Linear polarization for Uplink

dl4eax · Nov 20th 2018

Hello,

I stumbled across a reasonably priced WLAN directional antenna.

https://www.tp-link.com/de/pro...cat-5691_TL-ANT2424B.html

According to the manufacturer, it has 24 dBi gain and is vertically polarized.

What would happen (except 3 dB loss due to RHCP) if this antenna would be used for the uplink?

73 Michael - DL4EAX

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Hallo,

ich bin über eine preisgünstige WLAN Richtantenne gestolpert.

https://www.tp-link.com/de/pro…cat-5691_TL-ANT2424B.html

Laut Hersteller hat sie 24 dBi Gewinn und ist vertikal polarisiert.

Was würde (außer 3 dB Verlust gegenüber RHCP) passieren, wenn man diese Antenne für den Uplink nutzen würde?

73,

Michael - DL4EAX

DH2VA · Nov 20th 2018

Maybe nothing except for the polarization mismatch loss. But as these antennas are not rated for high (>=10W?) TX levels, you might run into problems here. This needs to be carefully tested, best with a circulator to prevent bad things from firing back into your PA.

g7iii · Nov 20th 2018

I checked the specs on this particular model According to Farnell (Hit the first link I found..),and that particular model is rated to 100 Watts, But as Achim says you want to be cautious to safeguard your nice 2.4GHz PA

dl4eax · Nov 20th 2018

Thanks for your input.

Just for my curiosity, why do we use RHCP for the uplink?

DH2VA · Nov 20th 2018

Because 'horizontal' is referenced to the local system. Linear H in Europe and linear V in Brasil generate the same signal at the satellite. RHCP will always be RHCP when it reaches orbit, no matter where it originates.

For uplink we chose this as this is kind of S-Band standard and space rated antennas are easily available. The same is true when using linear on X-Band downlink (as you might see when checking your TV satellite programme settings). We need both polarisations to decouple the WB and the NB transponder and as the local definition of horizontal/vertical is depending on your location, you need to apply LNB skew, which can be calculated here:

Satlex Az/El/Skew Calculator

oh2aue · Nov 21st 2018

One way to go circular is to scrounge for something like this:

https://www.ebay.com/sch/i.htm…c+dish+reflector&_sacat=0

...and build e.g. a 90 degree, 3dB quadrature hybrid from coax or design a PCB version.

pe1chl · Nov 21st 2018

Nicest would be a project to construct a 13cm feed that can somehow fit around a satellite LNB. My LNB (and I think most of them) has a feedhorn diameter of 50mm which is a bit large to fit 13cm feeds.... but maybe someone has an innovative idea?

dl4eax · Nov 21st 2018

Quote from DH2VA

Because 'horizontal' is referenced to the local system. Linear H in Europe and linear V in Brasil generate the same signal at the satellite. RHCP will always be RHCP when it reaches orbit, no matter where it originates.

For uplink we chose this as this is kind of S-Band standard and space rated antennas are easily available. The same is true when using linear on X-Band downlink (as you might see when checking your TV satellite programme settings). We need both polarisations to decouple the WB and the NB transponder and as the local definition of horizontal/vertical is depending on your location, you need to apply LNB skew, which can be calculated here:

Satlex Az/El/Skew Calculator

Thanks a lot for this excellent explanation.

DB8TF · Nov 21st 2018

i read somewhere that linear polarization could cause fading of the signal when it passes through the atmoshere, i don't know if thats true...

vy 73

DB8TF

DH2VA · Nov 21st 2018

Maybe you mean Faraday rotation. A linear radio signal will rotate its plane when passing the ionosphere. However, if the receiving antenna is RHCP (as it is for Phase-4A), this has no influence on the overall radio link, even if the transmitter is using linear (you just lose 3dB). If you receive linear as well, then of course any linear mismatch will cause 'fading'..

DB8TF · Nov 22nd 2018

thanks for the good explanation.

i will compare my andrew t2400 linear polarized Wlan grid 24db antenna to a 90cm dish with lhcp 4 turn helical when the sat is released for ham use.

73 de db8tf

DH2VA · Nov 22nd 2018

I am not quite sure about your setup (maybe I misunderstood, my apologies!), but if you use the Andrew T2400 Reflector with a LHCP feed, you will still get a linear signal.

The reason is the large spacing of the reflector gaps in one direction. When used without mods, this reflector will only reflect one polarisation plane and be transparent for the other. If you want to use this reflector for circular polarisation, you have to line it with a mesh which has a mesh opening of < lambda/10 (so less than 1.3cm) (rule of thumb).

DB8TF · Nov 22nd 2018

My Setup is one 90cm dish with 4 turn LHCP helical feed for TX Uplink and

a 130cm dish with octagon PLL LNB for vertical linear RX.

At first i thought the Wlan grid antenna should also work satisfying as Uplink

antenna but after i read About the Problem with the linear polarization i build the dish with the helical feed.

So i will compare the Wlan grid dish with the helical feed dish as soon as we can use the satellite.

vy73

DB8Tf

g7iii · Nov 22nd 2018

Hi DB8TF,

Along with my planned ranging and timing experiments, I hope to be doing something similar, having discovered just how many potential feeds I have in the 'junk box'. I'm also hoping to be comparing the linear polarisation loss in conjunction with my local radio club who have a 2.4GHz TX and Linear Polarised YAGI (they just need a new Crystal...)

It will be very interesting to characterise just how low we can go with regards to both uplink and downlink budgets. Just how small and really portable a station can we build. I have some 45cmx35cm, can acquire 60cm, and have 90 and 110cm dishes, so fully intend to test them all. A 16db gain helix is another option that I hope to test (comparing that to the LP YAGI should show up the LP loss)

(And any that don't work can be used for other projects, such as a Solar Radio Telescope, Or terrestrial use!)

73s

Iain

I8LYL former I0LYL · Nov 22nd 2018

Which position would you choose between these two?

ik4idy · Nov 22nd 2018

Lucio, I remember an article (may be I8CVS RIP), about this argument. He said that "the position of the LHCP feeder is with the corresponding focus, on the plate reflector of the helix ant". The right place may be # 2, and is more simple to manage, for the installation.

In my opinion the difference in gain between the two configuration are irrelevant, but only an istruments can get punctual measure about it.

Regards.

DB8TF · Nov 22nd 2018

i mounted the reflector of the helix on the usual plastic lnb holder on the outer side of the holder facing away from the dish.

But those 10mm shouldn't really make a big difference in gain.

VY73

DB8TF

DB8TF · Nov 22nd 2018

Here you see how i mounted the helical.

The right angle was adjusted after this picture was taken.

Here is a link to a Wimo dish feed and this one is mounted like a standard LNB.

http://www.dd1us.de/Downloads/…er%202400%20MHz%201v1.pdf

Vy73

DB8TF

oe7dbh · Sep 1st 2020

Good antenna for SSB-CW 2,4GHz UPlink.....

https://www.ebay.co.uk/itm/Ant…68e6394ffffcd20%7Ciid%3A1

[Blocked Image: https://i.ebayimg.com/images/g/TbQAAOSw6ZRdZt7z/s-l500.jpg]

DD0KP · Sep 1st 2020

Darko, you find this cheaper here:

https://www.wlan-shop24.de/alf…t-wlan-grid-antenne-24dbi

Linear polarization for Uplink

dl4eax Nov 20th 2018

DB2OS Mar 30th 2019

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