Antenna thread

S

s-band

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Vipersan said:
Ouch that hurt ..
couldn't get a 50mtr drum ..so had to opt for 100mtrs ..
RG58 Mil Spec ...
Click to expand...
It has about 0.7dB/m loss at 1.2GHz. The loss shouldn't matter if you've got enough gain ahead of it, providing nothing local (e.g. mobile phones) overloads anywhere in the system.
 
A

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Vipersan said:
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
Click to expand...
Source, please.
I ditched all my RG-58 many years ago togeter with all the NE1000/NE2000 compatible Ethernet adapters... need to find some new stuff again.
 
Vipersan

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Vipersan

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2x VboxII AZ-EL
2 m+ Alcoa PF + BSC421 C-Band lnbf...
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st1 said:
merci.
Click to expand...
vous êtes les bienvenus

I _do_ hope Adams Mix4All comes to market soon ..
it will make it so much easier I think..
 
battenfan

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Vipersan said:
the first quarter turn running parallel to the reflector at a height of approx 3mm ..
Sound Ok ?
Click to expand...
For a 2 mm wire and 50 Ohm match, 0.15 mm
75 Ohm match, 0.75 mm
Matching Helical Antenna

Regarding phase center at dish focus, it's complicated.
Code: 
www.w1ghz.org/antbook/conf/Helical_feed_antennas.pdf
 
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battenfan said:
For a 2 mm wire and 50 Ohm match, 0.15 mm
75 Ohm match, 0.75 mm
Matching Helical Antenna

Regarding phase center at dish focus, it's complicated.
Code: 
www.w1ghz.org/antbook/conf/Helical_feed_antennas.pdf
Click to expand...

w1ghz has some good stuff.
Somehow mine works, it wasn't based on much design time! To quote your 1st link "we just bend it until it works" I've added a pic with ruler for scale. It's not the most accurate helical and the spacing doesn't match the calculations. maybe a case of many wrongs making a right. It's a few dB from prefect circular polarisation. That's probably where the messy construction has had its effect.
I haven't found a simple way to determine phase centre but, in practice, it only needed to be within a cm or 2 when using it as a very offset feed on the PF dish.
L-Band_Helical_30.JPG SCRN14.JPG
 
Vipersan

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Well fwiw ..I'm ready to tear my hair out on this project ...
Basically I can't get enough signal ...
I now have a single straight run of 50 ohm RG58 from the antenna to Airspy (about 20 mtrs) .._with_ the LNA4ALL in circuit and powered by the Airspy ...
The antenna is obviously working ..but surely crap.jpg ..cannot be that deaf ...
Could it be I'm too far out of footprint ?
The antenna is mounted on Carl ...but not at the focus ...but I'm getting less signal indoors with the LNA than I was outdoors without it ..??
The only conversions in line now are sma to BNC ...which are both 50 ohms ..
I'm getting really frustrated now..
grrrr
This is the best I can do with decimation at 8 on Airspy ...and FREE control of the gains ...
rgds
VS
 
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S

s-band

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VS, how long is the RG58?
The PSA4-5043+ has about 15dB gain at 1.5G and 1dB NF. If you've go a long bit of RG58 you may be losing a lot
Your S/N on the 200kHz wide sig is at least 20dB less than I was getting using <1/2 of the 1.5m's area. You're looking for a gross problem not the last few dB.
Are you seeing preamp noise when you enable it? You should be if it is overcoming the cable loss
You're still in the footprint
 
Vipersan

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2 m+ Alcoa PF + BSC421 C-Band lnbf...
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I've added the cable length to the original post ...about 20 mtrs

I get sod all with the bias tee ie no supply to the LNA ...
I'd have to remove it to get a comparison ..

Just out of curiosity ...SB
Could the soldered connection at the base of the helix where it joins the sma bulkhead be an issue ..
Impedance matching wise ..
Also ...what height above the ground plane is your first 1/4 turn of the helix where it runs parallel to the ground plane ? I too am using 2mm copper wire ...
 
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S

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Various L, S, C, X & Ka bits. 1.2m S/X/Ku/Ka Prodelin on Az-El (being refurbished), 1.8m Precision PF with Bullseye Ku LNB or various C & X bits
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Vipersan said:
I've added the cable length to the original post ...about 20 mtrs

I get sod all with the bias tee ie no supply to the LNA ...
I'd have to remove it to get a comparison ..
Click to expand...
Use the software switch in SDR# to enable/disable LNA
Here's my offset feed
L-band_offset_feed.jpg

Assuming Airspy NF = 4dB
Cable loss = 14 dB
LNA gain 15dB NF 1dB
Cascade NF is 5.08dB
So you will have a worse S/N than with the SDR near the antenna.

