Polyphase board


Mike Hadley
 

Has anyone changed resistor values on this board to increase the bandwidth for better ssb recovery? 


ajparent1/kb1gmx
 

Have to ask.   How much bandwidth do you need?
 
Nearly 3000hz is wider than most filters used in SSB transmitters.
Most of mine are 2.1 and 2.4Khz and 2.8khz is considered wide.
Also despite your RX band width width the amount of transmitted
information is far more limited and you will not hear "more" other
than greater adjacent frequency interference that is within your
pass-band.


However you may need to alter C3-C6 to a lower value.  Try 33nF or 10nF
Reason for this is the  detectors are low pass in nature and those capacitors
are part of that.

I'd go on line and find a calc or spreadsheet for recalculating the values
before going there.  High order RC filters tend to have a lot of interaction.

If your using a computer to render audio from I&Q then the polyphase board
is not needed.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Mike Hadley
 

Thanks for that Alison. The bandwith of the board (as supplied) tops at 1800Hz, Hans suggests that ssb should be okay but am I wrong in thinking 2400 would sound much different?


I would be using both methods of reception, I Q into my pc and polyphase when mobile/portable.


Not sure if any other polyphase users have carried out mods to this board. Guess I'll wait until its fully assembled and use the monitors either side of my head, hi.


Mike G4JXX

Sent from my Xperia™ by Sony smartphone


ajparent1/kb1gmx
 

1800hz, no idea where you get that.

See the plots on the stor page   http://qrp-labs.com/polyphase.html

It mentions to 1800 hz for things like WSPR and other digital modes but
the board does as shown.

1800hz for SSB  would be on the narrow side.  But thats not the intended application
other than incidental.  Tweaking the Polyphase alone likely will not get you what
you want as its mostly GIGO.

The yabut is the 4 caps I mentioned last time and that also colors the bandwidth
as will the output transformers.

So the QDS detector caps C3-6 must be smaller.
Also the bandwidth of the 600ohm transformer will be only as specified if loaded
to 600 ohms, even then there will be significant roll off under 300hz and likely
the high side too.  They are designed to old school hard-copper telephone
bandwidth (not Iphone) is 200hz at the low end is maybe about it.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Hans Summers
 

Hi all

Attachments show measurements I performed here during development of these kits. 

"response.gif" and "unwanted.gif" show USB and LSB (unwanted) audio response of the receiver module and polyphase module. It isn't bad for SSB. These are in the manual.

"transformer.gif" shows my measurements of the 600:600-ohm isolation transformers. They were better than I had expected. Even down at 100Hz and up above 10kHz.

73 Hans G0UPL 

On Sun, Jun 7, 2020, 01:22 ajparent1/KB1GMX <kb1gmx@...> wrote:
1800hz, no idea where you get that.

See the plots on the stor page   http://qrp-labs.com/polyphase.html

It mentions to 1800 hz for things like WSPR and other digital modes but
the board does as shown.

1800hz for SSB  would be on the narrow side.  But thats not the intended application
other than incidental.  Tweaking the Polyphase alone likely will not get you what
you want as its mostly GIGO.

The yabut is the 4 caps I mentioned last time and that also colors the bandwidth
as will the output transformers.

So the QDS detector caps C3-6 must be smaller.
Also the bandwidth of the 600ohm transformer will be only as specified if loaded
to 600 ohms, even then there will be significant roll off under 300hz and likely
the high side too.  They are designed to old school hard-copper telephone
bandwidth (not Iphone) is 200hz at the low end is maybe about it.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Mike Berg
 

FWIW, I've connected the output of my polyphase board to amplified computer speakers and listened to some pleasant sounding SSB as long as the band isn't crowded.

73

Mike  N0QBH


Mike Hadley
 

Maybe I've jumped the gun a bit. This will be my first experience with polyphase demodulation as I am so used to listening through 2.5 and 3.0 Khz 8 pole crystal filters. These have been difficult to design and implement in the past so you can understand my thoughts on a seemingly narrow bandwidth. When my rx is complete I will post my findings, no doubt I will be pleasantly surprised.

Mike G4JXX

Sent from my Xperia™ by Sony smartphone


ajparent1/kb1gmx
 

Mike,

This will be an experience for you.  After decades of crystal filter IO/Phasing radios
are like a whole level of less distortion.  Less distortion, less group delay, it sounds
much cleaner when a bunch of station in the pass band.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting