[OZAPRS] On loops v whips mobile
vk5zm at bistre.net
Fri Dec 8 09:40:25 AEDT 2017
Yes thanks Carlos for sending that through, it was certainly a good read.
You might like to look at Steve VK5SFA's loop he's built for 160m, his DX
count on 160m CW has improved out of sight from a suburban setting with
this antenna. A lot of good work being done by Steve and the team.
I've used his prototype 40m TMLA a few times and the results are impressive.
On 8 December 2017 at 07:36, Glen English VK1XX <
glenlist at pacificmedia.com.au> wrote:
> 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
> 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:
>> 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).
>> Carlos VK1EA
>> On Thursday, December 7, 2017, Glen English VK1XX <
>> glenlist at pacificmedia.com.au <mailto:glenlist at pacificmedia.com.au>>
>> > I was doing some quick numbers of loops versus whips at 10 MHz and 7
>> > 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
>> > Increase the loop circumference to 5m and the efficiency increases to ~
>> > 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
>> > 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
>> > **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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