80 meter driven array

[W1IA]

Ok guru's, I forgot a critical part of the project....matching!

Frank asked me how I was going to match the input impedance to the elements. I scratched my head and realized I need to solve this problem for different phase angles.

The design info:
A) 2 full size 1/2 wave dipoles cut for approx. 3850khz; height above ground 60 feet
B) 55 foot spacing between the dipoles
C) Each element fed with LMR400 into a matching network to be determined?
D) The plan is to drive it at 0, 125, and 180 degree phase angles.
E) 125 degree angle switch to each element to switch NE or SW

Frank suggested 1/4 wave length 75 ohm of RG-11 in each feeder. What about other phase angles...the model shows high variations of input impedance at 0 degrees and 180 degree phase angles.

Thanks Brent W1IA

[W1VD]

2 cents...

With the dipoles in phase you'll have a straight up gain of about 6.85 dBi. With 125 degree phasing you already have a straight up gain of 5.41 dBi.

180 degree phasing makes a nice overhead null - which will help to knock down the locals when working DX. However, if DX is your bag you'd be better off with a beverage or K9AY for receiving than the dipoles.

Building the system to allow for 0 and 180 degree phasing might not be worth the trouble.   

[KF1Z]

Have been listening to you talk about this.... tried to get in this morning, to no avail....

But, the way Tim described the "phasor", seems like that would be the way I'd go....

If you use the 1/4 wave matching sections, how far from 3.850 will you be able to go before your impedance matching has lost it's desirable effects?
Since obviously those are frequency dependant.

Just my "non-guru" thoughtz

[W1IA]

Have been listening to you talk about this.... tried to get in this morning, to no avail....

But, the way Tim described the "phasor", seems like that would be the way I'd go....

If you use the 1/4 wave matching sections, how far from 3.850 will you be able to go before your impedance matching has lost it's desirable effects?
Since obviously those are frequency dependant.

Just my "non-guru" thoughtz

Not sure what the useable bandwidth will be, but model suggest about 150 kHz's

I may have to work with a different set of matching stubs to solve the mutual impedance problem?

It would be nice to have he flexibility Jay, but may not be worth the technical problems.

Brent