Thanks Tom and Karl-Arne for the informations.
I know that the relais are too much, but using only the vacuum SPST
would be too risky: 1500W into receiver if some failure happens...
What do you suggest, do you think that would be better to use the
smaller 30A relais (more compact design) instead of bigger vacuum relais?
Thanks again and 73
Guido, ik2bcp
Tom W8JI wrote:
> Guiado,
>
> First, I have never seen in single case in all the hundreds of relays
> I have tested at high power RF where the contact RF behavior is an
> issue. Sometimes the contact support, which can be steel or an alloy
> with high resistance or exaggerated skin effect is an issue with
> heating, very often the flexible wire leads are an issue with heating,
> but I've yet to see a contact heat issue if the contact is OK at low
> frequency and the same current. I have tested many relays!!
>
> On your switch, my feeling is you are going through far too many
> relays and the connection lengths will be too long. I understand what
> you are doing to make it safe, but I'm afraid with so many relays and
> so much connection length isolation and SWR will not be so good.
>
> You could compensate for this with capacitors (like the 47pF you show)
> and with selection of layout and materials, but large numbers of large
> relays in the path makes isolation and SWR more difficult above a few
> MHz. If you find that not a problem, then all is well.
>
> Watch your groundplane! It carries as much current as the center
> conductors do, and is just as responsible for isolation.
>
> 73 Tom
>
>
>
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