Date   
Re: Octagon Frequency Locking Conumdrum

Richard <richard@...>
 

That gives a foundation to being able to measure offsets those , like me , using decent TCXOs in their LNBs,
SiTime, Conner Winfield etc
Have you kept a plot of a waterfall display over a few hours of the beacon ?
And Although you have everything locked to your Cs standard , did you also lock the clock in the SDR ?

Richard

On Wed, 2019-03-27 at 10:35 +0000, Andy G4JNT wrote:
Was wondering that ...

Anyway, the 100Hz or so 'error' on the beacon frequency also appears on the upper beacon, the null of teh PSK lobes appearing exactly the smae mount above nominal.  

And the final test, it's the satellite LO that gives that offset.
I'm transmitting a 2400.06MHz carrier, about 20dBm EIRP and it's appearing 104.7Hz high

Which is almost , bit not exactly the same offset as the CW beacon from it's .55000 nominal, that is currently 106.9 Hz high

The 2.2Hz error yet needs accounting for, but as I'm on free run on the HP5061 could just about be due to that.   The Caesium take 2 hours to warm up, so that can wait.   Always assuming the ground station is using a similar accuracy of standard.



On Wed, 27 Mar 2019 at 10:13, Colin G4EML <colin@...> wrote:
Could it be that the offset is deliberate to improve the stability/spurs/phase noise? In its intended application with the original crystal an offset would not be detectable. 

I have one of the octagon LNBs that uses a 25MHz crystal and a different chip. I will repeat the experiment on that and see how that differs.

Colin. 




On 27 Mar 2019, at 09:42, John Fell <john.g0api@...> wrote:

Assuming your test gear can be cross calibrated to ensure frequency accuracy , that 50HZ offset is interesting.

With common synth chips in use in other LNBs for 4k/3D , we should expect similar results - does anyone have any measurements to offer ?

When doing 10GHZ EME in 1994 , we (G4RFR)  would have marvelled at an accuracy of 50HZ !

Having used locked Octos for 5 years on my tropo system , I cannot recall any "gross " frequency error during Summertime , but possibly using one of the 25MHZ versions on EME recently may have had issues retaining locking .
The quality /accuracy of the 25MHZ Xtal is considerably worse , on average , compared to the 27MHZ version; this poses problems if the Xtal is retained on the LNB .(to condition the external reference and allow free running when ext. source removed) .

That is why we   recently opted for an external PLL 25MHZ reference , tied to a GPS source , to the 25MHZ version - this also removes the temperature related issues to a more stable environment under temperature extremes .

For QO100 measurements it is easy enough to use pre-amplification stages at the feed and pass these down Heliax to a modified LNB in the shack - that will also remove the temperature extremes and help with system calibration issues perhaps ?

73
John
G0API


On Wed, 27 Mar 2019 at 08:13, Andy G4JNT <andy.g4jnt@...> wrote:
Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Andy G4JNT
 

Was wondering that ...

Anyway, the 100Hz or so 'error' on the beacon frequency also appears on the upper beacon, the null of teh PSK lobes appearing exactly the smae mount above nominal.  

And the final test, it's the satellite LO that gives that offset.
I'm transmitting a 2400.06MHz carrier, about 20dBm EIRP and it's appearing 104.7Hz high

Which is almost , bit not exactly the same offset as the CW beacon from it's .55000 nominal, that is currently 106.9 Hz high

The 2.2Hz error yet needs accounting for, but as I'm on free run on the HP5061 could just about be due to that.   The Caesium take 2 hours to warm up, so that can wait.   Always assuming the ground station is using a similar accuracy of standard.



On Wed, 27 Mar 2019 at 10:13, Colin G4EML <colin@...> wrote:
Could it be that the offset is deliberate to improve the stability/spurs/phase noise? In its intended application with the original crystal an offset would not be detectable. 

I have one of the octagon LNBs that uses a 25MHz crystal and a different chip. I will repeat the experiment on that and see how that differs.

Colin. 




