[TenTec] DDS Dilemma

[CSM(r) Gary Huber]

I am the original owner of both a Corsair II and model 263 ext. VFO which 
seem to be operating well (except for noisy pots on the Corsair II). Both 
VFOs remain as smooth as the first day I used them and except for a few 
vacation trips and a half dozen Field Day forays, they have been in a 
temperature and humidity controlled basement ham shack, in almost daily use 
chasing DX.

I recapped and replaced the driver transistors in the stock display about 
ten years ago after making a mistake in the display connecters after 
cleaning the display pins.

All that given I intend to keep the Corsair II and 263 stock, but I could 
see a replacement remote (using a N4YG board) as an alternative to keep the 
Corsair going.


73 es DX,

Gary - AB9M
-----Original Message----- 
From: Ron Notarius W3WN
Sent: Tuesday, August 02, 2011 8:18 PM
To: 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] DDS Dilemma

Considering how relatively rare the remote VFOs for the Corsair & Corsair II
are, Steve's post makes one wonder if it would be cost effective for a third
party to make a "new" RVFO using the N4YG board as it's heart.

And if it was cost effective, would there be enough of a demand for one?

73

-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Steve Hunt
Sent: Tuesday, August 02, 2011 5:55 PM
To: Discussion of Ten-Tec Equipment
Subject: [TenTec] DDS Dilemma

A while ago I replaced the PTO in one of my CorsairIIs with the  DDS
board from N4YG. Once I had modified it for single rail operation I was
pretty happy with the results; but part of me regretted making the radio
"non standard", and I missed the "Spot" button functionality. However I
love the smooth tuning action of the DDS. What to do?

I decided to restore the radio to original condition, and use the DDS as
a replacement for the PTO in my 263 remote VFO instead. I kept all the
normal 263 switching functions - including the "split" function - and
used the DDS as a simple PTO replacement; all I retained of the DDS
functionality was the twin memory, which I toggle using the 263
"Reverse" button. Here's a few observations on the mod:

* Very easy to install the DDS board - there's bags of space in the
remote VFO

* Taking the DDS board out of the radio and feeding it through the LPF
which is built into the 263 switching board seems to have removed the
few spurii I had when it was inside the radio

* I had to find some way to disable the DDS output when the 263 is
switched to "VFO A". A few tests showed that if you don't disable the
DDS there is only about 40dB isolation; in other words a signal at "VFO
B" (DDS) frequency would be heard 40dB below a similar strength signal
at "VFO A" frequency, even though only VFO A was selected. I achieved
this by shunting to ground the signal from the DDS to its buffer when
VFO B is not required; I then measured over 80dB of isolation. Split
operation at high keying speeds showed no ill effects.

* I like that I still have a "standard" Corsair radios but can still
enjoy the silky smooth tuning of the DDS and can easily toggle between
the two DDS memories. If I ever thought the Rx capability was being
compromised by the DDS I can simply switch to VFO A and use the PTO.
It's now very easy to put the DDS and the PTO on the same frequency and
switch quickly between them for a comparison - so far I've not found any
difference in Rx capability on any of the signals I've tried.

* It would have been very easy to retain the DDS "Split" functionality -
the control signals are all available in the remote VFO - but I thought
I might get confused having two "layers" of split, and I would have
needed to add an LED to indicate the DDS split mode had been activated.

Hope that may be of some interest to others.

73,
Steve G3TXQ
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