[HBR] HBR-8 Questions

Thu, 25 Apr 2002 10:53:35 -0400

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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