[GreenKeys] Questions on troubleshooting an antenna

[hwhall at compuserve.com]

 It would help to know what band you intend to operate it on before anyone can say if the dimensions are close to being right. What taps you put into the coil (turns between taps) may be useful too.

Insulated wire for radials lying on the ground should be OK.

> When I get near the coil - about a foot away, the background noise picks up ALOT (so do the signals).

You're tuning/detuning the antenna with body capacity. It's probably to be expected. Similarly, the metal gutter is affecting the antenna tuning as well. You may be better off assembling the thing where you expect to use it because any dimensions and tap settings you find will probably need changing when you construct the actual antenna.

> When I tap the coil, weird things happen

Sounds like a poor connection somewhere.

You're seem to be fighting two problems at once, and that is a very bad troubleshooting scenario. One: you don't
know the antenna resonant frequency. Two: you're trying to find a good impedence match with the taps but that is 
probably changing the resonant frequency.

Wayne
WB4OGM


 

 

-----Original Message-----
From: hunybuny <hunybuny at eskimo.com>
To: Green Keys <greenkeys at mailman.qth.net>
Sent: Sat, Jun 26, 2010 4:14 pm
Subject: [GreenKeys] Questions on troubleshooting an antenna


GE OMs;



I threw together an antenna and I'm having some problems with it.

If anyone has any ideas, I'd be delighted to hear them.



First, the set-up:



I put down about 25 radials. They're around 10-15 feet long in a

spoke pattern. They're lying on top of the dirt and I covered

them with paving bricks.



(Did I mess-up bigtime by using insulated wire for the ground radials?)



I pounded a 4' angle iron into the ground.



I wound a 2'coil around a 4" PVC pipe, using #12 insulated copper wire.

There is no gap in the windings othen than what the insulation provides.



The lower 2' of the PVC is strapped to the angle iron using

hose clamps (the coil is above the angle iron).



For testing, I have about 20' of wire coming off the end of

the coil. It's just hanging on the end of the garage roof. The

actual antenna will be about 18' (vertical - because that's all

the space I have).



The coax connector is at the bottom of the PVC. The ground

wire bundle is connected to the case. Should I have also

connected that to the cold water pipe (see symptoms below)?



The station equipment is all grounded to each other, but not to

an earth ground (cold water pipe or something like that).



-- 



Since I don't have a grid dip meter, I turned on the transceiver, put on

headphones, and went to play with the coil taps.



I'm using about 5 watts during testing.



Here's what I'm experiencing:



o When I get near the coil - about a foot away, the background noise

picks up ALOT (so do the signals).



o > When I tap the coil, weird things happen: either I have a 1.0:1 VSWR

or a 3:1 or greater (too high for the rig to report).

When I have the 1.0:1 VSWR, if I go up or down the band, at some arbitrary

point it goes to 3:1. There is no curve (rise or fall) from 1.0:1 to 3:1.



o Question on tapping the coil:



o The "far end" of the coil is connected to the antenna wire.

Should the "near end" be connected to the coax center conductor and

the tap lead - or does it "float" unconnected - and the center of the

coax is only connected to the tap?



There is an aluminum rain leader about 6' away from the coil. At 5W do

you think there is any coupling effect? If there is a chance, I can take

it apart for testing - and R/R it with plastic if it does cause a problem.



I'm bummed-out that I sold my Heathkit grid dip meter. I checked eBay and

there are some but I'm thinking that I can buy one from Alfa for $89, use it

for testing, and then put it on eBay for maybe $60-70. The ~$30 loss

might be worth it just so I don't wind up with a piece of junk that

doesn't work - or worse.



UE,

W6ESE - tony

NNNNZCZC





-- 

Tony J. Podrasky | Even Popeye didn't eat his spinach

                  |    until he absolutely had to.



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