[Hallicrafters] Getting on-the-air question.

[Rich Oliver]

John N. Schwartzberg wrote:
> At 09:46 AM 10/31/2003 -0800, Waldo Magnuson wrote:
> 
>>    First the news:  I got my dipole antenna up (70 ft. up)- I used 
>> RG-8X for the feed line, I got my HT-37 recapped and operating,  and I 
>> just passed the General and Code tests.
> 
> 
> Good for you!
> 
>    And finally,  ARRL and other handbooks say keep the ground wire as 
> short as possible - I'm in the second story with a ground wire maybe 25 
> ft. long.  The books say this could be a 1/2 wave radiator but don't say 
> what to do about it.  Any suggestions - or just connect the ground to 
> everything and go?
> 
> If you are concerned about radiation from a long ground path, try this 
> trick.  Use some old coaxial cable for your ground line.  Couple the 
> center conductor to the braid via a 1 uF 1kV coupling cap on each end, 
> which makes the ground line look like it has no electrical length at 
> HF.  I used this lash-up when I lived in an apartment building many 
> years ago, running some old RG8 this way from the third floor to the 
> basement outside the building.  Worked for me - couldn't sniff an RF off 
> the ground line with a field strength meter.  You might have to adjust 
> the capacitance value depending on length, but I doubt it for 25 feet.
> 
> Good luck!
> 
> John

John,

I am glad you came up with a clean ground but I have serious doubts 
about this "zero length" scheme.  Using the shield of a coaxial line for 
a ground connection is a good idea because its large diameter gives it 
low impedance, but no theory I am familiar with would predict any effect 
from capacitors connected to the inner conductor.  It is not clear to me 
if any other connection is to be made to the inner conductor; if some 
connection results in series resonance at the operating frequency then 
yes, you will get an enhanced ground.  Someone suggested using an 
"active ground" and that is indeed how such a device works.

Waldo,

I did not see any mention of a low-pass filter between the transmitter 
and tuner; such a filter is strongly recommended in any case.  Once the 
filter is installed I suggest that you fire it up as-is to see if you 
have a problem.   Check for interference on your TV and telephones, and 
look to see if any lights on dimmers change intensity with RF.  Also 
check to see if any GFI outlets in your bathroom of kitchen trip off. 
If you have close neighbors they may see such problems even if you 
don't, especially with telephones.  How you deal with this is your 
business; I can only tell you that I think it is best to tell my 
neighbors I'm a Ham and explain what sorts of interference are possible. 
  I make it clear that I do not want any of that going on and make them 
promise to call me if they think they are seeing the effects of 
interference.  By all means keep a good log; one of the many benefits is 
that you can see if you were operating at the time of any suspected 
interference.  Telephones can be particularly troublesome since some 
models are unhappy even with proper transmitter operation, but that 
topic is too deep to delve into here.

If no interference is found then get on the air and talk to us! 
Otherwise, I would suggest either installing a Balun transformer at the 
antenna feed point or switching to balanced feedline.  Ladder line is 
great but common 300 Ohm TV twinlead works fine up to a hundred Watts or 
so, and it is really cheap.  Your feedline length sounds like it is 
close to a half wave on 40 so you should have no trouble matching it 
using the balanced output of your tuner.  Either way you should have 
eliminated most of the source of stray RF by making a proper transition 
from your unbalanced transmitter output to your balanced antenna.  Only 
after doing this does it make sense to get excited about heavy duty 
grounding beyond what is needed for lightning protection.  Do plan on 
disconnecting your antenna during storms, BTW.

Please keep us posted on developments.

73, Rich, KC9GQ