Roy Lewallen wrote:

I believe that what you said is true, but only for AM. What other kind
of modulation requires better frequency accuracy from a direct
conversion receiver LO than from a superhet LO? I believe that only a
small fraction of today's amateurs are interested in AM reception, but
of course it's the bread and butter of the SWL and BCL.

Roy Lewallen, W7EL

Andy responds

I don't disagree with anything you've said. However , i've
found it a lot easier to make the final frequency adjustments
in a superhet since it can be done at a lower frequency.
Trying to sync up at 915 is more challenging than at 455 khz,
obviously. And for systems like FSK and SSB, you gotta
do it somewhere..... And with FM, since the beat formed
by the carrier depends on the modulation index of the
received signal, getting rid of it can be squirrelly.....

Like youself, I've built both types , both as home projects,
and as commercial products, for a long long time. In the
DC versions, if I use I/Q and combine them to form the
audio, the AGC is the same as with superhet SSB. And I generally
use PIN diodes before the front end for the first AGC stage...
But, that's just my own preference.....

Andy W4OAH

I don't disagree with anything you've said. However , i've
found it a lot easier to make the final frequency adjustments
in a superhet since it can be done at a lower frequency.
Trying to sync up at 915 is more challenging than at 455 khz,
obviously. And for systems like FSK and SSB, you gotta
do it somewhere..... And with FM, since the beat formed
by the carrier depends on the modulation index of the
received signal, getting rid of it can be squirrelly.....

You mentioned FM. I have a general question about the Tayloe mixer. Is it
possible to receive NBFM or FSK from VHF with it? I'm a little lost in the
question how to use the for outgoing phases or I/Q to demodulate FM. All I
found on the Net was doing shortwave SSB demodulation.
Are there other analog switches going higher than the mentioned 70MHz for
FST3253 or 74HC4066? Perhaps video switches? What is better: Tayloe 4-phases
or a switched mixer with one output only? In the latter case I would need a
conventional IF filter after the switching mixer?

If I need a DSP at the baseband doing math with the phases or I/Q I would
think of an www.wavefrontsemi.com DSP AL3101/2CG DSP-1K will suffice? Wolud
it suffice? It is a little simple DSP mainly for doing FIR - but FAST and
with 24-bits including audio AD converters ip to 50KHz. The DSP runs with
50MHz up to 1000 instructions long until it repeats the prog. The nice think
is a very low pin-count package and cheap too.

There is maybe a middle way with a device like the www.cypress.com PSoC
family of mixed-mode Microcontroller with programmable analog cells. There
even exists a PSoC app note describing a heterodyne FSK receiver for 130KHz.

Maybe a www.microchip.com dsPIC is better?

Would it better having the IF not at zero but at a usually higher IF, say
25KHz (remember the NFBM!)?

regards -
Henry

Henry Kiefer wrote:

You mentioned FM. I have a general question about the Tayloe mixer. Is it
possible to receive NBFM or FSK from VHF with it? I'm a little lost in the
question how to use the for outgoing phases or I/Q to demodulate FM. All I
found on the Net was doing shortwave SSB demodulation.

Provided you implement the Tayloe mixer with sufficient baseband
bandwidth (probably about 20 KHz for NBFM), you can mix, say, a 2 meter
FM signal to baseband and demodulate it with an audio discriminator
(some sort of audio frequency to voltage conversion scheme). Mix the
signal to be either exclusively in the upper or lower sideband of the
output. So, for example, a NBFM sig at 146.000 MHz mix with the Tayloe
mixer set to 145.990 MHz and select the upper sideband. The upper or
lower sidebands are, as you probably know, selected by phase shifting
and summing circuits following the Tayloe mixer (implemented in
software in SDRs). Note that SDRs like the Flex-Radio SDR 1000 do not
process incoming signals near 0 Hz anyway, but mix the desired signal
centered around about 11 KHz (I think).


Are there other analog switches going higher than the mentioned 70MHz for
FST3253 or 74HC4066? Perhaps video switches? What is better: Tayloe 4-phases
or a switched mixer with one output only? In the latter case I would need a
conventional IF filter after the switching mixer?


The Tayloe mixer is a passive mixer terminated in large capacitors, and
similar performance can be obtained at VHF, UHF and microwaves with two
FET ring mixers driven with quadrature signals and also terminated with
capacitors (that is, no wideband transformer on the mixer outputs, but
capacitors followed by HiZ input differential audio amps). I've done
this with the Peregrine Semiconductor FET mixers.

If I need a DSP at the baseband doing math with the phases or I/Q I would
think of an www.wavefrontsemi.com DSP AL3101/2CG DSP-1K will suffice? Wolud
it suffice? It is a little simple DSP mainly for doing FIR - but FAST and
with 24-bits including audio AD converters ip to 50KHz. The DSP runs with
50MHz up to 1000 instructions long until it repeats the prog. The nice think
is a very low pin-count package and cheap too.

There is maybe a middle way with a device like the www.cypress.com PSoC
family of mixed-mode Microcontroller with programmable analog cells. There
even exists a PSoC app note describing a heterodyne FSK receiver for 130KHz.

Maybe a www.microchip.com dsPIC is better?

Only familiar with the dsPIC, though the others sound okay. The dsPIC
would work, though its 12 bit A/D doesn't give a lot of dynamic range.
Plenty for NBFM though, especially since you can run the signal(s)
through a limiter first. For NBFM sixteen bit DSP is sufficient.

Regards,
Glenn

Thanks for responding Glenn!

Provided you implement the Tayloe mixer with sufficient baseband
bandwidth (probably about 20 KHz for NBFM), you can mix, say, a 2 meter
FM signal to baseband and demodulate it with an audio discriminator
(some sort of audio frequency to voltage conversion scheme). Mix the
signal to be either exclusively in the upper or lower sideband of the
output. So, for example, a NBFM sig at 146.000 MHz mix with the Tayloe
mixer set to 145.990 MHz and select the upper sideband. The upper or
lower sidebands are, as you probably know, selected by phase shifting
and summing circuits following the Tayloe mixer (implemented in
software in SDRs). Note that SDRs like the Flex-Radio SDR 1000 do not
process incoming signals near 0 Hz anyway, but mix the desired signal
centered around about 11 KHz (I think).
So the phase shifter is NOT for flatten the group delay variance (source is
the Tayloe mixer low-pass)?

Is multiplying I with Q enougth to demodulate FM as in a quadrature
demodulator?
I cannot find a suitable theory page to look for.


The Tayloe mixer is a passive mixer terminated in large capacitors, and
similar performance can be obtained at VHF, UHF and microwaves with two
FET ring mixers driven with quadrature signals and also terminated with
capacitors (that is, no wideband transformer on the mixer outputs, but
capacitors followed by HiZ input differential audio amps). I've done
this with the Peregrine Semiconductor FET mixers.
Thank you for given the link to Peregrine. I read the datasheet. How do you
mix it?
At the moment I prefer the Tayloe mixer because of it's simplicity.
BTW: They have a nice low-power consumption PLL being compatible to
National.

At TI I found nice tinylogic capable of switching like a 4066 down to 500ps
....
Should be possible to run the mixer at 150MHz with it.

Only familiar with the dsPIC, though the others sound okay. The dsPIC
would work, though its 12 bit A/D doesn't give a lot of dynamic range.
Plenty for NBFM though, especially since you can run the signal(s)
through a limiter first. For NBFM sixteen bit DSP is sufficient.
How much dynamic range do I need? I thought about 100dB?
If I recall theory I loss 2dB if limiting the signal to remove AM sensitivy.

regards -
Henry

Henry Kiefer wrote:

So the phase shifter is NOT for flatten the group delay variance (source is
the Tayloe mixer low-pass)?
If I understand your question correctly, that is true. The IQ output
from the Tayloe mixer (or any IQ mixer) is not upper and lower
sideband. To get those you must do further signal processing, which
usually involves shifting the I and Q channels ninety
degress with respect to each other then summing or subtracting the
channels depending on which sideband you want.

Is multiplying I with Q enougth to demodulate FM as in a quadrature
demodulator?
I cannot find a suitable theory page to look for.

I can't either. The IQ signals multiplied do not make an FM quadrature
detector as the phase does not really shift much over the NBFM
bandwidth. There may be a clever way to extract FM more direcly from
the IQ channels without first detecting a sideband, but I don't know
it.

Thank you for given the link to Peregrine. I read the datasheet. How do you
mix it?

Maybe the wrong part? I'm talking about the PE4140 FET ring mixer.
You use two, driven with LOs ninety degress out of phase with respect
to each other.

At the moment I prefer the Tayloe mixer because of it's simplicity.
BTW: They have a nice low-power consumption PLL being compatible to
National.

At TI I found nice tinylogic capable of switching like a 4066 down to 500ps
...
Should be possible to run the mixer at 150MHz with it.

Yeah--digital just keeps getting better. Good luck.


How much dynamic range do I need? I thought about 100dB?
If I recall theory I loss 2dB if limiting the signal to remove AM sensitivy.techniques,

You need good dynamic range up to the limiter. This can be done with
analog circuits as discussed. After the limiter an A/D converter is
not even needed in theory--a fast-running timer hooked to a digital
port could do the trick. I don't remember any loss by removing AM in
the limiter (since all the the information is contained in the
frequency of the signal), but my theory is in the distant past, back
when FM meant 'funny math'.

