[ICOM] Icom 746 cotton wool modification

[Alex]

Mike K9MI wrote:

>I didn't know the 746 had a stability problem? Mine seems fine even on 
>digital modes.

John Geiger wrote:

>I noticed that someone
> has done the "cotton wool" modification as the
> alternative (a much cheaper one) to the TXCO option.

> Does this modification really work as intended?  Does
> it really improve the stability of the Icom 746?

Perhaps the rig was used on 2 meters for PSK operations? On our VHF digital net (PSK/Olivia/Domino) we've seen quite a few rigs that presented an unacceptable drift problem without a TCXO. They're fine on HF, but on VHF it can be quite a problem.

The cotton wool will never be an alternative for a TCXO. The idea behind a TCXO is to raise the temperature of the crystal above the ambient temperature so it will not be affected as much by ambient temperature variations. The cotton wool may have some positive effect because it does insulate the crystal somewhat. Much better would be a piece of styro foam on the crystal. 

A cheaper (real) alternative to a TCXO would a PTC soldered onto the crystal.

A German ham, whose call I forgot, sells a temperature controlled heater pad that can be mounted onto crystal with some shrink tubing. It goes for 10 bucks or so.

73,
--Alex KR1ST
http://www.kr1st.com