[TMC] SBE-3 & SBE-6 on AM

[Duncan Brown]

On 01-Mar-14 10:49, John Vendely wrote:
> Make sure the sideband filters are in good shape.  I've found these 
> old crystal lattice filters (made for TMC by Bulova Electronics), have 
> often aged considerably, and are well out of their original specs.  
> They often suffer from severe passband ripple and poor opposite 
> sideband rejection.

I did a quick check on the SSB filters in the SBE-6 by manually sweeping 
the audio input frequency from a HP generator and watching the received 
signal level on my Elecraft K3/P3 on 75M.  Both passbands were flat 
within ~2db (resolution of the P3)  out to 4 Khz and unwanted sideband 
rejection was > 55db below 2 Khz and >50db from 2-4 Khz.  (I didn't 
bother looking above 4 Khz.)

So the SSB filters are probably OK (no big holes or spikes in the response!)

Our original desire to make the SBE-6 work on AM was only because we 
thought it should! Now that we know that it is not supposed to work well 
on AM, we won't expect it to or try to modify it from its original 
specs. (The Museum has other, real, AM transmitters.) As a museum, our 
goal is to preserve equipment (and get it operating as it originally 
did, when possible).  We don't modify equipment just to make it work 
better unless it was an official factory modification.

That said, I think I will try throwing together the carrier phase shift 
network, just to see what it does for my own curiosity.

Thanks for everyone's help & comments.

73,

Duncan Brown, K2OEQ
USASA  31J

Antique Wireless Association Museum Asst. Curator, Commercial Equipment
(also Chief TTY operator & repairman)
http://www.antiquewireless.org/


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