SSB

[Ken Smith]

Hello,

Just want to build a SSB modulator with MC1496 chip.
The phasing method (second way) is desired.

[....]
A doable way to get a 90 degree signal is to use
a PLL. A PLL adjusts the VCO such that the resulting
signal is 90 degrees to the reference. 30Hz to 16kHz
is a bit much for a single VCO stage. It'd be doable
with a difference VCO though.

That won't work for a complex waveform. A pair of filter strings is a
good way to do it for things like voice.

 

[Ken Smith]

Methinks the OP was talking of the All-Pass approach to phase shifting
the AUDIO for use in an SSB modulator.

PLL's do 90° phase shift only with analog phase detectors... which
have terrible useful frequency range, before harmonic locking and
other nuisances.

The best way with a PLL is to run the VCO at 4X, use a div4 in the
feedback loop, with edge-matching phase detector, then peel off the
90° with an extra div2 from within the div4 chain.

No that isn't the best way to do it.

------------------------------------------
! ------- ------- !
---!D Q!---------------!D Q! !
! ! ! ! !
CLK--!> ! CLK--!> ! !
! ! ! ! !
! Q/!----X0 ! Q/!------+--X90
------- -------

This only takes a single 74HC74

 

[Jim Thompson]

No that isn't the best way to do it.

------------------------------------------
! ------- ------- !
---!D Q!---------------!D Q! !
! ! ! ! !
CLK--!> ! CLK--!> ! !
! ! ! ! !
! Q/!----X0 ! Q/!------+--X90
------- -------

This only takes a single 74HC74

[snip]

I think that's what I meant, but couldn't quite remember the
implementation ;-)

...Jim Thompson

 

[Phil Hobbs]

Yes I am thinking that it is not working with that wide bandwidth.
I have seen the below 90 degrees phase shift circuit which is working
from 20Hz to 20KHz with 1% of error.
it uses 12 op amps to do the job while the first circuit is using just
4 with the same circuitry

http://img187.imageshack.us/my.php?image=image22zr8.gif

When you multiply two signals together, their phases add. To get one
sideband to cancel and one to add, you need two 90-degree phase shifts.
(If you use one 180-degree phase shift instead, both sidebands cancel.)

So, to make an SSB modulator, you can use 90 degree phase shifters in
any two arms of the mixers. There's no magic about doing it at
baseband, so one can just use a divide-by-4 Johnson counter on the LO
inputs (as others have proposed), drive the baseband inputs in phase,
and use a narrowband 90-degree phase shifter on the mixer outputs. The
90-degree phase has to be very accurate at the frequency of the
_unwanted_ sideband.

Cheers,

Phil Hobbs

 

[[email protected]]

On a sunny day (Sat, 10 Feb 2007 14:20:46 GMT) it happened Fred Bloggs

Actually some do.

'Width of the band used' makes no difference, and in fact the Americans have a
tendency to split words, unlike the Dutch and Germans who seem to want to write
very long words.

And quote what and who you are replying to.

\~~~~~~~~~~~~~~~~~~~~/
\ water for flames /
\ to follow /
\______________/

(I was lying, it no water but petrol ;-) )

______
[ exit ] click here to close window of opportunity.
------

If that's the case and his highest frequency component is only 16KHZ,
then I would say a simple digital scheme sampling at 4x16K=64KHz with
simple sorting and inverting every other sample to produce perfectly
quadrature data streams to D/A may even be within range of an 8-pin
PIC-or two, dunno. Almost anything beats that ancient mess of analog
filters.

The scheme you described produces the I and Q stream, but this is not
what is needed to generate SSB. However, there are DSP techniques to
make Hilbert transformers.

 

[Joerg]

Methinks the OP was talking of the All-Pass approach to phase shifting
the AUDIO for use in an SSB modulator.

Methinks so, too. In the olden days before DSP became somewhat
affordable we had to do that for demodulation in Doppler receivers. We
used plain old RC lattices. But what a pain that was for the purchasing
department, all those caps with 1% or better tolerance.

Adam: Audio phase shifters can be found in publications such as the ARRL
Handbook, at least in older editions. Usually only for audio from 300Hz
to 3kHz but one can then calculate the additions for more. If it's a
one-off build you could measure out capacitors and combine to get to
less than 1%. Otherwise finding the caps on the market can take much
longer than calculating the values.

