Testing results with FIM outdoors with BETS and FCC

Mark · 2026-05-18T03:46:31Z

So Gerry from Procaster and I today went out to the park next to his house and did some testing for field strength at 3 meters and 30 meters distances using the Procaster FM. The transmitter was on a tripod 6 ft off the ground and the FIM receiving antenna the same height. 30 meters is where the Canadian BETS measurements are taken, 3 meters is where FCC part 15 is measured from.First we did measurements with 250 uV/M at 3 meters. I took a Sangean radio that has better than average reception. We had a tape measure to measure 30 meters from the transmitter and 3 meters away and marked the two distances with a stick in the ground.I have to say that 200 ft that is talked about as the max distance that can be heard on a radio at 250 uv at 3 meters(FCC) is false information. At 15 meters(50 ft) the carrier was gone and just the inter-station noise. We then moved the FIM 30 meters from the transmitter which is just less than 100ft. The FIM reading was 2 or 3 uV/M, if that. That is not enough field strength to create enough signal for even the best of receivers to hear without some elaborate antenna system. No way a 250uV signal at 3 meters is receivable at 200ft(61 meters). That is misinformation. It takes the better of 10uV/M for a high quality receiver to hear a decent station and get out of the inter-station hiss.Now for the BETS readings. 30 meters is quite a distance. Farther then I thought it would be.We found that to get 100uV/M at 30 meters(Canadian measurement) You need 3000 uV/m at 3 meters to get that field strength at 30 meters. Still just slightly under. Real world measuring with a calibrated FIM meter. ISED says BETS-1 signals should die out at 30 meters? Not accurate. At 30 meters from the transmitter with a 100uV signal on the FIM the Sangean receiver still had a strong full quieting carrier. Like a local. I started walking back farther and could walk considerably farther than the 30 meters before the reception got spotty and tilting the radio/antenna one way or another still brought in a clean signal. So Canada is much improved over the FCC 250 uV at 3 meters.Also as mentioned for a decent signal on a high quality receiver you need about 9 or 10 uV/M.Then we tried a couple of commercial stations to see what the field strength was as the FIM is measures that also. Interesting. Strong signals have a field strength of give or take 1500 uV/MSo that's our findings.It is really surprising to see how puny the 250 uV at 3 meters is.

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Mark

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@richpowers You have a point. I will see if I can switch it to general radio discussion.
Moved to general radio discussion...done.

This post was modified 2 months ago 2 times by Mark

Posted : 23/05/2026 11:34 am

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