives well in excess of 50W but I have turned the A200 down to avoid over-driving it so it only outputs 50W.
I have learnt so much from this project about receivers, transmitters, construction techniques and fault finding. Unfortunately I have also found, along with my optician, that my close up vision is now very different between each eye. This makes soldering difficult as I find it difficult to judge depth of field, so any sort of SMD construction is definitely not for me. Another visit to the optician is due and I'll try to get a pair of glasses that makes soldering easier.
To augment my horizontal dipole I have made a Moxon Rectangle antenna for 4m using this design. Now this is on the mast I have found that I can receive the GB3BUX, GB3RAL and GW3MHW beacons all the time rather than only by aircraft scatter.
The distance between my QTH and GB3BUX is 153 miles. The path profile is shown below:
My QTH is on the left, the first piece of high ground is the North Downs in Surrey, the second is the Chilterns around High Wycombe and the next piece of high ground is the Peak District south of Buxton.
I have left the dipole on the mast attached to my FunCube Dongle SDR. I'll use this for spotting Sporadic-E openings. I noticed last year that some of the tones I receive around 70.230 - 70.240 Mhz get much, much stronger when there is Sp-E around, so they are a useful indicator of propagation.
Now, roll on the Sporadic-E season!