AM Detector Using FM Chip
Jim Weir
A few days ago I read a post from somebody on this group that used an FM
chip to do AM detection by feeding the amplifier around the limiter or
something like that. I believe the author was from Europe, probably from
one of the Scandanavian or Northern European countries. I emailed him and
got it bounced back with an invalid address. My computer urped and I lost
the name.
If that person would post here with a valid email address so I could ask a
few more questions, I'd really appreciate it.
Jim
Jim Weir, VP Eng. RST
A&P, CFI, and other good alphabet soup
Michael Black
On Tue, 20 Jan 1998, Jim Weir wrote:
> A few days ago I read a post from somebody on this group that used an FM
> chip to do AM detection by feeding the amplifier around the limiter or
> something like that. I believe the author was from Europe, probably from
> one of the Scandanavian or Northern European countries. I emailed him and
> got it bounced back with an invalid address. My computer urped and I lost
> the name.
The post, that I just grabbed off dejanews, is below. I'm sure you'll
hear from him yourself, since he is a regular.
He mentions a specific IC, but I've seen the thing done with other FM
detector ICs. The important point is that the actual FM detector be a
balanced demodulator; some are, some aren't. For FM use, the built in
limiter feeds one input of the balanced demodulator, and a phase shifted
version feeds the other input. When using it as an Am detector, your
incoming signal feeds the limiter and the other input to the demodulator;
the limited signal acts like a constant reinserted carrier, and mixes
the incoming signal down to audio, just like in a product detector.
It is a neat trick using an FM detector IC. The same idea has been seen
in other articles, but using separate IC's. The QST article mentioned
below does it, using an NE602 as the balanced demodulator. Years ago,
you'd see the same thing done with an MC1496 as the balanced demodulator.
Michael Ve2BVW
-----------------------------------------------------------------
Subject: Re: Need info/source of AM sync det chips/parts/kits
From: la...@no.spam (J M Noeding)
Date: 1998/01/16
Message-ID: <34bfc90a...@news.online.no>
Newsgroups: rec.radio.amateur.homebrew
[More Headers]
On 16 Jan 1998 14:19:34 GMT, crabt...@aol.com (Crabtreejr) wrote:
>On Thu, Jan 15, 1998 @ 01:01 EST, Cal Eustaquio
<ceus...@volta.ee.calpoly.edu
>
>wrote:
>
>>Anyone have a line on synchronous detection stuff for AM? I
>>had some info a while back but it slipped through my hands. Any
>> thing on the subject will do.Tnx. Cal, N6KYR.
>
>One reference is 'A synchronous detector for AM reception',
>by J. Vermasvouri, QST, July 1993
>
>73's John Crabtree
>
>
>
>
>
I designed a circuit 10 years ago using TI SN76660N/TBA120
(=Telefunken SO41P) FM quadrature demodulator. max 25mV IF signal was
fed either to limiter input and quadrature detector input, It has much
better quality for AM - in particular during fading, and you could
read signals when they seem to fade down into the noise using standard
envelope detector. SM6HYG Carl-Gustaf copied my circuit and found it
very useful for mediumwave dx'ing
----
Jan-Martin Noeding -email: la...@online.no
N-4623 Vaagsbygd, Norway
Tel.+47-380-87178
Joseph Consugar
Michael Black wrote:
> On Tue, 20 Jan 1998, Jim Weir wrote:
>
> > A few days ago I read a post from somebody on this group that used an FM
> > chip to do AM detection by feeding the amplifier around the limiter or
> > something like that. I believe the author was from Europe, probably from
> > one of the Scandanavian or Northern European countries. I emailed him and
> > got it bounced back with an invalid address. My computer urped and I lost
> > the name.
>
<SNIP>
I've seen the same thing done using a MC1330 video detector chip. The article
used a MC1350 as a wideband rf amplifier followed by a '1330 to demodulate
the AM for a two chip AM radio. I believe the author referred to it as a
homodyne.
Joseph
Michael Black
On Tue, 20 Jan 1998, Joseph Consugar wrote:
[stuff deleted]
>
> I've seen the same thing done using a MC1330 video detector chip. The article
> used a MC1350 as a wideband rf amplifier followed by a '1330 to demodulate
> the AM for a two chip AM radio. I believe the author referred to it as a
> homodyne.
>
> Joseph
>
Something like this is shown in "Amateur Radio Techniques" published by
the RSGB. It's in the sixth edition that I have. It uses a CA3028 for an
RF amp, but now that you mention it, the MC1350P/MC1330 combination sounds
familiar.
The MC1330 (and I once found an equivalent in a junked tv set) is meant
for this; in the Motorola databook it's labelled a "low-level video
detector". Interestingly, the circuit configuration is not such that it
can be used as a double balanced mixer for other purposes.
