Dear Dick / Bob and Lofers,

 

Does the computer calculate the earth losses in the return path from the aerial system to the transmitter? If it would then the earth losses in a T should have been significantly less then the L alternative. There are two separate return currents
(parallel resistance) and each with a smaler physical length (lower R-earth)  in a T system resulting in more ERP if compared to an L system.

 

Greetings and best wishes for a (LF) radio-active 2004 to All.

 

Mike, PC4M (ex PA3BSH)

 

-----Oorspronkelijk bericht-----
Van: [email protected] [mailto:[email protected]] Namens Dick Rollema
Verzonden: maandag 29 december 2003 16:37
Aan: [email protected]
Onderwerp: Re: LF: Re: "T" versus "L"aerial

 

To All from PA0SE

Bob, ZL2AC wrote:

Dick PA0SE,
 
Fine on the test result.  As you stated, the tested T has twice the amount of top loading wire (2x 20 metres) than the L (1x 20 metres).
 
It would be interesting to know if a T is better than an L for constant length top loading i.e. what the difference is if the upwire joins at the end or the middle of the horizontal top wire (theory suggests the T is better as there is minimal horizontally polarised component).
 
Bob,  I cannot answer your question by a practical experiment but used computer simulation instead by means of K6STI's program Antenna Optimizer.

I modeled two antennas with a vertical element of 20m.  One an Inverted L-antenna with a horizontal top load wire of 40m. The other a T-antenna with a top load of 2 x 20m.
Both antennas  without losses, over perfect ground and fed with 1kW.

At a distance of 10km (so well outside the near field region) and over perfect ground both antennas produced a vertically polarised field of 29.9mV/m. The horizontally polarised field was zero; but this is to be expected because over a perfect conducting ground a horizontal field component cannot exist.

73, Dick, PA0SE

Original message:

To: LF-Group

Sent: Sunday, December 28, 2003 3:09 AM

Subject: LF: "T" versus "L"aerial

To All from PA0SE

Further to my e-mail of 26 December I measured the field strength as radiated by the aerial in

Inverted L-configuration. From this I found EMRP = 57 milliwatt.

This confirms the benificial effect of top loading. The T-aerial radiated 140 milliwatt.

So going from a single 20m top load wire for the "L" to 2 x 20m for the "T" resulted in an improvement by a factor 2.46 (3.9dB) in radiated power.

The vertical part of the "T" consisted of an open wire feedline of 11m with the two wires connected in parallel in the attic shack. For the "L" one of the feedline wires was removed. I assume this did not appreciably affect the EMRP.

73, Dick, PA0SE