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Seeking field strength meter

P

perenoel6218

We are a very low budget NCE in Indiana hoping to find a used
FM field strength meter to buy or borrow for a month or less.
Please contact Jim at 919witt.org
 
Getting anything that resembles "real" field measurements on FM essentially requires renting the guy who knows how to do this along with the meter.

FM propagation is approximated by the FCC with the 50/50 and 50/10 charts. Those charts show the best guess on field strength at a given location, with the antenna 30 feet up, either 50% or 10% of the time--averaged over 50% of the locations.

FM signal strength at any given point is just like Midwest weather. If you don't like it, just wait, it will change shortly.
 
Pretty true assessment TomT. City--there's a cheap way to at least get a feel for what you have though. The Tecsun PL-390 radio has signal meter calibrated in dbu and while it will not be accurate as far as being able to confirm that you have your predicted signal strength at a given location, it will allow you to do two things with reasonable accuracy : 1) compare your signal to others on the dial and 2) get a rough idea of where the nulls and peaks caused by the mounting of your antenna are located. I've driven a "square circle" around a class A mounted on a 24" face tower & stopped every few tenths of a mile and recorded readings. Per this radio, there's better than a 10dbu difference between the 'best' and 'worst' directions--and this has been borne out by real world results. Fortunately, the null is in a non-populated area...just where I planned it to be. Great little radio for $66.... http://www.ebay.com/itm/New-Tecsun-...28398?pt=Shortwave_Radios&hash=item3a6cc318ee

One thing to be aware of...the sensitivity on this radio will drop off when you are within a mile or two of another FM transmitter. So if you go to the antenna farm at 79th & Township Line Rd and look at 91.9, the signal level will probably be less than expected on this radio. But as long as you stay more than 2 miles from the nearest FM transmitter, it's a remarkable tool for the money.
 
I brought in a consultant once to do FCC submitable measurements on an interference case. He had a 30 foot inflatable mast on a trailer, a calibrated antenna and fim-71. We spent about three hours taking measurements about every six feet over about a 50 span. And then everything was double checked for accuracy. It was not cheap, but it was better than submitting my spectrum analyzer prints with a Terk antenna held aloft.
 
The Grundig G-8 also has a field strength meter, it's available on Amazon for around $50.00. May actually be an Asian cousin to the Tech-sun radio.
 
Field strength and relative power measuring is something that interests me (but not something I do, I normally leave it to the specialists).

I too have been looking around for something that will allow me to perform coverage testing and to get a fairly accurate indication of radiated power on a given frequency.
We have 'low power FM' here which allows free use of parts of the spectrum as long as the EIRP doesn't exceed 1 watt. I think it's similar to 'Part 15' in the US.

There are a lot of operators on these frequencies and not all of them adhere to the rules. To be able to go out into the general area of their transmission, lock on to the frequency and say "yes, they're running around 1 watt" or "why is my meter pegged on the 5 watt scale?" would be quite useful.

The Tec-sun and Grundig G-8 radios might give the results, but I was hoping for something a little more suited for testing work, perhaps something with analog meters on it, calibrated to a known source?

If I had a credible measuring system I could then document the results and if the transmission was over the allowable level, approach the authorities with my results.

I'm prepared to spend more than $50 on such a device, I would spend $500 if it was a good instrument, but I can't afford (or justify) the several hundred thousand dollar price tag of the units the specialists use.

Suggestions?
 
The Grundig G-8 also has a field strength meter, it's available on Amazon for around $50.00. May actually be an Asian cousin to the Tech-sun radio.
Click to expand...

The "dBµ" indication on the Tecsun and Grundig screen is not an absolute measure of the electric field strength arriving at the internal loopstick or whip of the radio. Field strength is stated in units of µV/m, which is a measure of the r-f voltage existing between two points in space that are separated by one meter.

These radios show the voltage in decibels with respect to 1 µV that exists across a fixed impedance at an internal sample point in the receiver.

RF
 
RadeoEngineer said:
... the "authorities" would have zero interest in 1 watt cheaters....
Click to expand...

Just to note that the FCC has interest in operators radiating much less than 1 watt. Below is a list of six unlicensed operators receiving FCC "NOUOs" in just the past several months.

There are many more receiving NOUOs in that time period, but this list was limited to those who could earn their citations using powers of less than 35 milliwatts (mW) applied to the input of a matched, 1/2-wave dipole, over a free space path.

The power required in these cases is shown in red following the entries in the list.

http://transition.fcc.gov/eb/FieldNo...-310314A1.html
The field strength of the signal on frequency 101.3 MHz was measured at 33,934 microvolts per meter (uV/m) at 3 meters, [0.21 mW]

http://transition.fcc.gov/eb/FieldNo...-310315A1.html
The field strength of the signal on frequency 88.9 MHz was measured at 1,416 microvolts per meter (uV/m) at 892 meters, [32.4 mW]

http://transition.fcc.gov/eb/FieldNo...-309813A1.html
The operation on frequency 88.3 MHz was measured at 2,846 microvolts per meter (uV/m) at 154 meters. [3.9 mW]

http://transition.fcc.gov/eb/FieldNo...-309815A1.html
The operation on frequency 101.1 MHz was measured at 3,906 microvolts per meter (uV/m) at 158 meters. [7.7 mW]

http://transition.fcc.gov/eb/FieldNo...-308807A1.html
The operation on frequency 87.9 MHz was measured at 36,711 microvolts per meter (uV/m) at 3 meters. [0.25 mW]

http://transition.fcc.gov/eb/FieldNo...-308259A1.html
The field strength of the signal on frequency 98.3 MHz was measured at 1,449 microvolts per meter (uV/m) at 80.5 meters, [0.28 mW]

RF
 
No need to export those NOUOs to New Zealand, where 1 W EIRP, and Studio1's operation, is perfectly legal. Compared to the US, our Kiwi friends seem progressive in so many ways. :)
 
RadeoEngineer said:
Yes, the "authorities" would have zero interest in 1 watt cheaters. They don't pay regulatory fees.
Click to expand...

The authorities here have no interest as long as the EIRP is 1 watt or less, and you aren't interfering with any licensed services, especially aviation and land mobile operations.
The problem is a number of operators believe they have the right to use significantly more power than the regulations allow for.
You are correct that no fees are paid by users on these frequencies, and accordingly the authorities have no budget to go investigating cases where users may be over-modulating or running excessive power.

As a radio engineer I often get called on when an operator believes that another station is using 'too much power'. I would like to be able to go out and measure the relative field strength and convert this into a meaningful reading in terms of EIRP.


ironbear said:
No need to export those NOUOs to New Zealand, where 1 W EIRP, and Studio1's operation, is perfectly legal. Compared to the US, our Kiwi friends seem progressive in so many ways. :)
Click to expand...

Just to clarify things, I don't run a station myself - I spend far too much time working on other people's. I presume that's what you mean by my 'operation'? Or maybe I have got the wrong end of the branch...
 
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