I'm not sure this device has seen as much use as it might be. Besides a
video detector, the only places I've seen it used in hobby publications is
in the receiver I mention above, and once in QST in a transverter to put a
49MHz walkie talkie on 220MHz, as a carrier detector.
Michael VE2BVW
J M Noeding
On Wed, 21 Jan 1998 00:16:59 -0500, Michael Black <blac...@CAM.ORG>
wrote:
>
>
>On Tue, 20 Jan 1998, Joseph Consugar wrote:
>[stuff deleted]
>>
>> I've seen the same thing done using a MC1330 video detector chip. The article
>> used a MC1350 as a wideband rf amplifier followed by a '1330 to demodulate
>> the AM for a two chip AM radio. I believe the author referred to it as a
>> homodyne.
>>
a quality demodulator using MC1330 was shown in wireless world (and TT
Radcom?), but I never succeeded using this circuit. Later a multimode
detector (AM/FM/SSB) using MC1351 was shown in Radcom. I used
TBA120/SN76660N in a similar circuit for voltage switched function
AM/SSB demodulator (without FM facility)
>> Joseph
>>
>Something like this is shown in "Amateur Radio Techniques" published by
>the RSGB. It's in the sixth edition that I have. It uses a CA3028 for an
>RF amp, but now that you mention it, the MC1350P/MC1330 combination sounds
>familiar.
>
>The MC1330 (and I once found an equivalent in a junked tv set) is meant
>for this; in the Motorola databook it's labelled a "low-level video
>detector". Interestingly, the circuit configuration is not such that it
>can be used as a double balanced mixer for other purposes.
>
>I'm not sure this device has seen as much use as it might be. Besides a
>video detector, the only places I've seen it used in hobby publications is
>in the receiver I mention above, and once in QST in a transverter to put a
>49MHz walkie talkie on 220MHz, as a carrier detector.
>
> Michael VE2BVW
>
>
----
Jan-Martin Noeding -email: la...@online.no
N-4623 Vaagsbygd, Norway (E/Loc: DS80b)
Tel.+47-380-87178
Jim Weir
la...@xnd.k.nor (J M Noeding)
shared these priceless pearls of wisdom:
->a quality demodulator using MC1330 was shown in wireless world (and TT
->Radcom?), but I never succeeded using this circuit. Later a multimode
->detector (AM/FM/SSB) using MC1351 was shown in Radcom. I used
->TBA120/SN76660N in a similar circuit for voltage switched function
->AM/SSB demodulator (without FM facility)
The problem with the MC1330 was that 12 volts was the absolute minimum
voltage that would make the thing work, and it was much happier at 15
volts. Using it at 12 volts would sometimes work and sometimes not as a
function of temperature, "12" volts being very slightly low, frequency, and
a whole bunch of things...
JM, I've been trying to send you email asking about your one-chip AM
receiver design and I've gotten mail bounced back three times. WOuld you
check your return address or send me an email with the correct address?
Jim Weir
la...@xnd.k.nor (J M Noeding)
shared these priceless pearls of wisdom:
->
->>
->>
->>On Tue, 20 Jan 1998, Joseph Consugar wrote:
->>[stuff deleted]
->>>
->>> I've seen the same thing done using a MC1330 video detector chip. The
article
->>> used a MC1350 as a wideband rf amplifier followed by a '1330 to
demodulate
->>> the AM for a two chip AM radio. I believe the author referred to it
as a
->>> homodyne.
->>>
Mark Zenier
In article <Pine.GSO.3.94.980120...@Stratus.CAM.ORG>,
Michael Black <blac...@CAM.ORG> wrote:
>
>On Tue, 20 Jan 1998, Jim Weir wrote:
>
>> A few days ago I read a post from somebody on this group that used an FM
>> chip to do AM detection by feeding the amplifier around the limiter or
>> something like that. I believe the author was from Europe, probably from
>> one of the Scandanavian or Northern European countries. I emailed him and
>> got it bounced back with an invalid address. My computer urped and I lost
>> the name.
>
>hear from him yourself, since he is a regular.
>
>He mentions a specific IC, but I've seen the thing done with other FM
>detector ICs. The important point is that the actual FM detector be a
>balanced demodulator; some are, some aren't. For FM use, the built in
>limiter feeds one input of the balanced demodulator, and a phase shifted
>version feeds the other input. When using it as an Am detector, your
>incoming signal feeds the limiter and the other input to the demodulator;
>the limited signal acts like a constant reinserted carrier, and mixes
>the incoming signal down to audio, just like in a product detector.
