Field strength meter options

[Need2Know]

I was exploring various field strength meters that I might use to determine the best location for my 2 meter/70cm antenna.

Option 1 is building it myself. This may be the cheapest option for many. But I doubt if it would be for me because everything I subsequently tested with it would probably be off by a magnitude of 26 to the 10th power. I don't trust my skills building test equipment.

I found two interesting options for field strength testing:

One is the MFJ 802 for $50 With the larger meter and different design, this appears to be a better choice than their earlier, more basic cheaper model.

Then with a little more looking around, I found this Trifield meter (see the specifications, below). For those who might want to use a field strength meter for more than the occasional times you would use it to test antennas, this one provides many other uses related to sensing other types of EMF and electrical fields.

My question is this: Based on the specifications below, would this meter be as effective at measuring the field strength of 2 meter/70cm transmissions as the MFJ meter, above? I could justify the price of this meter for multiple purposes ONLY if the primary purpose of antenna testing was satisfied.

What are your thoughts?

SPECIFICATIONS: Trifield® Meter Model 100XE
AC Magnetic Fields: (3-axis; shows true magnitude)
Frequency Range: 40 Hz – 100 KHz (see frequency weighting)
Accuracy @ 60 Hz (50 Hz): +/- 20% of reading
Range/Resolution (@ 60 Hz or 50 Hz): 100 milligauss / 0.2 milligauss
Standard Version Frequency Weighting:
*Sensitivity is proportional to frequency from 40 Hz to 500 Hz; flat from 500 Hz to 2000 Hz
*Sensitivity is inversely proportional to frequency from 2K Hz to 100K Hz
Flat Frequency Version: +/- 20% from 50 Hz to 500 Hz; inverse frequency above 500 Hz
AC Electric Fields: (3-axis; however, note that E-field is affected by the body position)
Frequency Range: 40 Hz – 100 K Hz (see frequency weighting)
Accuracy @ 60 Hz (50 Hz): +/- 30% of reading
Range/Resolution: 1000 V/m / 5 V/m (Original Version: 100 KV/m / 0.5 KV/m)
Frequency Weighting: Same as magnetic (above).
Frequency Range: 50 MHz – 3000 MHz (3 GHz)
Radio Microwave: 1 Axis (detect E field)
Range/Resolution: 1 mW/cm2 / 0.01 mW/cm2
Accuracy: ½ x to 2 x of reading
Meter Size: 5.0 x 2.6 x 2.4 in (129 x 67 x 62 mm)
Weight: 8 oz
Battery: 9 volt alkaline (~ 40 hour life) / "Low Battery" indicator

 

[Beetle]

So at 60 Hz, this "instrument" has a stated accuracy of "±20% of reading", and it's "frequency weighted" (whatever THAT means) at 2M and 70cm to something like ±100% of reading (2x reading)?

This thing is basically designed for power frequencies (and to feed the fear of those whose karma is disrupted by electromagnetic fields at those frequencies). It may give up-scale indications at higher frequencies, but how much are you going to trust those indications?

 

[twister252]

note that E-field is affected by the body position) :wub:
so if you want a different reading just move around a bit<<More audio>>

have to agree w/ Beetle:thumbdown:
prolly would be a great ghost detector :drool:

 

[Need2Know]

Has anyone here used the MFJ 802 or ANY field strength meter when testing antenna location or desgin?

I take it from Beetle's and Twister's comments that the MFJ meter might be the better choice since it didn't receive the chortles that the Trifield did.

 

[twister252]

there are a few people here that come to mind, to answer that question. several antenna builders. homerBB is one. captain kilowatt is very knowledgeable. marconi is another. just to name a few. these guys are here nearly every day. BoB 85 is another...

I would trust many here, lots of good info, and good people here!!

mfj 229 is A GOOD ONE, BUT A BIT PRICEY

 

[Need2Know]

there are a few people here that come to mind, to answer that question. several antenna builders. homerBB is one. captain kilowatt is very knowledgeable. marconi is another. just to name a few. these guys are here nearly every day. BoB 85 is another...

I would trust many here, lots of good info, and good people here!!

mfj 229 is A GOOD ONE, BUT A BIT PRICEY

The MFJ229 appears to be more of an SWR meter than a Field Strenth Meter. It connects in-line with the antenna cable. A Field Strength Meter is not connected to anything and just receives and measures the antenna propagation. Please correct me if I'm missing something.

