The “Faraday mat” or “EMF screen” as it is sometimes marketed is a piece of polyester cloth that is coated with a pattern of conductive paint (a nickel/copper mix) on both sides. Despite this, the material is still very flexible and is fully conductive.

It is sold on Amazon and elsewhere as a material to be used to screen items such as smartphones from being “hacked” by means of RFID, Bluetooth, WiFi or indeed cell phone signals. It also cuts off any contact to GPS satellites. 

From an amateur radio viewpoint, we don’t want to reflect signals away, or do we .. ?

When used as a ground plane to a vertical antenna, this material is far simpler to deploy than multiple radial wires but it might (hopefully) serve the same purpose.

The piece of “EMF Screening cloth” that I bought was 44″ x 36″ (110 x 91 cm) and cost  €24 plus shipping.

My test setup consisted of the following:

• Rig Expert AA-30 antenna analyser
• Modified SLIK Mini-II digital camera tripod (modified with the addition of an SO239 socket, coax feed cable and radials connection crocodile clip).
  
• Komunica Power HF-PRO2-PLUS-T loaded HF/VHF vertical antenna.
• A short clip lead to attach the EMF-Screening material to the earth side clip on the tripod.
• The “EMF-Screen” material.

I decided to test the material connected to the tripod using the clip that I normally attach its radials to and simply stand the tripod on the polyester material and see with the antenna analyser how it performed.

It did not perform well, in that when the antenna was tuned to a band the SWR was highest when connected to the mat, lower when the tripod was just sat on the mat but not connected and LOWER STILL when not sat on the mat at all (i.e. no ground plane on the antenna apart from perhaps the metal in the micro-Tripod and the sheath of the feed-line). This was especially noticeable on 15 metres and above.

So was this idea a FAIL?

Well, it would have been except that I had another idea that I wanted to try out. Using the analogy that the metallised cloth could be considered similar to a car roof, I removed the tripod from the equation and connected the antenna to a single magnet car roof mount base from OPEK and sat that in the middle of the EMF screen cloth. There is no “hold” to the nickel and copper on the mat, purely gravity holds it there (so this wont work in high winds). There was no connection between the mat and the mag base which was insulated by it’s rubber base covering (needed when sat on a car roof so as not to scracth the paint).

Testing the antenna now, the SWR readings were much better and when I moved the mag mount and antenna off the mat, the SWR shot up – so in this configuration, the EMF screen mat was indeed acting as a ground plane of sorts.

I went through and calibrated each Amateur HF bands between 40m and 10m plus 80m with an additional coil added to the antenna (this antenna cannot correctly support 60m). All gave good reading with one exception – 20 metres! I was seeing an over 3:1 SWR across the band and no “true” dip that I had on other bands. I have seen this strange behaviour before and had an idea what it might be.

I took the magnet mount down to my workshop and measured the length of coax on it – as close as I could measure it was around 4.72 metres long, which, allowing for the velocity factor of the coax was fairly close to a quarter wave on 20 metres! I shortened the coax by 30 cm and went back outside to re-test. This time I got a true 1:1 SWR at 14.098MHz and less than 1.5:1 from 13.8 to 14.38 MHz. That was the problem! In the majority of cases, these mag bases are used for 2m or 70cm mobile antennas so the length of coax would not have affected those bands.

So again, I ask was this purchase a waste of money? NO in fact this simplifies portable / static-mobile operation. When operating from the car – perhaps a POTA activation, the vertical antenna sits on a mag mount on the car roof. When you go truly portable, you take the same mount, coax and antenna with you along with this lightweight mat and set up your portable station without the need of a tripod.

 These results were obtained with the antenna model, magnetic mount and mat described above. Your results may vary, however for under €30 delivered I think the mat as an addition to your existing car mag mount and the loaded vertical antenna is worth looking into.

I have heard that on HF the area of metalised material is far too small and multiple square metres would be needed. That theoretical advice was (I believe) related to a true 1/4 λ vertical and NOT to a loaded whip, which from its design expected to sit on a small area of metal (a car roof). This Faraday mat is simulating the car roof. 

73 Ed.