Programming the Transmitter Idle Frequency on the MTR2000

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This page was developed by Mike Morris WA6ILQ
from an email discussion sent to Repeater-Builder
by Eric Lemmon WB6FLY

To: Repeater-Builder From: Eric Lemmon WB6FLY While tuning up a UHF MTR2000 repeater, I became aware that the "receive" LED on my monitoring handheld radio was blinking (indicating the channel was busy), although the repeater was idle. On a hunch, I shut off the repeater and the blinking stopped. After thinking about it for a moment, I theorized that the transmitter's VCO was running all the time, and a very low-level signal was being emitted, but strong enough to be received in the immediate area. This exciter leakage is often seen in MICOR repeaters, especially when the shields are left off by a careless technician. While wondering about what to do with this problem, I remembered that the RF Option page of the Channel Information screen (see the image below) had a "TX Idle" button and frequency window. I also remembered that the Help file said that the transmitter idle was important for simplex operation (otherwise you'll block your own receiver), and could be set the same as the transmitter frequency for repeaters (since the receiver is on a different frequency). I thought, "What if I set the transmitter idle frequency to something other than the repeater transmitter frequency?" So, I entered a TX Idle frequency that was on another channel about 50 kHz away. As soon as I wrote the codeplug back to the repeater, the low-level carrier moved to the new transmitter idle frequency. Gee, the "TX Idle" feature allows the user to set the frequency at which the exciter idles! Oddly, neither the MTR operation manual nor the service manual mentions this important application for a repeater. If the exciter leakage is a problem (or merely an annoyance) with your MTR2000, simply program a frequency in the TX Idle window that is offset from the normal TX frequency by at least 20 kHz or so. Be careful NOT to set it to a frequency that is an input of another repeater, or on a simplex system, remote base or link channel. There did not seem to be any transmitter delay introduced by offsetting the exciter idle frequency. This issue can occur on ANY band, not just UHF. The MTR2000 RSS Help file suggests these formulas for calculating the TX Idle frequency: 1. If the TX frequency is more than 50 kHz from the RX frequency: Set TX Idle frequency = TX frequency. Else (the TX frequency is within 50 kHz of the RX frequency): Set a TX Idle frequency at least 50 kHz from the RX frequency. 2. The recommended value for TX Idle = TX Freq - 50 kHz. If this frequency is outside the band, use TX Idle = TX Freq + 50 kHz. 3. The TX Idle frequency must use the same VCO as the TX frequency. If the TX frequency is within the overlapping area of high and low ranges shown below, the TX Idle frequency must be in the same area. VHF high range: 152.5 MHz---------------174.0 MHz VHF low range: 132.0 MHz---------------153.5 MHz UHF high range: 436.0 MHz---------------470.0 MHz UHF Low range: 403.0 MHz---------------437.0 MHz 73, Eric Lemmon WB6FLY

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This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.