EMRFD Message Archive 4584

Message Date From Subject
4584 2010-04-26 19:03:35 Phil Sittner 14mhz Receiver
I'm finishing up a copy of Wes' 14mhz receiver and have a question regarding the product detector (Fig 6.76, 1st printing). Would there be any advantage to replacing the 6dB pad shown on the audio output with a diplexer similar to that shown in fig 6.72? I would think the diplexer would present a good termination.
Does anyone have thoughts about this?

Phil kd6rm

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4585 2010-04-26 20:29:51 w7zoi Re: 14mhz Receiver
Hi Phil and gang,

I suspect that you would be better off with the pad, for the audio system of Fig 6.78 just uses an op-amp in a circuit that has a 1K input R. If you put a diplexer in, change the audio input circuitry accordingly. For that matter, if you were to change to a diplexer, you may as well do a good one. Some of the stuff in Chapter's 8 and 9 is more refined.

The diode ring is a good product detector for the IMD is low. Signal levels are high, so there is no problem with the loss of a pad, and that will certainly provide the needed wide band termination for the ring.

Have fun.

73, Wes
4588 2010-04-27 07:43:45 Tim Re: 14mhz Receiver
I can't see how termination-wise it makes any difference. But my experience with the audio qualities:

I liked the post-mixer diplexer in my R2Pro so much (the smooth audio rolloff in particular) that I retrofitted it into my homebrew 8-pole crystal filter superhet's product detector. I was expecting some of the "smoothness" to somehow rub off
4590 2010-04-27 16:55:07 Phil Sittner Re: 14mhz Receiver

You've confirmed what Wes mentioned in his response. I'll finish things up in the manner shown in EMRFD and give her a go. Thanks for the input.

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4591 2010-04-27 17:05:59 Phil Sittner Re: 14mhz Receiver

Thanks for the prompt response. Tim gave a similar view of the idea so I'm sticking with the original as published. I can't wait to see what this rig sounds like.

Phil, kd6rm
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