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T41 Alternative VFO arrangement but will it work?

 

I was planning to convert my V10 system to run like V12 with two clocks phased 90 deg apart and was wondering what to do with the 74AC74s which are already mounted on the V10 QSD and QSE boards.

I¡¯m going to try a different system which may have some advantages over V12 or, of course, it may not work at all.

I am going to run two Si5351 clocks at the same frequency as in the V12 but I¡¯m not going to use phase control.? For that reason, the clocks can each run down to about 1MHz.? I am going to turn on invert on one clock so that the clocks are now 180 deg apart (they will be on the same PLL and there will be a PLL reset to sync them.

Both Si5351 clocks will run at twice the wanted output frequency and will each be divided by 2 by half a 74AC74 to give two output signals at the right frequency and separated by 90 deg ready to drive the demodulator and modulator in the QSD and QSE respectively.

The two clocks will tune down to about 500kHz which will allow top band to be included and they will probably still allow 6m at the other end.

I¡¯m about half way through modifying the QSD so if you think this won¡¯t work please explain why and save me some effort!!

One remaining issue is to sync the two divide by 2s so that their behaviour is predictable.? I think I have a simple solution.

Harry GM3RVL
 

I suggest checking the propagation delay through the inverter.? It will be somewhat temperature dependent but nearly constant in time for a particular device.? Constant in time means a different number of degrees in phase, depending on the frequency.? Analysis should show whether this is important or not.
Andy KB3KX

On Monday, September 18, 2023 at 12:44:31 PM EDT, Harry Brash <harry.brash@...> wrote:


I was planning to convert my V10 system to run like V12 with two clocks phased 90 deg apart and was wondering what to do with the 74AC74s which are already mounted on the V10 QSD and QSE boards.

I¡¯m going to try a different system which may have some advantages over V12 or, of course, it may not work at all.

I am going to run two Si5351 clocks at the same frequency as in the V12 but I¡¯m not going to use phase control.? For that reason, the clocks can each run down to about 1MHz.? I am going to turn on invert on one clock so that the clocks are now 180 deg apart (they will be on the same PLL and there will be a PLL reset to sync them.

Both Si5351 clocks will run at twice the wanted output frequency and will each be divided by 2 by half a 74AC74 to give two output signals at the right frequency and separated by 90 deg ready to drive the demodulator and modulator in the QSD and QSE respectively.

The two clocks will tune down to about 500kHz which will allow top band to be included and they will probably still allow 6m at the other end.

I¡¯m about half way through modifying the QSD so if you think this won¡¯t work please explain why and save me some effort!!

One remaining issue is to sync the two divide by 2s so that their behaviour is predictable.? I think I have a simple solution.

Harry GM3RVL
 

Hi Harry-

What you are describing will work and it is very similar to what I am already working on to fix the 10 meter problem.? I posted a video demonstration of "QSD2" which is the first working prototype.
Do you have access to QEX?? There is an article from earlier this year which describes almost exactly what you are proposing.

--
73 Greg KF5N
 

Hi Greg

Thanks for your reply

I don't have access to QEX.? I appreciate your assurances that this will work and will continue to modify my system as intended.

It seems to offer a better solution than the V12 boards as it includes "Top Band" and could include 6m.

Best wishes
Harry? GM3RVL
 

Thanks Andy

I'll check that

73 Harry
 

Hi Harry, my goal is a drop-in replacement for the V11 boards.? I suppose they should be called V11.1.
The software change required is trivial.? In fact, you can run a combination of V11 and V11.1 boards if you want to.
I have already successfully done that with my QSD2 prototype and a V11 QSE.

--
73 Greg KF5N
 

¿ªÔÆÌåÓý

The difficulty will, of course, be keeping the two clocks phased without using the same PLL¡­?

?

?

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ

?

Owner - Operator

Big Signal Ranch ¨C K9ZC

Staunton, Illinois

?

Owner ¨C Operator

Villa Grand Piton ¨C J68HZ

Soufriere, St. Lucia W.I.