[...]

 

[Michael Black]

You'll note that it's not the *same* circuitry; it's only similar.

The first schematic you posted uses 2 capacitors per op amp, while this
one only uses 1 per op amp. With 2 capacitors per op amp, this circuit
could be reduced to 6 op amps instead of 12.


This circuit obviously came from:

http://webpages.charter.net/wa1sov/technical/allpass/allpass.html

The author of that page explains how to design these circuits. His example
circuits are designed for a 20Hz to 20 kHz bandwidth. I would think that
for radio communications something like 300-3000 Hz would be appropriate.

That's interesting. IN this case, I assumed he had some specific need
for the very wide bandwidth, but now that you mention it, it might be
simply that he doesn't realize SSB for communication would never be beyond
that.

And of course, you can get by with relatively simple phasing networks for
such a narrow bandwidth, so long as you can live with limited opposite
sideband suppresion. Once you take out the carrier, whatever you get rid
of in the opposite sideband may just be the icing on the cake.

ANd unlike using the phasing method at the receiver, you can control what
the phasing network has to deal with when it's in the transmitter. Either
your voice won't be much beyond that 300 to 3000Hz range, or you can even
filter it before it gets to the phasing network, so the network only
has to deal with that limited range. PUt the phasing network at the receiver,
and it has to deal with a much wider range of signal, the incoming radio
spectrum.

Michael

 

[John Larkin]

If that's the case and his highest frequency component is only 16KHZ,
then I would say a simple digital scheme sampling at 4x16K=64KHz with
simple sorting and inverting every other sample to produce perfectly
quadrature data streams to D/A may even be within range of an 8-pin
PIC-or two, dunno. Almost anything beats that ancient mess of analog
filters.

But there's no such simple sorting scheme. A DSP approximation to a
Hilbert transform will give the proper wideband allpass phase shift,
but it's rather compute intensive, too much for a PIC. But even a
smallish FPGA could do it, and then you may as well do the carrier 90
degree shift and the mixing/summing stuff in there as well.

Somebody must have done the entire SSB chain in VHDL somewhere.

John

 

[Michael A. Terrell]

Methinks the OP was talking of the All-Pass approach to phase shifting
the AUDIO for use in an SSB modulator.

Methinks so, too. In the olden days before DSP became somewhat
affordable we had to do that for demodulation in Doppler receivers. We
used plain old RC lattices. But what a pain that was for the purchasing
department, all those caps with 1% or better tolerance.

Adam: Audio phase shifters can be found in publications such as the ARRL
Handbook, at least in older editions. Usually only for audio from 300Hz
to 3kHz but one can then calculate the additions for more. If it's a
one-off build you could measure out capacitors and combine to get to
less than 1%. Otherwise finding the caps on the market can take much
longer than calculating the values.

[...]

Then there is the crystal filter, or mechanical filter methods
without so many critical adjustments.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Steve Kavanagh]

I would think that
for radio communications something like 300-3000 Hz would be appropriate.

MUCH simpler networks have been used for 300-3000 Hz. The Barker &
Williamson model 2Q4 phase shift network, which was much used in early
SSB transmitters contained only 4 resistors and 4 capacitors, I
believe. No op-amps !

Steve

 

[Joerg]

Jim Thompson wrote:

Adam wrote:


Hello,

Just want to build a SSB modulator with MC1496 chip.
The phasing method (second way) is desired.
Well, the phasing method needs a Hilbert transformer to change the
audio signal by 90 degrees. I saw the below circuit in an electronics
book, the author mentioned that the circuit produce a 90 degree phase
shift with an 1% error from 30Hz to 16KHz .
Most of the filters I have seen for this job are using more
complicated circuits
But with much lower band width!
Do you think the below circuit is able to generate the 90 degrees of
phase shift over that band width?

http://img251.imageshack.us/my.php?image=untitledwc7.jpg


A doable way to get a 90 degree signal is to use
a PLL. A PLL adjusts the VCO such that the resulting
signal is 90 degrees to the reference. 30Hz to 16kHz
is a bit much for a single VCO stage. It'd be doable
with a difference VCO though.