On 27 Mar 2019, at 09:42, John Fell <john.g0api@...> wrote:

Assuming your test gear can be cross calibrated to ensure frequency accuracy , that 50HZ offset is interesting.

With common synth chips in use in other LNBs for 4k/3D , we should expect similar results - does anyone have any measurements to offer ?

When doing 10GHZ EME in 1994 , we (G4RFR)  would have marvelled at an accuracy of 50HZ !

Having used locked Octos for 5 years on my tropo system , I cannot recall any "gross " frequency error during Summertime , but possibly using one of the 25MHZ versions on EME recently may have had issues retaining locking .
The quality /accuracy of the 25MHZ Xtal is considerably worse , on average , compared to the 27MHZ version; this poses problems if the Xtal is retained on the LNB .(to condition the external reference and allow free running when ext. source removed) .

That is why we   recently opted for an external PLL 25MHZ reference , tied to a GPS source , to the 25MHZ version - this also removes the temperature related issues to a more stable environment under temperature extremes .

For QO100 measurements it is easy enough to use pre-amplification stages at the feed and pass these down Heliax to a modified LNB in the shack - that will also remove the temperature extremes and help with system calibration issues perhaps ?

73
John
G0API


On Wed, 27 Mar 2019 at 08:13, Andy G4JNT <andy.g4jnt@...> wrote:
Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Colin G4EML
 

Could it be that the offset is deliberate to improve the stability/spurs/phase noise? In its intended application with the original crystal an offset would not be detectable. 

I have one of the octagon LNBs that uses a 25MHz crystal and a different chip. I will repeat the experiment on that and see how that differs.

Colin. 




On 27 Mar 2019, at 09:42, John Fell <john.g0api@...> wrote:

Assuming your test gear can be cross calibrated to ensure frequency accuracy , that 50HZ offset is interesting.

With common synth chips in use in other LNBs for 4k/3D , we should expect similar results - does anyone have any measurements to offer ?

When doing 10GHZ EME in 1994 , we (G4RFR)  would have marvelled at an accuracy of 50HZ !

Having used locked Octos for 5 years on my tropo system , I cannot recall any "gross " frequency error during Summertime , but possibly using one of the 25MHZ versions on EME recently may have had issues retaining locking .
The quality /accuracy of the 25MHZ Xtal is considerably worse , on average , compared to the 27MHZ version; this poses problems if the Xtal is retained on the LNB .(to condition the external reference and allow free running when ext. source removed) .

That is why we   recently opted for an external PLL 25MHZ reference , tied to a GPS source , to the 25MHZ version - this also removes the temperature related issues to a more stable environment under temperature extremes .

For QO100 measurements it is easy enough to use pre-amplification stages at the feed and pass these down Heliax to a modified LNB in the shack - that will also remove the temperature extremes and help with system calibration issues perhaps ?

73
John
G0API


On Wed, 27 Mar 2019 at 08:13, Andy G4JNT <andy.g4jnt@...> wrote:
Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Andy G4JNT
 

Cross calibrated with another synth source, and ADF4351 (but I knew the Systron Donner was spot on, anyway)
50Hz +/- 0.1Hz  error is very definitely there.
Colin 'EML reported similar




On Wed, 27 Mar 2019 at 09:42, John Fell <john.g0api@...> wrote:
Assuming your test gear can be cross calibrated to ensure frequency accuracy , that 50HZ offset is interesting.

With common synth chips in use in other LNBs for 4k/3D , we should expect similar results - does anyone have any measurements to offer ?

When doing 10GHZ EME in 1994 , we (G4RFR)  would have marvelled at an accuracy of 50HZ !

Having used locked Octos for 5 years on my tropo system , I cannot recall any "gross " frequency error during Summertime , but possibly using one of the 25MHZ versions on EME recently may have had issues retaining locking .
The quality /accuracy of the 25MHZ Xtal is considerably worse , on average , compared to the 27MHZ version; this poses problems if the Xtal is retained on the LNB .(to condition the external reference and allow free running when ext. source removed) .

