RTL1090 thread

[Llew]

Yes, that would be the way to go for a stricter controlled test. I don't think though that there is a significant enough difference, at least on this particular frequency. Maybe different at higher/lower ends of the receiver's stated reception range.

There's an air show with a flying display of Yankee aircraft on Sunday and Monday at the IWM Duxford, ten miles from me. Have to check if there'll be anything interesting up on VRS.

 

[Vipersan]

So ...I have my suppository LNA in the system about 2 feet from the base connector of the antenna itself ...and then a few mtrs of RG58 to the modified RTL dongle I did recently which provides about 3.5 volts of phantom power to the LNA ...
Colinear Antenna at full vertical extension ....I can now see a lot further ..
Tonight I have seen planes as far south as Bath ...and as far west as the Isle of Man ...as far East as Hull and North of the Lake District ..
The new Dongle when it arrives _might_ provide a little more ....but I am happy with the current state of affairs tbh ..
Dont think I need any more mods to the ADSB system really..
Time to concentrate on ADSA and ADSC I think..
rgds
VS

 

[Vipersan]

Thought you might like to see inside one of these 'new' rtl dongles Llew ..
The one I ordered arrived today ...
You can clearly see the TCXO ..
Redesigned pcb ..and link pads for Phantom power ..
Not tried it yet ..as I opened it up to perform the Bias Tee link operation ..
rgds
VS

 

[Llew]

A handsome beast VS. I was out when it arrived on Saturday, so I have to wait until tomorrow to pick it up from the depot.
Let us know how the voltage survives the trip up to your LNA when the phantom power is enabled.

 

[Vipersan]

..didnt use a link to bridge the pads Llew...but instead ..another 10uH inductor ...
Substituted for my homebrew modded dongle and powered it up ..
Yep 'tis driving the remote suppository lna no problem ...
In fact ..I could be imagining it ..but planes over bath and reading ..
maybe this has a bit more reach ...
If so it's minimal ...but should be more stable at higher frequencies ..
I'll test it at 1.5ghz later ..
rgds
VS

 

[Vipersan]

So ..tried it at 1.5ghz ..
....and yes it appears stable ...but simply not enough gain ..
Not surprised by this as Airspy does have another internal lna ...RTL dongles do not ..
So ..stable traces in the waterfall ....in roughly the right area of the spectrum ...but never more than 4 db ...
cest la vie..
A nice device ..and nice build quality but limited at higher frequencies gain wise..
rgds
VS

 

[Llew]

Some people add another LNA4ALL down the line, presumably where long cable runs are involved.

I'll play with mine when I have a break from shifting the Gibby's pole a few feet from its present location, necessary because at last I'm attaching the Gibby polar mount I've had stored for ages to the dish - I envisage getting a 1.5M Gibby at some time (1.2 ATM), and good though the SMW PM is, I know it would protest at any weightier dish.

Where the dish is now it would intrude over my neighbour's garden with the Gibby PM attached. A major job, but I've been meaning to do it for a couple of years. Progress (if any) to be reported in the appropriate section. If this rubbish weather keeps up - inches of mud in the garden at present - I'll do some checks with the new dongle.

 

[Vipersan]

Some people add another LNA4ALL down the line, presumably where long cable runs are involved.

I'll play with mine when I have a break from shifting the Gibby's pole a few feet from its present location, necessary because at last I'm attaching the Gibby polar mount I've had stored for ages to the dish - I envisage getting a 1.5M Gibby at some time (1.2 ATM), and good though the SMW PM is, I know it would protest at any weightier dish.

Where the dish is now it would intrude over my neighbour's garden with the Gibby PM attached. A major job, but I've been meaning to do it for a couple of years. Progress (if any) to be reported in the appropriate section. If this rubbish weather keeps up - inches of mud in the garden at present - I'll do some checks with the new dongle.

