I just bought an ICOM AT-150 antenna tuner to go with my ICOM IC-735 (still looking for that elusive object, a moderately priced PS-55 matching power supply in good condition!).

The tuner has four antenna "ports" on the back. #1,2,and 3 all have SO-239 connectors and are clearly for 50 ohm balance line antennas/feedlines. The fourth port is simply a push-insert-release wire terminal. The manual states that this port may be used for attaching a long-wire antenna for general coverage reception. However, it also states that all 4 ports may be used for transmitting, as long as the SWR is already 3 to 1 or below.

Now I am curious, if this port is for a long-wire antenna (a balanced load, if the unit is well grounded, right?), does that mean there must be a balun inside the box, and does it have some ratio other than 1:1 (i.e. 4:1, 6:1) if it is to match the 50 ohm input to a high impedance output like a long-wire. Or am I confusing the terms "long-wire" and "random-wire". Would a "long-wire" antenna be a balanced load if it is resonant on some band?

I really would like to know what kind of antenna and/or feedline I could use on this single-wire port for transmitting. Is there a 50 ohm ladder-line that would be a match if I connect the other wire to the ground? Please help!

"The tuner has four antenna "ports" on the back. #1,2,and 3 all have SO-239 connectors and are clearly for 50 ohm balance line antennas/feedlines."


Ooops! I meant "50 ohm UN-balanced (coaxial-fed) antennas/feedlines"

In article ,
KC0JBJ wrote:

I just bought an ICOM AT-150 antenna tuner to go with my ICOM IC-735
(still looking for that elusive object, a moderately priced PS-55
matching power supply in good condition!).

The tuner has four antenna "ports" on the back. #1,2,and 3 all have
SO-239 connectors and are clearly for 50 ohm balance line
antennas/feedlines. The fourth port is simply a push-insert-release
wire terminal. The manual states that this port may be used for
attaching a long-wire antenna for general coverage reception. However,
it also states that all 4 ports may be used for transmitting, as long
as the SWR is already 3 to 1 or below.

Now I am curious, if this port is for a long-wire antenna (a balanced
load, if the unit is well grounded, right?)

Not right, alas.

does that mean there must
be a balun inside the box, and does it have some ratio other than 1:1
(i.e. 4:1, 6:1) if it is to match the 50 ohm input to a high impedance
output like a long-wire.

Based on what I see in the manual, it appears to me that the
random/long-wire attached to ANT4 is simply being driven against your
station ground. It's an unbalanced feed, just like the other three
ports.

It really seems to be intended for just what they say - receiving -
where the impedance mismatch between the wire and the rig/tuner isn't
all that important.

Or am I confusing the terms "long-wire" and
"random-wire". Would a "long-wire" antenna be a balanced load if it is
resonant on some band?

No... at least, not in this case. Even if it's resonant, you're still
feeding it in an unbalanced fashion against ground (a "Marconi"
antenna).

I really would like to know what kind of antenna and/or feedline I
could use on this single-wire port for transmitting.

A vertical wire cut to approximately 1/4 wavelength, plus a
counterpoise wire cut to approximately the same length and attached to
the tuner's ground, could give you an impedance in the necessary
range. However, you may run into various "RF in the shack" problems.

The AT-150 doesn't appear to have a very large matching range... it's
similar to the internal autotuners build into many of today's HF
transceivers. It's suitable for adjusting the feedpoint impedance of
resonant and near-resonant dipoles and etc., in order to allow your
transmitter to operate into its design impedance and deliver full
power. It doesn't really have a wide enough matching range to be
useful for a broader range of antenna types (e.g. random-length
dipoles fed via balanced feedline, random wires, etc.).

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

It does seem kind of pointless (accept for SW receiving) to have a long-wire antenna port on a ham-band tuner. Is there any reason I could not just wire in a short length of co-ax with a female UHF connector (center to antenna #4 and braid to ground, of course) or mount and wire in another S0-239 connector and have 4 working unbalanced co-ax feed lines coming out of the shack? Minimizing unshielded feedlines minimizes stray RF problems, right?

So what was ICOM's thinking in designing this port the way they did, including front-panel push-button actuation, when all the other ports are automatically selected by band? What would be the best way to take advantage of this scheme setting in up my transmitting antennas?