Re: [Repeater-Builder] UHF Power

Sun, 12 Feb 2006 09:57:05 -0800

was and still have a lot of Micro repeaters on the air (same receiver as the TAC units)  and been changing to Kenwood TKR-840 repeaters.  Find the Kenwood TKR-840 will do better that the Micors and even a factory tuned TKR-850.   Have all three on the same tower, on the same antenna's .
all UHF 460 to 470 band.
 
----- Original Message -----
From: N9WYS
Sent: Saturday, February 11, 2006 7:04 PM
Subject: RE: [Repeater-Builder] UHF Power

For what it’s worth - and since this thread started because of my mention of the 150W transmitter – I should note that the RX sensitivity on the Kenwood that I am currently running IS about .25uv…  However, when I get the remote RX site(s) operating, I’ll be using Micor (AKA: SpectraTAC) units, so I’m hoping for a bit better RX sensitivity.

 

Mark – N9WYS

 

From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Kevin Custer
Sent: Saturday, February 11, 2006 5:33 PM
To: [email protected]
Subject: Re: [Repeater-Builder] UHF Power

 

I disagree that a typical ham rig will have better sensitivity than a repeater receiver with a good preamp.  I have tested many repeaters with a good preamp, and many typical Japanese mobile radios, and there is about a 3 to 6 dB of difference in most cases, sometimes even more, with the repeater always being better.  If not, something is way wrong (deaf repeater receiver).

A few weeks ago, Scott and I tested a 220 Micor conversion with a good preamp (ARR).  It breaks squelch at -133 dBm and has a 12 dB SINAD rating of -128 dBm.  Most of my UHF repeaters have similar sensitivity.  Most of my Japanese mobiles make 12 dB SINAD at .25 uV or -119 dBm.  This relates to a 9 dB greater receiver capability, not including site conditions, or anything else, just basic sensitivity.  Even if it were only 6 dB better, (very typical), you would need 140 watts for a matched system (considering a 35 watt mobile), or 200 watts, considering a 50 watt mobile.

The math is simple, and with good repeater site conditions, this better receiver sensitivity can be realized.

Besides the math, in real practice it's easy to see how well matched a properly working 200 watt repeater operates.  If it didn't make a difference, no one would pay the price to run this much RF.  The equipment costs more, as well as the electric bill, and I don't know anyone around here that would enjoy running a repeater that out-talks the receiver.

Kevin


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