[Elecraft] 160m loop experiment a big failure

[goldtr8 at charter.net]

Based on all my research today it is apparent that the loop as put up 
will have to come down.

As Don points out, I dont want to be in the middle of the microwave.   I 
just never thought about this other than the nice layout of trees.

Basically I will be pulling it down and use some of my trees and then 
have to put two poles up for two corners.

Plus it is clear since I want to use it on multiple bands that I will 
have to get a 4:1 current balun.

At least the radio warned me that I was making a microwave by all the RF 
in the shack.

I am not as smart on this stuff as I thought I was, as I did research on 
the loop and length and so on, but never figured the effect on being in 
the middle.

But my dipole works just fine and I will continue to be on the air.

Thanks
Don


~73
Don
KD8NNU


On Sat, Oct 15, 2011 at 2:41 PM, Don Wilhelm wrote:

> Since the loop surrounds your house, you have put the house (and 
> shack) directly into the highest RF Field for that antenna.
>
> If your house provides good shielding - metal roof and a metal mesh 
> shield for the siding, with every piece of metal bonded together, you 
> are going to have a lot of direct RF in the shack just from the 
> antenna field.
>
> How much power are you attempting to run.  You may get away with QRP 
> levels, but at higher power, you should expect problems.
>
> I suggest first doing an RF Emissions Safety study to determine just 
> how much radiation you are getting at the house location, and protect 
> yourself and your family as a first order of business.
> If you cannot move the antenna to another location, perhaps you can 
> get it higher which might help a bit.
>
> I just looked at one of L B Cebik (SK) modeling studies for a 1 
> wavelength diameter horizontal loop, and if it is 0.15 wavelength 
> above the ground (80 feet at 160 meters) the radiation is a maximum at 
> 52 degrees from the plane of the loop.  At lesser heights, the maximum 
> radiation will be closer to perpendicular to the plane of the loop. 
> That does place your shack directly in a high RF Field.
>
> 73,
> Don W3FPR
>
>
>
> On 10/15/2011 12:14 PM, goldtr8 at charter.net wrote:
>> I set up a 160m loop in the yard to try one out from all the great
>> reading I did regarding the antenna.
>>
>> For me I can get it to tune with no problems except the RF in the 
>> shack
>> is terrible.
>>
>> I ran 450 ohm ladder line from the antenna to my balanced line
>> connections on my MFJ 962 d tuner.
>>
>> As soon as I connect the ladder line the RF is bad, basically 
>> everyone
>> states that I sound like I am in a jet airplane.
>>
>> Now there is also a bit more to the story as the loop surrounds the
>> house as that is how the trees are plus the dipole is also very close 
>> to
>> one of the edges on the inside of the loop.
>>
>> So I dont know if the problem is that everything is in the middle of 
>> the
>> loop, or running ladder line into the shack is a bad thing, maybe the
>> tuner internal balun is not the correct one.
>>
>> Bottom line is the K3 was real unhappy with this scenario so the 
>> ladder
>> line is pulled out of the shack and coiled up on the tree next to the
>> loop outside.
>>
>> One thing I have researched this morning is that I need a current 
>> balun
>> and I should have it external to the shack and run coax between it 
>> and
>> the shack.  Also I should have the shield grounded like I do with the
>> dipole to direct ground.
>>
>> So I thought I would share my current failure while I ponder my next
>> move or give up on the loop.   Ok I wont give up, YET!
>>
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