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
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