Gary, not sure I understand the question - the PTO can't overload due to
high RF. Using a PTO won't make a front end more immune to overload from
high RF than using a DDS, etc.
But there was a bit of real magic in the Corsair front end design. K0CQ
posted this to the reflector in 2007:
The bipolar RF (and first IF) stage uses transformer feedback with a
three winding transformer. Its a circuit developed for the output stages
of cable TV distribution amplifiers where acceptable intermod is 70 dB
down and in Ulrich Rohde's book on receiver design he sees nothing close
to having its performance. A double gate MOSFET doesn't come close. I've
run Kenwood with MOSFETs and those MOSFETS don't come close to the
strong signal handling of my Corsair II.
That circuit is covered by an Anzac patent or two and that may be why
Tentec went to the grounded gate JFET circuit in the Omni V and VI.
Those use four JFETS in parallel with individual source resistors to
make them balance better. I've not seem their performance compared
directly to the Anzac circuit, but the Omni V and VI seem to do quite
well in the intermod department.
Schottky ring mixers are hard to beat and the higher the LO power (so
long as the mixer is designed for it) the better the strong signal
performance. Its also important that at least two of the three ports of
the ring mixer be terminated over a wide range of frequencies, else NF,
mixer loss, and intermod can be a lot worse. The mixer output often sees
a crystal filter and that is the worst thing that can be done, one book
on mixers says that can cost 30 dB intermod range. The Corsair II, Omni
V and VI use a broad band IF stage with lots of dynamic range to provide
that IF port broad band load and it shows. It works.
Don't know about the Omni V and VI, but the "attenuator" switch on the
Corsair II actually removes the RF stage from the circuit.
73, Barry N1EU
On Fri, Oct 3, 2014 at 11:43 AM, Gary - AB9M <glhuber@msn.com> wrote:
> The tale question referred to a Volt of RF on the RX antenna terminal.....
>
> 73 & DX,
>
> Gary - AB9M
>
>
> -----Original Message----- From: Barry N1EU
> Sent: Friday, October 03, 2014 3:18 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Modern version of the Tec Tec Corsair - please Ten
> Tec!
>
> On Fri, Oct 3, 2014 at 12:23 AM, Gary - AB9M <glhuber@msn.com> wrote:
>
> Rick, is there any truth to the old RF Technician's tale that it takes
>> more than a Volt of RF to overload a PTO on a Corsair II?
>>
>
>
> There is no RF input on a PTO.
>
> 73, Barry N1EU
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