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Patrick Turner Patrick Turner is offline
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Default AM synchrodyne radio with PLLexplained.

I am searching for part 1 of Linsley Hoods's 1986 3 articles for
Electronics & Wireless World.
I have paper copies of part 2 and 3, which contain basics if direct
conversion process, with block diagrams.
The "practical" block diagram shows 4 chips,
74H04, VCO,
74H74, Divide by two,
74H86, Wxclusive OR,
MC1496, Phase detector.

Linsley has RF input to 1:1 RFT, untuned, to 3N201 with AGC then
second RFT with 400pF tuning gang, then
to second 3N201 + AGC with third RFT taken to input of phase detector.
VFO 74HO4 has coil plus 390p across coil, plus 30pF trimmer, and all
with one end grounded. The varicap diode is a BB1058 in series with 1N
across coil and other C.

The whole BC band is thus tuned, and oscillator F adjusted by dc fed
to varicap diode via 220k, so a long time constant exists with 220k
&1N.

So it seems it IS POSSIBLE to tune the whole BC band between 550 and
1,700kHz.
Linsley says it would have been good to have a 3 gang tuning cap but
they are hard to find. I have plenty though.

There are numerous other ICs for the radio.

I also came across Mike Gruber's article at
http://www.olifantasia.com/projects/...9209qex009.pdf

Worth a read. But no tubes, and very complex, although some will say
its terribly simple.

Patrick Turner.

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Patrick Turner Patrick Turner is offline
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Default AM synchrodyne radio with PLLexplained.

On Aug 1, 5:03*pm, flipper wrote:
On Sun, 31 Jul 2011 20:56:22 -0700 (PDT), Patrick Turner





wrote:
I am searching for part 1 of Linsley Hoods's 1986 3 articles for
Electronics & Wireless World.
I have paper copies of part 2 and 3, which contain basics if direct
conversion process, with block diagrams.
The "practical" block diagram shows 4 chips,
74H04, VCO,
74H74, Divide by two,
74H86, Wxclusive OR,
MC1496, Phase detector.


Linsley has RF input to 1:1 RFT, untuned, to 3N201 with AGC then
second RFT with 400pF tuning gang, then
to second 3N201 + AGC with third RFT taken to input of phase detector.
VFO 74HO4 has coil plus 390p across coil, plus 30pF trimmer, and all
with one end grounded. The varicap diode is a BB1058 in series with 1N
across coil and other C.


The whole BC band is thus tuned, and oscillator F adjusted by dc fed
to varicap diode via 220k, so a long time constant exists with 220k
&1N.


So it seems it IS POSSIBLE to tune the whole BC band between 550 and
1,700kHz.


Well, yes. That's what I was saying. 'Tuning/station select' is done
the way it was before, with the 'big pointer knob on the tuning cap',
and the 'VCO' just needs to 'fine tune' for lock.

Linsley says it would have been good to have a 3 gang tuning cap but
they are hard to find. I have plenty though.


There are numerous other ICs for the radio.


I also came across Mike Gruber's article at
http://www.olifantasia.com/projects/...onous_am_detec...


Worth a read. But no tubes, and very complex, although some will say
its terribly simple.


He does, however, mention that various prior construction projects
used tubes. Too bad he doesn't say which one(s).

Btw, Curtis's patent is here.

http://www.google.co.uk/patents?id=4...c=abstract&sou....


That's a VERY INTERESTING schematic indeed, and from an initial
perusal of the schematic there does seem to be quite a considerable
number of very unfamiliar ideas to be understood, and my mastery of
the understanding would take quite some time. The tube diodes at the
schematic top look like a foster seely FM discriminator.


He doesn't use the magic words but it's a PLL.

I was suggesting maybe it could be simplified a bit. Like, I doubt
anyone would object to SS diodes instead of the tube(s).


Depends. Shotky diodes might be best, but at BC band frequencies maybe
6AL5 is OK, RDH4 seem to think they work fine in FM discriminators and
ratio detectors at 10.7Hz.

But the whole circuit uses lots more parts and complex ideas than a
superhet which by 1939 had become fairly easy for anyone to build.


Second, one of the problems with balanced tube mixers is balancing the
tubes, which also age unequally, but the 6ME8 (and variants) was
(were) specifically designed to take care of that issue since it's
'one tube'. A 6AR8 might be better because it's easier to bias but I
think in terms of the '6ME8' because one of the online stores has them
on permanent 'dollar days' sale so it sticks in my mind.

Assuming it could be made to work that gets the tube count down to
4... but one would probably like to add the article mentioned envelope
detector as a tuning aid.

An interesting side note, this guy made a single tube direct
conversion receiver with a 6JH8 and, subsequently, a 6ME8.


I find those, and his single tube 6ME8 double reflex regen,
fascinating.

http://electronbunker.sasktelwebsite...TubeSuper.html



I guess the guys in the class of 1939 could not have guessed what
might happen in 2008 with a guy using some little known tube such as
6ME8 for an AM radio.

