Snide Filters.

[Wendymott]

Hyas peeps. At present I am building a 2 m and 6m transceiver. Its based on the Old FT290 2M transceiver. As I had two "scrappers", I harvested the Filters from one of the sets. The filters are based around 10.81 Mhz. Yes a bit strange, but Yaesu must have had good reason.
There are two 3 pin HC18 canned filters just after the mixer, in series, the circuit worked ok in the setup I have.
So to save time, I built a copy of the first module, inserting the second pair of filters from the other scrapper. I was having great difficulty getting the same responses from the second module.
I removed both sets of filters.... put them on the Spectrum analyser, and one pair centred around the marked frequency of 10.81 Mhz. The other pair centred around 10.7 Mhz, although marked at 10.81 Mhz. As this pair are used as a "roofing" filter, prior to the SSB filter and I.F, I wondered if this radio ever performed ? With over 100Khz shift I doubt it.
I can only surmise the filter supplier marked up some 10.7's as 10.81.... I guess the owner of one of these radio's suffered a lack of sensitivity. So its not only prudent to check the markings, but the actual spec too

[Jon_G4MDC]

Can't see that getting through final test at Yaesu to be honest Wendy.
It would be a disaster.

More likely the specified loading is different between suppliers and they ran different BOMs to compensate the matching.

[Wendymott]

Hi Jon. Both sets of filters were tested identically. As they were taken from identical circuits. I can only surmise that some filters were mis marked and got into the system, and those testing were not smart enough to see the difference in performance... Incidentally the case sizes are different in height by 2mm ..

[Cruisin Marine]

Did the dodgy filter look like it had been soldered after manufacture on the PCB?
What I am implying is, has it has been changed since going out in to the open big wide world?
I in my own experience not found any Yaesu stuff not to have been released on the open market that was not as promised, but, there is always a first time I guess.

[Jon_G4MDC]

That's a theory I suppose. A well meaning tinkerer having a go.
It wouldn't be the first time but then the soldering would bear witness marks (or shine) wouldn't it?

[Wendymott]

I get your meaning Cruisin... but the cans are marked 10.812 Mhz... Thus if any were retro fitted the wouldnt be marked as such.. anyways... I have made my thoughts.. please close mod.. Thanks

[Nuvistor]

Is there a failure mode that could cause theses filter to drift down frequencies so much?

[Wendymott]

Hi Frank. TWO ? to the same frequency.. I doubt it... My guess is these ended in the wrong "bin" before casing.. and obviously there would have been quite a few..