Rene


Methinks the OP was talking of the All-Pass approach to phase shifting
the AUDIO for use in an SSB modulator.

Methinks so, too. In the olden days before DSP became somewhat
affordable we had to do that for demodulation in Doppler receivers. We
used plain old RC lattices. But what a pain that was for the purchasing
department, all those caps with 1% or better tolerance.

Adam: Audio phase shifters can be found in publications such as the ARRL
Handbook, at least in older editions. Usually only for audio from 300Hz
to 3kHz but one can then calculate the additions for more. If it's a
one-off build you could measure out capacitors and combine to get to
less than 1%. Otherwise finding the caps on the market can take much
longer than calculating the values.

[...]

Then there is the crystal filter, or mechanical filter methods
without so many critical adjustments.

Crystal filters is what I used. But 30Hz-16kHz can be financially
painful. Even 300Hz-3kHz easily set you back $150 in 1980's Dollars.
AFAIK only Collins used mechanical filters. I remember these being even
more expensive and guys literally took them apart and reassembled them
to dodge the expense for a new one. One of them said "If I can't fix it
I'd have to mortgage the house".

 

[Ken Smith]

Jim Thompson wrote:


Adam wrote:


Hello,

Just want to build a SSB modulator with MC1496 chip.
The phasing method (second way) is desired.
Well, the phasing method needs a Hilbert transformer to change the
audio signal by 90 degrees. I saw the below circuit in an electronics
book, the author mentioned that the circuit produce a 90 degree phase
shift with an 1% error from 30Hz to 16KHz .
Most of the filters I have seen for this job are using more
complicated circuits
But with much lower band width!
Do you think the below circuit is able to generate the 90 degrees of
phase shift over that band width?

http://img251.imageshack.us/my.php?image=untitledwc7.jpg


A doable way to get a 90 degree signal is to use
a PLL. A PLL adjusts the VCO such that the resulting
signal is 90 degrees to the reference. 30Hz to 16kHz
is a bit much for a single VCO stage. It'd be doable
with a difference VCO though.

Rene


Methinks the OP was talking of the All-Pass approach to phase shifting
the AUDIO for use in an SSB modulator.


Methinks so, too. In the olden days before DSP became somewhat
affordable we had to do that for demodulation in Doppler receivers. We
used plain old RC lattices. But what a pain that was for the purchasing
department, all those caps with 1% or better tolerance.

Adam: Audio phase shifters can be found in publications such as the ARRL
Handbook, at least in older editions. Usually only for audio from 300Hz
to 3kHz but one can then calculate the additions for more. If it's a
one-off build you could measure out capacitors and combine to get to
less than 1%. Otherwise finding the caps on the market can take much
longer than calculating the values.

[...]

Then there is the crystal filter, or mechanical filter methods
without so many critical adjustments.

Crystal filters is what I used. But 30Hz-16kHz can be financially
painful. Even 300Hz-3kHz easily set you back $150 in 1980's Dollars.
AFAIK only Collins used mechanical filters. I remember these being even
more expensive and guys literally took them apart and reassembled them
to dodge the expense for a new one. One of them said "If I can't fix it
I'd have to mortgage the house".

Don't overlook the option of doing both. The crystal could do the higher
frequencies but lets say 30Hz to 300Hz could be done with sin() and cos()
functions. This would ease the requirements on the filter a whole bunch.

 

[Gibbo]

Don't overlook the option of doing both. The crystal could do the higher
frequencies but lets say 30Hz to 300Hz could be done with sin() and cos()
functions. This would ease the requirements on the filter a whole bunch.

Or doing as I just did and buying a broken SSB CB rig for 10 GBP.
Contains a nice 10.6975MHz SSB, 2.5KHz crystal filter. Not sure on the
spec yet as I haven't measured it yet.

