[amsat-bb] Re: 3/4 Wave Vertical Omni

[Bob Bruninga <bruninga@xxxxxxxxxxxxx>]

Sorry.  One-more-post on this subject.   Now I have combined both the 3/4
and 1/4 wave plots onto the same graph, so that the difference is easier
to see.  Now does anyone want to build a model turnstyle, lindenblad or
eggbeater scaled from 435 to 1575 to run for comparison?

On Mon, 17 Jul 2000, Bob Bruninga wrote:

> Last week I posted the results of a 435 MHz 3/4 wave vertical whip
> satellite antenna (2m 20" whip) on a scale model car roof.  Last night I 
> re-ran the test using a standard 1/4 wave vertical so I could get a
> benchmark for comparison.
> 
> The 1/4 wave did have a better pattern at low angles down to about 10
> deg, but the 3/4 outperformed it everywhere above 27 deg by 3 to 4 dB or
> more.  Since the satellite is closer there too, that is why this
> antenna does well for mobile satellite reception.  AND it is dual band
> for the 2m uplink as well.  See the updated plot (side-by-side) on the WEB
> page below.
> 
> On Wed, 12 Jul 2000, Bob Bruninga wrote:
> 
> > For the mobile Satellite operator looking for an Omni, I finally did a
> > real-world antenna plot of a 3/4 wave 435 Mhz WHip over a car roof
> > to see how well it matches the EZNEC predictions.  The results confirm the
> > almost 8 dBi gain from about 30 to 80 degrees elevation:
> > 
> > See near bottom of:   http://web.usna.navy.mil/~bruninga/astars.html
> > 
> > I did this by building a 1575 MHz scale model of both the antenna and a
> > miniature car roof and connecting them to a GPS receiver.  Then ran the
> > GPS all  night with my SIGPLOT.BAS program that then plots the GPS signal
> > strength of all satellites for many hours from ALL azimuths and ALL
> > elevation angles.  THus you get a calibrated signal source over all the
> > sky and get a REAL plot of the actual antenna pattern.
> > 
> > Tonight I will change the model to do a simple 1/4 wave vertical to see
> > how well it fills in the low angle stuff below 30 degrees.  BUT I doubt it
> > will do any good for mobile satellite work, because:
> > 
> >   1) The 1/4 will only have about 5 dBi (3 dB worse than the 3/4)
> >   2) The satellites will be further away for another 3 to 6 dB loss
> > 
> > Combined, the loss is 6 to 9 dB compared to the 3/4 wave and there is just
> > not enough signal from the PACSATS to be heard by any omni reliably at
> > that level. 
> > 
> > Probably the only way to fill in the low angle is to go to a high
> > gain vertical (to get 9 dBi below 30 deg) and switch between the two.
> > during each pass.  But given the complexity, I just stick with the 3/4
> > wave (20" vertical) since it is inherrently dual band being an excellent
> > 1/4 wave 2 meter antenna as well for the uplink.  THus, your 2meter 20"
> > whip in the center of your car roof will serve very well as a mobile
> > satellite antenna whenever the satellite is above 30 degrees, and most
> > mobiles cant see much below 30 degrees anyway due to trees.. (back east
> > anyway...)...
> > 
> > For APRS messaging, though, this is all you need, since the APRS SAT/Igate
> > will only send your traffic to your mobile when you are within that cone
> > of coverage, (APRS always knows where everyone is) and conversly, your 2m
> > mobile uplink has a 18 dB advantage so your outgoing traffic can get into
> > the satellite at ANY elevation angle...
> > 
> > To see the entire discussion of mobile satellite operation including the
> > discussion of these antenna plots see:
> > 
> >   http://web.usna.navy.mil/~bruninga/astars.html
> > 
> > Come join us on SUNSAT and any other satellite that may have UI
> > digipeating enabled...
> > 
> > de WB4APR, Bob
> > 
> > 
> > 
> > ---
> > You are currently subscribed to htaprs as: BRUNINGA@NADN.NAVY.MIL
> > To unsubscribe send a blank email to leave-htaprs-3559T@lists.tapr.org
> > 
> > 
> 
> APRSdos REPLY/COMMENT:
> 
> Reply mail addr:   wb4apr@amsat.org   
> US mail address:   115 old Farm Ct, Glen Burnie, MD 21060
> See DAYTON97 HISTORY:    http://web.usna.navy.mil/~bruninga/dayton.html
> See Maryland APRS LIVE:  http://web.usna.navy.mil/~bruninga/aprs.html
> See GPS on ANY radio:    http://www.tapr.org/tapr/html/mic-e.html
> 
> 
> ---
> You are currently subscribed to aprssig as: bruninga@nadn.navy.mil
> To unsubscribe send a blank email to leave-aprssig-10461M@lists.tapr.org
> Questions regarding the SIG go to the SIG administrator: wa1lou@tapr.org
> 
> 

APRSdos REPLY/COMMENT:

Reply mail addr:   wb4apr@amsat.org   
US mail address:   115 old Farm Ct, Glen Burnie, MD 21060
See DAYTON97 HISTORY:    http://web.usna.navy.mil/~bruninga/dayton.html
See Maryland APRS LIVE:  http://web.usna.navy.mil/~bruninga/aprs.html
See GPS on ANY radio:    http://www.tapr.org/tapr/html/mic-e.html

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