Problem is Llew ...that there are already 2 LNAs inside the antenna back box ...so these 2 are as close to the actual aerial ...and as far frm the airspy as possible ...
So adding another at the full extent of the cable might well produce instability ....
You would then in effect have ..
Helix > LNA1 > Filter > LNA2 > LNA3 > Cable > RTL Dongle
I may try one fitted close to the Dongle as this would be more like Airspy...thus compensating for the known db drop of the cable..

Helix > LNA1 > Filter > LNA2 > Cable > Airspy LNA > Airspy proper

...

 

[s-band]

View attachment 94655
So ..tried it at 1.5ghz ..
....and yes it appears stable ...but simply not enough gain ..
Not surprised by this as Airspy does have another internal lna ...RTL dongles do not ..

Unless I've lost the plot (quite possible), I understood that the Airspy only has the R820T2 as a front end without an extra LNA. The LNA control in the software operates on the R820

The main advantage of the Airspy is that it has a better ADC (12 vs 7.5 bits) giving a better instantaneous dynamic range and resolution.

Problem is Llew ...that there are already 2 LNAs inside the antenna back box ...so these 2 are as close to the actual aerial ...and as far frm the airspy as possible ...
So adding another at the full extent of the cable might well produce instability ....
You would then in effect have ..
Helix > LNA1 > Filter > LNA2 > LNA3 > Cable > RTL Dongle
I may try one fitted close to the Dongle as this would be more like Airspy...thus compensating for the known db drop of the cable..

Helix > LNA1 > Filter > LNA2 > Cable > Airspy LNA > Airspy proper

...

Assuming:
LNA NF = 1dB, Gain 15dB
Cable Loss NF = 10dB Gain =-10dB
RX (Airspy or RTL) NF = 5dB
Using HP/Agilent Appcad AppCAD
LNA1 > Filter > LNA2 > 3dB atten for stability > LNA3 > Cable > RX gives NF of 1.22dB (NF without atten 1.21dB )
LNA1 > Filter > LNA2 > Cable > RX gives 1.41dB NF
LNA1 > Filter > LNA2 > Cable > LNA 3 > RX gives 1.28dB NF

For satellite you really need to play with the whole budget including the antenna. Try plugging some of the figures into this calculator: Noise temperature, Noise Figure and Noise Factor

All theory though! I haven't tried an RTL dongle with L band JAERO although the performance on C band (where the NF is determined 99.9% by LNB ) was the same using an Airspy or RTL

 

[Vipersan]

So ..
all about phrophets and mountains imo ...
Since I know the signal degradation is due to cable losses ...to a very large extent ..
I removed the coax from the equation again ...
Using the long wire screened usb repeater ...I'm able to get this new dongle directly on the Antenna back box ....
Thus the only data transfered over distance is digital ...
The results are conclusive and astounding ..
See for yourselves..
rgds
VS

 

[s-band]

So ..
all about phrophets and mountains imo ...
Since I know the signal degradation is due to cable losses ...to a very large extent ..
I removed the coax from the equation again ...
Using the long wire screened usb repeater ...I'm able to get this new dongle directly on the Antenna back box ....
Thus the only data transfered over didtance is digital ...
The results are conclusive and astounding ..
See for yourselves..
rgds
VSView attachment 94664

Looks good, makes me wonder if Airspy is well or something else is amiss.
What DC voltage is actually at the LNAs on Airspy vs. RTL?
What's JAERO report as Eb/No?
To get an exact comparison using spectra, set the sample rate to the same rate in both RTL & Airspy

 

[Vipersan]

To conclude this experiment ...which strictly speaking is in the wrong thread ..(will move now to the Aero thread)
A quick data sample screen grab to prove data is flowing ...from the new dongle.
rgds
VS

 

[s-band]

To conclude this experiment ...which strictly speaking is in the wrong thread ..(will move now to the Aero thread)
A quick data sample screen grab to prove data is flowing ...from the new dongle.
rgds
VSView attachment 94665

That's more like it. Something's weird with the Airspy set-up

 

[Vipersan]

That's more like it. Something's weird with the Airspy set-up

Hmm ...
I guess Airspy could be faulty ...but how to prove it ..and would they be interested in replacing if it were ?
I doubt it ..