I tried that and it did attenuate the signal but not by much. Not
enough for the kind of isolation I wanted.
73
Rob
K5UJ
On Wed, Mar 18, 2020 at 3:50 PM Richard (Rick) Karlquist
<richard@karlquist.com> wrote:
>
>
>
> On 3/18/2020 6:41 AM, Rob Atkinson wrote:
> > Last year I purchased an Airspy HF+ Discovery SD receiver. Eventually
> >
> > grommetted hole for the USB cable's exit. I mounted a pair of relays
> > in the feedline to the receiver inside the box and put RF chokes in
> > series with the DC line to the relay coils (24 v. DC) at the entrance.
> > I figured two relays in series in the line would add some protection.
> > Amazingly none of this helped much as a 20 w. carrier on 160 m.
> > produced a disturbingly strong signal trace on the receivers
> > panadaptor. I wanted to see little or no signal at a few hundred
> > watts to feel comfortable about operating at higher power. I was
> > using typical ice cube style relays. The contact spacing isn't much
> > so I think the relays were just acting like low value air dielectric
> > capacitors in the line. RF went right through them.
> >
>
> This behavior is completely predictable. When you should have done is
> have one set of relay contacts in series with the signal and another
> set of relay contacts after those that shunt the signal to ground.
> Then you would get a lot more isolation. This is what all well designed
> RF switches use. You already had two relays, so you had all the parts
> you needed on hand.
>
> > Rob
> > K5UJ
>
> 73
> Rick N6RK
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