The guy does mention he has a few bothers using the set, but it is
extraordinarily inventive and clever.

Oddball tubes rarely needed now for spares may be abundant someplace.
I know a bloke here who's about 75, and has 25,000 tubes. He was
cleaned right out of all the good audio tubes long ago, but the rest
of his collection from buying up boxfulls at government and other
auctions many years ago is impressive, except when you realise its
tragic because when he dies all that stuff might be re-cycled through
a crusher.

But what was, cannot be again, and the past ends up the past and not
the present eventually.

I gave thought to using a limiter with huge gain in a synchrodyne to
create constant level RF signal which may be used to better lock an
oscillator so that lock happens as soon as you are within 20kHz of a
station and thus avoid tuning whistles. But last time I tried it, it
still dropped out of lock when the mod % was high, and then when you
closely look at just what you get when you increase the amplitude of
an am signal it isn't all perfectly clear you'll get exactly the
carrier F.

If one considers FM stero encoding, the L-R audio signal is used to AM
modulate a 38kHz carrier and the the 38kHz carrier is removed, leaving
upper and lower side bands. Its called the DSB signal, Double side
band. But FM stereo has a pilot tone of 19kHz, which is taken in by
the set and detecetd, amplidied, then doubled, then added to the DSB
signal and yea, you get the AM signal with L-R audio info. The simplex
way to detect L&R was with a 4 diode ring, but you need very good
stable 19khz and 38kHz coils and stable capacitors to ensure you get
good stereo separation over a wide F range. Often tube based stereo
decoders added more noise and distortion to listening than when used
with a mono signal taken from the Composite Signal without any
processing through an MPX decoder circuit.

I built an MPX unit using old bits and peices from other old tubed FM
sets and based my design on Quad's MPX add-on MPX decoder for the
early Quad FM tuner. That Quad decoder used 3 germanium transistors,
somewhat primitive like the Leak thinge. But I used tubes for a higher
dynamic range, but Ge point contact diodes. I got got only fair N&D
results but NOT at good as most generic stuff with chips. And when I
got my FM tuner just right it worked well until some damn connection
somewhere began to become intermittent and I never could find where,
and so I don't use the unit much.
Maybe a dud connection in the RF input section. Tracking down crook
intermittent connections in old stuff is a PITA.

With things like the 1939 circuit for a homodyne, methinks you'd have
to spend a month getting bugs out of such a thing to get it to work as
properly as it might.

And when its all said and done, a superhet offers unquestionable
selectivity, and multi bands. With the BC band, usually a 6BE6 mixer
and and 6BA6 IF amp does well to produce several volts of audio with
strong local MW stations. The need to use any more compexity just
isn't there, although with older tubes with lower figure of merit, ie,
lower gm, the use on an RF amp on the front end ensures even short
wave signals are going to get high enough to not be much affected by
diode threshold distortion at low levels. In fact, having heaps of
extra gain with higher gm is not really needed when its better to have
more tuned circuits - certainly for long distance MW and SW, where
trying for real hi-fi is a waste of time.

I give you a tip on AM antennas. In a recent re-build of an old 1937
radio I took out the usual RF input transformer and replaced it with a
ferrite rod job which reacts mainly to the magnetic portion of the
wave, not to the electric field effect on a typical length-of-wire
type of antenna. Such bits of wire pick up bad hum created by
fluorescent lamps somehow modulating incoming AM MW bands, and
although there's no hum off stations, but when on a station, usually a
favourite, there's dreadful hum.

My antenna consided of a bit of 25mm dia PVC conduit with about 40
turns of PVC insulated solid telephone hook up wire which is just tin
plated and about 0.6mm dia. Easy to find around, if not, one strand
taken from a Cat-5 data cable is fine.
The insulation keeps turns apart to give the coil low self capacitance
of around 6pF. The RF resistance is a bit high and Q is a bit low, but
one don't need a huge Q for the input RF circuit for MW. I used 3 x
120mm long x 10mm dia ferrite rods glued with silicone inside the PVC
pipe. I found it had more gain than with one long rod, and was less
directional. Gave plenty signal. Getting such a coil to track with
oscillator takes some doing by moving the ferrite a bit after
adjusting the oscillator to give the widest band, usually a bit more
than in 1937, because the band now goes up to 1,710kHz. Anyway, the
ferrite position is critical, and so are turns, and maybe a few turns
off or on have to be done but at the end you can usually get wide
enough tuning with some old and rather primitive tuning gang with not
quite enough C change range.

But let's just consider single side band reception. Suppose you have a
normal AM signal and remove the carrier and say the upper side band,
so you have only the lower sideband.

