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Frequency error correction?


Jim Barbour 2021/02/24 12:25

Maybe I'm missing it, but is there a method for correcting error in the frequency, as noted when using CW mode? My SAA-2N is about 4KHz off, which is a huge amount when you're trying to tune a cavity or other high-Q tuned circuits.

John Gord 2021/02/24 13:42

Jim,
The frequency step size is fairly large. (Up to 12kHz above 140MHz, IIRC). The ojisan firmware has smaller step size.
--John Gord

On Wed, Feb 24, 2021 at 12:27 PM, Jim Barbour wrote:

Jim Barbour 2021/02/24 14:23

Isn't there a reference oscillator or something?

John Gord 2021/02/24 17:15

Jim,
There is a reference oscillator, U501 in the schematic. I think it is around 25MHz or so. It is shown as having a control pin on the schematic, but I don't know if the oscillator actually used actually responds to voltage on that pin (the pin is not connected on the schematic). You could check your unit to see how close the U501 output frequency is is to the nominal value.
--John Gord

On Wed, Feb 24, 2021 at 02:23 PM, Jim Barbour wrote:

Jim Barbour 2021/02/25 23:31

Ah ha! Yeah, that's worth checking out, tnx!


On 2/24/2021 8:15 PM, John Gord via groups.io wrote:

Siegfried Jackstien 2021/02/26 12:42

i am guessing the unused pin is inhibit (switch off clock) ... thats why
it is not connected

but ... you can change the tcxo to a tuneable device and add a multi
turn trimmer (and maybe two fixed resistors to spreaden the inner tuning
area a bit for finer setting with the trimmer)

greetz sigi dg9bfc

Am 26.02.2021 um 04:31 schrieb Jim Barbour:

Jim Barbour 2021/02/26 09:25

So some further investigation-I guess not surprisingly freq error varies by frequency, and there seems to be a cutoff somewhere between 250 and 300 MHz-ish. At 146 or 225, it's under 200 Hz error, but somewhere around 250-ish it jumps to about 3 KHz or more, increasing to well over 5 KHz around 2.5 GHz or more. So I guess for VHF cavities and down, it's good, but UHF it might be off a bit, and you would want to fine tune with something more accurate.

BTW, the unit I have came from R & L, and the sticker says it was made by Zeenko. Haven't seen that name come up before. It's well made, comes in a steel case, very rugged and heavier than expected. Nice semi-hard zip up case too!

Chris 2021/04/22 04:06

I would expect, that a frequency correction option can be implemented in te firmware as it is done with the EU1KY analyzer an its many variants.

Chris

DiSlord 2021/04/22 07:57

Frequency step after 140MHz = 6000Hz for V2

John Gord 2021/04/23 14:38

The ojisan firmware for the V2 can provide much smaller step size above 140MHz.
--John Gord

On Thu, Apr 22, 2021 at 07:57 AM, DiSlord wrote:

DiSlord 2021/04/24 01:42

>The ojisan firmware for the V2 can provide much smaller step size above 140MHz.
Then need add it to ojisan firmware?

PS
in my variant of fw and ojisan much smaller step size above 140MHz
< 275MHz step 6k/16 = 375Hz
< 550MHz step 6k/8 = 750Hz
< 1.1GHz step 6k/4 = 1.5k
< 2.2GHz step 6k/2 = 3k
greater step = 6k
Also in my variant < 140MHz frequency step = 1Hz

PSS
In ojisan fw should exist problems on switch range frequency (275M, 550M and so on) if look close to it

n2msqrp 2021/04/24 09:52

Where can we find the latest versions of your firmware?

Mike N2MS

DiSlord 2021/04/24 09:04

It not provide frequency correction
You can try
https://groups.io/g/NanoVNAV2/message/1371
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