 

[Beetle]

I posted a reply on your other thread associated with FSMs. Twister 252 has the technique down perfectly: move around and try different positions until the meter reads what you want it to.

I haven't looked at the MFJ-229, but you're right. A FSM can't be hard-wired to anything.

 

[Need2Know]

Well, the results of this thread, as well as the opinions of several others within my local ham community is this regarding the use of field strength meters to deetermine optimum antenna location inside the home:

The short answer: Save my money.
Middle length answer: These meters are not very effective or accurate.
Two directly answered the question and said the MFJ would be more accurate than the Trifield at the frequencies in question.

My interpretation of the answers: No one has direct experience with the two models noted except for understanding the specs and general usage better than I do.

My wishful thinking: That the MFJ would work best and could produce usable results IF 1) used along with the optional remote unit attached by wire (to eliminate influence of the human body touching or in the vicinity of the sensing unit) 2) taking readings from several fixed and noted locations outside the home (so the locations can be exactly replicated on later iterations of the test) in the general direction of the location you want to contact 3) repeated with each respositioning of the antenna to determine the best location.

My hunch: The majority of hams do not use a field strength meter for determining optimum antenna location for three reasons: 1) It is too much trouble to use in a manner that gets meaningful results. 2) It is more fun and productive to test the signal via actual communicating with someone than it is to stand around in the yard taking dozens of test readings 3) on an a type of instrument that has a reputation for producing variable/unreliable results.

It would be interesting if there was someone who used the MFJ in a manner similar to what I described under "wishful thinking" and whether that process worked for him or not.

I have a 4th hunch why this method isn't used, and this applies especially to me now that I think about it. In some communities, especially retirement communities, neighbors can be especially suspicious of ham radio operators next door. If I was outside for a couple of hours with a couple of meters and a hundred feet of wire I would attract every neighbor within eyeshot. Word would get around that I have a ham radio that will interfere with Dancing with the Stars every night. In fact this has already happened. My wife was at the neighbor's house and the neighbor complained to my wife "my tv set is acting up - it went out a couple of times last night - I understand you husband is a ham", all in the same breath. My wife had to explain I didn't even have a radio yet!

 

[Beetle]

The only time I ever actually gained any significant information from a FSM was when I was plotting the pattern of my quad. For that, I had an old SWR meter that converted into a FSM by plugging in a ~6" piece of wire that served as an antenna, and positioning the meter on the trunk of a tree about 80 yards away.

With the quad aimed straight at the meter, I adjusted the sensitivity for about 3/4 scale, and then went in the shack where I could see the meter with a very good pair of binoculars on a tripod.

Results were roughly comparable with what I expected: most of the RF squirted forward, with nulls off the sides and back and DEEP nulls off the corners. How deep were the nulls? A device like this sort of FSM won't tell you that -- they are for relative readings only.

I'd be leery about the "remote unit" -- if it's attached by wire, how much does the layout of the wire affect the reading? I'm supposing you can reroute the interconnecting cable and again, get any reading you want.

 

[Captain Kilowatt]

The only time I ever actually gained any significant information from a FSM was when I was plotting the pattern of my quad. For that, I had an old SWR meter that converted into a FSM by plugging in a ~6" piece of wire that served as an antenna, and positioning the meter on the trunk of a tree about 80 yards away.

With the quad aimed straight at the meter, I adjusted the sensitivity for about 3/4 scale, and then went in the shack where I could see the meter with a very good pair of binoculars on a tripod.

Results were roughly comparable with what I expected: most of the RF squirted forward, with nulls off the sides and back and DEEP nulls off the corners. How deep were the nulls? A device like this sort of FSM won't tell you that -- they are for relative readings only.

I'd be leery about the "remote unit" -- if it's attached by wire, how much does the layout of the wire affect the reading? I'm supposing you can reroute the interconnecting cable and again, get any reading you want.

This is good info. If you are looking simply for the best location of an antenna and not looking for true gain/loss figures then a simple meter with a diode detector works fine. All you are looking for is relative measurements, which location gives the higher meter reading. I did the same thing Beetle did several years ago when I build my 6m yagi. I used an old 100 microamp meter and a diode detector. I aimed the yagi straight at the meter and set the meter for full scale.Then I rotated the yagi looking for any peaks or nulls that should not have been there. It was all relative readings and worked like a charm.

 

[Need2Know]

I'm only working to position an omnidirectinal J-pole. Obviously not as much precision is required in aiming as a Yagi, but precision is needed in finding the optimum location in the attic. By the way, this is the one I ordered.