[HBR] HBR-8 Questions

Thu, 25 Apr 2002 11:29:24 -0400

The product multiplier does exactly what it say's it does. It multiplies the
input signal with the injection of the BFO to create a difference which is
at audio. Remember, sin(f1)*sin(f(2) = Sin (f1- f2) + Sin (f1 + f2). The
difference frequency is the one at audio and then is amplified by the AF
stage. With AM, not counting synchronous AM demodulation, as you point out
all you need is a rectifier, that is why you do not need the product
detector. If you were to still have the BFO injection on then you would
continue to hear the heterodyne beat note. If you turned it off, well than
the product detector should have no output as it only has one input and it
depends on both to generate it's output. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ, 07731
(732) 901-9193

----- Original Message -----
From: "Glenn Finerman" <[email protected]>
To: <[email protected]>
Sent: Thursday, April 25, 2002 10:53 AM
Subject: RE: Re: [HBR] HBR-8 Questions

> Thanks for the replies and info Kees and Helmut;
>
> Ok, I understand you need rectification to receive AM, guess I was just
> confused about the BFO since I thought BFO carrier injection was required
to
> receive CW and SSB regardless of the product detector? then why shut it
off?
>
> Glenn K2KL
>
>
>
> -----Original Message-----
> From: Sandy and Kees Talen [mailto:[email protected]]
> Sent: Thursday, April 25, 2002 10:04 AM
> To: [email protected]
> Subject: Fw: Re: [HBR] HBR-8 Questions
>
>
> Yep, and that's why the April 63 issue includes the first modification
> for the HBR-11 ....adding an AM detector. The schematic is on the
> HBR web site. Good luck on your project.
>
> 73s  Kees K5BCQ
>
> --------- Forwarded message ----------
> From: Helmut Usbeck <[email protected]>
> To: <[email protected]>, <[email protected]>
> Date: Wed, 24 Apr 2002 21:46:30 -0400
> Subject: Re: [HBR] HBR-8 Questions
> Message-ID: <20020425134720.NURV8115.out016.verizon.net@gemini>
>
> >Howdy folks;
> >
> >This is my first post to the HBR list. I've been a ham for 30 years
> >now and
> >I'm finally getting around to homebrewing some receivers. I'd like
> >to start
> >with the simple HBR-8 but was wondering if it would be possible to
> >just add
> >an AM detector without the other changes via the HBR-11. I'd like to
> >also
> >use the receiver to listen to AM SW broadcasts in the 40 mtr band.
> >Please
> >forgive this next stupid question but I noticed there is a BFO
> >switch on the
> >HBR-8 yet the article mentions "treating the AM signal exactly as
> >though it
> >were SSB".
> >
> >I guess what I'm asking is, why is there a BFO switch if carrier
> >injection
> >is always required to receive CW and SSB with the product detector?
> >Doesn't
> >turning off the BFO disable you from receiving SSB and CW? I would
> >think
> >just shutting off the BFO would allow you to receive AM. (with a
> >diode
> >detector?)
> >
> >
> >Thanks for the help gang! I'm looking forward to some building fun
> >in the
> >future!
> >
> >
> >
> >Glenn K2KL
>
> There's no reason why you can't include a diode detector for AM
> detection.  The HBR-11 doesn't have an AM detector either  You should
> be able to receive SW stations with the 40 meter coils.  Coils for
> other SW bands can be wound.  To receive AM with a product detector
> one must zero beat the station.  This sometimes referred to as
> exalted carried detection of AM signals.  I prefer using some type of
> an AM detector though.  If one turns off the BFO on a well designed
> product detector you shouldn't hear much of the AM signal.  The
> product detector tube is really a mixer, not a rectifier.  A study of
> the receiver section in the ARRL handbook would clarify this for you.
> --
> Helmut Usbeck, WB2ADT [email protected] on 04/24/2002
>
>
>
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>
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>
>
> HBR mailing list
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> construction notes...... via http://www.qsl.net/k5bcq/
>
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