[HBR] Yet Another HBR Concept

[Dan Merz]

Hi guys,  I've been following some of this thread because I once tried converting my 80/40 receiver from the 63 handbook to a  Junior Miser's dream receiver a few years after I built it,  with 7360,  but it never worked very well and I ended up re- hooking up the original circuit which I
still have after almost 40 years,  now sitting on the floor most of the time but worth the occasional look and memories.   It's lost with the neighboring HBR's and other boatanchors.  Until now this was the most elaborate homebrew receiver I built - the HBR's came from the efforts of
others.    As I "listen" to the ideas flying around,  I wonder where my latest homebrew fits in - it's a Marconi detector with moving iron wire that uses changing magnetic field as the wire passes N-S poles to convert an rf pulse to an audible click caused by the field change - none of
the refinements that permeate this thread.  But I suddenly realized that it is a homebrew and it's real beauty would be realized if instead of trying to narrow the  bandwidth with the receiver,  we could be sharing the spectrum timewise rather than by frequency and just allow each
transmitter to occupy as much of the bandwidth as possible so any old non-selective receiver would work. (laughing is allowed)   With good computers and accurate clocks, we would look for the desired signal based on the time at which it was transmitted.  What I'm looking for is a better
transmitter to use with my detector,  one that puts out a broad band signal of controllable pulse duration.  Back in 1904,  this was a spark gap which evolved into arc transmitters which I think were still in use in the 1940's.  My magnetic detector is just that - the detector coupled to
the antenna by a single coil with no apparent tuning.  Any thoughts on an appropriate transmitter - maybe that cheap battery powered drill I bought from H.F. for $10 !!  Maybe there's somebody that's already built and explored this detector.  I apologize for being a bit far afield but
sometimes we have to go back and look at  even older technology.     best regards,  Dan.

N2EY@aol.com wrote:

> In a message dated 10/6/2003 1:00:52 PM Eastern Daylight Time, waltah@earthlink.net writes:
>
> > Okay ... let's try to put it all together in an idea for Yet Another HBR.
> >
> > 1. No RF stage.   Not needed for sensitivity below at least 10 meters,
> > useful as variable (AGC-controlled) attenuator but let's keep this
> > simple.
>
> OK - and we can stick an attentuator outboard if desired.
> >
> > I have done a no-RF-stage receiver before -- they work okay if you
> > have enough IF gain and use a 2nd detector with gain.
> >
> > 2. Antenna tuned circuit is push-pull, drives grids of 6ES8 (or 6AQ8?)
> > mixer in push-pull.  That ought to give excellent IFDR ... like around
> > 100 db.  This idea is from the G2DAF Mk II receiver except that the
> > push-pull RF stage is omitted.
>
> Right - but ya need at least two tuned circuits in the front end before the mixer. Not that complex - use two big air coils link coupled or some such. Build the whole thing as a subassembly.
> >
> > 3.  IF is 6 Mcs.  VFO tunes 4.25-4.75 Mcs.   Premixed with multiple
> > of 1.75 Mcs to get f+6 Mcs, for example 4.25-4.75 + 5.25 = 9.5-10
> > Mcs to tune 3.5-4 Mcs.   I *believe* this conversion scheme has no
> > spurs in the low four bands -- does anyone see something I've
> > missed?
>
> You wanna run that through the spurs chart first. From my limited premixer experience, the VFO and xtal osc are way too close together. Listen to the birdies sing...
> >
> > Hummm ... 2nd harmonic of the VFO comes very close to the output
> > frequency on this band.  Might be well to move the IF down a little
> > and reduce the VFO freqs -- maybe 5.75 Mcs and 4.0-4.5 Mcs or
> > something close to that.
>
> Keep going and ya wind up with the classic 5/9 combo.
>
> > And/or might balance the premixer to
> > reject the VFO.   For example push-pull VFO premixer input, crystal
> > controlled signal injected on cathode, single ended premixer output.
> > (Unusual form of mixer -- might not work!  Need to check ...)
>
> Ya just built a push-push doubler for the VFO and a grounded grid amp for the xtal osc.
>
> > A push-
> > pull VFO has very low 2nd harmonic output.  It would require a two-
> > gang VFO capacitor but you get some help with stability because
> > tube capacitances are effectively halved.     But stability for a VFO at
> > < 5 Mcs is easy anyhow -- might not even bother with a 'unit VFO'
> > design.
> >
> > The oscillator chain output is ganged with the mixer grid tuning --
> > requires a three gang cap.   Three coils (center tapped mixer grid,
> > crystal osc output, oscillator chain output coil) must be
> > bandswitched -- counting the antenna winding on the grid coil, a total
> > of five contacts.   No two coils on the same frequency.
>
> You do like ganged caps.
> >
> > 4.  The multiple of 1.75 Mcs is produced by a Hahnel oscillator
> > which is basically an oscillator locked on multiples of a crystal
> > frequency.   They were investigated by the military in the 50's as a
> > possible way to do bunches of crystal controlled channels.   The
> > thing will do amazingly high multiples -- in the 100's -- with 30db or
> > so purity.  It isn't too complicated -- can be one tube with at most
> > two tuned circuits -- although the circuit parameters have to be
> > carefully adjusted.   And output must be link coupled from the
> > multiple tank circuit since RF voltage at both the crystal frequency
> > and the multiple is found throughout the circuit.
>
> One word: Overtones.
> >
> > 5.  Drive to mixer is on cathode -- single ended.   Mixer output push-
> > pull via transformer to 6 Mcs ladder filter.   The matching is not too
> > hard via a capacitive voltage divider.   I need to check what strong
> > SWBC stations are on or very near 6 Mcs -- with only one premixer
> > tuned circuit, one wouldn't want to be spot on one of those religious
> > megastations.
> >
> > An IF trap will be needed in the antenna circuit in any case.
>
> Oyez...
> >
> > 6. Two stages 6EH7 IF @ 6 Mcs.   The high gain means great care
> > in shielding and bypassing.
>
> Another subassembly.
> >
> > 7.  BFO is 'rubber crystal.'   At 6 Mcs you can get plenty of swing to
> > receive both sidebands.
> >
> > 8.  Usual 12AX7 AGC/audio plate detectors and 6U8->2x6AQ5 audio.
> >
> > That's all.   I wish someone else would build this thing first.
>
> How 'bout this:
>
> Put the filter on 5.25 MHz or thereabouts. VFO tunes 8.75-9.25 or so for 80/20, no premix at all. Subtract from ~21.5 xtal for 40 meters (premix out 12.25 to 12.75) For 15,  subtract VFO from 27 MHz xtal. Use third overtones if needed (40 meter Novice rock at 7.135 and 9 mc cb rock...
>
> Or if you're really brave, give up 15 meters and make the VFO bandswitching. Only two ranges needed (8.75-9.25 and 12.25-12.55) and they're not far apart. Use the same coil and switch a capacitor or two. Big heavy unit construction might not drift too bad. W2YM circuit will do.
>
> I didn't invent this scheme - National did, for the NCX-3 and "National 200" transceivers. Worked.
>
> Use a lot of subassemblies. Front end tuner is one, unit VFO another, IF, BFO, audio. No big chassis needed, just a panel and frame.
>
> 73 de Jim, N2EY
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
>
> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr