[Lowfer] lowfer transmit antenna

[Eric NO3M]

Curious how you determined the efficiency?  N6LF comments in his 630m 
antenna notes that a "small" loop (ie. mag loop) has a theoretical limit 
of 4.2%.

Also, don't forget that you have to account for antenna gain in EIRP 
calculations.  If you really are getting 25% efficiency, and a small 
loop has 4.82 dBi perfect-ground gain which is a factor of approximately 
3 (or you can use gain over real ground if you know your local 
characteristics at MF - different than HF), then 4W TPO would result in 
3W EIRP.

On 05/29/2018 01:28 PM, James Fisher wrote:
> I have been experimenting with magnetic loop antennas and am now operating
> portable on 160 meters. I note that a 250' long conductor in a magloop will
> radiate a signal on the 600 meter band with a efficiency of 25% so 4 watts
> into the antenna gets you 1 watt eirp. My magnetic loop is made with 2 inch
> wide strips of aluminum flashing. The strips are pop rivited together using
> 20 rivets at each join and the heads and bases of each rivet are soldered
> to the aluminum using harbor freight aluminum solder. On 160 meters I
> recieved a report of s-9 for a qrp contact at 5 watts ssb with a 100' long
> strip of aluminum. Please note that this length is MUCH longer than normal
> for a mag loop, but it works really well! Pictures are on facebook- san
> angelo amateur radio hams. The magloop was in a delta shape for easy
> installation. the feed was a gamma match using 20' of wire wrapped around
> the conductor and then grounded to the aluminum at 20' from the apex which
> was the coax ground. I tried feedloops but had no luck as the swr's were
> very high. The gamma match worked the first time.
>