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About Polyphase network in receiver
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Leif M
A receiver with a Tayloe detector seems to be a good way to listen to HW. For SSB I need polyphase network, that much I know.
Polyphase network is critical. But there are versions 4 inputs and others with I and Q inputs. A book called Experimental methods in RF design gives some formulas. But it is a bit difficult to find instructions which fit together, and give part values. It looks like I should buy the whole thing. But the polyphase network I would make differently myself. I would use parts I linked below. There are capacitors with +-1% tolerance and SMD resistors with 0.01% tolerance at Digikey, and surely elsewhere too. Here is one 22nF capacitor https://www.digikey.com/en/products/detail/vishay-roederstein/MKP1837322161G/5392952 And a 0.01% resistor for example. These are 0805 https://www.digikey.fi/en/products/detail/susumu/URG1608L-472-L-T05/4552652 These resistors are not cheap, but there are others less accurate, like 0.1%. They are probably good enough. If I buy a receiver with a Tayloe detector, can I or should I use these components to listen to SSB? What if I design a PCB with part I showed. |
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Alan G4ZFQ
On 19/03/2023 21:20, Leif M wrote:
There are capacitors with +-1% tolerance and SMD resistors with 0.01% tolerance at Digikey, and surely elsewhere too.Leif, I see links here http://qrp-labs.com/polyphase.html that seem to say extreme accuracy is not so important if attention is made to good matching and component selection. See the pdf linked there. 73 Alan G4ZFQ |
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Leif M
On Mon, Mar 20, 2023 at 10:07 AM, Alan G4ZFQ wrote:
if attention is made to good matching and component selection.Sure. But where or how I can measure capacitors better than at +-1% accuracy. |
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ajparent1/kb1gmx
You do not have to measure them. Its far easier to MATCH them.
Also QRPL supplies a Polyphase network to match their receiver. See... http://qrp-labs.com/receiver.html http://qrp-labs.com/polyphase.html from those pages find information on component matching. -- Allison ------------------ Post online only, please no email. |
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Alan G4ZFQ
On 20/03/2023 17:00, Leif M wrote:
where or how I can measure capacitors better than at +-1% accuracyLeif, I made this https://sites.google.com/site/vk3bhr/home/lcm1 and tested this https://sites.google.com/site/g4zfqradio/lc100a-terminals-on-the-right While testing requires some close tolerance capacitors you are not looking for accuracy, just a close match. Is 1% actually required? Unless you have very good test techniques you will not know the difference. 73 Alan G4ZFQ |
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Gerald Wolczanski
To add to Alison's post, it was vastly cheaper to buy 100 or 200 capacitors and find matched
groups with an LC meter than it was to buy a handful of "precision" caps. Jerry W KI4IO Warrenton, VA |
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Pim Niessen
Leif,
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John Kirby
And here is very nice (free) PC Sound Card Oscilloscope download with spectrum analyzer and function generator
>>>https://www.zeitnitz.eu/scope_en<<< If components to build Pim's PA2PIM excellent suggestion are not available... ...a smile "parallel" L/C network plus a 'grid dip' meter or SWR Meter work well, you supply the C then measure frequency then cull the "best match" 72 73 John N3AAZ |
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Johan Bodin
Many thanks Pim,
the best I have ever read about polyphase filter design! 73 Johan SM6LKM Pim Niessen wrote: http://antennoloog.nl/data/documents/Polyphase_PA2PIM_2.4-20060324.zipand http://antennoloog.nl/data/documents/Understanding_and_designing_Polyphase_networks_V4.0.pdf |
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vbifyz
My experience is not about polyphase, but the all-pass opamp circuit. I think it is still somewhat relevant.
I matched 10nF capacitors from a bag of 50 5% parts to be within 1% of each other, using a $25 LC-meter/transistor tester from eBay. Resistors are 1% from E24 row (so the values are not ideal), no matching. LTSpice shows about 40dB unwanted SSB suppression over 300..3000Hz range, the real life value is very close. With other RX circuits added, the suppression is a bit worse, about 35dB, because of the phase mismatch in RF components. So the precision on the AF side is actually not that important. This is still good enough for a homebrew project. 73, Mike AF7KR |
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Johan Bodin
I have built all-pass phase shifters a few times and they do work well when carefully adjusted. QuadNet software is a convenient design tool http://tonnesoftware.com/quad.html.
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73 Johan SM6LKM vbifyz wrote: My experience is not about polyphase, but the all-pass opamp circuit. I think it is still somewhat relevant. |
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Pim Niessen
Johan, e.a. |
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Hans Summers
Hi Pim As I'm sure you know but for the benefit of everyone else - the polyphase network is said to have greater unwanted sideband suppression compared to all-phase networks using components with the same tolerance. However there are also other factors involved. A criticism of polyphase networks is that they do not have a flat response across the audio passband. This is in fact not necessarily true; if one abandons having all the capacitors the same value (or resistors the same value) and is prepared to change both resistor values AND capacitor values from column to column, then the voltage gain of the network can be set to 1.0 and very flat across the audio passband. Yet another factor is the noise figure of a polyphase network - given that it is composed of resistive elements as well as capacitive... op-amps of course also have an input noise. The question becomes more complex than simply unwanted sideband cancellation since now you have to include the rest of the receiver design in the question, op-amp performance, system gain distribution and impedances. A lot of ins and outs. I have used polyphase networks in homebrew rigs and in the QRP Labs receiver module, and active all-pass networks in QCX. So some experience of both, and could say that I have always been pleased with the results, both ways :-) On Wed, Mar 22, 2023 at 4:35 PM Pim Niessen <pa2pim@...> wrote:
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