On the current AO-51 S band downlink i notice the "always" present deep fades period during a pass as the S band antenna are Dual band L/S
Open Sleeve (1/4 wave stub) it confirm why my actual linear "WI-FI" stacked yagi perform better than my BBQ grill and dish with circular
Foliage and blocking structures "seems" to have a lesser effect on the yagi than on the circular polarisation antenna. On one QSO with
Clare VE3NPC we noted that theses fades does not happen at the same time at our respective QTH (Ottawa and Sorel-Tracy) making the
following excerpt quite accurate.
>From down to earth web site: http://www.docstoc.com/docs/5178447/down-to-earth
Satellite antennas are usually whips or dipoles. The satellite may slowly tumble, changing the orientation
of the antennas. If you happen to be "off the end" of its antenna, the signal may be too weak to work. Even
if you remain out of its "null", the direction of the linear polarization of the satellite downlink signal
changes relative to you during the pass. If the polarization at some instant happens to be perpendicular to
the polarization of your receiving antenna, there is about a 20dB (100x) signal loss.
I think i will give up in the fades elimination fight 100X signal is nearly impossible to compensate at the receiving side. It is probably
an AO-51 S band limitation. Could be the internet can be a solution if each station can feed their downlink audio on Skype or echolink it
will be possible to listen on theses various downlink sources making possible to have a full pass reception as there will be always one
receiving station out of the fades.
DSTAR on S mode
As the first DSTAR satellite transmission has been made on AO-27 i don't know if the same test can be perform on AO-51. If someone with
DSTAR capabilities is interesting to "test" it on mode V/S just let me know. Why on mode V/S it's because i will have to be in half duplex
as my DSTAR transceiver is a monobander. It is a very "dangerous experiment" here as i will have to manually TR switching between the VHF
antenna and the downconverter line.
But it will be interesting to know if a DSTAR digital signal can passed through AO-51 first? I can try to send a couple of CQ on the last
mode V/S evening pass listening what goes out too?
Luc Leblanc VE2DWE
WAC BASIC CW PHONE SATELLITE
Lots of fun using my old AO-40 (sobsob) gear. Worked Scotty-VE6ITV solid contact. Heard XE2BHL, I think he sorta heard me, near his LOS. Tracking the fast moving AO-51 with a three foot dish by manually is tricky, I have a LVB tracker on order. Thankyou Drew, and the other control ops, this is neat stuff.
73 Bob W7LRD
Dan N8FGV said
> Mark's original point is still a valid one and has not been addressed...
> An amateur-built bent pipe transponder in geosynchronous...
> orbit will be vulnerable to the same sort of unlicensed abuse...
> how exactly do we protect it from this sort of abuse?
This may have been worked to death, but the discussion quickly changed
to '-wish we had a GEO-', then came back around to '-how do we protect-'.
It's not like we are gonna arrive quickly at a perfect solution.
It has always seemed to me that some of the best protection we have had,
is in the simple fact that a moving target is less likely to be of value
or interest to pirates. Our feeble low-powered, fast-moving, doppler-
shifting transponders are not very attractive targets for freeloaders.
Just like internet hackers, they are not interested in a 386 w/4MB ram.
Something like an antique Navy GEO with lots of power is an easy mark.
I'm not suggesting we only deploy obscure low-power LEO birds, but the
higher we push the frequencies, and stay in motion, the less attention
we attract. As much convenience as GEO offers, it would also bring a
following of pirates. A GTO like AO-13 that requires at least scheduled
pointing, would likely not be seen as such an easy mark. A small flock
of APRS birds like BobB mentions would probably not appear of much
interest to pirates either.
No easy answers, but maybe we can avoid making it too easy to hijack.
<- Licensed in 1976, WB5RMG = Alan Sieg * AMSAT#20554 ->
<- http://www.somenet.net * http://wb5rmg.somenet.net ->
<- http://www.linkedin.com/in/alansieg * My 'Day Job' ->
Mark Spencer wrote
>Kind of makes you wonder what would happen if there was a geo stationary
>amateur satellite that was easy to use.?? If pirates will hack military
>satellites then I doubt they would have any qualms about using an
Mark's original point is still a valid one and has not been addressed yet in
this discussion. An amateur-built bent pipe transponder in geosynchronous
orbit will be vulnerable to the same sort of unlicensed abuse that FLTSATCOM
is experiencing, and we amateurs will not have the same ability to prosecute
the offenders that the US military has. If we build such a system, how exactly
do we protect it from this sort of abuse?
Dan Schultz N8FGV
It seems that this subject comes up once or twice every decade. I have
never used anything but a metal cross boom since I joined AMSAT in
1974. Later there were some tests run by Kent Britain, WA5VJB. His
measurements resulted in the following recommendations:
1. Mount the antenna with the tips of the elements as far from the
support boom as possible. Instead of mounting them in a + form, mount
them as an X in relation to the cross boom.
2. Saw off any excess cross boom so that it doesn't extend past the
3. Avoid mounting the boom 1/2 or 1 wavelength from the driven
elements. (I would modify that to multiples of 1/2 wavelength)
4. Run the coax out the metal boom and down the antenna boom. Keep the
turning radius of the coax small but not to the extent of damage to the
I have never detected any bad effects of this arrangement and had
stumbled into this configuration years before Kent published his
findings in the 1993 AMSAT Symposuim Proceedings. I did it to avoid
having the coax from hanging off the rear of the antennas and dragging
on the roof of my house and changing fore/aft balance with ice loads.
Incidentally, I think I recall that Jim, G3RUH was also using this
method. If anyone wants a photo of the antenna setup and contacts me
directly I will send it to him.
Roy -- W0SL