Scott, After you pulled and bypassed the final, what was the lowest power you could get out of it while still being stable? I'm thinking about doing the same to a VHF maxtrac to use as an exciter for a cont duty PA, but it only needs about 400mw to drive it to full output. Thanks.
Kevin K2KMB -----Original Message----- From: wn1b8 [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 06, 2004 11:03 AM To: Repeater-Builder@yahoogroups.com Subject: [SPAM] - [Repeater-Builder] Re: Motorola Radius/GM300 - Email found in subject --- In Repeater-Builder@yahoogroups.com, "Steaven Rogers, W4YI" <[EMAIL PROTECTED]> wrote: > Has anyone here used a Radius or GM300 to make a repeater? I have a > pair of Radius (M120) UHF mobiles wired up and working, but I would like > to add a third one to use as a link to a second repeater. Can anyone > give any input on how to go about hooking up the third radio to make it > work properly?. This will be used for temporary installations only. > Aside from the heat issue are there any other pitfalls or concerns I > should look at for. These will be run on LOW power when being used to > help with the heat. > > Thanks, > Steaven, W4YI Hi Steaven, I have been playing around with the GM300s for a couple of weeks now with plans to use them as UHF link radios. In my humble opinion, they are a nice little radio and should do a good job. This, of course, will be proven or disproven in due time. Here are some of my observations: The heat issue can be a problem. Turning the power output down only adds to the heat problem. Instead, I took Kevin's (and others') advice and pulled and bypassed the final. The radio does about 3.5 watts this way. The output is very clean (I looked -70 dB and didn't detect a thing) and stable. I observed this into load with a 1:1 SWR as well as a 2.5:1 SWR. Aside from the (still) moderate heat produced, there were no detectable problems during a 35 minute keydown period. To overcome the heat issue, I simply added a computer processor fan to the back of the radio pair that triggers on from the receiver's COR (or tone squelch) and shuts off one to two minutes after the carrier or tone drops. (See Kevin's web site for the circuitry) My radios didn't display any significant drop in power until I tuned down around the low end of 433 MHz. The 16 pin connector has descriminator output, mic input, and PTT available on it making interfacing quite easy. The one drawback I have detected is the built in Tx delay. When added to the inherrent delay from an aftermarket tone decoder, which I am using on the VHF receiver married to this transmitter, the overall delay borders on the undesirable. I have a GM300 service manual and schematic en route, but without it I haven't determined a work-around. I suspect this delay is intentional and can be altered through minor component or circuitry changes. I hope this helps. Good luck. Scott Madison, WN1B Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
