Brian, I very familiar with those radios (small ICOM Land Mobile Dealer) one solution is to try a small preselector on the receiver .
I have two F121s in the back of a fire dept rescue vehicle with antennas about 3 feet apart and it works fairly well. The FD has told me they can be several miles from the truck and still hit the repeater full quieting. The split is a little over 5MHz. I do have a Sinclair FP20401B-2-1 preselector and I separated the radio from each other with a heavy sheet of stainless steel between them . If I hook them up any other way the transmit will completely squash the receiver. E-mail me directly I may be able to help you further John [EMAIL PROTECTED] -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] Behalf Of Brian Rau Sent: Tuesday, February 13, 2007 11:22 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Icom portable repeater help Thanks for your input, I was hoping to hear from someone who had experience with this kind of rig. I've been trying the vertical antenna separation tactic, which *in theory* puts the antennas in each others' nulls, but I think the reality is that there's enough pattern distortion, signal reflection, etc to make it unworkable. I just was looking for a sanity check before spending the bucks on the duplexer. Brian K9JVA --- In Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> , "covertp9" <[EMAIL PROTECTED]> wrote: > > I would think you'd be best served by getting the duplexer ASAP. If > your intent is to have a smaller, portable, quick to set up > repeater... the duplexer allows you to eliminate one antenna & > feedline, sets up more quickly, and works immediately without antenna > jockeying, tuning, etc. (assuming your duplexer is properly tuned). I > have the IC221s combo up as a UHF repeater using a mobile duplexer. > Until I got the duplexer correctly tuned, the desense made the setup > unusable. However, now that it's tuned I get a 15-18 mile radius > coverage from the colinear ground plane 18 feet above the back of my > garage rrof. It works as expected. > - WB2ULR > > --- In Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> , "Brian Rau" <brau@> 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 <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 > > >
