Antenna thread

[Vipersan]

Carried on trying last night ...until about 2:30 ..
Never one for giving up easy ...I have improvised some SMA male connectors for the RG58 Cable ends ...using pcb based SMA conectors and in line joint pieces ...
Only taped over atm ...so ordered some crimp connectors and crimpers ..
another £20 gone ...but worth it I guess ..
So ..dumped the BNCs ..and here is the result ...
LNA in line of course ..
Not perfik ..but certainly an improvement ..
The wideband 10500 still eludes be ...but at least I can get data from one of the narrower channels ..
It's a start..
rgds
VS

 

[hairybadger]

Ouch that hurt ..
couldn't get a 50mtr drum ..so had to opt for 100mtrs ..
RG58 Mil Spec ...
£38 delivered..
just hope Mil Spec means something ...and not just a label..
lol

If my understanding of the wiki article is correct, "mil spec" just means "RGXX is wot the military call it"

RG-58 - Wikipedia, the free encyclopedia

 

[Vipersan]

Hmm ...
Periodically ...keep getting bursts of something real strong but off screen re- the zoomed waterfall on SDR# ..
So can't actually see what it is ..but my word it doesn't half affect the agc ...
Noise floor swings up n down from -60db to -55db ...
Anyone fancy designing some filters .. ?
lol..

 

[Vipersan]

got a few nice metal boxes coming ...found on aliexpress for a few quid ..
4 to be precise ..for $22 delivered..
Hopefully suitable for mounting LNAs outdoors ..and provide much needed screening ..

 

[s-band]

Hmm ...
Periodically ...keep getting bursts of something real strong but off screen re- the zoomed waterfall on SDR# ..
So can't actually see what it is ..but my word it doesn't half affect the agc ...
Noise floor swings up n down from -60db to -55db ...
Anyone fancy designing some filters .. ?
lol..

Could be cellular or almost anything close by with the wide open front end. What about this ADS-B filter 1090 MHz: L-band (Inmarsat, Thuraya, Iridium, GPS) filter
from your mate? Get another LNA while your there and try the filter in the middle of 2 LNAs

 

[Vipersan]

Could be cellular or almost anything close by with the wide open front end. What about this ADS-B filter 1090 MHz: L-band (Inmarsat, Thuraya, Iridium, GPS) filter
from your mate? Get another LNA while your there and try the filter in the middle of 2 LNAs

The only problem I can see is powering the LNA close to the Helical ...as the one closest to the receiver would have its input cap coupled ...
Possibly a spur could be taken from the ghost powered LNA to the more isolated LNA to supply it's 5v ...assuming of course the current drain on Airspy would not be excessive ..
Next question ..is regarding the filter ..which if 'active' would also need a supply..

 

[s-band]

The only problem I can see is powering the LNA close to the Helical ...as the one closest to the receiver would have its input cap coupled ...
Possibly a spur could be taken from the ghost powered LNA to the more isolated LNA to supply it's 5v ...assuming of course the current drain on Airspy would not be excessive ..
Next question ..is regarding the filter ..which if 'active' would also need a supply..

Airspy info is confusing as one place it says 50mA but here http://airspy.com/wp-content/uploads/2014/11/AirSpy_NOS_R2_PinAssignment.jpg it says 250mA. Maybe they changed the design. I'd just try it, I've drawn 100mA from it.
I haven't looked closely at the LNA for all but it seems to have multiple configuration options. Use the output LNA's bias tee and feed DC from there to the supply in of the 1st LNA. Check with the vendor how to configure them.
Filter is passive. It looks like he's used a Mini-circuits LPF/HPF combination

 

[hvdh]

VS, all along my guts were saying, at 1.5 GHz a nice, long, helical antenna (without dish) would be the better way to go.

 

[s-band]

VS, all along my guts were saying, at 1.5 GHz a nice, long, helical antenna (without dish) would be the better way to go.

