[GreenKeys] Might be a bad weekend...

[Ralph Mowery]

----- Original Message ----- 
From: "Ron Ott" <ronott at sbcglobal.net>
To: "Ron Ott" <ronott at sbcglobal.net>; <jhhaynes at earthlink.net>; "Bob Camp" 
<ham at cq.nu>
Cc: <greenkeys at mailman.qth.net>
Sent: Saturday, December 01, 2007 3:05 PM
Subject: Re: [GreenKeys] Might be a bad weekend...


> Ooops, I meant you can make filters for 425 and 850Hz shifts with toroids 
> and tubes.
>
> Ron
>
> ----- Original Message ----
> From: Ron Ott <ronott at sbcglobal.net>
> To: jhhaynes at earthlink.net; Bob Camp <ham at cq.nu>
> Cc: greenkeys at mailman.qth.net
> Sent: Saturday, December 1, 2007 12:03:58 PM
> Subject: Re: [GreenKeys] Might be a bad weekend...
>
> I believe that 170Hz shift became practical with the advent of op amp 
> filters. On the other hand, you can make adequate filters and 
> discriminators with toroids and tubes.
>
> Ron, W6XY
>

It is just about as easy to make the narrow filters with tubes as it is with 
the op amp filters.  It may just take more time to tune them as you have to 
add or remove turns or capacitors instead of just adjusting a pot.  The 
higher impedance of the tubes made it easier to build narrow filters out of 
coils than the transistors.

It became practical when the transmitters and receivers did not drift 
frequency as much.

Hoff had some narrow filters for his tube demodulators.  Some of the older 
tube military demodulators also had the narrow shift filters.  I am thinking 
they may have had some around 85 hz also, but may be mistaken.