[HCARC] Antenna Coupler vs Antenna Tuner (Gary J's weekly test tosee if the Reflector is still working)

[Kerry Sandstrom]

Hi Gary,

There sure hasn't been much on the reflector lately.

I'm not sure there is any difference between an antenna coupler and an 
antenna tuner.  If you have a XCVR/XMTR that is designed for 50 Ohm output, 
and if you are using a transmission line that has a different impedance, 
then you need an impedance matching network between your XMTR and the 
transmission line.  It could be an RF transformer or it could be an antenna 
tuner/coupler, and it could be manual or automatic.  Many antennas have 
matching networks.  A gamma match is a matching network: it transforms the 
50 ohm transmission line impedance to the impedance required to drive the 
driven element.  Just because it looks like its part of the antenna makes it 
no less of a matching network.  A lot of things in radio have multiple 
names.  A good example is condenser and capacitor.  Condenser is the 
historical name and capacitor is the modern name.  Old transmitter finals 
typically had two controls: "Final Tuning" and "Loading".  Early 
transmitters often had two controls labeled "Final Tuning" and "Coupling". 
The "Coupling" control was often a mechanical adjustment that changed the 
inductive coupling between the primary and secondary coils of an RF 
transformer.

A quote from the ARRL Radio Amateurs Handbook, 25th Edition 1948.  "The 
apparatus used to cancel line reactance and match the line resistance to the 
transmitter is commonly called an "antenna coupler" or "antenna tuner." 
(The name is really a misnomer, because the coupling and tuning equipment at 
the input end of the line does not have any effect on the antenna itself; if 
there is any antenna tuning to be done it must be doone at the antenna, 
independently of the line.)"  The handbook goes on to show several designs 
for "Antenna Couplers"s all intended to be in the radio shack next to the 
transmitter.  Incidently, all are for parallel wire transmission lines since 
this is from right after WWII and hams had not yet started to use coax 
cables.  The 1968 handbook still had an article on a "Wide-Range  Coupler 
for Balanced Transmission Lines."

As you can see there is no difference between an antenna coupler and an 
antenna tuner.

There is nothing dangerous about an antenna switch.  There are two problems 
with antenna switches.  First, most people use them for convenience and 
don't disconnect their antennas from there equipment to prevent lightning 
damage.  They rely on the switch to protect their equipment.  DON"T!!  IT 
WON'T.  The second problem is all switches and relays have leakage.  The 
formerly popular Dow-Key coax relays are good for about 60 dB of isolation 
at HF.  At VHF and UHF, the isolation gets very low.  In days past, hams 
have literally fried their low noise receiver front ends (expensive tubes 
and transistors!) because of leakage between the transmit side and receive 
side of coaxial relays.  Coax switches have the same problems.  Typically a 
station will use a coax switch to switch between a couple matched 50 Ohm 
antennas, a 50 Ohm dummy load and an antenna tuner.  There is nothing 
inherently unsafe about this.  By the way, if you're looking for a coaxial 
T-R switch for a high power/low noise station setup at UHF, expect to pay 
$1000 or so for that relay.  They aren't cheap and they don't use 
PL-259/SO-239 UHF Connectors.

Kerry