Saturday, August 29, 2009

QDFA Antenna Countdown, 7 Days Remaining

Only a week now until OJ Sagdahl and I will test run the QDFA antenna. All primary and secondary main supports are up. Four 200-ft lengths and one 300-ft length of twin-lead wire have been cut and ends tinned. Two 17Ah batteries for the QDFA preamp are fully charged. The four 60-ft horisontal lengths of the deltas are cut and will be mounted today.

And I got my second Perseus SDR a week ago.


Guy Atkins said...

Hi Bjarne,

How high will the delta loops' horizontal wires be above ground in your QDFA? You may have heard from Dallas that his recent EZNEC modelling shows that the best nulls are maintained when the horizontal component of the loops is some distance above ground (approx. 1+ meter). He says this is especially true if your ground is not level, varying between the four masts.

That said, during our April tests the QDFA loops had the bottom wire a mere one-third meter (~1 foot) above ground, and the array worked superbly.

Best wishes to you and OJ for a hot-performing QDFA! I look forward to learning of your experiences with the antenna.

Guy Atkins

Bjarne Mjelde said...

Yes, we discussed this a bit. I decided to go for 90 cm (3 ft) base wire elevation. Loops 2,3 and 4 (counting towards target) are on very even ground while the ground under loop 1 slopes quite a bit. The elevation has a practical side as well since I don't want the base wires to be buried in snow and ice. The area usually blows clean though.