SSB

Well, it certainly wouldn't take very long to slap one together and look and see!

From my limited knowledge of actual design, I'd say that it does look like phase shifters, but I have no idea how to analyze the circuit completely.

Maybe you could use one of those simulator programs; then you wouldn't have to buy any parts or a protoboard.

What's the application? Homework? ;-)

Good Luck! Rich

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

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.

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

...Jim Thompson

The op needs a linear network that shifts a wide range of signals by

The schematic he posted is trickier than the standard active allpass, so I can't say if it would work to his specs. Williams&Taylor's filter book has tables for the more conventional allpass:

where each opamp has one cap and three resistors.

So his 4 opamp thing may be dicey.

John

That won't work.

He needs the phase shift network for audio, which implies a complex waveform of varying frequency and amplitude. Even if a PLL can track that, it will strip off any amplitude variation.

Michael

I'm sorry I don't have it handy, but there is an old paper that has a family of low pass filters designed such that the phase difference between the filters is 90 degrees. This is not as good as having a real Hilbert transformer, but this is real life. ;-) The paper is stone age. I got it out of Terman, which is where Jim ought to be handing out rather than Sunnyvale pubs! [Stanford is nice enough to let any fool use Terman library. You can't check anything out, but you can certainly copy papers to your hearts content. You can also use their on-line database searches from dinky Macs in the library. The results from the search can be mailed off campus.]

Not quite as optimal as that stone age design, but it seems to me you could take two bessel filters and shift the corner frequencies to get

In a datacom circuit, an octave worth of 90 degrees phase shift was fine. In your case, you are trying to do over 9 octaves. I don't see how you expect this to be simple. Also, you will probably have trouble with any circuit that isn't a ladder filter since ladders have the least sensitivity to component tolerances.

This circuit as shown has an error. The branch consisting of a 1n cap and a 47k and 3.3k in series is shown going from the - input to ground. This branch should in fact go from the + input to ground.

Then the entire circuit gives a phase shift difference of 90 degrees, +-

The usual op amp phase shifter has only 1 capacitor per stage. This two capacitor stage has 2 pole-zero pairs per stage, at the cost of greater sensitivity, but I think it will be ok in this relatively low performance circuit.

On a sunny day (Sat, 10 Feb 2007 01:57:29 +0100) it happened Rene Tschaggelar wrote in :

No he is talking audio for an SSB transmitter, so amplitude can change significally.... The standard diagram I have somewhere from the RSGB handbook for this... There are a zillion of those audio 90 degrees phase shift ciruits on the web. Here for example, 100% passive:

A 2 degree difference gives a 35 mV of a sine wave against 1 V , side band attenuation. About 28x, so 20log(28) is about 29 dB or so, not very good for sideband suppression. I'd want to see 50 dB or better :-)

SSB modulators do not phase shift the baseband. And the word is "bandwidth" and not "band width."

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

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

The OP should also have a look at:

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:

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.

Following the procedure from the Bedrosian paper, decide how much unwanted sideband suppression you want, and that will determine how many op amps you will need.

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

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.

On a sunny day (Sat, 10 Feb 2007 15:08:14 GMT) it happened Fred Bloggs wrote in :

write

Yes, indeed, well for SSB there is basically 2 methods, the phasing method (as discussed here), and teh filter method (more frequently used commercially i think), in the last one a crystal or some other steep filter simply filters out the unwanted sideband. Very old hands here may remember XF9A and XF9B crystal filters.....

You are right, it seems digital is the way to go, is PIC fast enough? FPGA is! Look what this guy did:

write

Actually I just viewed that earlier. Note that he does not phase shift the baseband, aka signal labeled "input," in the diagram. A nice digitalization of the standard Weaver SSB modulator.