Hi this is Frank
In this video I show how I have increased the size of my magnetic loop to improve transmit performance and may be give you ideas on how you can improve your own magnetic loop.
VE2FGJ
Usually we have small portable loops that are convenient, but the efficiency is limited mostly on transmit.
Having a Chameleon F-Loop 3.0 with the standard 102 in loop and the 146 in Booster cable, I wanted to improve the transmit efficiency by increasing the loop size.
With the 66pacific.com web site (link is in the description) I calculated the efficiency of the
Standard 102 in loop to be: 52% on the 20M band
Booster 146 in loop to be: 76%
I had the idea to join 2 x 102 in loops together but instead of doubling the loop I would use it as 1 single big loop
The length is 205 in and the efficiency is: 90% on the 20M band
Link: [ Ссылка ]
Now let’s look at the 3 loop sizes on 20M 40M and 80M
With the 102 in loop I got: 52% 9% 1%
With the 146 in loop I got: 76% 22% 3%
Lastly with the 205 in big loop I got: 90% 44% 8%
When using a bigger loop like the 205 in as a single loop, we immediately find that:
1. The supplied telescopic mast is too short, so we replaced it with a 5 ft Monopod, which is normally used for cameras and adapt it to fit using several 3d printed parts, nuts and bolts. This allows to use the smaller loops as well as bigger loops.
2. The supplied inner loop is too small, so we made a new inner loop using aluminium, the approximate ratio is 1/5th (or 20%) of the outer loop, in this case it is 13.3 in. Using several tools, we were able to reproduce a inner loop that looks very much like the original.
Magnetic loop contacts with S51DX and E71A.
Using the 205 in loop provides a wider bandwidth and is also easier to tune. After several successful transmisions up to 30W in CW we decided to get ride of the coupling barrel in between the 2 loops to make 1 single cable.
This is important, What we discovered with this new cable is, we could not get a good SWR above 10W, that puzzled us for a while, after several tests we put the previous cables back with the barrel coupler and yes the SWR was good all the way to 30W in CW.
We eventually realized that both PL-259 connectors were making contact on the inner loop, that certainly changes the coupling behaviour. I am not an engineer, I cannot explain how or why, but it does work much better if the outer loop makes contact with the inner loop with this scenario. May be some of you watching can comment and explain why this is happening.
With a bigger coaxial loop expect that the wind will bend the coax and may de-tune the coupling as it wobbles, my solution is to orient the loop 90 degrees perpendicular to the wind direction, that pretty much minimizes the wobble.
In conclusion, you can improve the efficiency of your magnetic loop by increasing the loop and the inner loop sizes, calculate what best fits your requirements, experiment and I would love to see your own experiences or questions in the comments below. Good luck on your build.
This is Frank signing out, thanks for watching! 73
Authors: VE2FGJ and VE2GIQ
Notes: Stepper Motor is dual shaft NEMA 17, radio is an ICOM IC-705 with RM Italy MLA-100 Amplifier, Mag Loop Controller is home made with a Teensy 3.5 Micro-Controller and HC-05 Bluetooth, the screen is a Nextion touch screen, all is programmed in C (Arduino), includes an Auto-Tuner, Pro-Active Tuner and multiples functions, it is 4400 lines of code and is built to use ICOM CI-V (via Bluetooth or Serial) to read SWR and VFO values, has been tested with IC-705, 7100, 7300, 7610. A SWR bridge was considered but we resolved to use the radio’s SWR meter (which goes up to 6.0:1) Not for sale, please do not ask for purchase.
The Goal of this video is to encourage you to increase your Mag Loop size, calculate your requirements, experiment and improve performances.
Building and optimizing is the spirit of Ham Radio enthusiasts.
73 from Quebec, CA
Music: Miami - Del
