RX888 MkI frequency discrepancies in recordings


D R
 

Hi Simon,

I think the message I posted on the sdr-radio.com forum a few days ago may have escaped your notice - it's had lots of viewings, but no replies, as yet :(.  Any chance of getting your thoughts on what might be happening?

Regards,
Dave


Simon Brown
 

Link?

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of D R via groups.io <robsond90@...>
Sent: 09 September 2022 12:17
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 
Hi Simon,

I think the message I posted on the sdr-radio.com forum a few days ago may have escaped your notice - it's had lots of viewings, but no replies, as yet :(.  Any chance of getting your thoughts on what might be happening?

Regards,
Dave

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D R
 


Simon Brown
 

Thanks,

Replied. Tried with my computer, frequencies are spot-on with the recording.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of D R via groups.io <robsond90@...>
Sent: 09 September 2022 14:33
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 

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D R
 

Thanks for that.  So were mine with the Mk II and Perseus, but I was using the earlier version of the software - I'll try again with the latest version and see what happens with the Mk I.

Regards,
Dave


Simon Brown
 

Maybe the oscillator in the Mk1 is off?

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of D R via groups.io <robsond90@...>
Sent: 09 September 2022 16:47
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 
Thanks for that.  So were mine with the Mk II and Perseus, but I was using the earlier version of the software - I'll try again with the latest version and see what happens with the Mk I.

Regards,
Dave

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D R
 

Hi Simon,

Please see the reply to your message in the other forum, as I think the problem will be easier to see from my latest screenshots.

Regards,
Dave


Simon Brown
 

OK,

Will look later. I expect the problem is the clock frequency of your SDR, this needs correction.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of D R via groups.io <robsond90@...>
Sent: 10 September 2022 01:50
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 
Hi Simon,

Please see the reply to your message in the other forum, as I think the problem will be easier to see from my latest screenshots.

Regards,
Dave

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D R
 

Hi Simon,

If it's the clock frequency, then I suspect that mine will not be the only one with the problem - but most users will not be aware of it.  Will the correction be via another adjustment in the calibration window?

Regards,
Dave


Larry Dodd
 

All, 
The RX888 MKII has an on board internal switch and ext. clock connection. Evidently they knew the internal clock could be improved. I modified one of my RX888 MKII receivers with external sma connector and switch. Trick is to apply a known stable accurate 27 MHz external clock. Works if you really need that level of accuracy. 
Larry K4LED 



On Sep 10, 2022, at 6:20 PM, D R via groups.io <robsond90@...> wrote:

Hi Simon,

If it's the clock frequency, then I suspect that mine will not be the only one with the problem - but most users will not be aware of it.  Will the correction be via another adjustment in the calibration window?

Regards,
Dave


D R
 

Hi Larry,

I'd planned to use my Bodnar GPSDO to do that when I got my MkII, but I must have got lucky and received one with a good XO, as it's quite stable and needs very little calibration adjustment - just the luck of the draw!  I may have got the short straw when it comes to the MkI, though, which is a pity as I've always thought the MkI has a slight edge over the MkII in sensitivity when it comes to LF/MW stuff, where I do most of my listening.

Regards,
Dave


Larry Dodd
 

Dave,
Understand. Seems there is a wide variation in quality. The Bodnar clock is great for 10 MHz but a little noisy at 27 MHz. Can’t beat their price. 
Larry K4LED 

_______________________

On Sep 10, 2022, at 8:11 PM, D R via groups.io <robsond90@...> wrote:

Hi Larry,

I'd planned to use my Bodnar GPSDO to do that when I got my MkII, but I must have got lucky and received one with a good XO, as it's quite stable and needs very little calibration adjustment - just the luck of the draw!  I may have got the short straw when it comes to the MkI, though, which is a pity as I've always thought the MkI has a slight edge over the MkII in sensitivity when it comes to LF/MW stuff, where I do most of my listening.

Regards,
Dave


Simon Brown
 

Yes,

Correction like calibration but it may also be temperature dependant.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of D R via groups.io <robsond90@...>
Sent: 10 September 2022 23:20
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 
Hi Simon,

If it's the clock frequency, then I suspect that mine will not be the only one with the problem - but most users will not be aware of it.  Will the correction be via another adjustment in the calibration window?

Regards,
Dave

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D R
 

Hi Simon,

I'll do cold/warm tests an hour apart to see if there's much drift, but usually the radios have been running for some time before they get used anyway, and room temperature is pretty constant.

Regards,
Dave


Simon Brown
 

OK.

For the price, these units are good but really do need a ref in which would make them better.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of D R via groups.io <robsond90@...>
Sent: 11 September 2022 13:12
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 
Hi Simon,

I'll do cold/warm tests an hour apart to see if there's much drift, but usually the radios have been running for some time before they get used anyway, and room temperature is pretty constant.

Regards,
Dave

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D R
 
Edited

Hi Simon,

I did a drift test earlier, but it turned out to be not very scientific due to both RWM and WWV fading rather too much.  It did, however, reveal that the MkI calibration drifts a lot in the first hour - about 40Hz - but the IF Display errors settle down after about 20 minutes.  I'm going to do a proper test tomorrow using a 10MHz signal from a GPSDO to see exactly how long it takes the unit to fully stabilise (or if it ever does!).

