Topband: RX 4 square

[Greg - ZL3IX]

Tom Rauch wrote:
>> birdies were not present on the transformer version.  I 
>> suggest to anyone
>> who does not believe this: try it yourself.
>>     
>
>
> I have, several times and the results were not good. It 
> would also be interesting to see how others who have built 
> arrays weigh in on this. I know ZL3IX and others use active 
> elements.
>
>
>   

My array uses a FET source follower on each element, for the exact 
reasons that Tom cites.  The series capacitance of a 3m element on 160m 
is around 20pF, a reactance of 4 kohm.  It's much easier to match 8 of 
these using a high Z amp, in my opinion.

A pair of J310's and a couple of passives probably costs less than a 
transformer in any case, and is not much more trouble.

One nice spin off is that the cable and amps are so easy to check from 
the combiner box.  I have a jig that injects 12V DC on to the coax and 
measures the current drawn.  In all cases it is 30 +- 2 mA.  Any 
deviation from this and I know that something is wrong.  With a 
transformer you can check for open circuit all right, but if the thing 
goes short, it's not quite so easy to see.

I must admit, I have never tried the transformer idea.

By the way, this is the second time I have tried to send this.  The 
first time i committed the sin of sending in HTML.  Hope this gets 
through the filters now!

73, Greg, ZL3IX