Me wrote:
In article
,
Bob Dixon wrote:


Adding any adaptor would seem to significantly move the radiating
portion of the antenna further away from the "ground plane" of the radio.
This should affect the operation of the antenna adversely. Comments?

Bob



Adding an adapter to a Transmission Line will have no effect, except to
add insertion loss of the adapter. Adding an adapter to the antenna
itself MAY cause the antenna charactoristics to change. Most SMA and BNC
connecters are used in Transmission Lines, and not antennas themselves.
The OP doesn't really explain where the adapter is to be used. Most
small handheld devices with external antenna connections have those
connection in the Transmission Line and not in the antenna itself.

Me

That is actually not quite true. On an HT, the transmission line ends
somewhere inside the radio. The SMA/BNC connector is part of the
antenna proper. If you add a sleeve (as the previous poster, "dixon",
says), you will be changing the antenna itself. ASCII schematic follows:

befo


|
| antenna
|
|
_ ground + bnc/sma
||
|| coax from PA strip
||
||

after

|
| antenna
|
|
||
|| shielded antenna (adapter)
||
_ ground (bnc
||
|| coax from PA strip
||
||

And as we remember, "maximum radiation at the current maximum" (that is,
the base of a classic 1/4 wave antenna), you are shielding the point of
maximum radiation.

From a practical standpoint, you will probably be using a gain-retarded
rubber duckie, and the 1 or 2 dB loss from even the worst adapter will
be swamped by the -10 dB gain of the duck (that is "minus 10 dB gain").
The rubber-duck will make a 5 watt transmitter sound like a 1/2 watt
one. Having another 1 dB of loss will make that 5-watt radio sound like
0.4 instead of 0.5. No big deal.

If you can keep your radio from being broken by using a quality adapter,
and with a negligible loss in performance, I say, "do it."

If you are talking about squeaking out every last bit of signal, such as
EME, the answer is "no". But if you are talking about walking around a
hamfest on 2m, then spend a few extra bucks to keep from fracturing your
antenna connector connection, which these days, most hams can't, or
don't know how to, fix. flames invited

Your mileage may vary.

Dave
KZ1O