[OZAPRS] On loops v whips mobile

[Glen English VK1XX]

interesting post Carlos, nice to see lots of data points in those tests.

well, there really is nothing new on mag loops in many years. The 
presentation seeks to recycles 40 YO knowledge for the benefit I guess 
of newbies. which is fine.

I found my 5m circumference loop about as good as a 2.7m long CB whip 
for 160m for >500km... I think.... and  superior to the whip for NVIS.  
I think.....

Certainly the loop was far more impedance stable. The whip, using the 
bottom of the car as a big cap to ground, tends to vary with the type of 
ground being traversed. The whip going anywhere near trees tends to go a 
mile, also. The loop doesnt care.


On 7/12/2017 10:11 PM, Carlos Peco-Berrocal wrote:
> COMROD makes both a half loop and a full loop for NVIS (being sold by 
> others under their own name). They are expensive to acquire/repair, 
> and tests revealed that they are no better than a tilted whip. As a 
> result, sales are not happening in the numbers they hopped for:
>
>
> http://www.hfindustry.com/meetings_presentations/presentation_materials/2010_feb_hfia/presentations/HFIA_loop_presentation.pdf
>
>
> The COMROD loop was on display the other day at Eylex stand at MilCIS 
> here in Canberra. I have some hi-res photos I took at another show 
> (Land Forces?) and Owen Duffy found the tech description in COMROD's 
> patents (in case someone wants to replicate it at home).
>
> 73,
> Carlos VK1EA
>
>
>
>
>
>
> On Thursday, December 7, 2017, Glen English VK1XX 
> <glenlist at pacificmedia.com.au <mailto:glenlist at pacificmedia.com.au>> 
> wrote:
> > I was doing some quick numbers of loops versus whips at 10 MHz and 7 
> MHz.
> > At 10 MHz, the whip may be more suited as you get very little 
> straight up at high angle, compared to a vertically orientated mag 
> loop. Most of the work at 10 MHz will be < 45 degrees takeoff
> >
> > So, some numbers
> > the Diamond 1.4m base loaded whip-
> > - Rrad = 1 ohm. yes 1 ohm !
> > - for Rground = 15 (pretty good)
> > efficiency will be about 6%
> >
> > Loop, 3m circumference, inch wide Aluminium strip. Not bad, Q=1000 
> capacitor.. reasonable
> > that's say a square loop 50cm tall, 1m long.
> > likely efficiency =  9%.  maybe less depending on its height above 
> the steel roof. might improve with various 'shield' plates.
> >
> > But not that much better considering the hassle, and the overhead 
> performance of the loop is not useful.
> >
> > Whip wins.
> >
> > *7 MHz*
> > similar sort of whips, same size loop :
> > Whip efficiency (0.5 ohm Rrad) = 3%
> > Loop efficiency same loop : ~ 3.3 %
> >
> > Now the difference at 7 MHz is that the high angle stuff is VERY 
> useful, because the ionosphere will provide plenty of reflection 
> vertical in the daytime, and the loop has plenty of output at 45 deg etc.
> >
> > The whip good for low angle stuff at night, but but really using the 
> high angle modes that 7 MHz is useful for,
> >
> > Loop wins.
> >
> > *3.5MHz *
> > Whip Likely efficiency :  (0.1ohm Rrad) 0.6%
> > Loop  0.4%
> > The high angle stuff is important here, Loop wins.
> >
> > However this tells up the loop is too small
> > Increase the loop circumference to 4m and the efficiency increases 
> to 0.9%
> > Increase the loop circumference to 5m and the efficiency increases 
> to ~ 1.3%
> > 1% is not bad!
> > I am taking into account the Rloss due to capacitor Q which varies 
> with loop size.
> >
> > The reality is that whips can be MUCH better than the base loaded 
> example
> >
> > Pretty hard to go past a continuously helically loaded whip on a 
> tapered fibreglass blank.
> > Think 2x the efficiency as the base loaded stinger.
> >
> > of course whips with capacitive hats are the trick, but that's 
> another story.
> >
> > **For more up radiation from a whip, consider taking a wire to the 
> top of a whip and pulling it backwards in a curve, sort of an inverted 
> L. There is very little current in the top (end) of the antenna , so 
> it wont do much but it will do something. Good time to have a 'loading 
> coil' 2/3rd up the total antenna in order to improve the current 
> distribution (ideally rectangular, usually triangular )
> >
> > -glen
> >
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