What's inside the yaesu 101 filters?

[linearone]

Even though the yaesu 101 is an ancient radio by today's standards they still get used, traded, and sold. In fact, I'd argue they are an easier sell when they are in working order than loads of their more modern counterparts. There are a handful of places that still repair them as well which is truly mind boggling.

The "am filter" that is much sought after has only gone up in value over the years. In some cases fetching almost the price of the radio itself.
What is inside of one? How does it work? Why hasn't any talented people recreated them for sale yet? The prices they fetch on the bay should warrant some clever individuals attention to doing this out of his shack/basement.

 

[nomadradio]

What is inside of one?

Quartz crystals. And impedance-matching parts like capacitors. Can't say I remember finding an inductor in one of these, but it's probably possible.

Anyone who wants to start making quartz crystals is free to dig down deep and build a facility, buy materials and train people to do the work. Without them, no crystal filters.

73

 

[linearone]

Quartz crystals. And impedance-matching parts like capacitors. Can't say I remember finding an inductor in one of these, but it's probably possible.

Anyone who wants to start making quartz crystals is free to dig down deep and build a facility, buy materials and train people to do the work. Without them, no crystal filters.

73

Can't we just open up the catalog and buy crystals from Mouser?

 

[nomadradio]

I remember a magazine article from 25 or so years ago about buying catalog-frequency crystals to make your own crystal filters. The idea was that you buy a few dozen of the same marked frequency and measure the error for each one. These become the crystals that set the upper and lower limit of your passband. Of course you were stuck with the stock frequencies offered in the catalog, but odds are that the off-frequency tolerances would provide some that were above and some that were below the filter's desired center frequency. Can't even remember what magazine this was in. Maybe 73? Probably not QST. Showed his setup for measuring the exact series and parallel resonant frequencies of the crystals.

This guy was making narrow-banded crystals for home-brew QRP CW receivers. Might not work so well for a wider bandwidth.

73