----- Original Message -----
From: "Steve" <ve3tu@rac.ca>
> I tried running two smaller (HF1250) amps each feeding one element of a
> phased vertical. One amp receives a lot of reflected power from the
> other element. I would like to know if there is a circuit to stop
> reflected power but allow the forward power ?
>
Very interesting (since this is something I'm also working on doing)..
The short answer is that there isn't a "simple circuit" that will do what
you want. In the microwave world, there are nifty things called circulators
which do exactly what you want. However, a circulator for HF is impractical
(haven't seen much waveguide around for 7 MHz, and I think that the entire
world supply of ferrite wouldn't be enough).
You've got several practical (in varying degrees) approaches open to you,
and you'll probably get lots of ideas (which I'd also like to hear!).
1) Reduce the mutual coupling of the antennas, either by moving them farther
apart or making them physically smaller. You can still phase them, but if
the mutual Z is smaller, you'll get less power coupled between them.
Negative power in an element implies a lot of mutual coupling (how close are
the verticals?)
2) Create a LC network which connects both antennas to both amplifiers, and
feeds the power appropriately. This might degenerate into a power combiner
and phasing network
3) Are you really getting reflected "active" power or is it just reactive
power circulating between amplifier and element? (that is, what's the phase
difference between fwd and reflected signals).. In a driven phased array,
there can be significant reactive power circulating in the feed line(s). In
this case, a suitable matching network that supplies the reactive power. If
you have one amplifier replaced by a dummy load, and you put power into the
other antenna, how much power comes down the feed line into the load?
Jim, W6RMK
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