[TenTec] OT: Indoor antenna

[Rsoifer at aol.com]

Jerry writes:
 
There is another school of thought that when those preferred lengths  
don't fit the premises or the wire on hand, is that the preferred length  
is the length that fits between the supports and the preferred feed line  
length is the length that fits from the antenna to the tuner in the  
shack. This can demand the tuner handle more obnoxious loads. This  
school believes tough tuning and being on the air is better than being  
quite bemoaning the preferred antenna won't fit the space  available.

Depending upon the situation, I agree with that school.   A practical 
example:
 
A couple of years ago, my wife and I rented a second home in the Texas hill 
 country.  It was in a no-antenna subdivision, but had 8 acres of property  
with quite a few trees.  I used an Outbacker for 6-30 meters, but it wasn't 
 very effective on the lower bands, even with the radials I put down.  So,  
with the help of a friend, I strung up an end-fed random wire.   
Unfortunately, the trees weren't very tall, so it was only 15-20 feet  high.  It was 
about 90 feet long because that's how much wire was on the  spool I had, and 
the orientation was "as far much from the house as  possible."
 
An MFJ tuner (962D) loaded it up to a 1:1 SWR at the transmitter, and with  
100 watts it worked the world on 40 and 80 CW.  At that low height, the  
free-space pattern didn't matter.  Most of the RF went straight up!   Yes, the 
trees absorbed some energy, but they also kept the neighbors from  
bothering me about either antenna because they weren't very visible from the  road.  
A good trade-off, IMHO.
 
73 Ray W2RS
 
 
 
 

 
 
In a message dated 11/29/2010 5:29:11 P.M. GMT Standard Time,  
geraldj at weather.net writes:

There  have been such tables since antennas began. Certain lengths of the 
top and  the feed are easier to feed being closer to resonance at a high 
or low  impedance point at the transmitter end of the feed. Often the 
feed plus  half the flat top length comes close to any multiple of a 
quarter wave.  When an even multiple the feed Z is high, when an odd 
multiple the feed Z  is low.

There is another school of thought that when those preferred  lengths 
don't fit the premises or the wire on hand, is that the preferred  length 
is the length that fits between the supports and the preferred feed  line 
length is the length that fits from the antenna to the tuner in the  
shack. This can demand the tuner handle more obnoxious loads. This  
school believes tough tuning and being on the air is better than being  
quite bemoaning the preferred antenna won't fit the space  available.

I notice in MFJ automatic tuner manuals that they don't like  antennas 
that present a high impedance resonant condition at the tuner.  Which 
means their tuners may be limited on voltage handling  capability.

When a wire gets to be several wavelengths long or longer,  the effects 
of a resonant length are much smaller because the part near  the feed 
radiates and there is less current at the open end to be  reflected. The 
wire acts like a traveling wave antenna rather than a  standing wave 
antenna. Many computation techniques, from days of old and  computers 
neglect that change in current from radiation and give erroneous  results 
on long wire antennas. In feed Z and Z vs frequency and the  radiation 
pattern.

But one might need to be more careful about the  length and orientation 
of a long wire if one wishes to work in a certain  direction. Like Europe 
from the USA because there are more DXCC countries  in that direction. 
Then its important to use a NEC based antenna analyzer  to learn the true 
current distribution and radiation  pattern.

Otherwise what you can put up will allow making contacts,  which is often 
a better situation that not being on the air for lack of an  antenna.

73, Jerry, K0CQ

On 11/29/2010 7:29 AM, kf6e at mail.com  wrote:
> Here's a link to an article listing the best lengths to use for  a random 
wire antenna:
>
>
>    http://www.hamuniverse.com/randomwireantennalengths.html
>
> I  didn't measure mine; I just strung up some wire.  I suspect you will 
have  better results if you use one of the lengths suggested in the  article.
>
>
>
> 73,
> Frank
>  KF6E
>
>
>
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