[TowerTalk] More on Array's from N0AH

[Pete Smith]

At 05:43 PM 8/9/00 EDT, Dinsterdog@aol.com wrote:
...
>I did hear from a few ops who had parasitic arrays using voltage fed systems 
>and they only get 10-12 db F/B-, tops- Pete, N4ZR I think stated he was 
>getting around 4 db F/B...... so if you are going to put up an array, you 
>might want to sit down and go with a current fed system- you will improve 
>your chances for a better F/B and perhaps get up to  20-25 F/B..........it 
>might cost a bit more as system to do it, but man- what's a dB worth eh?

That wasn't me ... mine models 15-30 dB MINIMUM SWR, depending on frequency
... ther is a high-angle notch that bring's closer-in stations down as much
as 30-40 dB. 
>
>Pete, N4ZR, posted some great notes on his parasitic array on Tower Talk 
>recently-He mentioned the possible disadvantages of having to dump power 
>using a Collins system vs his parasitic array set up-  a good point, 
>but............
>
>What's the difference of dumping power into a dummy load due to resonant 
>points vs having it reflected back into the rig as measured with higher SWR 
>with other types of systems??

Because it isn't, in fact, lost in the rig, as long as the rig's output
system is capable of a match; that's what a conjugate match is all about,
as I understand it.  The only issues in that case are feedline losses,
which are minimal at 80m, and whether the array behaves well off its design
frequency.  
...
>I did consider making my 40 meter array a parasitic system........What you 
>do, is incorporate the feedlines to make the unused dipoles appear to be 
>longer vs the dipole that is in use-  each dipole must have a separate
ground 
>for the system to work- and you need an antenna switch box using DPDT relays 
>so as to keep the grounds isolated on the dipoles you are not using-..by the 
>time I figured out how much this would cost to home brew-  I decided to just 
>keep with Comtek Systems-  They have great instructions and a device that 
>works out of the box- take that MFJ! 
>
>(Parasitic arrays are for the die hard home brewers as I don't know of a
DPDT 
>antenna relay box out there-!!!)

Actually, I stole the cable-less design of the Heath remote coax switch and
replicated it for the shield side.  4 DPDT relays.  Built it in a plastic
weatherproof box.  Total cost including phone cable for the control voltage
was ~80 bux.  Pretty simple project.



73, Pete Smith N4ZR

The World Contest Station Database 
is back up and running at
http://www.qsl.net/n4zr 



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