Consider the carrier may have been at 1,000kHz. If the audio tone was
2kHz, then the lower SB is a signal at 998kHz.
Now if that audio F changes between say 50Hz and 3kHz, then the SB
signal changes in F between 999.950kHz and 997kHz. So the SB signal in
effect is like a narrow band FM signal with amplitude modulation.
but when you add a carrier at 1,000kHz in the set by means of a BFO,
hey presto, the AF is resolved. Often this is done at the ned of the
IF strip with BFO at 455kHz, tunable with a small C gang. Reception of
the SB signal though normal AM set sounds quite unintelligable, just
garbled squawking, and the inteligibility depends on just the right F
fo the BFO. Hi-fi is not easily possible. Great for radio hams though,
no doubt about that.

So the two side bands of a normal full AM wave seem like two FM
signals with AM added with a carrier.

So despite the presence of two sidebands and a carrier in a normal AM
wave which seems to momentarily vanish at 100% mod, a simple envelope
detector can work very well without the complexity of a synchronous
detector.
A homo detector is something I have not had to always work on and
keeping me arse to the wall wards off homos. I don't mind homos of
course because I'm the tolerant type, and they have a place in the
tapestry of life. Apologies to those expecting me to expand upon how a
gayodyne receiver works. My inbuit dykodyne antenna works fine.

Patrick Turner.

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John Byrns John Byrns is offline
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Default AM synchrodyne radio with PLLexplained.

In article ,
Patrick Turner wrote:

On Aug 1, 5:03*pm, flipper wrote:

Btw, Curtis's patent is here.

http://www.google.co.uk/patents?id=4...c=abstract&sou...


That's a VERY INTERESTING schematic indeed, and from an initial
perusal of the schematic there does seem to be quite a considerable
number of very unfamiliar ideas to be understood, and my mastery of
the understanding would take quite some time. The tube diodes at the
schematic top look like a foster seely FM discriminator.


Exactly, that's why I suggested in an earlier post that an off the shelf 455 kHz
Foster Seeley discriminator transformer could be used in an IF frequency version
of the synchronous detector. The same type of discriminator transformer could
also be used in the audio demodulator section, and the two pentode tubes could
also be eliminated in favor of two more diodes.

He doesn't use the magic words but it's a PLL.

I was suggesting maybe it could be simplified a bit. Like, I doubt
anyone would object to SS diodes instead of the tube(s).


Depends. Shotky diodes might be best, but at BC band frequencies maybe
6AL5 is OK, RDH4 seem to think they work fine in FM discriminators and
ratio detectors at 10.7Hz.

But the whole circuit uses lots more parts and complex ideas than a
superhet which by 1939 had become fairly easy for anyone to build.


The synchrodyne uses an extra tube or two over a suberheterodyne tuner, the
superheterodyne uses 2 active tubes and one diode while the synchrodyne uses 3
active tubes plus 4 diodes, both circuits use 4 coils/transformers. Sure the
synchrodyne uses complex ideas, but where are the "lots more parts"?

I find those, and his single tube 6ME8 double reflex regen,
fascinating.

http://electronbunker.sasktelwebsite...TubeSuper.html


Actually it's much more than a double reflex regen, it's a triple reflex regen
superhetrodyne!

I guess the guys in the class of 1939 could not have guessed what
might happen in 2008 with a guy using some little known tube such as
6ME8 for an AM radio.

The guy does mention he has a few bothers using the set, but it is
extraordinarily inventive and clever.


I think these designs are to fit into the Crystal Radio Group's single active
device contest category, no one in their right mind would do this otherwise,
except for the challenge, it is quite clever and a great accomplishment though.

I give you a tip on AM antennas. In a recent re-build of an old 1937
radio I took out the usual RF input transformer and replaced it with a
ferrite rod job which reacts mainly to the magnetic portion of the
wave, not to the electric field effect on a typical length-of-wire
type of antenna. Such bits of wire pick up bad hum created by
fluorescent lamps somehow modulating incoming AM MW bands, and
although there's no hum off stations, but when on a station, usually a
favourite, there's dreadful hum.


While my experience with AM antennas is similar to yours, there are those that
say there is another way. Part of the problem is that the piece of wire is only
half of the antenna system, the ground is the other half of a wire antenna and
the typical ground system inside a home is highly polluted with noise. Some
people suggest installing the wire antenna in the back garden along with a
ground system separate from the ground system in the house. The antenna and
ground system are then connected through a suitable matching network to a
coaxial transmission line to the receiver in the house, where a transformer with
an electrostatic screen between the primary and secondary is used to connect the
transmission line to the receiver. The object is to separate the antenna ground
from the receiver's ground that is tied into the noisy electrical system of the
house. I haven't tried this system so I can't speak to its efficacy, but it is
interesting an sounds plausible. As you would expect there are web sites
describing this antenna setup. Also some antenna system kits of the 1930's used
this sort of scheme, with a balanced transmission line, to isolate the antenna
system from electrical system in the house.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/
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