[ICOM] Icom 746 cotton wool modification

[Mike K9MI]

Ok, I see. Mine rarely gets off of hf, so that is why I wouldn't have 
noticed. I've used 2m ssb once, and need to get with my friend that does my 
tower work and see if a 6 meter beam, then a 2m horizontal beam at the top 
of the mast is feasible. Then I would be getting more use out of the 746. 
Thanks for the explanation...

73, Mike K9MI


----- Original Message ----- 
From: "Alex" <extraham at earthlink.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Monday, March 05, 2007 14:27
Subject: Re: [ICOM] Icom 746 cotton wool modification


> 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
>
>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
>