Tagged: Calibration Charts
- February 25, 2019 at 6:00 am #109781
I apologize if you have already seen this.
- February 25, 2019 at 8:14 am #109782
- February 25, 2019 at 8:16 am #109787
- February 25, 2019 at 10:32 am #109790
It appears that those three pages are written in short-hand language for FCC Inspectors and not for part 15 end-users.
Understanding some of the points requires prior knowledge about aspects that are not fully expressed in the abbreviated wording.
- February 25, 2019 at 10:45 am #109791
Carl: You are correct. Guidelines for inspectors. Still waiting for our Resident Hobby Agent give it a thumbs up or down.
Mark: Yes I excerpted a 100 plus page document. This is the only section that applies to AM radio transmitters.
- This reply was modified 4 months, 2 weeks ago by AMRadiolegend.
- February 25, 2019 at 11:34 am #109795
It’s too bad that some of the points (i.e., elevated installs with long ground lead to the ground plane) haven’t been put directly into the rules. Instead, the rules (which should be the reference point) are left open to interpretation.
Although that could be what they want.
- February 27, 2019 at 8:10 am #109857
Total posts : 56
II put my Radio Shack transmitter module away up in the rafters, and I just connected my 8 track player amplifier output to the speaker in my collector tomb stone radio, that way I will have no problem meeting the part 15 rules and regulations- Thats the way I did it years ago so that’s the way I will end up doing it, put the tape player in a box under the radio nobody knows the difference and nobody can say I caused some kind of interference or imposed on somebody playing some kind of goofy music nobody wants to hear anyway. I wonder if I should contact my congress person and have them draft a bill creating this method I use as law- I think this would be a good law to have on the books, but the audio must be from an 8 track player or there would be heavy fines.
- February 27, 2019 at 10:00 am #109862
I don’t believe there is any reason to mothball your transmitter, if it’s compliant with the Part 15 rules.
From what I’ve read and can see, the pirate bill that just passed is mostly political, and the intent is to demonstrate publicly (by both lawmakers and the FCC) that the pirate problem is being taken seriously.
As far as I can tell, no new money has been allocated to FCC enforcement. The penalties have been upped for blatant pirates, there are new standards for FCC reporting, the role of states in handling pirates has been confirmed, etc. Largely housekeeping on the practical side.
The bottom line is that if you are using an FCC certified Part 15 transmitter, or you are technically competent and can prove that the non certified transmitter you are using is compliant, you really have nothing to worry about.
The rest is all fear mongering by others because they have their own agenda.
There may, and I do stress may, be some potential concern that Part 15 operators could be mistaken for pirates. But I don’t think that local police, or whomever ultimately does the enforcement, are going to smash down doors and go into people’s homes with guns blazing. They have to follow due process, and determine if you really are a pirate. AMRadioLegend’s suggestion that you print out a copy of your ‘authorization’ to be on the airwaves (i.e., the Part 15 rules) and keep it in your studio is a good one. But then, it was always a good suggestion, as anyone, even before the PIRATE act passed, could have initiated a complaint with the FCC or local authorities, and earned you a visit.
Bill DeFelice over at Hobbybroadcaster is concerned that there is no distinction in the rules between pirates, and Part 15 operators who may be slightly out of compliance “by mistake”.
There are really only two possible cases here. The first is a nudge nudge, wink wink mistake, such as a long ground lead with an elevated install, which any reputable operator should fully know is not within the rules. Those people who are operating in the so-called gray area (not really, but it’s been called that) of the rules might be advised to rethink what they are doing.
The second is where there truly might be a mistake, such as a defective transmitter. But as RichPowers (End80 elsewhere) has pointed out, the range of Part 15 compliant transmitters is well known, and if you’re getting significantly more than that (i.e., into pirate range territory), you should figure that something is wrong.
There has to be some responsibility on the part of the Part 15 operator.
