[AMRadio] Re: new antenna and matchbox a bust.


Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Tue Jan 30 23:32:44 EST 2007


You guys are mixed up.
I had 50 feet each side on the antenna, for 80 meters,
about 65 feet each side would be resonant (roughly), so
I am 15 feet short.
I then had 42 feet of open wire line running down to almost 
ground level, where it went into 2 runs of RG214, each leg
of open wire line was tied to the center conductor of each
coax cable.
It had the shields soldered together, ran through a PVC pipe
with the ground wire and other coax cables, into the basement.
I had 2 connectors on the ends that screwed onto connectors
on the bottom of the cabinet, then two short coax runs to the tuner,
center conductors went to the balanced tuner inputs on the matchbox.
I also tried connecting the cables directly to the matchbox
inputs, without grounding (passed through the open cabinet door).
No difference in how it worked.
The antenna would not tune up using the matchbox on 80 or 40 meters,
best swr was about 4 to 1.
Each leg of coax was about 15 feet long.


Tuning was around 50, matching was at 100, not enough matching
range I expect.

Could I have made it work, open wire line into the basement,
and/or adding coils or caps to the feedline?
Most likely I could have.

But the matchbox is only good for 275 watts, so I would have
to build a tuner.

On the other hand, connecting the open wire line to the RG214,
center and shield, into the heathkit tuner, seems to work well.

I assume some of the open wire line acts like the missing 15 feet,
and/or carries the bad voltage and current points, not the coax.

Brett
N2DTS

    

 
> As I look at my station, the shields of the few feet of coax 
> that I use to
> connect receiver, transmitter, dow-key, etc they are tied 
> together too! All
> connect to SO-239's, to each other, and the radios chassis 
> are grounded.
> Still unbalanced. Sort of like the antenna described. Apples 
> & bananas but
> the shields are tied together. Coax isn't balanced. Nothing 
> to balance the
> outside shield. Ask the engineering staff of the company that 
> makes coax,"Is
> your coax balanced". I know what the answer will be. But, yes 
> it can be used
> in different ways, you could use it to wire all the 120VAC 
> receptacles in
> your house too.
> 
> Yes, I can see what Brett is trying to do. But why that way. 
> Two runs of
> coax,(weight to be suspended in air, shields tied together at 
> the feed point
> (places for water to get in and ruin coax). Yes, coax can be 
> used in many
> different ways, balun, impedance matching, stubs, etc.
> 
> Don, K4KYV, has a good view as to a fix for the issue. Short 
> antennas and/or
> the wrong length of feed line are asking for problems. Bretts 
> original post
> was for 50 feet of wire on each side of the dipole, feed with 
> 40 feet of
> open wire, then 2 RG214 runs to the johnson tuner. " A worse 
> working thing I
> ever put up."
> 
> Not sure why the switch from open wire to RG214, maybe impedance
> matching,,?? Not sure why just 100 feet of wire trying to get 
> on 80 meters.
> Not impossible, just not as efficient as a full size antenna. 
> That's why the
> suggestion to try a loop. My small city lot will not hold a 
> full size 80
> meter dipole either, tried loading coils but they just arc 
> under any power.
> 
> But it is fun trying,
> 
> Craig,
> 
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