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Author Topic: Hammarlund HQ-100 BFO mods  (Read 3467 times)
W8RMV
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« on: February 17, 2010, 01:10:16 PM »

In the review section of eHam, W3DBJ notes some changes he made to get the BFO to work better on SSB.  Does any one have any suggestions/links/mods on how to do that?  My HQ-100 can sometimes tune SSB pretty good & other times it is pretty difficult.  It is not the HQ100A model.  Thanx/73's  Bob V
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KA5N
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« Reply #1 on: February 17, 2010, 05:00:27 PM »

Most mods for improving SSB performance (and CW as well) is to add a product detector instead of using the existing diode detector.  A product detector is simply a mixer which mixes the IF signal with the BFO signal and produces an audio signal.  You need a tube a few resistors and capacitors and appropriate way to switch between AM and CW/SSB.  Older handbooks and back issues of QST, CQ and 73 magazine abound in such conversions.
Allen
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W8JI
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« Reply #2 on: February 17, 2010, 05:48:42 PM »

I never understood all the fuss about a product detector. A diode detector makes a damn good low-distortion product detector if the BFO injection is high enough to switch it hard.

Maybe the mod was to increase the injection level?

:-)

 
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W8RMV
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« Reply #3 on: February 17, 2010, 07:42:43 PM »

The issue is overload with strong SSB signals.
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N2EY
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« Reply #4 on: February 18, 2010, 05:17:22 AM »

The original HQ-100 does not have a separate BFO. Instead, it uses the Q multiplier as a BFO. There was an extra-cost option to add a fixed-frequency BFO.

The HQ-100A had a separate BFO. If I had an HQ-100, I would get both manuals from BAMA and figure out what was needed to add the separate BFO to it.

Overload/distortion on SSB signals often results from not using the receiver correctly. Most older receivers do not have the kind of AGC needed for CW or SSB reception, and so the correct operating procedute is to turn the AGC off (sometimes this is done automatically when the BFO is turned on), turn the AF gain all the way up and turn the RF gain down as far as possible while still hearing signals.

Of course this means the S-meter doesn't work and that you have to "ride" the RF gain control. But that's how it was done back-when.

73 de Jim, N2EY
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W8RMV
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« Reply #5 on: February 18, 2010, 11:05:10 AM »

Hi Jim,  I thought of that but, BAMA only has the HQ100.  I'll keep looking for a 100A schematic.  Then I can do a compare & see if I can do the mods w/o messing up the appearance & other operation.

Your description is like what is found in the HQ100 manual.  I know it is sick to some, but that is what makes the HQ100 "fun".

Thanx & 73's!  Bob V
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W8RMV
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« Reply #6 on: February 18, 2010, 01:23:48 PM »

I found a HQ100A online courtesy of N9SOR Hammarlund.org. It is a very good quality copy, too!

The changes aren't trivial, but doable. 6AL6 is swapped for a 6BV8 along with added parts & re-routes.
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W8JI
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« Reply #7 on: February 18, 2010, 03:34:57 PM »

My first receiver had a self-oscillating IF stage as a BFO.

Yuk.

No wonder it is a mod to improve the HQ100.

The problem will be getting the parts to build a BFO. It would take a pretty special BFO coil to build a conventional BFO at 455 kHz. If it were me, I'd consider a solid state or tube BFO using a Colpitts  (Clapp) circuit.

Tom
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W3DBJ
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« Reply #8 on: August 03, 2010, 12:18:56 PM »

Hello,

I did the 100A mods for those that posted. I didn't see any private message on the subject, so apologies for not seeing this sooner.

Right now I'm working up an HQ-120X in between the move to an apartment and work, but the circuit isn't as condusive as the HQ-100. For this, I'm going to build an external BFO that's remarkably still available from Ten Tec
 
http://www.tentec.com/index.php?id=60

I know it's a terrible thing to do, but there's not a lot of space under the chassis, not neally enough room to mount another tube circuit, and I can use the front panel mounted switch position for the new BFO so that it retains the outward appearence of being original.

May be something you might wish to consider if you don't want to go the route of 100A modifications.
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