Mike:
This is all very helpful, and clarifies my initial confusion as to what I
was finding with my continuity checks.
The window mount works great when connected in the home shack to my outdoor
Diamond X200 antenna on the roof of the house, so I now know that the mount
is sound electrically.
If I can get an NMO to PL259 adapter of some kind, I would like to try
connecting my
Diamond 770 mobile antenna to it, but I'm going to have to check it's
length, since the documentation on the window mount clearly says that it
cannot accommodate an antenna greater than 40 inches long.
If I can't use the 770, I'm sure I can either make an antenna like has been
suggested here, or buy one at the next swap.
To me, the Window mount may be a better alternative than the magmount, since
the magmount can be a bit of a pain to remove from the top of the car when
needed, such as when the car goes in the garage.
Anyway, thanks for all this info, Mike, and we'll see how things shake out
from here.
73 from Tom Behler: KB8TYJ
----- Original Message -----
From: "Mike Duke, K5XU" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, April 05, 2011 6:46 AM
Subject: Window Mounts One More Time
Wow, I have no idea where the nervous breakdown occurred in the first =
message I tried to send on this subject, so I'll try again.
Some of what I said has been covered in other postings, so I will =
shorten this new message a bit.
The manner in which the matching coil is connected at the base of most =
5/8 or half wave antennas is what causes the DC short indication when =
you check between the center pin and the shell of the PL259, or whatever =
is on the radio end of your coax. This is only a DC, or electrical =
short, not an RF short. After 42 years of playing with antennas, I =
sometimes don't understand all I know about that statement myself, so =
for the purpose of this discussion, just know that it does indeed work =
that way.
If you replace the 5/8 wave antenna with a simple quarter wave antenna, =
or remove the antenna altogether, there is no loading coil at the base, =
and you will not see a DC short unless you have a problem in the coax or =
in the connector.
I use an MFJ window mount which, as the Comet info described, is =
intended for use with an HT rubber duck, or at the most, a quarter wave.
I run mine with a homemade quarter wave that is exactly what somebody =
else mentioned earlier, a PL259 with a 19 inch whip soldered to the =
center pin. Mine was actually brazed, because I used the remains of a =
steel whip which was salvaged from a broken CB antenna.
I simply adapt the PL259 to the BNC connector on the MFJ mount, hang it =
on the window, and away we go.
I tried adding two radials inside the car by slipping 2 #26 gage wires =
under two of the screws which hold the MFJ mount together. I then spread =
the wires apart, and held them in place along the bottom of the right =
side rear seat window with small suction cups.
This assembly resembled the shape of the print letter Y.
Adding the two radials did make a difference in the performance, but not =
as much as I thought it would.
This Comet mount sounds like a good one, and for Tom at least, the price =
was certainly right.
If you can't find an MNO to PL259 adapter, there are numerous antennas =
out there which will fit that SO239 mount.
Mike Duke, K5XU
American Council of Blind Radio Amateurs
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