Increase LNA gain to 30dB with everything else the same and the cascade NF is 1.21dB
Play with different configurations using AppCAD Download

Matching about 2mm above ground but see post #107 above
Anything from the SMA on can affect it.
You could try a dipole with reflector, that should only be 3-4dB down on circular.
 
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Vipersan

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2x VboxII AZ-EL
2 m+ Alcoa PF + BSC421 C-Band lnbf...
+SS2/TwHnS2-3200 pci/TBS6925 pci
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Some pics of my feeble attempt ..
DSCF0001.JPG
 

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PaulR

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I'm a bit suspicious about the Christmas tree of adapters. It might be worthwhile getting that reduced with a single adapter or a plug for the cable straight onto the LNB (if that's even remotely possible). And make sure that it is/they are the correct impedance as well.
 
Vipersan

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2x VboxII AZ-EL
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How do I increase the LNA gain to 30db SB..
the slider only goes up to 15 ??
 
Vipersan

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2x VboxII AZ-EL
2 m+ Alcoa PF + BSC421 C-Band lnbf...
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PaulR said:
I'm a bit suspicious about the Christmas tree of adapters. It might be worthwhile getting that reduced with a single adapter or a plug for the cable straight onto the LNB (if that's even remotely possible). And make sure that it is/they are the correct impedance as well.
Click to expand...
The LNA uses SMA connectors which are _supposed_ to be 50 ohms ...
But I have to fit something on the RG58 ...and I can only fit BNC atm ...I dont have facilities to fit SMA ...
presumably ..a crimp tool of some sort would be needed ..and suitable crimp on connectors ..?
Which explains the Christmas tree..
Sadly
 
S

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Vipersan said:
Some pics of my feeble attempt ..
View attachment 93554
Click to expand...
Helical puts mine to shame.
Be careful hanging heavy stuff from the LNA. It is very easy to crack the surface mount capacitors if the PCB is stressed. If that happens you will lose a lot.
The R/A BNC is a bit dodgy at GHz but I can't see that losing the 20dB that's missing.

30dB = 2 of the existing ones cascaded but I was just working out what you'd need to overcome the cable loss.
 
Vipersan

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IP9000HD +
TD110 Dish and TD88 Dish in Tandem
66°East to 60°West.
AZbox PrmHD + OpnbxS9HD + Skybox + DrHD F15
2x VboxII AZ-EL
2 m+ Alcoa PF + BSC421 C-Band lnbf...
+SS2/TwHnS2-3200 pci/TBS6925 pci
1.5 Fortec Star -Gbox - HtoH Ku/Ka/C
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Looks like I need something like what this guy uses ?
 
Vipersan

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IP9000HD +
TD110 Dish and TD88 Dish in Tandem
66°East to 60°West.
AZbox PrmHD + OpnbxS9HD + Skybox + DrHD F15
2x VboxII AZ-EL
2 m+ Alcoa PF + BSC421 C-Band lnbf...
+SS2/TwHnS2-3200 pci/TBS6925 pci
1.5 Fortec Star -Gbox - HtoH Ku/Ka/C
My Location
UK
.
s-band said:
Helical puts mine to shame.
Be careful hanging heavy stuff from the LNA. It is very easy to crack the surface mount capacitors if the PCB is stressed. If that happens you will lose a lot.
The R/A BNC is a bit dodgy at GHz but I can't see that losing the 20dB that's missing.

30dB = 2 of the existing ones cascaded but I was just working out what you'd need to overcome the cable loss.
Click to expand...
..Then of course I have the same cascade config indoors ...reducing again RG58 to BNC ...to SMA ...DSCF0006.JPG
 
Vipersan

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IP9000HD +
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66°East to 60°West.
AZbox PrmHD + OpnbxS9HD + Skybox + DrHD F15
2x VboxII AZ-EL
2 m+ Alcoa PF + BSC421 C-Band lnbf...
+SS2/TwHnS2-3200 pci/TBS6925 pci
1.5 Fortec Star -Gbox - HtoH Ku/Ka/C
My Location
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Ffff ing rain stopped play here ...
A lot of work gone into this project ...
I do hope I eventually solve the problems.
cest la vie.
 
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