WXSat proof of concept

[Analoguesat]

15's going over you now, but 18's right behind it.

Over Europe 18 is transiting with Meteor M2 atm - and they are on the same frequency! The result is not a good one for N-18....

 

[Archive-8]

Over Europe 18 is transiting with Meteor M2 atm - and they are on the same frequency! The result is not a good one for N-18....

So that may well be the cause of my interference, the pi can’t handle multiple passes at the same time like window can.

It’s one of the drawbacks.

 

[Terryl]

OK guy's here is an improvement for the dongle, I found that these little SDR dongle's get quite warm when in use for a long period of time, this seems to degrade their performance. (thermal noise)

So I found an old CPU heat-sink and used a zip tie and some heat sink paste, zip tied the dongle to the heat-sink and the thing seems to work better, some of the noise floor dropped a bit.

Here is the new MK-10 antenna, the improved version will follow.



And here is the dongle on the heat sink.



A USB extension cable is used to get it away from the PC, the PC also contributes to the over all noise received by the dongle.

 

[Terryl]

I know I know the MK-10 looks just like a turnstile antenna, but it's not, it is a center fed dual half wave with 1/4 wave reflectors.

 

[Archive-8]

OK guy's here is an improvement for the dongle, I found that these little SDR dongle's get quite warm when in use for a long period of time, this seems to degrade their performance. (thermal noise)

So I found an old CPU heat-sink and used a zip tie and some heat sink paste, zip tied the dongle to the heat-sink and the thing seems to work better, some of the noise floor dropped a bit.

Here is the new MK-10 antenna, the improved version will follow.

View attachment 116796

And here is the dongle on the heat sink.

View attachment 116797

A USB extension cable is used to get it away from the PC, the PC also contributes to the over all noise received by the dongle.

@jeallen01 didn’t you have similar issues with heat killing a couple of your dongles?

If I remember rightly you tried adding a cpu heatsink?

 

[Archive-8]

OK guy's here is an improvement for the dongle, I found that these little SDR dongle's get quite warm when in use for a long period of time, this seems to degrade their performance. (thermal noise)

So I found an old CPU heat-sink and used a zip tie and some heat sink paste, zip tied the dongle to the heat-sink and the thing seems to work better, some of the noise floor dropped a bit.

Here is the new MK-10 antenna, the improved version will follow.

View attachment 116796

And here is the dongle on the heat sink.

View attachment 116797

A USB extension cable is used to get it away from the PC, the PC also contributes to the over all noise received by the dongle.

Just had a thought, I wonder if it’s the gain over loading on the dongle?

 

[Terryl]

If you have your AGC set to auto then it shouldn't.

What is your over all noise floor at?

Mine is around -110 DBm, goes up to around -90 DBm at the 137 MHz band, satellite signals are around a -55 DBm at my location.

 

[Analoguesat]

SDR# with a couple of addons - an audio processor & IF processor. Im trying to reduce the pagers up at 138MHz which are causing all sorts of interference on my signals.

Very much work in progress atm as Im fiddling with the settings! (NOAA18 pass)

 

[Archive-8]

SDR# with a couple of addons - an audio processor & IF processor. Im trying to reduce the pagers up at 138MHz which are causing all sorts of interference on my signals.

Very much work in progress atm as Im fiddling with the settings! (NOAA18 pass)

View attachment 116814

Have you worked out your ideal gain value? Or can it be left on agc?

I am still using the pi in the garage.

 

[Terryl]

You guys should take a look at SDR Console, I find it much more forgiving on the interference as you can set your own IF bandwidth, and do a lot more to limit the noise.

http://www.sdr-radio.com/

It's donation ware (if you want to) and I use the version 3.

 

[Analoguesat]

I think the main problem is just that the pages are so strong and the dongles so wide open that the pagers just swamp the front end of the dongle. I see spurious peaks right up and down the 137MHz band at times when the pagers cut in.

The pagers peaks are at least twice the height of the NOAA's signal on the spectrum graphs - very often off the top of the scale.

Here in the UK we need some bit of equipment with decent front end filtering that only lets 137MHz through. Which preferably isnt too expensive!

 

[Terryl]

The only thing I can think of is a tuned cavity filter, they are very very sharp and low loss, but very expensive.

If your going to dedicate the dongle to just the 137.0 to 138.0 MHz band then its a good choice.

 

[Analoguesat]

FWIW heres a before & after comparison for the local pager on 138.1 MHz These were taken just a few seconds apart. the white fuzz to the left is the strong Meteor M2 signal - completely flattened by the bloody pocsag!

 

[Archive-8]

The only thing I can think of is a tuned cavity filter, they are very very sharp and low loss, but very expensive.

If your going to dedicate the dongle to just the 137.0 to 138.0 MHz band then its a good choice.

The uputronics pre-amp has a saw filter. I have moved the dongle away from the pre-amp/pi/psu/network switch with an usb extension cable.

A few from today, not adjusted any settings yet, that’s a job for tomorrow.

 

[Archive-8]

Just been playing with the scripts to schedule passes, control the correct frequency, and record the output.

I found the script was using max gain, I have now changed that to 38.6 and also added meteor-m2 to the list.

Fingers crossed for the next pass.

 

[Analoguesat]

Todays keplers are well screwed - the passes are actually running ~10 minutes later than they indicate!

 

[Archive-8]

Grabbed this after adjusting my settings

 

[Archive-8]

Some odd results so far today, after I lowered the elevation angle in one of the scripts to 15° or above.

 

[Terryl]

I have my elevation angle set to 10 degrees, it all depends on the height of the antenna above any obstruction and if you have clear line of sight all the way out to the satellites first horizon. (when it first peeks over the horizon)

If the bird is comming right over you and you have a clear sight North and South (like over the Ocean) then you can set it to zero.

 

[Archive-8]

I have my elevation angle set to 10 degrees, it all depends on the height of the antenna above any obstruction and if you have clear line of sight all the way out to the satellites first horizon. (when it first peeks over the horizon)

If the bird is comming right over you and you have a clear sight North and South (like over the Ocean) then you can set it to zero.

I will knock it lower down to 10 and see how I get on.