Yaesu FT101E USB Problems

[Ricardo]

I am continuing to check out my FT101E, which has been unused for many years.

I have replaced the main power supply electrolytic capacitors and the high voltage mic capacitors feeding the valve grids.

Having resolved a few issues with dirty switch contacts, etc, it is now generally working on both RX and TX. However the received audio on USB doesn't sound very good and the transmitted power output on USB is significantly lower than on LSB for the same level of mic gain.

The carrier frequencies for USB and LSB both measure OK.

The problem seems to be that the crystal filter for SSB on the low frequency IF amplifier board has drifted somewhat high in frequency. I have attached a photo showing the frequency response of this filter (XF-32A). The signal generator is set to sweep from 3.175 MHz to 3.185 MHz. The marker is at 3.180 MHz and is centered on the screen [dim trace to left of marker & bright trace to the right].



The SSB crystal filter should be at 3.180 MHz and I assume that means the centre of the passband, but from my measurements it is more like 3.182 MHz. This would seem to be sufficiently far out to be causing the problems I am having.


Any suggestions as to how to resolve this problem would be welcomed. Is the filter likely to be repairable? Do I have to find either another XF-32A filter or is there a more modern replacement I could use instead? I don't want to start shifting the frequency of the carrier oscillators to try to compensate.


Regards,

Richard

[orbanp1]

Hi Richard,

I do not have an FT101E (I have the Mk1 Z version), but here it goes (meaning I could be wrong):

The FT101E is a single conversion radio, so irrespective of the accuracy the IF frequency, one can put (tune) the receiving band of the receiver right across the USB spectrum of the received signal.
If the IF frequency is out of spec, possibly the USB BFO oscillator could be pulled to give proper reception.
There is a trimmer cap in the X-tal BFO oscillator. Hopefully it can give enough adjustment for the BFO oscillator for good SSB reception.

If you have more than one IF-filters, like wide and narrow, and one of the filters are indeed off frequency, then this might not be the solution.

Regards, Peter

[Radio Wrangler]

The FT101Z and ZD are not much related to the earlier FT101 versions except in name. The Z suffix ones are cut-down versions of the FT902D and FT902DM.

The plot of the filter shape looks to have gone ripply which suggests something is wrong. It's worth checking source and load impedances.

If the individual crystals inside the filter are in soldered-together cases, like some common HC6 and HC25 versions, then they do have a known issue with ageing and also the effects of loose muck inside the cans... soldering spatter. I have in the past unsoldered crystal cans, cleaned things very carefully and put them back together. This is an act of desperation, but I did manage to get a radio belonging to a severely disabled amateur going again when one of his carrier crystals had gone off frequency and low activity. It doesn't always work. Cold-welded cans make for better reliability and less drift.

I've got a collection of crystal filters. 9MHz, 1.4MHz, 10.7 and 21.4 but those are all routine centre frequencies. A couple of oddballs on 100kHz and 68.6MHz.

It's an unusual choice of IF, so if you do go looking for another filter, it will have come out of an early FT101. Plenty of sets were sold, so they must be out there somewhere.

Plan B would be to make a ladder structure filter, but you'd need a source of crystals on the right frequency... at least they'd all be the same.

David

[Jon_G4MDC]

What were the measured frequencies for USB and LSB Crystals please?

The filter is certainly higher than 3.180 and it looks rather narrow as well as having the ripple. It will be interesting to know where the crystals sit in comparison.

[G6Tanuki]

I'd be looking at the components around the source- and termination-circuits of the problematic filter.

Filters generally "expect" to be driven from sources, and drive loads, with controlled impedances - if the source or load goes 'off' somehow it can cause the filter's passband to shift or become-ripply in a whole range of difficult-to-predict ways.

[Jon_G4MDC]

Dirty switch contacts were mentioned.
As the CW + SSB filters are diode switched according to mode what about a problem there? Diodes not turned on properly...diode faulty etc?
Maybe the USB contact is high resistance when LSB isn't? These select the same filter but different CIO crystals so presumably the two are on a different wafer or section.

Does it have a CW filter fitted?

[Ricardo]

Thanks for all the responses.

To answer some of the questions asked.

The USB and LSB oscillator frequencies measured are 3.17843 MHz and 3.18156 MHz respectively.

The IF Unit is fitted with both the 2.4 kHz SSB filter in question and a CW filter. There is some issue with the mode switching of these two filters which I haven't fully investigated yet. The SSB filter seems to be selected in all positions of the mode switch, including CW, and the CW one does not get selected.

I will take another look at the weekend.


Regards,

Richard

[Jon_G4MDC]

Good luck with it. I wouldn't want a CW filter in all the time either although that did seem to be what Yaesu intended.

I like to use the SSB filter to listen above and below unless band conditions dictate otherwise. Maybe a switch has been hidden or re-purposed for that and you haven't found it yet?

Oscillator frequencies look fairly close for 3.180 as filter centre.

I think I would lift the ends of D1 and D3 and measure your USB filter response again.

On a later edit... another thing I might check is that C9 and C10 are not fitted. These are what connects the SSB filter in the CW position if the CW filter is not fitted. I'm fairly sure when you fit the CW filter the instructions will say remove them.

Just supposing someone fitted the CW filter but left them in place? Your SSB filter would look very nasty...both filters in all the time no matter what position the mode switch?

[Ricardo]

Hello Jon,

Thanks for the additional info. I have now found out that the CW filter on my set can be switched in and out by means of the 'PROCESS' switch, when the mode switch is in the CW position.

I haven't found any documentation which describes this. I purchased it second-hand back in about 1978 and so perhaps it was a modification done by the original owner.

Anyway now that I have figured that out I need to take another look at the frequency response of the filters on the low frequency IF amplifier board.


Kind regards,

Richard

[Radio Wrangler]

There have been all sorts of mods published for the FT101 series, so it could have been messed with a bit.

David