[amsat-bb] Re: Funcube dongle results Jan 16th
howard at howardlong.com
Mon Jan 17 12:01:10 PST 2011
Particularly regarding your attempt to receive the ISS, do you see a
significant increase in noise floor when you connect the antenna at VHF,
potentially 20dB or more?
If so, it may be being overloaded from the sum of VHF signals coming into
the radio. When you use a preamp it almost certainly has a bandpass filter
in it. The filtering on the FCD at VHF is rather wide bandpass with 3dB
cutoffs between about 60MHz and 270MHz. Thus if there's significant pager,
band II FM, or Band III DAB etc traffic the front end gets a bit swamped,
and your noise floor rises.
We're already looking into simple recommended methods of alleviating this.
The first thing is to make sure you're using the 18c firmware as this
implements tighter filtering. I also found that simply using the VHF port of
a V/U di/duplexer worked well in some situations. The best results I found
were with the middle port of a CFX-514 triplexer. If you have close in pager
interference then you'll need something rather tighter. In the UK for
example, we often have pagers at 138 and 153MHz.
At UHF and above, the FCD uses tighter programmable bandpass filters so we
don't tend to experience this at these frequencies.
The front end of the FCD is pretty sensitive, with all units measured and
targeted for 0.15uV for 12dB SINAD on NBFM. But if there are fairly strong
out of band signals, this will inevitably raise the noise floor.
73, Howard G6LVB
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of PA3GUO
Sent: 16 January 2011 21:10
To: amsat-bb at amsat.org
Subject: [amsat-bb] Funcube dongle results Jan 16th
Some more FUNCube dongle results:
(not much new information, just want to share my few hours
time today to spend on the FCD which I really enjoyed)
Using 2x6 elements 145 MHz:
- VO52 USB downlink great, with and without preamp
Using 1x12 elements 435 MHz
- AO51 FM downlink great with preamp, without noisier
- HO68 CW beacon great with preamp, good without
OK. So with the normal antennas the FCD works great.
Time to try thew absolute minumum: Outside in the garden, laptop
plus a simple vertical for 145 MHz; ISS packet: nothing heared/seen.
Was a surprise to me, as ISS is normally extremely strong.
Also tried AO51 FM with just a dipole outside: nothing heared/seen.
Both passes were >80 degrees elevation.
So for now I guess you need either a beam or a preamp.
Then again, the unit is the size of a USB memory stick and
has a range 60MHz -1.7 GHz - no complaints !
Overal I am still very impressed. The dongle connected to my
normal antenna system (beams + pre-amps) gives great results.
Just listened twice to a VO52 pass, and listening in USB was very
comfortable, audio sounds very nice until 0 degrees elevation
Amazing to be able to watch the entire downlink spectrum, and
see a few QSOs in parallel, seeing multiple stations tuning (their
signals going from left ro right and back until they hear themselves).
Of course everyone else had SDR for satellites already :-) For me
this is just amazing. Great work by the FUNCube Dongle team.
We often see discussions on how to get SSB for a few $'s and start
to compare various conventional transceivers. Well, the FCD is surely
an option to reduce cost on the downlink: all mode / all bands.
Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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