[TenTec] FW: Corsair vs Corsair II

[Jerry Haigwood]

Hi Steve,
    Ah, this is funny.  I was typing this email to inform you that I think
the value of L5 should be 0.33 UHy when I received your email.  I didn't
measure L5, I just took a guess that it might be 0.33 uHy and plugged that
into the resonance formula.  As you know it comes out at 8.76 MHz - much
closer to 9.0 MHz.  So, it appears TenTec chose to use a diplexer with a
higher Q - perhaps 18-20 based on the predicted value of L6.  I have never
tried a high Q diplexer so I cannot comment on whether this better or not.
I have noticed prominent receiver designers typically use a Q of 1.  One of
the reasons I speculate is that a diplexer with a Q of 1 is a bit more
tolerant of component values.
Jerry W5JH
"building something without experimenting is just solder practice"




-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Steve Hunt
Sent: Wednesday, March 13, 2013 3:13 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] FW: Corsair vs Corsair II

Jerry,

It's yet another error on the schematic! I lifted L5 this morning and
measured it: 330nH, not 3.3mH; it resonates with C16 (1000pF) close to 9MHz.

L9 and L10 on that same schematic are similarly in error.

73,
Steve G3TXQ



On 13/03/2013 20:01, Jerry Haigwood wrote:
> Hi Steve,
>      I agree with you.  I don't quite understand what is going on with 
> the convoluted Bridge-Tee diplexer on the Corsair II.  A properly 
> designed Bridge-Tee diplexer with a Q of 1 would have L5, L6 of 0.88 
> uHy with C15,
> C16 having values of 354 pF.  I could understand TenTec using a Q 
> different than 1 but from looking at their values, it appears they are 
> concerned with terminating frequencies below 88 KHz.  Like you stated 
> we have no way of figuring out what they are passing but one would 
> figure they want to pass 9 MHz.  If I had some extra time, maybe I 
> could build a proper Bridge-Tee diplexer and try it out.  However, I 
> am not sure how to make any definitive measurements since the Corsair II
already has excellent dynamic range.
> Jerry W5JH
> "building something without experimenting is just solder practice"
>
>

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