RE: [amsat-bb] Effects of Strong Uplink Signals on AO-40 Beacon andPassband

[Alberto Iglesias Darriba <ea1dld@xxxxxxxx>]

Dear Charles, thanks very much for your interesting research activities on
AO-40.

I would appretiate if you can tell us the antenna and power used by G3WDG
and I8CVS in their tests.

Well Charles, thank you for the information. 73 to you and DJ1KM, I8CVS.

Al I. Darriba. XE1RDV - EA1DLD.
mailto:xe1rdv@amsat.org
http://www.qsl.net/xe1rdv
http://www.findu.com/cgi-bin/find.cgi?xe1rdv


----- Original Message -----
From: Charles Suckling <charles.suckling@ntlworld.com>
To: <amsat-bb@AMSAT.Org>
Sent: Saturday, April 06, 2002 1:14 PM
Subject: [amsat-bb] Effects of Strong Uplink Signals on AO-40 Beacon and
Passband


>
> Effects of Strong Uplink Signals on AO-40 Beacon and Passband
> ===============================================
>
> Introduction
> -----------------
>
> There has been some correspondence recently on the AMSAT-BB concerning the
> effects of strong uplink signals on other users of A0-40.
> In response to this, on 5 April from 1000z for about 45 minutes DJ1KM,
> G3WDG and I8CVS made some tests to determine exactly what effects strong U
> and L uplink signals have on both the beacon and passband signals.
Passband
> activity was fairly quiet at the time, and there were no other "very
> strong" signals active. We hope that these tests did not disturb other
> stations too much!
>
> L-Band Uplink effects on Beacon and U-Band generated passband signals
> --------------------------------------------------------------------------
---------------------------------
>
> The first test was to see how the beacon level was affected by a strong
> uplink signal on L-Band. DJ1KM used his panoramic receiver to monitor the
> beacon, and G3WDG provided the L-Band signal in the form of a steady
> carrier. With the uplink power set to provide a downlink signal equal to
or
> slightly stronger than the beacon, DJ1KM saw the beacon level drop by
> approximately 3dB when the uplink carrier was on. This drop was also
> observed by I8CVS.
>
> The second test looked at the effect of the L-Band uplink on a U-Band
> generated passband signal. I8CVS transmitted on 435 a steady carrier at a
> level to put his downlink signal approximately 10dB below the beacon.
DJ1KM
> and I8CVS both observed the level of this passband signal to drop when the
> L-Band uplink as mentioned before was on, again by about 3dB.
>
> U-Band Uplink effects on Beacon and U-Band / L-Band generated passband
signals
> --------------------------------------------------------------------------
-----------------------------------------------
>
> The third test repeated the above experiments, this time using a U-Band
> uplink provided by I8CVS.
>
> Again a carrier was used, which did not seem to attract the attention of
> Leila and so was not nulled out. The results were similar to those
obtained
> with the L-Band uplink, ie a very strong U-Band uplink can suppress both
> the beacon and other U-Band generated passband signals. The amount of
> suppression of both the beacon and other U-band generated passband signals
> seemed greater than for the L-mode uplink (up to 10dB was observed briefly
> at one point).
>
> The last test involved looking at the effect of a very strong U-Band
uplink
> on a passband signal coming from an L-Band uplink. In this case, the
U-Band
> uplink did NOT affect the level of the passband signal.
>
> I8CVS also transmitted a cw test transmission with deliberate high power.
> For most of the transmission Leila ignored the signal. SSB was then tried,
> and Leila locked on very fast and nulled the signal.
>
> Conclusions
> ------------------
>
> With a U-Band and L-Band uplinks, excessive erp will suppress both other
> U-Band generated passband signals and the beacon. The effects are greater
> for U-Band, justifying the existence of the Leila system for that uplink.
>
> With U-Band uplink, there are probably two causes for the suppression -
agc
> action of the U receiver depressing the levels of other mode U users
> (larger effect) , and power sharing effects in the transponder (smaller
> effect). It is not clear to us why L-Band generated passband signals are
> not affected by U-Band uplink level.
>
> With L-Band uplink, the suppression probably comes only from power sharing
> effects.
>
> Recommendations
> ---------------------------
>
> The use of excessive erp on U-Band and L-Band uplinks reduces the level of
> the beacon and Mode U uplinked passband signals.
>
> If stations operate with only enough uplink erp to generate passband
> signals which are not stronger than 10dB below the level of the beacon,
> then suppression effects caused by one individual user will be very small.
>
> Stations using L-Band should be especially vigilant not to use excessive
> uplink erp - there is no Leila to remind them of their antisocial
> behaviour! Means of adjusting and monitoring transmit power are desirable
> since the erp requirement is a strong function of squint, and what may be
> just OK at 20 degrees will certainly be excessive at 5 degrees.
>
> Stations using cw on U-Band should also take special care, since Leila may
> not be as quick of reminding them that they are too strong, as it does
with
> ssb.
>
>
> 73 de G3WDG, DJ1KM and I8CVS
>
> ----
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