--- In [email protected], "Brian Rau" <[EMAIL PROTECTED]>
wrote:
>
> I'm putting together a portable "suitcase" repeater for our search
and
> rescue team, using Icom F121 radios per this article:
>
> http://www.repeater-builder.com/icom/repeater-mod-for-icom-ic121-
221-series.rtf
>
> I've got the two radios together and working, my question is: has
> anyone had success with this configuration using two separate
antennas
> (no duplexer)? I've tried using two twinlead J-poles, one at the
top
> of a 25' mast and one at ground level (tried both RX and TX at the
> top, TX at top seems to work better), I've also tried a home-built
1/4
> wave with four radials at the top (TX) with a 1/4 wave magmount on
a
> car directly below. I can hit the repeater with a 5W handheld
from a
> good long distance away, and get the squelch tail for the
programmed
> hang time. However, I don't get any audio repeated much farther
than
> a half mile to a mile away. I can do handheld-to-handheld simplex
a
> good deal farther than this.
>
> I have permission to use a 5.5 MHz split pair of frequencies in
the
> 150 MHz range, which is what I've done all testing on. It sure
acts
> like the TX is desensing the receiver. We ultimately may want to
> incorporate a mobile duplexer (Sinclair or similar) into the box
> anyway just to be able to use a single antenna, but I'm surprised
this
> isn't working better with two antennas mounted directly above/below
> each other. Interestingly, Icom apparently offers this
configuration
> (two F121 mobiles in a Pelican case) as a standard "portable
repeater"
> product now, and the duplexer is an option, so I'm wondering under
> what circumstances this thing will work without a duplexer?
>
> Any comments or suggestions are appreciated.
>
> Brian
> K9JVA
>
Hi,
from the experiments carried out here in the U.K. on in-band and
cross-band portable and mobile repeaters vertical separation is
nowhere near as good as horizontal.This also offers the chance
to get the recieve antenna in a "null" from the transmitter.Also
it might be better to use a crystal-controlled rig for this work
due to noise generated in the Tx signal providing there isn't a
requirement for too many channels too far apart (less than 1%) of
the centre frequency.
Adam G8UMX
