Rick, you might have been wrong but thanks for the discussion and posting
Jerry's response here! Very mucn appreciate technical discussion of the
older Ten-Tec receivers.
73,
Barry N1EU
On Wed, Mar 13, 2013 at 8:42 AM, Rick - DJ0IP / NJ0IP <Rick@dj0ip.de> wrote:
> PLEASE DISREGARD MY PREVIOUS POST, WHERE I THOUGHT A BROADBAND TERMINATION
> WAS NOT NECESSARY.
>
> Guys, in my previous post on this topic, I WAS WRONG. :-(
> (sri)
>
> Jerry was kind enough to point that out to me off-line, and showed me where
> I could read more... where I discovered that my 1970's state of the art
> mindset on this topic is well behind the power curve.
>
> Looks like this old dog needs to go back to school and learn some new
> tricks
> about RX technology.
> I will switch into "READ-ONLY" mode for the rest of this thread.
>
> JERRY'S RESPONSE TO ME IS BELOW...
>
> THANK YOU JERRY!
>
> 73
> Rick, DJ0IP
>
> -----Original Message-----
> From: Jerry Haigwood [mailto:jerry@w5jh.net]
> Sent: Wednesday, March 13, 2013 3:33 AM
> To: 'Rick - DJ0IP / NJ0IP'
> Subject: RE: [TenTec] Corsair vs Corsair II
>
> Hi Rick,
> If you have ever looked at the output of diode ring mixer using a
> spectrum analyzer, I doubt if you would have made the statement, "So as I
> see it, it is not so important to have "broadband termination" as it is to
> have "TWO specific terminations", one for the desired signal and one for
> the
> unwanted signal." There are many signals present at the output of a diode
> ring mixer - not just two. All of these signals need to be terminated
> properly. That is why diplexers are broadband. Take a look at VE7BPO's
> page, especially figure 9:
> <http://www.qrp.pops.net/sbl1.asp>
> Todd gives a pretty good description of what the diode ring mixer does and
> how it does it. He gives you a spectrum analyzer view of the output of a
> diode ring mixer (figure 9). Todd also discusses diplexers here:
> <http://www.qrp.pops.net/dip2.asp>
> I prefer the Bridge-Tee diplexer designed by Joe Reisert, W1JR. It is easy
> to build, broadband, and works very well at terminating a diode ring mixer.
> Jerry W5JH
> "building something without experimenting is just solder practice"
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Rick -
> DJ0IP / NJ0IP
> Sent: Tuesday, March 12, 2013 8:11 PM
> To: 'Discussion of Ten-Tec Equipment'
> Subject: Re: [TenTec] Corsair vs Corsair II
>
> The biggest problem with mixers feeding directly into a crystal filter is,
> the mixer always has TWO outputs (the sum and the difference frequencies).
> One of them is the desired frequency (i.e. 9 MHz), the same as the crystal
> filter, and the second one is on another unwanted frequency.
>
> The crystal filter has a design impedance which should be designed to match
> that of the output of the mixer, but it is only that impedance on its
> design
> frequency (i.e. 9 MHz). It terminates the desired frequency just fine,
> but...it's this second signal that causes the problem, because it is not
> properly terminated by the crystal filter. This lack of proper termination
> for this one specific signal causes standing waves at that point.
>
> So the culprit is specifically the standing waves caused by improper
> termination of the unwanted signal, which may causes ~30 dB of degradation
> the IP.
>
> The best way to deal with this is with a "diplexer", which is a splitter
> which separates the two signals, routes the wanted signal to the crystal
> filter (where it is properly terminated) and routes the unwanted signal to
> a
> tuned circuit or trap, resonant on its frequency.
>
> The diplexer is inserted between the mixer output and the crystal filter
> and
> traps the unwanted signal, preventing it from reaching the crystal filter,
> thus preventing the standing waves and maintaining a high IP.
>
> So as I see it, it is not so important to have "broadband termination" as
> it
> is to have "TWO specific terminations", one for the desired signal and one
> for the unwanted signal.
>
> Broadband termination is also a way of addressing this, and it also works,
> but it is not nearly as effective as using a diplexer.
>
> Les Hayward, W7ZOI popularized this concept in the mid 1970s.
> If I dig deep enough in my files, I can probably find one of his articles
> explaining this, which as I recall, were published in Ham Radio Magazine.
>
> BTW, as I recall, Ten-Tec introduced a diplexer with its first OMNI but
> that
> was long ago and my old grey cells may be failing me on that point. Easy
> enough to check if someone has an Omni schematic handy.
>
> 73
> Rick, DJ0IP
>
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Barry
> N1EU
> Sent: Tuesday, March 12, 2013 11:54 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Corsair vs Corsair II
>
> On Tue, Mar 12, 2013 at 10:32 PM, GARY HUBER <glhuber@msn.com> wrote:
>
> > Mike,
> >
> > You are welcome. I regret that I cannot locate the document where I
> > originally saw the reference to Corsair / Corsair-II having ANZAC
> > receiver design and later commentary on later TEN-TEC receiver design
> > being changed to avoid Copyright or similar legal issues.
> >
>
> Here you go, posted 2007 to this list by Jerry K0CQ.
>
> 73,
> Barry N1EU
>
> 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. There is no
> attenuator.
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