[amsat-bb] Re: Arrow antenna reconfiguration results - UPDATE
Edward Cole
kl7uw at acsalaska.net
Sat Sep 26 09:19:48 PDT 2009
Folks,
I think you are focusing only on transmitting loss and have
overlooked the impact that loss has on noise figure. If your HT has
a low NF (doubtful) adding 3-dB loss in Rx will raise the NF 3-dB
higher. The actual loss of sensitivity could be more than that.
Filter's size determines efficiency and insertion loss. The tiny
diplexer in the Arrow is a compromise between performance and
size. I have a Comet 416B and even it has some loss about 47w out
for 50w in. But that is not anywhere near 3-dB. I use mine to
connect my dual-band vertical to my FT-847 which has separate
connectors for 2m and 70cm. I used this antenna to contact the ISS a
few years ago (worked well because the ISS never rises above 11-deg.
elevation, here).
But I do not use if for SSB or other weak-signal use.
Ed - KL7UW
At 02:26 AM 9/26/2009, Jeff Yanko wrote:
>Hi Joe and all,
>
>I doubt if the Arrow diplexer has 20dB of loss. If it did, we'd never
>receive a signal! :)
>
>I believe somebody here on the -bb will be performing a test on the Arrow
>diplexer using a vector/network analyzer. It will be interesting to say the
>least. There were preliminary reports saying the device had a loss anywhere
>from 2.65 to 2.80dB. That's close enough to 3dB which is technically half
>power loss. Add the loss of a short piece of coax and it will certainly be
>pushed over the 3dB line.
>
>If I recall correctly, cross polarity is also a 3dB loss. I have noticed
>that when I rotate the antenna I might get a stronger downlink but I never
>lose it when I rotate it back. Before, when I would do that it would drop
>once I rotated in either direction from the peak signal. Basically what is
>going on is the lossy device is removed and replaced with a more efficient
>one, that extra net gain you just boosted now shows how the system on the
>antenna side of the diplexer is truly performing.
>
>I don't have an antenna analysis program to perform a test, but what does a
>7 element 440 yagi pattern look like and what is its overall gain?
>
>What we need to do is break down the antenna configuration into 3 segments,
>see what their losses and gains are then combine them for the overall
>figure. The 3 segment would be the antenna, the diplexer and the coax.
>Each one will be tested individually to give an accurate number for each.
>
>
>73,
>
>
>Jeff WB3JFS
>----- Original Message -----
>From: "Joe" <nss at mwt.net>
>To: "Gary "Joe" Mayfield" <gary_mayfield at hotmail.com>
>Cc: "'AMSAT-BB'" <amsat-bb at amsat.org>
>Sent: Friday, September 25, 2009 6:42 PM
>Subject: [amsat-bb] Re: Arrow antenna reconfiguration results - UPDATE
>
>
> > as in the texts below, there is something else going on here.
> >
> > That Diplexor can not be all that bad. two reasons.
> >
> > How many db down is the front to side of that antenna?
> >
> > and I can not imaging someone would sell a diplexor that has greater
> > than 20 db of losses.
> >
> > because of the statement that how criticalpolarity was with the
> > original, and now the antenna has to be nearly 90 degrees cross
> > polarized to make it drop out uhh
> >
> > that close to 30 db,
> >
> > at least 20,,
> >
> > something else is going on here
> >
> > Gary "Joe" Mayfield wrote:
> >
> >>>
> >>>Another issue I came across was how wide the beamwidth is of the Arrow
> >>>Antenna between the Arrow diplexer and the new diplexer. I was wondering
> >>>
> >>>
> >>if
> >>
> >>
> >>>this was going to happen and it did. The reason that this happened was
> >>>
> >>>
> >>with
> >>
> >>
> >>>the old diplexer, the signal attenuated so much that you had to be
> >>>pointed
> >>>right smack dab on the bird, a few degrees off and you lost the signal.
> >>>Now, with the new diplexer, you can point the beam in the general
> >>>
> >>>
> >>direction
> >>
> >>
> >>>and still copy the bird. In most cases I had to turn the beam 90 degrees
> >>>before I completely lost the downlink! Twisting the antenna to make
> >>>polarization changes makes absolutely no difference now. This also
> >>>attributes to the fact that now I'm copying the entire pass without
> >>>
> >>>
> >>dropouts
> >>
> >>
> >>>or fades. Makes sense. What I've regained over the lossy diplexer makes
> >>>
> >>>
> >>up
> >>
> >>
> >>>for any polarization differences, etc. for a better copiable signal.
> >>>
> >>>Next weekend I will have to try more passes and get a feel of how much
> >>>
> >>>
> >>this
> >>
> >>
> >>>system has changed.
> >>>
> >>>
> >>>73,
> >>>
> >>>Jeff WB3JFS
> >>>Las Vegas, NV
> >>>DM26
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>_______________________________________________
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> >>
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> > _______________________________________________
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>
>_______________________________________________
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73, Ed - KL7UW, WD2XSH/45
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