On Sat, 24 Jan 2004 12:43:39 -0500, Jeff
wrote:

Hello.

I live in a third floor apartment without a balcony. As such, finding a
way to erect an antenna has been a challenge. My home station is a 2M
mobile transceiver (Yaesu FT-2800M) which I've been attempting to find
an optimal antenna arrangement without satisfaction.

I originally constructed a J-pole from 450-ohm ladder line that I had

We've got a wall air conditioner sticking out the side of our building

My speculation is that the larger mag-mount base needs a larger ground
plane than the AC box can provide, while the smaller MFJ magmount is
sufficiently matched.

Does anyone have a suggestion on why this is occuring? Better yet, is
there a way I can possibly put a larger mobile antenna on this AC box
and get satisfactory SWR?

For reference, a good ground plane should be a least a radius of 14
wavelength around the base of the antenna. Two strips of metal at
right angles works reasonably, and the plane need not be solid, aas
long as the holes are not too large in relation to the wavelength.

Theoretically speaking, a ground plane for 2M should be a radius of
19.25 inches.

Practically speaking, I have had good results with a magmount 2M on a
standard cookie sheet, inside the house (single story wood
construction).

There is a book called "Stealth Antennas" which may help you.

Also keep in mind that a vertical antenna can hang down from the feed
point, as well as going up from there.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

In article ,
Gary S. Idontwantspam@net wrote:

For reference, a good ground plane should be a least a radius of 14
wavelength around the base of the antenna. Two strips of metal at
right angles works reasonably, and the plane need not be solid, aas
long as the holes are not too large in relation to the wavelength.

Theoretically speaking, a ground plane for 2M should be a radius of
19.25 inches.

The AC box is rectangular and I've got about 19" on two sides, but less
than that in the other two.

My understanding is this ground plane requirement for a magmount doesn't
change much with each magmount? It could be the larger 5" magmount
requires more metal?

Practically speaking, I have had good results with a magmount 2M on a
standard cookie sheet, inside the house (single story wood
construction).

I could do that, but I want to keep the antenna as far away from people
as possible since I'm on 65W simplex frequently.

Long story short, I'm trying to figure out why the metal AC box
functions just fine for a smaller magmount, but not the larger one.

There is a book called "Stealth Antennas" which may help you.

I'll keep my eye out, though most stealth antennas seem to require
access to space than I can provide.

Also keep in mind that a vertical antenna can hang down from the feed
point, as well as going up from there.

Absolutely, though I don't think our neighbor below us would appreciate
the whip hanging in front of his window.

73s
Jeff
--
--
J. Rogers KB1HOL
KB1HOLatARRLdotNET

Jeff

-----
Long story short, I'm trying to figure out why the metal AC box
functions just fine for a smaller magmount, but not the larger one.

-----

One possible explanation is that it isn't the AC's box that's
different, but the amount of capacitive coupling furnished by
the
larger magnet mount. One way of finding out is by extending the
length of the antenna slightly to compensate for the greater
coupling.
If that lowers the SWR to a reasonable level (or even if it
doesn't, but
does lower the SWR), then you know you're onto something and can
'fiddle' with it till it's 'right'.
'Doc