[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: S-Band Antenna Comparisons, etc.



Cliff, you are incorrect.  The linear polarisation is determined by the 
"Dipole" Element in the center and not by the direction of the grid.

The reflector has nothing to do with it.

Dave
At 14:17 1/7/01 -0500, you wrote:
>Cliff,
>
>The bar-b-que style of dish that Jerry is using can, I believe, only
>support linear polarization, in the direction of the bar-b-que rods.  It
>could support any polarization, however, if it was lined with metal
>screen.  That shouldn't be hard to do, by the way.
>
>
>Clifford Buttschardt wrote:
> >
> > Jerry, it is not clear to me if the dish antenna is linear or were you
> > able to compare both with RHC?  Truthfully, I have had a devil of a time
> > with the small dish and about ready to go to the helix regardless of gain.
> > Cliff K7RR
> >
> > On Sun, 7 Jan 2001, Bob Snyder wrote:
> >
> > > I did some quick helix antenna runs using NEC.  These runs use an
> > > infinite backplane, so they are only approximations, but may be useful
> > > for comparisons.  The 7-turn helix you describe (with 44 mm dia. i.e.
> > > 1.106 wavelength circumference; and 37 mm spacing, i.e. 15 degree pitch)
> > > has 11.9 dBi gain.  The 16-turn helix (I assume it is built to nominal 1
> > > wavelength circumference and 12 deg pitch) has 14.8 dBi gain.  The
> > > parabolic reflector on the 7-turner may be enhancing it's gain somewhat.
> > >
> > > 73,
> > > Bob KD1VV
> > >
> > >
> > > K5OE@aol.com wrote:
> > > >
> > > > I did some antenna experiments this AM when AO-40 came over my 
> horizon (1200
> > > > utc, MA=4.5).  Those window-shopping the various options may be 
> interested in
> > > > these observations.  What can be determined from current 
> observations with
> > > > respect to the final satellite configuration is subject to considerable
> > > > speculation:  these observations were taken with a squint of 
> greater than 140
> > > > degrees on AO-40's low gain antenna at low power.  What one can 
> extrapolate
> > > > to a favorable orbit, orientation, and squint, plus the change to the
> > > > high-gain antenna and the high power amplifier, is clearly just 
> speculative
> > > > at this time.
> > > >
> > > > In a quasi-designed-experiment, I used several antenna and 
> downconverter
> > > > combinations using a Drake 2880 and my Yaesu FT-100 as a receiver, and
> > > > recorded the results enumerated below.  One unknown in my 
> measurement system
> > > > is the accuracy of the meter on the Yaesu.  I have previously 
> "calibrated" it
> > > > using a variable power 2 m FM signal, but only in the crudest sense 
> (after
> > > > all, I am an "amateur").
> > > >
> > > > 1.  The 24 dBi dish antenna (bar-b-que style, borrowed from KK5DO), 
> does
> > > > indeed offer a 12 dBi gain (2 full S-units) over my 16-turn helix 
> (estimated
> > > > at 12 dBi).  This was consistent with-and-without a preamp.  Note 
> to those
> > > > without automatic antenna tracking:  this antenna's beamwidth was 
> so narrow,
> > > > that 12 dB of signal was lost in +/- 5 degrees of movement.
> > > >
> > > > 2.  The Conifer preamp does NOT provide the rated 10 dBi gain, but 
> appears
> > > > much closer to 6 dBi (when close-coupled to the Drake).  It was 
> difficult to
> > > > judge the impact on S/N ratio with this setup, but I believe it was
> > > > substantially improved, even though the noise floor is up 6 dB as well.
> > > >
> > > > 3.  At MA=18, I could detect the beacon with a coffee can and 
> preamp/Drake
> > > > combination, but it did not move the S-meter.  I could not hear the 
> beacon
> > > > without the preamp.
> > > >
> > > > 4.  Using an unmodified Drake 2880, I could not detect the beacon 
> at 121.3xx
> > > > MHz with both the dish and the preamp in line.  This surprised 
> me.  If I have
> > > > the frequency conversion for the stock crystal wrong, please let me 
> know.
> > > >
> > > > 5.  In comparing the 16-turn helix I have been using for a month to 
> a much
> > > > smaller one built for me by my friend Oleg, RV3TH, the two were fairly
> > > > comparable.  The interesting thing is that helix is only 
> 7-turns!   Oleg's
> > > > helix employs some non-conventional metrics:  the diameter is about 
> 44 mm and
> > > > the turns spacing is about 37 mm, plus it uses a 100 mm semi-parabolic
> > > > reflector.  I will report more on this after I completely 
> reverse-engineer it
> > > > :-)
> > > >
> > > > For those interested in seeing the hardware, I have put a few 
> pictures of
> > > > this equipment at:
> > > > http://home.swbell.net/k5oe
> > > >
> > > > 73,
> > > > Jerry, K5OE
> > > >
> > > > ----
> > > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > > > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> > > ----
> > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> > >
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org


----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home