RCA phono jacks on Heath gear

Bob Miller bmiller at CALWEB.COM
Sat Oct 31 18:15:35 EST 1998

It's easy to measure and calculate.

    Coax Z=138 log (inside diameter of outer conductor/outside diameter inner

    How much difference the Z bump makes depends on what you are doing with the
transmission line.  As to losses, probably not much as ham stuff goes.  If it is
part of a broadband transmission system even a small vswr can cause group delay
problems and subsequent degradation to the transmitted signal(s) especially in
70Mhz broadband IF systems carrying FM message traffic/or FM video traffic.  A
return loss greater the 26 db was about a mininmum spec for IF  and or Baseband
interconnects across the appropriate swept spectrum.  And while a single
mediocre Return Loss profile would not cause a system to cave in, the aggregate
of a few hundere mediocre return loss profiles would add up to a pile of
Picowatts of noise at the distant end.  Suffice it to only rated connectors were
used for 70 Mhz and 140 Mhz fm IF stuff back in those days before fiber optics
and you would not find RCA's, BNC;s or UHF connectors or even F connectors in
that service..most always  70 ohm rated 'N' connectors..
    If you want quick connect/disconnet and fairly good Z matching, rated into
the Ghz range, fairly good power, and rugged connector may I suggest the type C

    Bob, KE6F

Jim Berry wrote:

> Hello Group,
> Bob Miller said:
> > interconnects  are 50
> > ohms and not a good match for F systems.
> Help me on this one folks.  Is the impedance of a connector determined by
> the pin diameter or the spacing between the pin and the connector outer
> body?
> Is there really that much difference between 50 ohm and 70 ohm?
> Does anyone know what the impedance of a RCA phono plug really is?  Does it
> really matter?
> I have been using and making up all kinds of jumpers using type F connectors
> and RG-6 (70 ohm coax).  What if I was to use F connectors and 50 ohm RG-58?
> That is if it can even be used with F connectors.
> 73 Jim K7SLI (Getting ready for all the gremlims and goblins to arrive)
> While I am at it, anyone got a manual for a Heath IM-13 VTVM?

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