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R: L-Uplink on AO-40

Antonio, EA1IW

Following our L1/S AO40 QSO i add this information for you.

The AIRCOM attenuation at 1296 MHz is 14,5 dB / 100 meters
at VSWR = 1

Your 30 meters transmission line attenuation is therefore  4,35 dB
without considering the additional loss due to VSWR.

Actually you dont own a  SWR meter for that frequency and so you
dont know your actual SWR

You cannot solve your problems without the above instrument.

Supposing that your SWR is close to 1 the cable loss  is  4,35 dB
or  2,72 time in power ratio.

If  your RF output power is really 80 W  than the incident power
reaching your antenna connector is 80/2,72 = 29,4 W

Using a good antenna system your 29,5 W are more than adeguate
for a strong signal back  from AO40 uplinking in L1 band  and having
squint angles below 15 degrees.

During our last QSO the squint was very low but your signal was very

If you remember i reduced my power to the level  necessary to balance the
level of your signal and i got your same level with only 2,5 W at my 4 x 23
element yagi array having a theoretical gain of  22 dBi

Now you shoud consider that my antennas are horizontally polarized
and your 4 x 10 turns helix array is RHCP and so in addition you have
the advantage of 3 dB for polarization matching.

I believe that someting is wrong at your antenna side and first of all
you should measure the SWR at the antenna connector or better the
incident power and the reflected power at the antenna connector using
a BIRD 43 model thruline power meter for example and than make the
 SWR calculation by your self.

Having made a QSO with you on L1/S band and supposing that really
your RF power is 80 W pep my opinion is that your antenna is not working
by some reason and you should discover why by measurements.

1) Measure your output power at the 80 W amplifier output connector.

2) Measure the incident power at the antenna connector.

The measurement 1) and 2) allow you to know exactly the real attenuation
of your transmission line and the real output power of your amplifier.

3) Measure the reflected power at the antenna connector.

4) Measure directly or compute the SWR at the antenna connector from
    the above measurements 2) and 3)

5) If the Incident power at the antenna connector is in the range of
    25 W  and the SWR is in the order of 1,2 to 1,5 than your signal level
    should be very loud provided the four helices are very well  and
    correctly  phased.

Since your signal was very weak you have two possibility:

a) Very high SWR ( and you must discover why)

b) Very low SWR (  more difficult because you must discover why your
     antenna is not working )

Suggestions in case b)

Remove the 4 x 10 turns helix array from the mast and replace it with a
single yagi horizontally polarized in the order of 23 elements or 18 dBi
than measure the SWR and make your comparizon.

To put the 80 W amplifier at the antenna actually helps you only by
4,35 dB but you don't solve your problem because if i add 4,35 dB to your
actual signal level i still  receive a weak signal from you in comparizon to
the terrific one you should exibit using about 80 watt  to the actual 4 x 10
turns helix.if correctly functioning.

I hope this help.

73" de i8CVS Domenico

----- Original Message -----
From: Antonio <ingelmo3@wanadoo.es>
To: AMSAT-BB <amsat-bb@AMSAT.Org>
Sent: Saturday, June 22, 2002 11:08 AM
Subject: [amsat-bb] L-Uplink on AO-40

> Hi all,
> I´m trying to be active on L/S mode AO-40.In ten last months I had
> uplink system with a TS70E transceiver giving 10 watts with the UT-10
> internal 1.2Ghz module.Then running 30 meters of coax (AIRCOM) to an
> horizontal Yagui 35 elements.My downlink could be listen but marginally in
> CW and worse in SSB,of course.
> I tried to improve my system with a nice antenna device from WIMO.It`s a
> four 10-turns helix phased array and also bought aaç DL2AM 80watts
> in my shack..,but as before,I have 30m coax between the transceiver and
> antenna.Results are so poor than I´m frustated.
> So,I need some advice.I was thinking to put the amplifier near of the
> antenna,maybe in an special water isolated box in the tower???.
> Solutions??.
> It seems that L uplink on AO-40 is certainly much more difficult that
> thinking previously..Elmer`s advicers??
> 73´s from Antonio (EA1IW)
> AMSAT-EA 259 * AMSAT-UK 5435
> ----
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