In the meantime, a screenshot of what happens to a 10MHz signal in the IF Display when the waterfall is shifted R - Centre - L in 1MHz hops: the apparent frequency changes in 70Hz steps.  I'll check in the next test whether that step size is temperature related, or whether it's just a function of the waterfall display width.

Regards,
Dave


Larry Dodd
 

I keep a 12 volt fan running in my RX888 receivers at all times to attempt to stabilize the temperature Not unusual for an oscillator to drift at first start up. The drift test should not be started until after it’s up to stable operating temperature.  At least 10 to 15 minutes. 
Larry

_______________________

On Sep 11, 2022, at 7:41 PM, D R via groups.io <robsond90@...> wrote:



[Edited Message Follows]

Hi Simon,

I did a drift test earlier, but it turned out to be not very scientific due to both RWM and WWV fading rather too much.  It did, however, reveal that the MkI calibration drifts a lot in the first hour - about 40Hz - but the IF Display errors settle down after about 20 minutes.  I'm going to do a proper test tomorrow using a 10MHz signal from a GPSDO to see exactly how long it takes the unit to fully stabilise (or if it ever does!).

In the meantime, a screenshot of what happens to a 10MHz signal in the IF Display when the waterfall is shifted R - Centre - L in 1MHz hops: the apparent frequency changes in 70Hz steps.  I'll check in the next test whether that step size is temperature related, or whether it's just a function of the waterfall display width.

Regards,
Dave

Attachments:


Simon Brown
 

Agreed,

The RX888 gets warm so a fan is important. Plenty of good USB fans are available.

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of Larry Dodd via groups.io <101science@...>
Sent: 12 September 2022 00:48
To: main@sdr-radio.groups.io <main@sdr-radio.groups.io>
Subject: Re: [SDR-Radio] RX888 MkI frequency discrepancies in recordings
 
I keep a 12 volt fan running in my RX888 receivers at all times to attempt to stabilize the temperature Not unusual for an oscillator to drift at first start up. The drift test should not be started until after it’s up to stable operating temperature.  At least 10 to 15 minutes. 
Larry

_______________________

On Sep 11, 2022, at 7:41 PM, D R via groups.io <robsond90@...> wrote:



[Edited Message Follows]

Hi Simon,

I did a drift test earlier, but it turned out to be not very scientific due to both RWM and WWV fading rather too much.  It did, however, reveal that the MkI calibration drifts a lot in the first hour - about 40Hz - but the IF Display errors settle down after about 20 minutes.  I'm going to do a proper test tomorrow using a 10MHz signal from a GPSDO to see exactly how long it takes the unit to fully stabilise (or if it ever does!).

In the meantime, a screenshot of what happens to a 10MHz signal in the IF Display when the waterfall is shifted R - Centre - L in 1MHz hops: the apparent frequency changes in 70Hz steps.  I'll check in the next test whether that step size is temperature related, or whether it's just a function of the waterfall display width.

Regards,
Dave

Attachments:


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jdow
 

Arrange to let the temperature drift while you monitor the frequency continuously taking periodic readings. TCXOs do not drift in the same manner as normal open loop XOs.

{^_^}

On 20220911 16:40:09, D R via groups.io wrote:

[Edited Message Follows]

Hi Simon,

I did a drift test earlier, but it turned out to be not very scientific due to both RWM and WWV fading rather too much.  It did, however, reveal that the MkI calibration drifts a lot in the first hour - about 40Hz - but the IF Display errors settle down after about 20 minutes.  I'm going to do a proper test tomorrow using a 10MHz signal from a GPSDO to see exactly how long it takes the unit to fully stabilise (or if it ever does!).

In the meantime, a screenshot of what happens to a 10MHz signal in the IF Display when the waterfall is shifted R - Centre - L in 1MHz hops: the apparent frequency changes in 70Hz steps.  I'll check in the next test whether that step size is temperature related, or whether it's just a function of the waterfall display width.

Regards,
Dave
MkI - 10MHz sig moved R-C-L across waterfall .jpg


Siegfried Jackstien
 

if the frequency changes with centre frequency shifting ... may it be the sampling rates do not match?? (just thinking)

greetz sigi dg9bfc

Am 12.09.2022 um 09:05 schrieb jdow:

Arrange to let the temperature drift while you monitor the frequency continuously taking periodic readings. TCXOs do not drift in the same manner as normal open loop XOs.

{^_^}

On 20220911 16:40:09, D R via groups.io wrote:

[Edited Message Follows]

Hi Simon,

I did a drift test earlier, but it turned out to be not very scientific due to both RWM and WWV fading rather too much.  It did, however, reveal that the MkI calibration drifts a lot in the first hour - about 40Hz - but the IF Display errors settle down after about 20 minutes.  I'm going to do a proper test tomorrow using a 10MHz signal from a GPSDO to see exactly how long it takes the unit to fully stabilise (or if it ever does!).

In the meantime, a screenshot of what happens to a 10MHz signal in the IF Display when the waterfall is shifted R - Centre - L in 1MHz hops: the apparent frequency changes in 70Hz steps.  I'll check in the next test whether that step size is temperature related, or whether it's just a function of the waterfall display width.

Regards,
Dave
MkI - 10MHz sig moved R-C-L across waterfall .jpg