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KSYN3 Range Extension below 500kHz

JohnG3PQA
 

Does anyone know if there is a way of adjusting or modifying the KSYN3 (original) synthesiser to tune a K3 below 500kHz?

I appreciate that a KSYN3A would extend the range, but they are difficult to find these days.
John G3PQA
Mel Marcus
 

i think you will also need the general coverage option

Mel
NE9A
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> on behalf of JohnG3PQA via groups.io <g3pqa@...>
Sent: Tuesday, August 30, 2022 1:14 PM
To: Elecraft-K3@groups.io <Elecraft-K3@groups.io>
Subject: [Elecraft-K3] KSYN3 Range Extension below 500kHz
 
Does anyone know if there is a way of adjusting or modifying the KSYN3 (original) synthesiser to tune a K3 below 500kHz?

I appreciate that a KSYN3A would extend the range, but they are difficult to find these days.
John G3PQA

Geert Jan de Groot
 

The authoritative answer needs to come from Elecraft, however:
The KSYN3 uses a "classic" VCO (Q1 on the schematics) whose frequency ranges are adjusted through adding and removing inductors and capacitors (K1, K2, K3, D1-D4).

The schematic says "8.7-46 MHz" and the K3 IF is 8.215 MHz. 8.7 - 8.215 is roughly 500 kHz and I suspect the restriction comes from that.
I don't know what the real range of the VCO is and if the software is actually allowing tuning that low.

The KSYN3A is essentially a DDS and the output frequency of that is essentially controlled by how fast (how slow) the software in U5.1 adds numbers. It is easier to make a low range, you don't need to add capacitors, etc.

Unless an authoritative answer comes from Elecraft, my suggestion would be "try it, but I'm not hopeful", for the reasons given above,

Geert Jan
JohnG3PQA
 

Jan and Mel,  Many thanks for your responses.
Frustratingly the UK (and ITU allocated) 630m band is 472-479kHz, just below the KSYN3 lower limit.
It is interesting that a spare KSYN3 card I tried gave a slightly lower frequency. The original card was 510kHz and the second 490kHz.. Both have the Elecraft recommended modified value of R20 of 25 ohms, and indicated a VCO voltage of 0.9 on the lowest frequency. Does this indicate a varying tolerance of the shunt capacitors, or is the lower frequency limited in the firmware anyway by dropping VCO voltage?
As you say Jan, the schematic (both revisions A2 and A4) show the VCO range is 8.7-46MHz on the input to Q3, but 8-46MHz is also shown at the output of T1, possibly indicating a wider range than specification.  8.7MHz was probably intended hence the lowest range of 500kHz approximately.
Relay K1 adds in 296+30pF capacitors so I could try changing the 30pF for a 47pF to see what happens. Even if this pulls the lower frequency down, is this likely to affect the indicated frequency calibration?
Would anyone else familiar with the Elecraft VCO and RX design care to comment?
John
JohnG3PQA
 

Sorry, poor eyesight, I misread the diagram. I think K3 may switch in the lowest VCO band. If so I couldl try paralleling a 10pF or 22pF mica C across C6 (110pF) and see what happens.
John
JohnG3PQA
 

Hmmm. Paralleling a 20pF capacitor across C6 (soldered to adjoining pads) produced the following results:-
1. ERR PLL1 message
2. tuning jumps across medium wave BC band and essestially non-functional
3. VCO cal routine (Tech Menu:  VCO MD Cal) restores the tuning and removes the error message
4. lowest frequency remains at 490kHz unfortunately
5. PLL1 voltage = 1.7 at 490kHz (previously 0.9v).

In summary, a nice idea but as suspected it does not work to lower the frequency range.
John
Ray Maxfield
 

Hi….I think your at Firmware STOP.. 

Ray WA6VAB K3

 

 

From: JohnG3PQA via groups.io
Sent: Saturday, September 3, 2022 10:30 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KSYN3 Range Extension below 500kHz

 

Hmmm. Paralleling a 20pF capacitor across C6 (soldered to adjoining pads) produced the following results:-
1. ERR PLL1 message
2. tuning jumps across medium wave BC band and essestially non-functional
3. VCO cal routine (Tech Menu:  VCO MD Cal) restores the tuning and removes the error message
4. lowest frequency remains at 490kHz unfortunately
5. PLL1 voltage = 1.7 at 490kHz (previously 0.9v).

In summary, a nice idea but as suspected it does not work to lower the frequency range.
John

 
WE6R
 

Ray is correct, the -Firmware- will not even let it tune below 490Khz, (unless it detects the newer KSYN3"A"). 
The K3 (non-S) should work down to 490Khz without any mods.

To go LowFer, down to 100Khz, you need the KSYN3A, KBPF3A -older ones must be modified, and you need the KXV3 and go in the RX antenna port to bypass the Low Pass Filters.
see; https://ftp.elecraft.com/K3S/Mod%20Notes%20Alerts/Operating%20630M%20with%20K3-K3S.pdf
Ketih WE6R Elecraft Tech
Ray Maxfield
 

Hi Keith……….. I will take another Stab at it !

If one were to Install a New KSYN3A and KBPFA

Or Trick the Firmware…. I think some Pin will need to be pulled Active

(High or Low) so its Happy and let you complete the Upgrade.

Happy Hunting………….. Ray WA6VAB  K3 Too.

 

 

From: WE6R
Sent: Tuesday, September 6, 2022 9:29 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KSYN3 Range Extension below 500kHz

 

Ray is correct, the -Firmware- will not even let it tune below 490Khz, (unless it detects the newer KSYN3"A"). 
The K3 (non-S) should work down to 490Khz without any mods.

To go LowFer, down to 100Khz, you need the KSYN3A, KBPF3A -older ones must be modified, and you need the KXV3 and go in the RX antenna port to bypass the Low Pass Filters.
see; https://ftp.elecraft.com/K3S/Mod%20Notes%20Alerts/Operating%20630M%20with%20K3-K3S.pdf
Ketih WE6R Elecraft Tech

 
JohnG3PQA
 

Hi Keith and Ray,
Many thanks for your replies and info..
When the K3 firmware was first designed to stop the older KSYN3 at 490kHz the exact frequencies of the new 630m band, (472kHz to 478kHz) were not allocated.
If KSYN3 could cover, say, down to 450kHz, this is hardly a fundamental change and would help many K3 owners who cannot now obtain or afford the KSYN3A and want to at least listen on 630m..
Is there is a real technical reason why this cannot be done easily by just a simple change of a number in a line of firmware and possibly slightly higher value for C6?
 A question for Elecraft designers and whether they can spare the time to look at this again.
John
Ray Maxfield
 

Hi John………

I agree with your incite.

I wish I were a PLL Engineer !

My first step would be to Modify the Firmware (to 470Khz)

Then Add Cxx as Required….. I would call it the Bench Way.

Thanks for you contribution.   Ray WA6VAB K3

 

 

From: JohnG3PQA via groups.io
Sent: Wednesday, September 7, 2022 5:48 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KSYN3 Range Extension below 500kHz

 

Hi Keith and Ray,
Many thanks for your replies and info..
When the K3 firmware was first designed to stop the older KSYN3 at 490kHz the exact frequencies of the new 630m band, (472kHz to 478kHz) were not allocated.
If KSYN3 could cover, say, down to 450kHz, this is hardly a fundamental change and would help many K3 owners who cannot now obtain or afford the KSYN3A and want to at least listen on 630m..
Is there is a real technical reason why this cannot be done easily by just a simple change of a number in a line of firmware and possibly slightly higher value for C6?
 A question for Elecraft designers and whether they can spare the time to look at this again.
John

 
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