[TenTec] Older Ten Tecs and Roofing filters

[Duane - N9DG]

--- John Geiger <johngeig at yahoo.com> wrote:

> In looking over the reviews and other on-line sources
> for rigs, it looks like some of the older Ten Tecs
> (Omnis, Corsairs I and II, but not the Paragons) use a
> low first IF (9 mhz or so) with crystal filters there,
> as well as in the 2nd IF.  So the filters in the first
> IF would be a roofing filter, correct?

Almost but not quite. In the case of the Corsair the 1st
mixer output feeds more or less directly into the 1st IF (9
MHz) filter. In the Corsair II there are two crystal filter
elements that then feed into the 8 pole 9 MHz filter. the
Omni VI is similar, (suspect the Omni V is too).

Also keep in mind that the letter series Omni's are all
single conversion where the V/VI's are are dual conversion
(sort of) and share much more in common with the Corsair's
(at least IF scheme wise) than they do with the original
Omni's or the Triton/54x series before them. BTW the Omni VII
is a very different animal than any of the previous Omni's.

>  Just like what
> Icom and Yaesu are now discovering, if I understand
> the roofing filter concept. This should make the close
> in spacing on the Corsair II and these other rigs very
> good, correct?

The key difference between Ten Tec's approach and the
Icom/Yaesu approach is that the roofing filter is at 9 MHz
vs. 69 or 45 MHz. It is easier to make a narrower low ripple
filter at 9MHz vs. VHF.

In the Sherwood chart the Corsair (not II) came in at 79 dB @
3 kHz spacing. This is close to the Omni VI+ in Sherwood's
chart. I'd be surprised if the Corsair II is not as good as
or slightly better than the Corsair.

http://www.sherweng.com/table.html
 
Duane
N9DG


 
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