[amsat-bb] New Duplexer and AO-85

[Jerry Buxton]

Hello Loon,

The difficulty you are experiencing in trying to access AO-85 is real,
but it is not because of the U/V configuration.  The UHF uplink takes
some getting used to because of the greater Doppler effect and certainly
full duplex is what you will want to use in order to be sure that you
are on frequency and being heard.  The VHF downlink is very strong and
can be received even with an omni antenna, and in fact Tuesday afternoon
I was receiving it loud and clear with my Arrow antenna pointed toward
the ground as I rested the antenna while I made some notes on my
testing.  In addition most users have found that the uplink receiver
frequency is about 5 to 10 kHz below the expected 435.180 MHz, most
likely due to the warmer temperatures than we modeled and tuned the
receiver for.

We have, since shortly after launch, been aware of reports of a lack of
sensitivity on the receiver (uplink) for AO-85 and we have been testing
that and investigating scenarios for a cause or causes.  That is why
AO-85 has not been officially commissioned yet.  You recall that we
talked the other night on AO-85, I was testing with various power levels
and that is why I asked about your setup and experience as well, to add
it to our knowledge base.

We have indeed identified some things with the help of the Fox-1Cliff
flight antenna configuration as a comparison, and are making changes to
Fox-1C and Fox-1D that should improve their receive sensitivity and
CTCSS detection.  We will characterize their receivers (and
transmitters) frequency change for the higher temperature range that we
are experiencing on orbit so that they should be much closer to the
intended numbers.  Once we have determined and addressed the causes that
we find you will find more specific information about it in the Nov/Dec
AMSAT Journal.  I am writing about all of the post-launch AO-85
commissioning and testing activities, in detail.  Some of the details
will be released in other AMSAT news outlets as well.

Thank you for posting your experience.  It helps us to improve.

Jerry Buxton, NØJY

On 10/28/2015 00:06, W3MAT . wrote:
> I received my duplexer through UPS yesterday and just gave it try on the
> 03:20 UTC pass of AO-85.  It seems to be performing well, and I did make
> contacts with K3NG and AD2KA.
>
> I had, and continue to have, extreme difficulty with getting into AO-85
> with just the HT's and Arrow antenna, and thought maybe it was because 2
> meter receive and 435 up are 90 degrees to each other on the antenna's
> boom.  I have had success working AO-85 with the Elk antenna and the Icom
> 2800 (transmits wide only), but *only* with the radios maximum 20 watts
> output on UHF, and even then it can be very difficult.  I thought using the
> duplexer, HT's with *narrow* band, and the Elk antenna may be the ticket.
> I thought wrong.  This was just as bad, or as difficult, as trying to get
> in with the Arrow antenna. In my opinion, AO-85 is certainly not every hand
> held radio and Arrow antenna operators easy to work satellite, like posted
> on a YouTube video prior to its launch.  I'm not a big fan of the U/V set
> up for those of us that work hand held set ups.  First it was very
> difficult to find the correct uplink frequencies in its early stages, and
> now that they have been posted and corrected in radio programming, its
> still difficult to know just when to switch for doppler, especially when
> its almost impossible to get into in the first place.  I don't have multi
> element, circular polarized antennas mounted on an azimuth/elevation rotor
> connected to computer driven tracking and radio control software constantly
> adjusting frequency, azimuth, and elevation, nor am I capable of
> transmitting 50 watts of power on the uplink.  I use simple, low power
> equipment (normally only 5 watts) capable of no more than 20 watts of power
> (Icom 2800). AO-85's FM performance certainly does not compete with the
> current SO-50, or the now gone AO-51 and AO-27 birds (rest their souls).
>
> Have a good night,
>
> W3MAT
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