- February 27, 2019 at 10:43 am #109864
RE: … if you are using an FCC certified Part 15 transmitter… you really have nothing to worry about. …
A gentle reminder: even transmitters that are officially certified for Part 15 (AM or FM) can be installed and/or operated in a non-compliant manner — for which, after a field inspection, the FCC may see fit to cite those operators.
Even the owners/landlords of installation sites not belonging to the Part 15 operators there have received FCC citations, along with the operators.
- February 27, 2019 at 11:02 am #109869
Whatever happened to the day when “Citations” were a good thing?
- February 27, 2019 at 11:02 am #109871
The full comment originally made by Artisan Radio is correct: ‘”…if you are using an FCC certified Part 15 transmitter, or you are technically competent and can prove that the non certified transmitter you are using is compliant, you really have nothing to worry about.”
By redacting the middle part of Artisan’s statement Rich shifted the meaning to something incorrect and incomplete.
Therefore Rich’s preach is invalidated as not fitting the context.
- This reply was modified 4 months, 2 weeks ago by Carl Blare.
- February 27, 2019 at 11:33 am #109878
RE: … The bottom line is that if you are using an FCC certified Part 15 transmitter, or you are technically competent and can prove that the non certified transmitter you are using is compliant, you really have nothing to worry about.” …
That bold text in AR’s post clip above required no followup comment(s), because it is true. If a technically competent operator can prove that his/her non-certified transmitter is compliant with the applicable rules of Part 15, and the FCC accepts that finding, then likely the FCC would not cite that installation.
It also would apply to the operator of any FCC-certified AM/FM transmitter whose operation and/or installation was questioned by the FCC.
- February 27, 2019 at 11:03 am #109873
Yes, we all recognize that, Rich. My point was that using an FCC certified transmitter goes a long way to demonstrating to any authorities investigating your station that you are at least attempting to be legal (and that you are not a pirate).
And as I stated, there is evidence that those who have been cited (when using certified transmitters) haven’t cooperated with the FCC during the investigation.
- February 27, 2019 at 11:04 am #109875
And Carl completes the rebuttal.
- February 27, 2019 at 11:42 am #109880
RE: And Carl completes the rebuttal.
Not for me — see post 109878 above.
- February 27, 2019 at 12:05 pm #109882
- February 27, 2019 at 2:37 pm #109887
From the Top
I got to thinking about the 3-page “Presentation” shown at the outset showing Field Inspection Tips, so I’ve returned to see them again.
In the 1st panel it says: “Use the General Checklist with the following frequent compliance issues…”
Do we have the “General Checklist”?
Next, looking over the various field tips I wonder if their un-detailed style might open an inspector to misinterpret what they say.
The Presentation falls short of slip-shod but is certainly slap-dash.
- February 27, 2019 at 3:01 pm #109889
The checklist referred to, as well as that whole slide presentation was prepared by the FCC for the benefit of the contractors who are hired by manufacturers to perform FCC compliance tests and assemble the results into a format acceptable to the FCC — the goal being that of getting FCC authorization/certification for the sale of a product for which FCC acceptance is desired or required.
- March 1, 2019 at 5:33 pm #109908
In Chart # 3 what is meant by the single word VERIFIED (?)
- March 4, 2019 at 6:37 am #109970
Verified: Mean from an accredited test lab have verified conformance of applicable standards. In the case of digital devices (Unintentional Radiators) the devices are classified as Class A and Class B with one being an industrial environment and one being a residential environment respectively. Class B devices require certification.
- March 1, 2019 at 7:07 pm #109910
I know this is an ignorant question, but what do they mean a rod antenna is not permitted for testing and that they must use a loop antenna?
- March 3, 2019 at 5:57 am #109929
The FCC inspector must be using a field strength meter that utilizes a proper antenna. Using a rod antenna to measure field strength is highly inaccurate.
However, in my real life experience when measuring FM field intensities a dipole adjusted to proper length for the frequency is desired, and is in fact provided with most FM FIM devices.