That is why we   recently opted for an external PLL 25MHZ reference , tied to a GPS source , to the 25MHZ version - this also removes the temperature related issues to a more stable environment under temperature extremes .

For QO100 measurements it is easy enough to use pre-amplification stages at the feed and pass these down Heliax to a modified LNB in the shack - that will also remove the temperature extremes and help with system calibration issues perhaps ?

73
John
G0API


On Wed, 27 Mar 2019 at 08:13, Andy G4JNT <andy.g4jnt@...> wrote:
Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

John Fell
 

Assuming your test gear can be cross calibrated to ensure frequency accuracy , that 50HZ offset is interesting.

With common synth chips in use in other LNBs for 4k/3D , we should expect similar results - does anyone have any measurements to offer ?

When doing 10GHZ EME in 1994 , we (G4RFR)  would have marvelled at an accuracy of 50HZ !

Having used locked Octos for 5 years on my tropo system , I cannot recall any "gross " frequency error during Summertime , but possibly using one of the 25MHZ versions on EME recently may have had issues retaining locking .
The quality /accuracy of the 25MHZ Xtal is considerably worse , on average , compared to the 27MHZ version; this poses problems if the Xtal is retained on the LNB .(to condition the external reference and allow free running when ext. source removed) .

That is why we   recently opted for an external PLL 25MHZ reference , tied to a GPS source , to the 25MHZ version - this also removes the temperature related issues to a more stable environment under temperature extremes .

For QO100 measurements it is easy enough to use pre-amplification stages at the feed and pass these down Heliax to a modified LNB in the shack - that will also remove the temperature extremes and help with system calibration issues perhaps ?

73
John
G0API


On Wed, 27 Mar 2019 at 08:13, Andy G4JNT <andy.g4jnt@...> wrote:
Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Dish Feeds

Martin - G8JNJ
 

Hi All,

I've been using a small PCB Log-Periodic to feed my 0.9m offset dish so that I can play on Oscar 100.

I've started looking at other types of feed in order to provide circular polarisation and I have some questions.

As A first step I've built a 5 turn helix, but It's a lot longer than I'd expected, and I'm wondering about where the phase center (for the purposes of properly illuminating the dish) of the helix is actually located.

With the Log-Periodic only a few of the elements are active on any given frequency, so the phase center is quite compact and seems to be contained within the focus of the dish.

However the helix is a lot longer, so is the phase center in the middle of the length of the helix or at the open end ?

Do long(ish) antennas work properly as feeds for small dishes ?

Is a patch a better option because it is likely to have a more compact phase center ?

Regards,

Martin - G8JNJ

Re: Octagon Frequency Locking Conumdrum

Andy G4JNT
 

The Eshail2 CW beacon on a fully locked and (I think) frequency corrected system
Rx tuned to 10489.549000MHz

image.png



On Wed, 27 Mar 2019 at 08:13, Andy G4JNT via Groups.Io <andy.g4jnt=gmail.com@groups.io> wrote:
Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Dave G8KHU
 

Hi Andy

 

OOPS!

Sorry I plead guilty to answering the question I thought you’d asked rather than the one you did, mea culpa.

 

Contritely ;-)

Dave

Re: Octagon Frequency Locking Conumdrum

Andy G4JNT
 

Second Octagon confirmed as also being 50Hz high

  -  27.00000000 MHz into external locking port
  -  Signal at 10400.00000 MHz 
  -  Resulting IF out measured on a frequency counter 650.0000500 MHz   +/- 0.1Hz gating uncertainty

So for the time being it can be considered systematic and the 50Hz offset programmed into the second downconverter

VERY WEIRD



On Tue, 26 Mar 2019 at 23:14, Richard <richard@...> wrote:
Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Richard <richard@...>
 

Hi Colin
that would account for about 20Hz a day ish
Its not an exact science, especially if you consider what we do with LNBs
When summer arrives there could be as much as 50 degrees change in LNB temperature even in the UK
You can get snow shields for LNBs , I suspect if these are fitted and the shiny side of Al foil is glued to the cover
we could minimise the shift to 20 degrees, probably worth doing.
For those who are muttering what load of Boll** just remember if you leave a sheet of metal out in the sun you can easily fry an egg
on it., so on a hot day indirect sunlight 50 degs is very conservative.
You really are asking a lot of something that was designed for wide band operation. Winter is a kind time for LNBs max temp shift is 20 degs
and the cold gives a better NF.
Trying to get an idea of what happening to the LNB is very worth while and NOT losing the plot.

