N2EY wrote:
Ken Scharf wrote in message ...


This is something I thought of building several times, but with
extensive modifications. I just don't care for the classic superhet
with the first oscillator a vfo. This requires calibration of each
band, and also tracking adjustments.


All of those things can be dealt with. To me the big problem with the
basic HBR design is the stability of the tunable HFO.


I prefer the variable first IF
and a crystal controled first oscillator. (Like the drake 2B).


Me, too. There are some pictures on the HBR site of a receiver I built
about 30 years ago using that principle. It worked very well, and cost
me almost nothing to build.


My
idea of a receiver project would be to add an additional rf/mixer
front end to the HBR with a first if of 3.5-4.1 (and 6.9-7.5). The
second IF would be 1.7khz (so it's an 80/40 band image front end).


In the 1965 ARRL Handbook there is a receiver described (the HB-65)
which is almost exactly what you are describing, except it used the
100 kHz Miller IFTs. The 85 kHz cans are probably much easier to come
by these days.


The final IF would be 85khz (guess where those IF cans came from).


Swords into plowshares...


Being a compactron nut, the front end would use a 6AR11 rf amp/mixer,
and the 85khz IF would use another 6AR11. A 6AV11 for the product
detector and bfo, 6AF11 for the AF stage and agc amp.


Nothing wrong with Compactrons, but you are begging for trouble with
that scheme because the layout and section-to-section stray
capacitances will make it difficult to isolate the various stages. The
skirt selectivity of the IF amp will be compromised as well. The
layout will also be a compromise.


Other tubes for
the rest of the rig TBD. Also thought of using toriods in the front end
and bandswitching them by mounting them in a standard turret tuner
chassis ripped out of an old TV set. (I've got some real old junk in my
junk box!).


The basic idea is very sound if the Compactrons are used differently.


I have several ARC-5 rx three gang variable
caps, these have a real nice vernier drive on them. Just attach a
larger dial, or a drive pulley for a slide rule dial and you have
something as nice as the Eddystone.


Yep! Note, however, that except for the 6-9.1 MHz version they have
plate shapes that won't yield a linear dial on the ham bands. The
6-9.1 MHz version is almost pure straight line capacitance, and is
only 62 pf per section or so.
I would think you want a 'stright line frequency' where the capacitance
changes as the square of the rotation. IE: at half open position the
capacitance is down to 1/4 of the value available at full mesh.

For the ultimate, though, use the capacitor from an ARC-5 tx, BC-221
or LM freq meter. Nice gear drives and an even bigger dial than the rx
versions. Only one section though, but good for "unit oscillator"
construction of the HFO. (Only needs to cover the range 5.2-5.7 MHz)

I have a few of those ARC-5 tx caps in my junk box, and at least one
with the dial drive. It binds just a bit though as if the drive shaft
is slightly bent. Just enough to be noticed while turning it with a
good sized knob attached.
With such a design, it would be a good idea to use a Pullen mixer and
no RF stage in the 80/40 bandimage section (at least). There's also
the problem of secondary images - you need a lot of selectivity in the
front end and 1.7 MHz IF section to avoid signals 170 kHz from the
desired one seeping into the second IF. The 2B used a 455 kHz
first-fixed-IF for this reason. IM performance is compromised by the
fact that the selectivity is so far from the antenna.
With a good 'roofing' filter ahead of the final mixer you should be able
to knock down the images from the 1.7mhz if before reaching the 85khz
one. I have three 1.7mhz double tuned cans available, with all three in
series top coupled with gimick caps I should be able to achieve enough
selectivity to avoid secondary image problems. The use of a 455khz IF
is also a good idea, and I have a few Collins mech. filters that could
be used there as well (a 2.0khz bw out of an R390, a 2.7khz that looks
like an S line filter, and a large unit of 1.8khz bw that came out of an
if adaptor for an HRO-50 or 60).


With proper layout and shielding I don't see a problem using the 6AR11
in the two stage IF. Hell, they were designed for use at 47mhz in a
dual stage TV if where cross coupling would be even more of a problem!
The 6AR11 is an excellent semi-remote cutoff amplifier with good
overload and cross mod specs equal to the pentodes used in the HBR.

Some alternatives to consider:

1) Get some xtals in the 1700 kHz range and build a filter or filters
so that the 85 kHz IF is not needed. Perhaps a variable-bandwidth
filter using a multigang variable capacitor could made, using 4
crystals and a three-gang capacitor. This approach solves the
secondary image problem, too.

2) Have a single tuning range of 3.5 - 4.1 MHz and the fixed IF at 455
kHz or thereabouts. Would require dual conversion on 40 but would also
allow use of standard 455 kHz IF filters. Or make your own from
FT-241A crystals (which is what I did way back when).

3) Use the filters and heterodyne xtals from a junked transceiver as
the basis of a homebrew rx. Hangar-queen/basket case HW-100s, -101s,
and SB-line units show up on ePay and at 'fests for quite low prices -
far below what the filters and xtals would cost separately. Other
types of transceiver can also be good parts sources (Tempo One comes
to mind - nice VFO mechanism in them, and the IF is 9 MHz IIRC). KJ4KV
turned an early-version FT-101 into a pretty interesting receiver this
way.

As for a new design with todays parts, well I have several ideas here
begging to be tried. I have quite a few 'Samples' from Analog Devices
including many DDS chips. The 400mhz DDS parts would make a great HFO
for a single conversion receiver with an IF at 9mhz (again more junkbox
filters, including about 1/2 dozen 9mhz 3.2khz 8 pole units out of
Gonset Sidewinder rigs purchased at Dayton years ago). Thought I'd use
three IF stages with a filter between EACH stage and a final one before
the detector. Probably use MC1350's or ancient CA3028's as the IF amps.
The front end would use a quad DFET (Siliconix) switching mixer that
was in the handbook for several years driven at twice the required HFO
frequency (to get push-pull drive using a D Flipflop). Bowing to the
junkbox, the front end would be a double or triple tuned filter using
toriods bandswitched using a standard coil tuner chassis as the switch.
(The toriods fit nicely in the tuner strips). An 8051 series micro
drives the DDS, frequency display on 7 segment LEDs (I have enough of
these to choke an alligator) and a rotary encoder drives the micro to
select frequency.

Maybe I'm crazy, but I still wonder about puting in a second conversion
down to 85khz to use those ARC5 IF cans! Anything wrong with a hybrid
radio using the latest IC's and microprocessors along with 60's
compactrons! (Just what kind of bandwidth will a properly aligned 85khz
if strip using arc5 cans give?)

The above radio would probably end up being a transceiver (cause the
extra circuity isn't much) but the finals would end up being 1 or 2 1625
bottles 'cause I have at least a dozen of 'em in the junk box. (Also
some IRF531 mosfets which might make a good linear final for about 25
watts a pair....though maybe not to 30mhz....).

I've rambled enough....
73's

Besides the HBR website, the HBR reflector offers receiver ideas that
range far beyond the classic W6TC HBR series designs.

(I sold an Eddystone I had in the junkbox a few years ago on ebay, it
fetched about $130 IIRC. Nice dial, but a RPITA to cut out the front
panel and mount correctly.)


I haven't used an 898 yet but with the template (which I have) it
shouldn't be too difficult except for that huge rectangular hole in
the panel.

So many great hollowstate rx ideas!

Indeed!