For AM, all professional field intensity meters have a loop antenna. In devices such as the Potomac FIM-41 or the Nems Clarke 120E for example, there is a calibrated loop antenna built into the flip up lid. To take readings you rotate the meter about it’s axis until you find the strongest signal. I do this regularly at work running checks on our directional night time antenna pattern.
When using my spectrum analyzer to do the NRSC performance measurements for our AM station I set up a large loop antenna on a tripod that feeds the analyzer.
Naturally the loop antenna helps insure that the only signal you’re picking up is the desired one.
This is necessary to get accurate field intensity readings.
- March 2, 2019 at 7:43 am #109917
RE: … a rod antenna is not permitted for testing and that they must use a loop antenna…
My guess is that it relates to the relative susceptibility for the performance of these two antenna configurations to be affected by their construction and/or adjustment, and their nearby physical environment.
- March 4, 2019 at 6:40 am #109972
Additionally, the loop antenna responds to the magnetic field as opposed to the electric field.
- March 3, 2019 at 6:07 am #109931
For those interested in reading all 164 frames of this document I have conveniently uploaded it as a pdf here:
It might offer some context.
- March 4, 2019 at 6:44 am #109974
TNX Tim, I could not get the pdf to load directly as the file size was too large. As a result I had to excerpt my submission.
- This reply was modified 4 months, 1 week ago by AMRadiolegend.
- March 4, 2019 at 7:05 am #109979
What is “73” mean?… I just noticed the same thing in an email response from https://www.arnewsline.org/ – I had asked if they were Part 15 friendly for rebroadcast; He answered:
Yes, we would be happy to have ARN on your unlicensed Part 15 hobby station!
- March 3, 2019 at 7:06 am #109939
Hmm.. third try:
Out of curiosity, for personal AM field strength readings has anyone ever utilized the SMR radio receiver that ISS offers? http://www.theradiosource.com/products/smr.htm They sell them for $144. Supposedly due to it’s S-meter which registers in 15-99 increments it’s able to provide rather accurate readings in comparison to a Potomac unit by using a supplied conversion chart..
This summer I’m thinking about buying one – not specifically for that purpose, because it would be so seldom using it and not really worth $150 to me, but more so just as a multiband receiver for everyday use, with the added luxury of calculating readings should you want to.
“..The SMR Receiver is the first device of its kind capable of measuring and displaying AM signal levels with a useful level of precision… This handheld, battery-operated receiver can be utilized in the field to estimate signal intensities of broadcast radio stations. Though not a calibrated measurement device, it displays relative signal intensity in dbu, which can be used for rough translation to millivolts per meter (mV/m) in a given frequency range using an included correlation chart..”
- March 3, 2019 at 8:29 am #109950
The Important Thing
The important thing being purchased for $144 is the Correlation Chart.
Similar radios with the same signal intensity readings are available for far less.
- March 4, 2019 at 8:00 am #109992
Dammit.. it deleted my post upon edit for spelling (changed usual to useful)..
Yeah, someone at the formerly ALPB forum mention that it was a Grundig receiver same as one he bought on eBay for $35.. He did not however have the conversion chart.
Addum: From a quick look about on the matter, apparently the precision and accuracy of AM radio S meters vary drastically and have different methods of utilizing one.. for example with some it’s just an extension modification of the AGC circuitry, others use other methods.. It’s all over my head but there’s some talk about this at http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm along with some external links of actual comparisons of certain receiver S meters.
I don’t know one way or the other, but ISS seems to emphasize that particular model “is the first of it’s kind” which enables the capability of a useful and accurate reading. Maybe he knows what he’s talking about.. maybe it’s just hype, but as far as quality multiband radio receivers go; $140 is really not an out of line price, so if it also has an exceptionally accurate SMeter (the common consensus seems to be most do not), then that’s an added bonus.