Richard g8jvm

On Tue, 2019-03-26 at 15:55 -0700, Colin G4EML wrote:
Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Colin G4EML
 

Looks like I posted at the same time as Richard.... 
I have found a site where someone has done some monitoring of the engineering beacon Doppler before the amateur transponder went into service. 
Destevez.net/2018/12/studying-eshail-2-doppler/
It looks like +-2ppb can be expected over a day. 

Re: Octagon Frequency Locking Conumdrum

Colin G4EML
 

Of course we don’t know how stable the satellite LO is.
Then there must be some Doppler as the satellite distance won’t be static. 
I am not sure how big this would be, an interesting thing to try to measure. 

Colin. 

Re: Octagon Frequency Locking Conumdrum

Richard <richard@...>
 

The other thing to consider is , are geostationary sats really what we think are geostationary, because if the orbit is not a constant distance from us
there will be some doppler shift, and that lump of rock they call the moon must have some effect.
But but your seeing is an error in the LNB PLL , and it would be nice to know if its a constant or variable
SO YOU HAVE DEFINITELY NOT LOST THE PLOT by trying to define it

Richard


On Tue, 2019-03-26 at 22:21 +0000, Andy G4JNT wrote:
Well, if there is an error there, hopefully it'll be systematic and completely calibratable.  

The beacon offset seems to vary a bit.  I reckon its 145Hz above .55 now; it was 123Hz earlier today, and you measured 92Hz.
Pity - was hoping it could be used as a frequency ref for anyone.  I could put up a better one that that - although not as strong

I'd love to be able to do some coherent signal testing via a geostationary satellite.  Goes back to work in the 1990's with the Inmarsat 3 precursor studies and bid.  Having long arguments / discussions with Inmarsat Co and ESA about how to test phased arrays in space.   SO complicated an idea, back then anyway,  they never went for a phased array for INM-3.   Sure my ideas for testing in-situ could have worked.  It would certainly have been worth testing.
10 Years later, Defford were doing semi-coherent open loop work between adjacent satellites for geolocation - some clever stuff there.

Satellite technology has moved on quite a bit in 30 years!

 


On Tue, 26 Mar 2019 at 22:09, Colin G4EML <colin@...> wrote:
Hi Andy, 

I can’t approach your level of accuracy but playing around with a GPS Locked Octagon and GPS Locked SDR I got very similar results. 

Tuned to 739.549 I got a tone of 1138Hz from the lower beacon. 
Generating a local 10489.550 using a second GPS source and diode multiplier I got a tone of 1046Hz. 

It does seem to point to the Octagon being around 50Hz low in frequency. 

As you say without knowing how the LNB Synth actually works its difficult to work out what is happening.


Colin

Re: Octagon Frequency Locking Conumdrum

Richard <richard@...>
 

If there is a HP5342A service manual pdf copy lurking somewhere I can check out why the Ext standard input is playing up
and I'll do the TCXO mod to the LNB and measure what the offset is on the 9750 MHz LO for what ever the 27 MHz TCXO is set at.
Thats if I can find enough of the LO to measure of course.
Richard


On Tue, 2019-03-26 at 15:09 -0700, Colin G4EML wrote:
Hi Andy, 

I can’t approach your level of accuracy but playing around with a GPS Locked Octagon and GPS Locked SDR I got very similar results. 

Tuned to 739.549 I got a tone of 1138Hz from the lower beacon. 
Generating a local 10489.550 using a second GPS source and diode multiplier I got a tone of 1046Hz. 