Rent it:

?

Moderator: North American QRO Group at Groups.IO.

Moderator: Amateur Radio Builders Group at Groups.IO.

?

email:? bill@...

?

?

From: [email protected] <[email protected]> On Behalf Of Harry Brash
Sent: Monday, September 18, 2023 11:44 AM
To: [email protected]
Subject: [SoftwareControlledHamRadio] T41 Alternative VFO arrangement but will it work?

?

I was planning to convert my V10 system to run like V12 with two clocks phased 90 deg apart and was wondering what to do with the 74AC74s which are already mounted on the V10 QSD and QSE boards.

I¡¯m going to try a different system which may have some advantages over V12 or, of course, it may not work at all.

I am going to run two Si5351 clocks at the same frequency as in the V12 but I¡¯m not going to use phase control.? For that reason, the clocks can each run down to about 1MHz.? I am going to turn on invert on one clock so that the clocks are now 180 deg apart (they will be on the same PLL and there will be a PLL reset to sync them.

Both Si5351 clocks will run at twice the wanted output frequency and will each be divided by 2 by half a 74AC74 to give two output signals at the right frequency and separated by 90 deg ready to drive the demodulator and modulator in the QSD and QSE respectively.

The two clocks will tune down to about 500kHz which will allow top band to be included and they will probably still allow 6m at the other end.

I¡¯m about half way through modifying the QSD so if you think this won¡¯t work please explain why and save me some effort!!

One remaining issue is to sync the two divide by 2s so that their behaviour is predictable.? I think I have a simple solution.

Harry GM3RVL
 

Hi Greg
I did alter the QSD 74AC74 to run on 5V to speed it up as it is out of spec at 3V3 and over 100MHz (Neville Marr's suggestion)? and the 10m RX worked well.? Previously I just got a lot of noise on 10m but I was getting good S/N with 1uV input.? I didn't modify the TX side.
73 Harry GM3RVL
 

5 volts on the flip-flops and also the 5 volt version of the multiplexer IC.? A combination which does good things for higher frequencies!? Rod Gatehouse has already shown that those changes work.
Combine that with divide-by-two instead of divide-by-four and things start to look even better.

--
73 Greg KF5N
 

Hi Greg
I've just about finished the RX board and the wiring from the main board with the 2 clocks.? Be interesting to see how the RX works with the divide by 2.
I Googled QEX.? It is an ARRL publication.? I must try to find the article you mentioned.? I'd be interested to know how it dealt with keeping a fixed relationship between the two div by 2s.
Harry? GM3RVL
 

The system described in the article uses an Si5340D, which can provide "complementary clocks" (180 degree) from a single programmed output.
That sounds exactly what you are proposing to do with the Si5351.? I have both the online and hard copy of the article.? I can send you the hardcopy
when I return home next week.? It's a very interesting article.

--
73 Greg KF5N
 

¿ªÔÆÌåÓý

How will you keep the two clocks synchronized?

?

?

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ

?

Owner - Operator

Big Signal Ranch ¨C K9ZC

Staunton, Illinois

?

Owner ¨C Operator

Villa Grand Piton ¨C J68HZ

Soufriere, St. Lucia W.I.

Rent it:

?

Moderator: North American QRO Group at Groups.IO.

Moderator: Amateur Radio Builders Group at Groups.IO.

?

email:? bill@...

?

?

From: [email protected] <[email protected]> On Behalf Of Harry Brash
Sent: Wednesday, September 20, 2023 5:39 AM
To: [email protected]
Subject: Re: [SoftwareControlledHamRadio] T41 Alternative VFO arrangement but will it work?

?

Hi Greg
I've just about finished the RX board and the wiring from the main board with the 2 clocks.? Be interesting to see how the RX works with the divide by 2.
I Googled QEX.? It is an ARRL publication.? I must try to find the article you mentioned.? I'd be interested to know how it dealt with keeping a fixed relationship between the two div by 2s.
Harry? GM3RVL

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