Regards,
Glenn

On 12 Sep 2006 13:34:58 -0700, "MadEngineer"
wrote:


Henry Kiefer wrote:

So the phase shifter is NOT for flatten the group delay variance (source is
the Tayloe mixer low-pass)?
If I understand your question correctly, that is true. The IQ output
from the Tayloe mixer (or any IQ mixer) is not upper and lower
sideband. To get those you must do further signal processing, which
usually involves shifting the I and Q channels ninety
degress with respect to each other then summing or subtracting the
channels depending on which sideband you want.

Is multiplying I with Q enougth to demodulate FM as in a quadrature
demodulator?
I cannot find a suitable theory page to look for.

I can't either. The IQ signals multiplied do not make an FM quadrature
detector as the phase does not really shift much over the NBFM
bandwidth. There may be a clever way to extract FM more direcly from
the IQ channels without first detecting a sideband, but I don't know
it.

FM the problem is not responding to amplitude changes but frequency
changes. So any system that can count and measure frequency and
render a pattern based on changing frequency.

Synthetic PLL or simple a software PLL. would do it.
The synthethetic PLL approach means a software oscillator locked
to a varying frequency external signal. The error word generated is
the demodulated signal (apply to D/A or use raw).

How much dynamic range do I need? I thought about 100dB?
If I recall theory I loss 2dB if limiting the signal to remove AM sensitivy.techniques,

Dynamic range is one of those the more the better but, many things
like noise eat away at it. These days a radio with 80db is good
and 90DB excellent, 100 Db is attainable.

You need good dynamic range up to the limiter.

You need good dynamic range up to the first selectivity that can
remove offending close in signals.

Then you can limit hard. If you limit before or without adaquate
selectivity you will have intermodulation problems.

This can be done with
analog circuits as discussed. After the limiter an A/D converter is
not even needed in theory--a fast-running timer hooked to a digital
port could do the trick. I don't remember any loss by removing AM in
the limiter (since all the the information is contained in the
frequency of the signal), but my theory is in the distant past, back
when FM meant 'funny math'.

If the signal is limited then zero crossings are enough. That could
be expressed as 1bit. Your now working in the time/frequency
domain.


Allison

FM the problem is not responding to amplitude changes but frequency
changes. So any system that can count and measure frequency and
render a pattern based on changing frequency.

Synthetic PLL or simple a software PLL. would do it.
The synthethetic PLL approach means a software oscillator locked
to a varying frequency external signal. The error word generated is
the demodulated signal (apply to D/A or use raw).
A digital detector will have problems if the SNR is to low! If the SNR is
high enought, the all-digital system is just simpler to realize and consumes
lower power.

You need good dynamic range up to the first selectivity that can
remove offending close in signals.

Then you can limit hard. If you limit before or without adaquate
selectivity you will have intermodulation problems.
Superposition prinzip.

Hi Glen -

Is multiplying I with Q enougth to demodulate FM as in a quadrature
demodulator?
The IQ signals multiplied do not make an FM quadrature
detector as the phase does not really shift much over the NBFM
bandwidth. There may be a clever way to extract FM more direcly from
the IQ channels without first detecting a sideband, but I don't know
it.
direct way:
I read about something like:
phase = (I * diff Q + Q * diff I)/(I*I + Q*Q)
but I cannot remember it exactly.


Thank you for given the link to Peregrine. I read the datasheet. How do
you
mix it?

Maybe the wrong part? I'm talking about the PE4140 FET ring mixer.
You use two, driven with LOs ninety degress out of phase with respect
to each other.
Yes, the correct part!
But I cannot see a great benefit using your concept. What is better than
others?

How much dynamic range do I need? I thought about 100dB?
If I recall theory I loss 2dB if limiting the signal to remove AM
sensitivy.techniques,

You need good dynamic range up to the limiter. This can be done with
analog circuits as discussed. After the limiter an A/D converter is
not even needed in theory--a fast-running timer hooked to a digital
port could do the trick. I don't remember any loss by removing AM in
the limiter (since all the the information is contained in the
frequency of the signal), but my theory is in the distant past, back
when FM meant 'funny math'.
Everywhere I read about the necessity to remove AM. If the band is used for
FM only, why then remove the not found AM in it?
I ran a simulation with Spice doing FM demodulator concepts comparision. The
difference between limited and not limited FM product detector was not of
significance. Doing the correct low-pass filtering after the detector was of
much higher importance.

- Henry

"Henry Kiefer" ) writes:

Everywhere I read about the necessity to remove AM. If the band is used for
FM only, why then remove the not found AM in it?

The limiting has nothing to do with receiving FM, it has everything to do
with getting rid of QRN.

Armstrong pursued FM because he wanted some system that was more noise
free than AM. Since FM does not have an amplitude componenet, that means
you can limit to clear out the QRN and some of the fading. The limiting
is what makes FM so appealling. Take out the limiter and the FM demodulator
will still work fine, but there'll be little point in switching to FM.

Michael VE2BVW