Jerry,
Both the L and the C in the diplexer parallel arm are fixed value; so
low Q sounds good, given the tolerance issue :)
However the L in the series arm of the diplexer is adjustable, and the
book says to tweak that for max received signal, as you'd expect.
73,
Steve G3TXQ
On 13/03/2013 20:29, Jerry Haigwood wrote:
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"
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