Thursday, September 02, 2010

The mystery of the failing filters

A couple of months ago I acquired a Kenwood TM-D710 dual band FM transceiver with APRS as it was the best solution to the problem of how to operate an APRS gateway without losing the ability to monitor for voice contacts on 2m when you do not have the space for two widely separated antennas. I have been quite pleased with the radio but rather alarmed at the number of reports of loss of sensitivity due to the failure of one or more of the IF filters. I asked on the Kenwood Yahoo group whether this was just a faulty batch of filters affecting radios of a certain age or a generic problem that was likely to affect any TM-D710 eventually and  was directed to this explanation in the blog of Tasos, SV8YM.

It has been a long time since I read such a well written explanation of a technical phenomenon and I'm sure you'll find it interesting, especially if you own a VHF radio with 455kHz IF filters. In fact I'm sure many of you will find other articles of interest in this blog. I've added it to my regular reading list.


Theodore said...

You are right Julian, a very clearly and interestingly written piece.
I must thank the author for now keeping me awake wondering if my filters are gradually growing dendrites!
Added to my angst with the lead free solder which is probably going to make my rig a doorstop in a few years I am thinking of resurrecting the old FT101B - guaranteed to contain no lead free solder.
Thanks for the link Julian, it was actually very interesting seeing how these filters are constructed and that they can be refurbished with care.

Daniel said...

Interesting piece, as a further bit of anecdotal evidence I have seen failure of these filters caused by cracks in the ceramic parts due to heat from the soldering process. The cracks eventually lead to failure of the filter after a year or two of temperature cycling. The dendrite issue is also concerning - I wonder if it explains the cracks I have seen in the filter elements.