Programming the Idle Frequency on the MSF5000 Station

MSF index
Motorola index
Back to Home Programming the Idle Frequency
on the MSF5000 Station
By Robert W. Meister WA1MIK

Many synthesized base stations and repeaters, like the MSF5000 and MTR2000, have two VCOs, one for the receiver, one for the transmitter. These are usually kept running at all times. The transmit VCO signal can often be heard by a nearby receiver if it's tuned to the same frequency. This means you could walk near the repeater and hear a dead carrier even though the station is not transmitting. There's an article about this situation for the MTR2000 that can be found here. You can learn how to deal with this on the MSF5000 by reading the rest of this article.

Repeaters that use two separate radios usually don't suffer from this situation, because the transmit radio switches to a receive frequency when idle, and is rarely heard on a nearby receiver. The MSF5000 and MTR2000, which have separate VCOs, have no reason to change frequencies when idle, so you can often hear the VCO signal. Even crystal-controlled repeaters could suffer from this problem if their oscillators were kept running when idle. Those older stations usually went to great lengths to insure that the oscillators were shut down when idle.

The RSS Mode or Channel choices give you access to the settings seen in the screen shot below.

If the "TX IDLE CALCULATION" field is set to AUTO (the default), RSS will automatically determine the TX IDLE FREQUENCY. If the TX FREQUENCY does NOT equal the RX FREQUENCY, as in a repeater station, the TX IDLE FREQUENCY is set to the TX FREQUENCY, where it usually won't bother anybody. If the TX FREQUENCY equals the RX FREQUENCY, as you'd have in a simplex base station, RSS chooses a TX IDLE FREQUENCY that's higher or lower than the RX FREQUENCY, usually by 50 kHz, so the receiver doesn't pick up the transmitter's VCO signal when idle.

The problem with setting the TX IDLE FREQUENCY equal to the TX FREQUENCY is that a nearby receiver can hear it. The solution is to move the TX IDLE FREQUENCY about 50 kHz to either side of the TX FREQUENCY, just like RSS would do if the TX FREQUENCY equaled the RX FREQUENCY. You first need to set the TX IDLE CALCULATION field to MANUAL then you can access the TX IDLE FREQUENCY field and change it to something else that won't bother anyone. The screen shot below shows this condition where the TX IDLE FREQUENCY has been set 50 kHz below the TX FREQUENCY. Now, when you walk near the repeater, your hand-held receiver hears nothing.

Note that this phenomenon can occur with stations on ANY band. Just make sure the idle frequency you choose is within the legal band for the service and doesn't interfere with any other nearby receiver.

Contact Information:

The author can be contacted at: his-callsign [ at ] comcast [ dot ] net.

Back to the top of the page
Up one level (MSF index)
Up two levels (Motorola index)
Back to Home

This page originally posted on Tuesday 22-Aug-2017

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.