The basic version of the high power (non duplex) micor mobile has the
minimal shielding kit, none of the bypass caps of the duplex version.
>From memory, the in cab desense version I found was in a UHF
conversion. Above about 35 watts output, we started to see the in
chassis RF make its way into unwanted places.
We simply ran the internal rf amplifier at 25 watts with the high
power final bypassed (actually replaced with a lower powered micor
final) and drove an external amp.
Might have been specific to that (one) micor model/version, but it was
there as also seen in some high power Mitrek conversions.
There was also an issue of the high power mobile heat sink not being
enough for repeater operation at full tilt.
Sometimes the free lunch comes with ham...
cheers,
skipp
(Getting geared up for IWCE and Dayton)
> Kevin Custer <[EMAIL PROTECTED]> wrote:
> skipp025 wrote:
>
> >Sometimes there is no free Commercial radio lunch... a standard
converted Micor Mobile will start in chassis desense at power levels
above 30-40 watts.
> >
>
> I have converted about 100 Motorola Micor Mobiles to repeaters. They
> have included types from Low Band, High Band, and UHF, and RailRoad
> versions.
> I have *never* seen an in cabinet desense issue, even with a 6 meter
> unit at 500 Kc separation, or a 2M unit with 600 Kc separation, either
> one running 110 watts, or more. Some Micor Low Band mobiles will
easily
> do 150 watts. While I won't run a mobile at those levels continuously,
> I have thoroughly tested them and have never seen one ounce of desense.
>
> In the units you have experienced these problems, have they been
> properly converted? Double shielded RX cabling? What band? Have the
> Audio & Squelch Boards had the duplex RF bypassing done? Where do you
> believe the desense to have been ingressing, at an RF level, or audio?
> Realize that the Micor Mobile AF amplifier will exhibit desense
issues.
> I have traced these issues back to the large filter capacitor on the
> interconnect board; which has dried out. Also, even when the AF amp is
> experiencing difficulty, the audio from the Emitter Follower is clean,
> and since this is where I choose to get the audio that is to be
> repeated, no ill effects are ever seen in real practice. So, are you
> sure the desense you heard was being retransmitted, or was it simply
> disturbing the local speaker?
>
> Brian Martens of ICS Controllers will be releasing a custom controller
> for the Motorola Micor Mobile repeater conversion (if he hasn't
> already). At my recommendation, he has included an on-board AF amp
that
> allows the OEM Micor AF PA to be removed, resulting in less current
> draw, and it gets around the Micor's audio amplifier's shortcomings
when
> a mobile radio is used as a repeater.
>
> >I'm sure the converted high powered mitreks also suffer from the
same problem.
> >
>
> I have experienced desense in *some* of the 2M conversions I have done
> on the Mitrek.
>
> Kevin Custer
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/