There's another way, too. If the FM if chip has a RSSI (logrithmic S
meter) output from the limiter, you can get AM signals by feeding that
into an antilog amplifier. (Never heard it, just a neat hack from
a posting here).
Mark Zenier mze...@eskimo.com mze...@netcom.com
J M Noeding
My email address is shown in the signature.
I don't know if I have missed some posts, but Signetics shows am
synchronous detector application for NE604/614.....
I have no idea what the sensitivity might be, but it was in the region
of 10-25mV RMS maximum for SN76660N and MC1351P....., and we even used
the MC1357P as 70MHz FM demodulator, the older types often run on
higher frequencies than the modern types. The reason is that they uses
fewer long-tailed pairs with fewer transistors and they are not
particularly designed for micropower operation. TBA120/SN76660N will
operate up to 20...30MHz, and I think MC1351P also goes similar. A
perhaps more interesting circuit is use of NE565N or similar PLL
device with MC1496 (or other) as phaselocked synchr. AM demodulator?
LA6MQ made many experiments using MC1310P (stereo decoder) as audio
oscillator/mixer (low frequency carrier frequency systems for multi
channels for 10GHz gunnplexer fm).
---
NE/SA604/NE614 (as quadrature AM demodulator)
Fig. 7 in the Signetics handbook shows how you can use NE614 as synchr
demodulator.
My suggested circuit - not tested (see TYPICAL FM APPLICATIONs) with
the following exceptions:
No connection to pin 9. Pse use EDIT to see the circuit diagram below.
AM |-----------
input-----|--10nF---10k----16 limiter input
max | input attenuator| 1500 ohm
25mV? RMS | |
|-------10nF----- 8 balanced modulator
| modulator i/p
|---10nF---- 14
| | 1000 ohm o/p
470 |
|------------12 1500 ohm i/p
R* not used | |
(or used to R* |--0u1-|--11 (IF input)
trim RSSI) | |gnd 0u1 |
|---------|--10 Ref.voltage
LA...@online.no |----------
2k2= 2200 ohm, 10nF = .01
Philips Components, Data Handbook(IC03): ICs for Telecom, Bipolar,
MOS,
Subscriber sets, Cordless
telephones
Philips Components, Data Handbook(IC17): ICs for Telecom, Bipolar,
MOS,
Radio Pagers, Mobile telephones,
ISDN
73
----
Jan-Martin Noeding -
email: la...@online.no
packet: LA...@LA9K.xnd.k.nor.eu (pse use SATGATE)
Tel.+47-380-87178
Jim Weir
la...@xnd.k.nor (J M Noeding)
shared these priceless pearls of wisdom:
->>It is a neat trick using an FM detector IC. The same idea has been seen
->>in other articles, but using separate IC's. The QST article mentioned
->>below does it, using an NE602 as the balanced demodulator. Years ago,
->>you'd see the same thing done with an MC1496 as the balanced
demodulator.
->I once made a morse demodulator using MC1496P where signal input was
->connected to pin 1 and 8. The two outputs where combined using a 741
->unity gain amplifier. It worked ufb, and seems possibly to be one of
->the best cw detectors I have made, but my apple 2E+ computer did not
->last forever, and I believe a better morse decoding program might have
->been written......?
Oh, FINALLY the light dawns. You aren't using the chip for anything but AM
demodulation. It isn't the IF amplifier, nor does it provide any
amplification at all. The raw IF signal is presented to both the limiter
input AND at one port of the balanced demodulator. The limited signal is
used as a constant "local oscillator" (to bend a phrase) to the other port
of the balanced demodulator. The "beat" signal between the limited IF
signal and the raw IF signal is the audio you are trying to detect.
Did I get this approximately correct? I'm sometimes slow on the pickup.
Jim
Jake Brodsky
Jim, there was a QST article from 1992 or 1993 which describes exactly
this. I breadboarded the stuff in that article for fun one weekend.
It had two detectors. One of them was just as you describe. The
other was a real synchronous detector which used the FM quadrature
detector as a VCO control line.
As you might suspect, the limited carrier system works, but not quite
as well as the full FM-detector-driving-the-VCO synchronous detector.
I believe the article called the former method "Quasi-synchronous"
detection. As long as selective fading doesn't reduce the carrier
below the level of the AM sidebands or some other interfering signal,
it will work, and it can sound pretty good.
The advantage of the "Quasi-Synchronous" detector is that aquisition
of the AM signal is immediate. There is no waiting for the detector
to "sync-up." I suppose had we attempted to build some kind of lock
detection circuit, we could have made selection of the carrier source
automatic. I never went that far, however.
73,
Jake Brodsky, AB3A mailto:fru...@erols.com
"Beware of the massive impossible!"