> >That's probably from a bad coax connector or bad cable..
>
> Well, I use RG58 everywhere, it's shield looks better than
in others "RG58"
> I've seen.
Funny thing about shields at LF through VHF. No matter how
they look they all seem to work very well. I use single
shields no trouble. The RG58 should be fine.
> All this cables are about 1 m long. Whatever it means,
this weekend I will
> disconnect all this stuff and will see what happens if the
main cable goes
> directly to my TRX. (should do this before... SRI..)
The most common problems I see with signal ingress is poor
connections on shields where connectors are installed. With
equipment it is poor connector layout or grounding on a
chassis or wiring inside.
> Honestly, I don't know if it's constructed well enough,
but I hope so. Any
> way, there are 3 relays switching between beverage's and
K9AY. I switch the
> coax center and shield of all cables / antennas.
As a general rule that is a problem. I would never switch
the shields in my station. It is begging for problems! The
shields should be solidly grounded to a common groundplane.
Only the centers switched.
All connections between
> relays and sockets are made of RG174 cable and are very
short. The box is
> made of plastic.
How the cable is grounded is important. Shields do no good
if they don't have a shield and center path at each end for
opposing currents. The shield does not require an earth
connection to be effective, but it does require the shield
and center conductors have equal and opposite currents and
voltages throughout the length of the cable.
I see many people stick coax in a box, ground the shield to
the chassis at one end, and have it float at the other end.
In that case it might nearly as well be single conductor
wire as have a shield. If the shield attaches to points that
cause ground loops it can make things worse. I see this in
commercial antenna switches. I see designers add a
groundplane that is improperly configured and it destroys
crosstalk. Sometimes 40 dB worse than with no GP at all!
I actually use very little shielded wire in my antenna
matrix box. Mostly I just dress the single conductor wires
along a PC sheet that is the groundplane. I get over 80 dB
isolation, more than enough. Of course every cable entering
does so through the groundplane with a chassis mount
connector.
I would worry about a good groundplane (it does not require
more than a flat sheet for 160, since the sheet length would
be very small in terms of wavelength). Not much worry about
a plastic cover, but I'd consider not switching the shields.
You can trace it back by removing components and making sure
the switch box is not a problem.
> >Is it RF bypassed on control cables?
>
> I think I'd need some more explanation at this point, what
does it refer to?
Relays always have some coupling between the coil windings
and the armature. The armature is near the signal leads.
Many relays actually have the steel pole piece inside the
coil actually connected to the armature, they might have
20pF capacitance directly from the common contact to the
coil. Other relays have long leads that pass the coil.
Unless you know the relay has very low RF coupling from
contacts to the coil, you should have a low impedance bypass
capacitor from the coil to ground and a very short ground
lead on the grounded coil terminal.
Otherwise you can have relay to relay crosstalk and relay to
control cable signal coupling.
73 Tom
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