Re: LF: A question about loops for 136 and 500kHz TX

[Warren Ziegler <wd2xgj@gmail.com>]

Roger,

        Running the conductor along the ground will increase ground losses. 
The late Reg Edwards G4FGQ had a program for calculating loops - Rjeloop or some such, you could see the losses go up and the radiated power go down as the bottom of the loop got closer to the ground.  Reg's Rjeloop program was calibrated to some unspecified ground condition - I found that my losses were less than his program predicted, but I believe that the trend for higher losses at lower elevations was correct.

      If you are running high power there will be considerable voltages from conductor to ground - I have a problem when its raining with the insulation breaking down and catching vegetation on fire. (My loop conductors are RG-11 and RG214 coax). I try to space the cable as far away as possible from trees, leaves etc and run high power (> 1kW) in dry weather which seems to be enough to prevent insulation breakdown.

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73 Warren K2ORS
                WD2XGJ 
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1

On Fri, Aug 13, 2010 at 11:08 AM, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

Having considered the antenna options for my small garden, I'm going to erect a TX loop antenna rather than a Marconi vertical for 136kHz: the earthing issues are removed and it is easier to build a capacitor selection box (to tune and match the loop) than wind a huge loading coil and match it. I've seen some of the webpages dealing with these and understand basically what is needed (large loop area, thick wire, capacitor match-box, dealing with high RF currents, etc). I understand the loop will have directionality and nulls.

My question is this. Is there any reason why the bottom of the loop cannot be laid along the ground rather than elevated a few metres? Most designs show the bottom elevated a bit, but if laid on the soil I could use thick coax or multiple wires for part of the loop so reducing the loop resistance.

Views appreciated, although it may be a case of "suck it and see".

73s
Roger G3XBM

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