An Impedance Question
 

I'm trying to build an antenna for my 40 channel transceiver. But the
(female) RCA connection (at the feedpoint) is throwing me off. Is it 50 ohm
or 75 ohm?

John Dos schrieb:

I'm trying to build an antenna for my 40 channel transceiver. But the
(female) RCA connection (at the feedpoint) is throwing me off. Is it 50 ohm
or 75 ohm?

CB-radios usually have 50 Ohms impedance.
But RCA-connectors are not specified.
Also PL-connectors do not have a specified impedance.

I know BNC-connectors having 50 and 75 Ohms impedance.
Below 50Mhz it doesn't make much differenc anyway....

"John Dos" wrote in message
ink.net...
I'm trying to build an antenna for my 40 channel transceiver. But the
(female) RCA connection (at the feedpoint) is throwing me off. Is it 50
ohm
or 75 ohm?


Hello, John (perhaps)

The reality is that it isn't the connector, it is the coax. Typically, cb
and ham radios these days have a 50 ohm impedance. The connector has
nothing to do with it; it is all in the coax. Purchase 50 ohm coax
(assuming you will be using the usual vertical).

Should one use a dipole, the impedance is 72 ohms (but varies considerably
as can a vertical based upon the ground type/conductivity locally). Would
you believe that a vertical over perfect ground (salt water is quite close
enough, thank you) exhibits an impedance of only around 36 ohms?

The SWR of a 72 ohm dipole (again, it varies considerably based upon ground
and mounting height) fed by that 52 ohm rig is not anywhere severe enough to
cause a problem.

Most problems will be caused by poor grounding (especially in a mobile
installation), poor solder joints, or lousy coax (such as coax which has
been exposed to many summers and winters and expecially if it hasn't been
properly prepared for the elements).


Best regards from Rochester, NY
Jim

On Tue, 30 Aug 2005 21:43:29 GMT, "John Dos"
wrote in
. net:

I'm trying to build an antenna for my 40 channel transceiver. But the
(female) RCA connection (at the feedpoint) is throwing me off. Is it 50 ohm
or 75 ohm?


It's an RCA connector? That's odd. What kind of radio is this?








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On Tue, 30 Aug 2005 21:43:29 GMT, "John Dos"
wrote:

I'm trying to build an antenna for my 40 channel transceiver. But the
(female) RCA connection (at the feedpoint) is throwing me off. Is it 50 ohm
or 75 ohm?


Must be an old antenna/design? Older CB radios commomly used RCA
connectors. If the older radios worked fine with a 50 ohm line then
you have to assume that your antenna would also work fine with the
RCA connector.

Hello John:

How do you know the RCA Female Connector is throwing you off?

I have used RCA Connectors for antennas, not a problem!

Jay in the Mojave

John Dos wrote:
I'm trying to build an antenna for my 40 channel transceiver. But the
(female) RCA connection (at the feedpoint) is throwing me off. Is it 50 ohm
or 75 ohm?

Jay in the Mojave wrote:
Hello John:

How do you know the RCA Female Connector is throwing you off?

I have used RCA Connectors for antennas, not a problem!

Jay in the Mojave

Hi Jay.

I need a recommendation for hooking up my new/used Icom 720A to my
Collins 30L1. It should be fairly straight-forward but there is the AGC and
stuff to consider. This will be my back up rig but I want it to be right,
gawd damit! :)

Those are those rca jacks, things again, right?

Hello Stevo:

Yep most ham amps use the RCA Jacks/Plugs for the PTT and AGC inputs.

The guy down the road has a Amertron Amp, uses two 3CX800's and pegs the
Bird Wattmeter with a 2500 watt slug on all the bands, driving it with a
older Icom.

The PTT is pretty simple, usually the rig supplies a ground for the AMP
to key when you key the mic.

The AGC voltage is supplied by the rig, to throttle back the amp and
keep it from going open loop nutzoid, and sounding better. Some of the
Icom rigs have to had the AGC Voltage turned down a little as the AGC
Voltage was way too much, causing the amp to turn off more than it should.

I played with a Icom 746 PRO and it was able thru its digital I.F.
processor in the receiver to attenuate stations on USB, while monitoring
LSB, allowing the LSB stations to be heard, pretty impressive. Usually I
would have to swing the Moonraker 4 or 6 around to attenuate the
stations on USB. So the Icom 746 PRO and a good beam will kick A$$.

The 720A and that Collins 30L1 on the Interceptor 10K ought to hum
pretty well, breaker breaker.

Jay in the Mojave


Steveo wrote:
Jay in the Mojave wrote:

Hello John:

How do you know the RCA Female Connector is throwing you off?

I have used RCA Connectors for antennas, not a problem!

Jay in the Mojave


Hi Jay.

I need a recommendation for hooking up my new/used Icom 720A to my
Collins 30L1. It should be fairly straight-forward but there is the AGC and
stuff to consider. This will be my back up rig but I want it to be right,
gawd damit! :)

Those are those rca jacks, things again, right?

Jay in the Mojave wrote:
The 720A and that Collins 30L1 on the Interceptor 10K ought to hum
pretty well, breaker breaker.

Jay in the Mojave

It should work as a back-up, the S-Line transmitter will still blast it out
of the waters for audio quality.

aaaaaauuuuuudddddiiiiio0 Jay!

On Wed, 31 Aug 2005 00:43:07 +0200, Volker Tonn
wrote:

+Below 50Mhz it doesn't make much differenc anyway....
******

Below one Hertz it makes no difference

james