 

[Joerg]

Michael A. Terrell wrote:

Joerg wrote:


Jim Thompson wrote:



Adam wrote:



Hello,

Just want to build a SSB modulator with MC1496 chip.
The phasing method (second way) is desired.
Well, the phasing method needs a Hilbert transformer to change the
audio signal by 90 degrees. I saw the below circuit in an electronics
book, the author mentioned that the circuit produce a 90 degree phase
shift with an 1% error from 30Hz to 16KHz .
Most of the filters I have seen for this job are using more
complicated circuits
But with much lower band width!
Do you think the below circuit is able to generate the 90 degrees of
phase shift over that band width?

http://img251.imageshack.us/my.php?image=untitledwc7.jpg


A doable way to get a 90 degree signal is to use
a PLL. A PLL adjusts the VCO such that the resulting
signal is 90 degrees to the reference. 30Hz to 16kHz
is a bit much for a single VCO stage. It'd be doable
with a difference VCO though.

Rene


Methinks the OP was talking of the All-Pass approach to phase shifting
the AUDIO for use in an SSB modulator.


Methinks so, too. In the olden days before DSP became somewhat
affordable we had to do that for demodulation in Doppler receivers. We
used plain old RC lattices. But what a pain that was for the purchasing
department, all those caps with 1% or better tolerance.

Adam: Audio phase shifters can be found in publications such as the ARRL
Handbook, at least in older editions. Usually only for audio from 300Hz
to 3kHz but one can then calculate the additions for more. If it's a
one-off build you could measure out capacitors and combine to get to
less than 1%. Otherwise finding the caps on the market can take much
longer than calculating the values.

[...]

--
Regards, Joerg






Then there is the crystal filter, or mechanical filter methods
without so many critical adjustments.

Crystal filters is what I used. But 30Hz-16kHz can be financially
painful. Even 300Hz-3kHz easily set you back $150 in 1980's Dollars.
AFAIK only Collins used mechanical filters. I remember these being even
more expensive and guys literally took them apart and reassembled them
to dodge the expense for a new one. One of them said "If I can't fix it
I'd have to mortgage the house".

Don't overlook the option of doing both. The crystal could do the higher
frequencies but lets say 30Hz to 300Hz could be done with sin() and cos()
functions. This would ease the requirements on the filter a whole bunch.

But I guess most people would use a DSP these days. Nowadays you can get
lots of MIPS for just a few Dollars. When I started out we used AD2105
and things like that but they cost a lot and the compiler was really pricey.

 

[Michael A. Terrell]

But I guess most people would use a DSP these days. Nowadays you can get
lots of MIPS for just a few Dollars. When I started out we used AD2105
and things like that but they cost a lot and the compiler was really pricey.

Where is the fun in that? A crystal or mechanical filter doesn't
need to have software loaded every time the radio is powered up, and
reduces the required current to operate the unit.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Ian]

I recommend you download a spice package, like LT spice. I've entered
the +45 degree phase shift circuit on my simulator and the amplitude
response is not close to flat (15 dB) and the phase response is very
nonlinear. There are some series resistors in the schematic. I'd say
something was lost from the original, but IMHO, this design won't
work.

Frank

There is an error in the schematic - the RC chain to ground on the first
opamp in the top pair should be connected to the +ve input of that opamp,
not the -ve input. Look at all the other opamp connections.

With that change, it does provide a reasonable 90deg difference and
constant amplitude response.

Regards
Ian

 

[Joerg]

Where is the fun in that? A crystal or mechanical filter doesn't
need to have software loaded every time the radio is powered up, and
reduces the required current to operate the unit.

And it doesn't quit working when its little backup battery dies ;-)

 

[Michael A. Terrell]

And it doesn't quit working when its little backup battery dies ;-)

I still have a new 455 KHz CF 2.1 KHz BW Collins mechanical filter in
my collection.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Rich Grise]

I still have a new 455 KHz CF 2.1 KHz BW Collins mechanical filter in
my collection.

USB, LSB, or center? ;-)

I remember reading about SSB in the 1963 Radio Amateur's Handbook (or was
that "Amateurs'?") and it seems that just an ordinary balanced modulator
and sideband filter was either cheaper or easier than the phase-shift
method.


Cheers!
Rich

 

[joseph2k]

Just goes to show that the circuit the OP found wasn't designed for
voice
communication over a radio link!

30 Hz to 16.6 kHz is a little excessive for that application, I think.

Actually from performance characteristics i think it is intended for AM
stereo broadcast applications.