Yaesu FT-90R Squelch Report

Introduction

Some users of Yaesu FT-90Rs have experienced squelch problems usually related to temperature and most noticeable on UHF.

I have experienced these problems with two FT-90R radios, and sought assistance from the Australian retailer and distributor to no avail. Both of the radios have been repaired under warranty for instability in the PLL, and the although the temperature problems were identified in the fault reports, they were not fixed.

Observations

I have two FT-90Rs and have just made careful measurements of their squelch behaviour.

I have realigned the squelch set-up and PLL reference oscillator as per the service manual, set the squelch control to mid position, frequency to 439.000 and applied a 10uV signal with 1kHz modulation set to 1kHz peak deviation.

I have then varied the carrier frequency high and low and noted the frequency where the radio squelched with each of the channel step values, on each radio.

The findings are that:

both radios were similar;
in 5kHz channel step, the receiver squelch opens with carrier within 2.5kHz of centre frequency;
in any other channel step, the receiver squelch opens with carrier within 9kHz of centre frequency.

With squelch open, an off-frequency signal is received equally well regardless of channel step, so the IF / detector bandwidth does not seem to be affected by the channel step setting.

Conclusion

There is an apparent change to squelch circuit operation if the VFO or Memory Channel has the channel step set to 5kHz.

Further, it is observed that the PLL reference is temperature sensitive and this radio runs red hot (up to 75 deg C case temperature). The transmit frequency varies by +/- 3kHz on 70cm as the radio heats up on a long transmission on high power.

This combination of lack of temperature stability and narrow tolerance of off frequency signals with the channel step at 5kHz are incompatible.

Given the widespread reports of these symptoms, I think that the measured results from my two units purchased 6 months apart are probably a strong indicator that Yaesu FT-90Rs have a design fault that makes operation with a 5kHz channel step unreliable.

If a radio does not exhibit these symptoms, it is probably because it is not used with the channel step set to 5kHz.

Circumvention

The good news is that if you are prepared to forgo 5kHz step operation, the problem will not be experienced. Alternatively, be prepared to un-squelch the radio whenever it gets hot (ie after one over).

Needless to say, I haven't purchased any Yaesu equipment since purchasing the second FT-90R (first one worked fine until I cloned it from the second one which I had accidentally set to 5kHz channelling in the local UHF repeater memory channel).