Hell.. I paid $150 for a Panasonic RF-2200 in beautiful cosmetic condition on eBay a few month ago.. unfortunately I get better reception on AM with my pocket radio than I do with this $150 let down which has some problems.
Still kicking myself in the ass for that one.
- March 4, 2019 at 7:37 am #109984
I’ll Take This One
End80 axes: “What is “73” mean?”
It is from HAM (Amateur) shorthand language and I think it means, “Have a good day and I hope your wife is pretty”.
- March 4, 2019 at 7:54 am #109987
That explains the 73 magazine title (from the 1970s)
- March 4, 2019 at 7:55 am #109989
The use of “73” in that context is a carryover from the days of using Morse code for radio communication, and was/is a shorthand way of saying “Regards.”
- March 4, 2019 at 9:56 am #109997
Total posts : 428
Tim, this thread has given me an idea. Since you have a FIM meter you could take one of these Tecson/Grundig radios with the signal strength meter and on AM and FM do the conversion charts comparing the reading on the radio and the meter at various frequencies the same distance from the antenna converting the dbu to mV/M and that can be converted to uV/M and it would do us a great service and then sell us the conversion charts. I’m sure all of us would like this and would buy it from you, myself included in addition to getting the Tecson radio.
This could be done with a transmitter going through the frequencies.
Just a thought for a project?
- March 4, 2019 at 10:26 am #109999
Best Idea of the Week!
From Mark: “Could take one of these Tecson/Grundig radios with the signal strength meter and on AM and FM do the conversion charts.”
Wow, that is a super idea!
- March 4, 2019 at 10:33 am #110001
Super idea if you disregard the consensus that a select few radios which employ S-meter are actually stable.
- March 4, 2019 at 11:07 am #110005
The radios we are talking about don’t have S-meters, they have LCD screens with numeric readouts and seem to be very stable.
Mine is a TECSUN PL-310.
- March 4, 2019 at 5:37 pm #110017
Just of note.. Radio Jay Allen compared the Grundig G8/Traveler II (the one ISS sells) against a Tecsun PL-310 (yours) he makes no mention of the S-meter but says the two perform about equal in AM, however he also compares those to the Eton Traveler III which says noticeably outperforms both of them.. maybe ISS should consider upgrading!
- March 4, 2019 at 11:13 am #110007
Unfortunately, the inexpensive receivers that show a signal strength value in “dBu” on their display screens are reporting only the conducted voltage that exists between the r-f input terminals of the receiver, not the field intensity value of the arriving radio wave — which is measured in units or sub-units of volts/meter.
The field intensity of a radio wave normally is defined as the r-f voltage of its electric field vectors existing between two points in physical space separated by a linear distance of one meter. No receiver or receive antenna needs to exist for that field intensity to exist.
The dBu values shown on those receiver signal displays are highly dependent on the construction of their internal loopstick antennas on each frequency the receiver is tuned to, which varies according to the physical construction (mostly the length) of the loopstick, and other factors. So the calibration of any particular one of those receivers against the field intensity measured by a calibrated field meter most likely will not apply accurately to any other of those receivers, perhaps even another one of the same design and manufacture.
Below is a link to an example of the difference that a Tecsun PL-310 showed to the known fields it was “measuring.” The errors shown in the far right-hand column are substantial, and non-consistent.
- March 4, 2019 at 4:07 pm #110015
Apparently I had missed when this all already had been discussed when it first came out in 2013: https://part15.org/forums/topic/big-big-news/
Upon finishing reading the entire thread, still came away with no conclusion on if the Grundig SMR radio they sell fared any better with accuracy than a Tescun or any other radio featuring an S meter.
- March 4, 2019 at 12:10 pm #110010
The FCC did nothing for FM hobbyists with 15.239. It is written only to the benefit of certifying labs.
And Tim in Bovey has proven that certified FM transmitters are not reliable, some of them are well above legal power, others below.
