AMATEUR RADIO FOR THE GREAT OUTDOORS
Antennas including linked dipoles, telescopic poles also ham radio kits - everything you need.
If you are thinking of leaving your ham shack with your radio, take a look. We can help.
Posted by Richard Newstead on 20th Feb 2017
Small transmitting loop antennas "magnetic loops" have become very popular. There is no doubt that they can provide good performance for their small size. While they are easy to build if you have (or can make) a suitable variable capacitor, many people opt for a commercial product. This usually means that the first opportunity to try it is after you have made a purchase. One way to experience operating under "loop conditions" is to use a known simple antenna type such as a half-wave dipole or quarter-wave monopole and reduce your power to simulate a loop.
Loop manufacturers seldom provide the efficiency figures for their antennas but fortunately they are easy to calculate. Loop efficiency will vary depending on the loop design and on the band of operation. A number of online calculators can be used to give an estimate of loop efficiency. I favour the calculator provided by Owen Duffy as this seems to give a reasonable worst-case.
Simulating the performance of a loop is simply a matter of reducing your power into your known antenna to take into account the loop efficiency. Your known antenna will have an efficiency of close to 100% (all the power you apply to it will be radiated). Bear in mind that the maximum power rating of most loops is less than 100 Watts so you will need to factor that into your experiment.
The following table shows the power levels to use.
The method is simple. Using an online calculator, calculate the likely efficiency of the loop that you are considering. Set up your dipole/monopole in an open area. Reduce the power of your radio according to that table above and go on the air with your "loop simulator". This simple test will quickly give you an impression of what life might be like with a loop. It's not perfect but it will be close!
Example: 1 m diameter loop constructed from LMR400 co-axial cable can be expected to give the following efficiency figures:
If you look around on the ham radio sites on the internet, you cannot fail to notice that QRP operating is very popular. There are good reasons for that; it's easy to build QRP gear and it is generally small, light and suitable for portable operating. However, some people do find QRP operating can give rather [...]
The Chameleon P-Loop is a popular commercial small transmitting loop antenna. I have bought two to use for propagation experiments using two WSPRlite antenna test systems. The P-Loops have not been bought for any special reason - I doubt that they are significantly worse or better than other similar products. My use of them is not an endorsement [...]
I covered this topic in a newsletter sent on 26 Feb 2016. Note that if clicking after this date, offers will likely have expired! Click here to read it.Be sure to sign up to our newsletter to receive more articles like this (not more than two a month).73 Richard G3CWI
This article was published in the first SOTABEAMS newsletter of 2016. If you find it useful, you may want to sign up to our newsletter!73 Richard G3CWI
The inverted Vee is a great antenna. I published this short article in the January 2016 SOTABEAMS newsletter.73 Richard G3CWI
A while ago I wrote an article on making a trap dipole. Since then I have made lots more - and in doing so have gained some greater insights into how they work. The original article is here. My additional tips are:1) When you add traps to the ends of the highest frequency section of the [...]
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