Friday, June 18, 2010

QDFA Project Version 3

Those who followed this blog last season know that we were very satisfied with the performance of the QDFA. There were however some problems:

1. The amplifier transistors blew due to static discharge. Proper surge arrestors were fitted by Dallas Lankford, and the QDFA v. 2 was up late November.

2. Another problem, probably related to static build-up, caused the transistors not to blow but produce excessive noise. The only explanation we can find is that replacing the battery in cold, dry weather caused the problem. Another fix was needed, and the coming season we will supply power to the QDFA box from within the house. Hopefully, the extra cable will not compromise the nulling properties of the QDFA.

3. The cheap angling rods, while surprisingly weatherproof, did not survive the winter entirely intact. One of them failed in January, and another in April. So we decided we need proper supports, and found them at Max-Gain Systems Inc. These are extremely sturdy fiberglass rods, fastened not by friction but with clamps. We got four 21-ft center supports, and eight 12-ft end supports. This allows us to double the area of each loop, giving us another 6 dB of gain. The visual appearance of the loops will be a "house" instead of the common "delta".

The QDFA v. 3 will be up and running as the Arctic DX Summit starts, early September.


Walter said...

Bjarne, I noted that the bottom of the band on the original version wasn't all that great, either. (See my January 3, 2010 01:00 Perseus file on Guy's blog). I'm pleased to see an improvement in gain. Looking forward to trying it out in a couple of weeks in Masset.

Bjarne Mjelde said...

Walt: See my latest blogpost.