The only useful yardstick is that FCC Document estimating that 200-feet would be the typical range of a compliant FM transmitter.
KDX-FM exists according to the 200-foot “rule”.
In fact, we have found that when the TECSUN dBu reading shows 07 dBu the FM signal drops into the noise, which we established at only 100-feet, which means we do not use our full legal reach, most of which is out in a street intersection.
- March 4, 2019 at 12:27 pm #110012
Why would the FCC care about FM hobbyists?
- March 4, 2019 at 8:01 pm #110024
Total posts : 218
The suggestion posted earlier in this thread that Tim could produce and publish/sell a calibration chart for a particular brand of radio with a built in signal strength meter correlating the reading with field strength sounds good at first read but it is not workable.
The reason is that unless a chart is made for a specific radio (not brand or model) there is no guarantee that the chart is accurate. I studied measurements formally and worked in a metrology lab and the underlying principle was to calibrate each individual instrument against a standard of known accuracy. You cannot test one typical instrument and conclude all others of the same type are going to present the same accuracy.
One reason the field strength meters are so expensive is that each unit manufactured has to be individually calibrated against a NIST (in the U. S.) traceable standard if it is to be used in commerce or regulatory applications, and in addition, are required to maintain their stated accuracy for a specified period of time which adds complexity to the design. Typically, in industry, instruments require calibration each one or two years while in service.
- March 5, 2019 at 2:22 am #110028
The key words in the description for the ISS radio are: “estimate”, “relative” and “rough”. And lets not forget “not a calibrated device”.
Now, this is not to say it wouldn’t have value. You can indeed use it to determine relative noise levels on various frequencies when determining which frequency to use for your station. The meter will handily show noise floor levels.
And it would indeed give you a relative field strength indication of your station at a particular location, which could signal trouble with your system. For this to work you’d have to choose a place for the receiver to sit, and then every so often flip it on and note the signal strength. If you were to notice a substantial drop this might indicate that your transmitter or antenna has gone awry and needs attention. However, even the slightest movement of the radio, as well as your position standing near it, will also affect this reading. So you can’t move it, or stand in a different spot while noting the readings.
I can promise you the tolerance in constructing these radios is not that good. Readings will vary from set to set under otherwise identical conditions.
You get a rough estimate of field strength with the chart. And you get relative information, that you can compare to it’s own readings over time as to how they relate to each other.
I don’t know of too many AM Part 15 folks who use the maximum field strength rule for their stations as this greatly limits range and is hard to measure without the right equipment. Most use the antenna/ground length rule coupled with 100 mW to the final input stage, things that are relatively easy to measure without buying expensive equipment. A radio like this only shows relative information, and nay radio with a FSM on it would do the same for relative readings. Communications receivers with sensitive meters have been available for decades and for these purposes would be just as accurate if not more so.
Note that this radio only references AM field strength accuracy and use, not FM, which is where it actually matters. Part 15 legality is determined ONLY by field intensity and these are not going to be accurate enough to determine if you’re legal on FM.
I just realized that I HAVE one of these little Grundig radios. It wouldn’t be to hard to determine my own field strength chart.
- March 5, 2019 at 3:09 am #110031
As I view it the TECSUN PL-310 (the radio we use at KDX) is TWO (2) test instruments in one:
The AM & FM receivers being very sensitive and stable, the radio can be used in ordinary listening tests to walk the neighborhood and make estimates about the performance of part 15 signals.
We have taken the technique of using radios to judge compliance as common place even though it is an imprecise means of measurement.
KDX is fortunate to have a spectrum analyzer and here again we have a “dull” tool for making relative measurements of our signals compared to other signals at our reception location.
Therefore, as yet another “ballpark” measuring device, the strength readings on the display screens of the radios we are talking about serve as a 3rd way of grabbing a generalized idea of what our signals are doing.
Part 15 operators get closer to accuracy with these dull tools.
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