[TowerTalk] Unique Inv L...Help!

[K4SAV]

The problem with end feeding a half wave wire on 160 (in this case 
configured as an L) is that most people who operate 160 soon discover 
that you need an amplifier.  That translates into big voltages at the 
feedpoint.  In this case the feedpoint of the antenna at 1.87 MHz is 
about 7000 ohms.  At 1500 watts that is 4600 volts peak.  So you need a 
large vacuum variable.  You also need a sizable coil. You also need a 
lot of margin to handle high humidity conditions.   All wires inside the 
matching network have to be well insulated to prevent arc-over during 
high humidity.  A little condensation is a major problem.

It's a lot easier at 100 watts.

But why would you go to all this trouble when a shorter antenna would 
work better, plus be much easier to match?  Well there is one reason I 
can think of, maybe if working DX is only a secondary consideration and 
you wanted the antenna primarily for local contacts.  But if that was 
the case, a dipole would beat it.

Jerry, K4SAV

Donald Chester wrote:

>  
>
>>From your description of your LW, you must have about 160 feet of 
>>antenna horizontal and about 100 feet vertical.  That's a total of about 
>>a half wave on 160, a very bad length to try and match.  
>>
>>Jerry, K4SAV
>>    
>>
>
>What is so difficult about trying to match a half wave antenna, fed at one end?  I have done this many times without difficulty, by using a parallel tuned circuit, with one end connected to the ground system and the other end connected to the antenna.  It can be fed by tapping the transmission line a few turns from the bottom end of the coil, or by winding a coupling link at the bottom end of the coil.  With proper placement of the tap or by carefully adjusting the number of turns on the link, a perfect 1:1 match to the transmission line can be achieved.
>
>An alternative is to wire the transmission line in series with the bottom end of the coil, with the shield of the coax connected to the ground system and the centre conductor connected to the bottom end of the coil. This forms a simple L-network. A perfect match can be had by adjusting the number of turns on the coil along with the setting of the variable resonating capacitor.
>
>Don, k4kyv
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> 
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