[amsat-bb] ISS packet 70cm weak?

Patrick STODDARD (WD9EWK/VA7EWK) amsat-bb at wd9ewk.net
Sun Dec 18 18:06:37 UTC 2016


If the two Ericsson HTs used on the ISS have the same power output,
70cm signals should be weaker than what we heard on 2m. There
would be higher losses in the coax between the radio and antenna,
along with a higher path loss, using 70cm. I also notice that how
I align my antenna is more important when working the ISS on
437.550 MHz than when it was on 145.825 MHz.

Uplink issues could be similar to what is happening on the ISS.
Transmitter power, coax loss, path loss... they all play a part
in this.

With all of that said, I am able to deal with having to twist my
Elk log periodic more, and also changing frequencies (memory
channels in my HTs) to compensate for Doppler on 437.550 MHz. It
takes a little more work, but for me it isn't much different
than working ISS or the weaker NO-84 digipeater (when active)
on 145.825 MHz. I think the shift to 70cm has been harder for the
home stations that use vertical antennas, and the radios are not
under computer control. Those stations are having a tougher time
coping with the operations on 70cm. Based on some comments I have
received directly and seen in a few online forums, those using
2m/70cm verticals with gain are really struggling. The radiation
patterns of many of those antennas on 70cm just isn't good for
working something up in the sky. Some of those antennas (for those
in the Americas) are also tuned for 440-450 MHz, and perform
poorly below that range.

Not as many gateway stations are listening to 437.550 MHz, but there
are a few using stations with computer control that are able to
track the ISS as it goes across the sky. That has helped to populate
the listing and map on ariss.net, but is not a perfect replacement
for the many other stations that are on 145.825 MHz. Regardless
of the number of gateways listening on 70cm, I'm still having fun
trying different antennas and seeing more stations give ISS packet
on 70cm a try.


Twitter: @WD9EWK

On Sun, Dec 18, 2016 at 1:20 PM, PA3GUO <pa3guo at upcmail.nl> wrote:

> Anyone else finds the signals weak ?
> Uplink as well as downlink?
> Maybe worse in EU compared to other continents?
> Henk

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