It does seem to point to the Octagon being around 50Hz low in frequency. 

As you say without knowing how the LNB Synth actually works its difficult to work out what is happening.


Colin

Re: Octagon Frequency Locking Conumdrum

Andy G4JNT
 

Well, if there is an error there, hopefully it'll be systematic and completely calibratable.  

The beacon offset seems to vary a bit.  I reckon its 145Hz above .55 now; it was 123Hz earlier today, and you measured 92Hz.
Pity - was hoping it could be used as a frequency ref for anyone.  I could put up a better one that that - although not as strong

I'd love to be able to do some coherent signal testing via a geostationary satellite.  Goes back to work in the 1990's with the Inmarsat 3 precursor studies and bid.  Having long arguments / discussions with Inmarsat Co and ESA about how to test phased arrays in space.   SO complicated an idea, back then anyway,  they never went for a phased array for INM-3.   Sure my ideas for testing in-situ could have worked.  It would certainly have been worth testing.
10 Years later, Defford were doing semi-coherent open loop work between adjacent satellites for geolocation - some clever stuff there.

Satellite technology has moved on quite a bit in 30 years!

 


On Tue, 26 Mar 2019 at 22:09, Colin G4EML <colin@...> wrote:
Hi Andy, 

I can’t approach your level of accuracy but playing around with a GPS Locked Octagon and GPS Locked SDR I got very similar results. 

Tuned to 739.549 I got a tone of 1138Hz from the lower beacon. 
Generating a local 10489.550 using a second GPS source and diode multiplier I got a tone of 1046Hz. 

It does seem to point to the Octagon being around 50Hz low in frequency. 

As you say without knowing how the LNB Synth actually works its difficult to work out what is happening.


Colin

Re: Octagon Frequency Locking Conumdrum

Colin G4EML
 

Hi Andy, 

I can’t approach your level of accuracy but playing around with a GPS Locked Octagon and GPS Locked SDR I got very similar results. 

Tuned to 739.549 I got a tone of 1138Hz from the lower beacon. 
Generating a local 10489.550 using a second GPS source and diode multiplier I got a tone of 1046Hz. 

It does seem to point to the Octagon being around 50Hz low in frequency. 

As you say without knowing how the LNB Synth actually works its difficult to work out what is happening.


Colin

Re: Octagon Frequency Locking Conumdrum

Andy G4JNT
 

Dave
That's the data sheet for the old VHF synth used for 10 to 27MHz conversion.  
That's not in question.

The info needed is a clue to what's going on with the synth internal to the LNB
 


On Tue, 26 Mar 2019 at 20:58, Dave G8KHU <david@...> wrote:
Hi Richard
This is the data-sheet I found https://www.nxp.com/docs/en/data-sheet/MC145170-2.pdf 
It looks like a buffered version of the reference can be enabled on pin 3
Cheers
Dave

Re: Octagon Frequency Locking Conumdrum

Dave G8KHU
 

Hi Richard
This is the data-sheet I found https://www.nxp.com/docs/en/data-sheet/MC145170-2.pdf 
It looks like a buffered version of the reference can be enabled on pin 3
Cheers
Dave

Re: Octagon Frequency Locking Conumdrum

Richard <richard@...>
 

Dave does that data sheet you have give any clue if the LO is available at any of the pins ?
Richard

On Tue, 2019-03-26 at 12:39 -0700, Dave G8KHU wrote:
Andy
If I've read the datasheet correctly the R and N divider outputs are available on pins 9 & 10. These should be within the range of a frequency counter and would give a clue as to whether the  the divide ratios in the two counters are performing as required.
Cheers
Dave

Re: Octagon Frequency Locking Conumdrum

Dave G8KHU
 

Andy
If I've read the datasheet correctly the R and N divider outputs are available on pins 9 & 10. These should be within the range of a frequency counter and would give a clue as to whether the  the divide ratios in the two counters are performing as required.
Cheers
Dave