Agreed.
A helical works for me The Aero Thread.. but it's more susceptible to interference than the dish.
There are some interesting comments here: http://www.wa5vjb.com/references/Antenna Measuring Notes-keb.pdf

 

[Vipersan]

..and this is the problem guys ..
I dont live out in the sticks ..and am surrounded on all sides by potential RF spillage from Routers ..DECT fones ...G4 masts ..traffic light and big brother cams ...the list goes on and on ..
In truth Town dwelling is flooded by carp ..
So ..the dish method seemed to me at least to give me the potential for tight-er beamwidth..
rgds
VS

 

[Vipersan]

Well ..surprise Surprise ...It's raining again ...
The dish surface is wet through ...and so would the the Helical antenna be ..If I can not popped a lemonade bottle over it ..
The bottle is covered in raindrops ..
But ..I didn't need to bring the antenna nor the LNA indoors ..
..and am still getting about 6 to 7db showing on AirSpy/SDR# at 1.545.037 ghz ..
Narrow bandwidth AeroH signal..
I guess that's a plus..

 

[s-band]

In truth Town dwelling is flooded by carp ..

If you can identify something specific using your SDR, your could try a 1/4 wave stub. You could tune it by snipping bits off until you minimised the interference. I've never used it but found this: The Quarter-wave stub

 

[Vipersan]

Whatever the problem RF is ..
it aint a constant signal ..
More like the kind of thing you get with Pager RFI ..
Heavy bursts of ...something...affecting the AGC and noise floor ..but not in the visible spectrum range..
If that makes sense ...
I'll try and grab a screen cap ...when one occurs ..
rgds
VS

 

[Vipersan]

and this is what I get when no RFI ..

 

[s-band]

and this is what I get when no RFI ..
View attachment 93662

I see what you mean, there's a few dB increase in noise ad well. Try running Spectrum Spy for a while and look at the waterfall to see if there's anything within the range. If the line goes all the way across it's most likely impulse noise e.g. dodgy thermostat. If it's at a specific frequency, that may be easier to eliminate. I get a lot of crud from the computers with the antenna indoors or on the window sill. The IRTE is about 10m away from most noise sources with it's back to them.

 

[Vipersan]

I see what you mean, there's a few dB increase in noise ad well. Try running Spectrum Spy for a while and look at the waterfall to see if there's anything within the range. If the line goes all the way across it's most likely impulse noise e.g. dodgy thermostat. If it's at a specific frequency, that may be easier to eliminate. I get a lot of crud from the computers with the antenna indoors or on the window sill. The IRTE is about 10m away from most noise sources with it's back to them.

No thermostat in play at my house atm ..
CH turned off ..
Next door to the left the house is empty ...and to the right ...No one Home atm..
I rather fancy this is outdoor RFI ..as the only active element exposed is the actual Helical ...and this _should_ be at least partly shielded by the dish reflector..
It's a mystery...with no apparent pattern to it ..time wise ..

 

[Channel Hopper]

How far from you is the nearest electric railway line ?

 

[Vipersan]

How far from you is the nearest electric railway line ?

The Nearest railway line is approximately 1/2 a mile ...but unsure if it is electrified..
That I'd have to check ..if need be ..

Anyway fwiw I am all set to try a bit of re-positioning of the Helix relative to the dish reflector ...
IF it ever stops raining ..that is ..

 

[s-band]

I checked the 2 PCs running here and they are awful. One is a 6yr old quad core 2.5GHz

the other a recent 3.5G i7.

Both put out crud near 1545MHz and the i7 has pulse structure to it. I also found out why I was getting rubbish on C band when the LNB was in the room - the i7. Measured with a 2cm long probe close to the cases. Using very low noise sat gear, some of that stuff is going to be detectable at over 100m with an antenna pointed at it.

 

[Channel Hopper]

I checked the 2 PCs running here and they are awful. One is a 6yr old quad core 2.5GHz
View attachment 93677
the other a recent 3.5G i7.
View attachment 93676
Both put out crud near 1545MHz and the i7 has pulse structure to it. I also found out why I was getting rubbish on C band when the LNB was in the room - the i7. Measured with a 2cm long probe close to the cases. Using very low noise sat gear, some of that stuff is going to be detectable at over 100m with an antenna pointed at it.

With modern processors, almost any frequency can be generated inside the 'modern desktop', it might also be appearing through an open port on the rear panel, ethernet, usb or unused video output. There has been additional work done on van Eck scanning since I was involved a couple of decades ago, I'll try to find something (Tempest ?)

Time to put those foil underpants to use in the short term though.