Part 15 FM System Performance/Measurement

I'm very glad you bring attention to this ongoing series of events, Rich, as it will continue to inform us regarding the part 15 devices, both here abroad and there... wherever it is they come from. 

Just earlier I was over there reading the two reviews posted for the Wholehouse 2.0, and noted the planned Wholehouse 3.0 review.

In a spirit of magnanimity I will follow their effort, if publicly available, as an outsider immigrant.

i have many opinions and thoughts about that guy and his behavior over there on the other forum and non of them are flattering or would pass moderator muster on this forum.

My opinion is, who cares what they do over there?

I don't have any confidence that we'll see the raw results from any of their testing, i.e. results that have not passed through various filters.

Tim's testing is pretty definitive (Thanks Tim!).  I await the results from the CM-10, a true Part 15 certified transmitter.

Now all we have to do is to make some sense of them.

I've seen some part 15 sites who claim to be all about the part 15:239 rules but advertise the very transmitter on their websites front page for all to see.  And even after it has been posted how that said transmitter is in no way legal in the USA has not stopped their affiliation with that said transmitter that was tested and the results were in no way close to legal.  So that makes these sites questionable as to their motives because being affiliated with a possible illegal item willfully in the USA makes them liable for association with said illegal transmitter and in the USA there is guilt by association.  Oh well I've seen other twists too of their view of the rules.  Take the "At property line" phrase they used instead of from the antenna.  And I've read how a user on that site I'm talking about posted how a DJ had a huge property and their overpowered transmitter didn't go beyond their property and yet got an NOUO but knew people high up and made it go away.  So seems like their view of the FCC rules is that they don't apply to all.  I'm just saying what I observed as an outsider nothing more.  And I'm not saying I'm perfect.  OK climbing down from the soap box and back to enjoying the hobby for now.  Time to bury the dead horse.

LOL. I posted the Oompah Hour update for the coming weekend over on "the other side" better known as hobbybroadcaster.net (for those who aren't paranoid).  As I know I have some affiliates that frequent that forum rather than this one.  One of the issues I have with the Part 15 community -- the fact that we're divided amongst ourselves, but I won't get into THAT.

I simply have landed on this site and enjoy it but there is much good information over there as well.  I bear them no ill will and believe we all have a common interest in Part 15 broadcasting and I don't want to get into any sort of battle between sites. 

I have many thoughts about some test procedures Bill has used on the FM transmitter tests he has posted (Yes, he has a NAME it's childish to avoid using it), although they all seem to be several years old now.   First of all, you can't get your transmmitter from the seller or manufacturer. You need to be sure it's a unit that wasn't hand picked. I noticed he had the transmitters on a ladder.  At first I thought it was metal, but it appears to be fiberglass with metal steps and parts.  This metal near the transmitter makes a difference.  I tested for this, and used a wooden pole to support the transmitter for my tests. The transmit and receive antennas, according to the Potomac manual, need to both be at either 7 feet or 30 feet above ground. In his photos the Potomac does not appear to be this high, but it's hard to say definitively as it's antenna does have a telescoping mast.  Is he accounting for antenna factor as described in the Potomac manual?  You can't read the actual field strength directly off the meter. Antenna factor depends on your test frequency either the 7 or 30 foot test height, and your reading must be multiplied by this factor. There's a graph in the manual. And in NO test I've ever seen on hobbybroadcaster is the actual field strength reading given. It's always -- it was a bit over or  under legal, it was stronger or less than the base transmitter, but we don't have the reading for that one either.  It also appears he's near a tree line in the photos.  Hard to tell the perspective exactly from the photos, but it was a concern. 

I would certainly expect his upcoming tests to have different numbers than mine, just based on the fact that I'm sure the transmitters vary in tolerance, and there are other factors to consider, plus the fact that the 7 foot tests have a 18% tolerance (note I figured this in and they were still well over legal). 

I think it's also important that the field strength once an audio cable is plugged in be included. The huge jump in output was clearly shown with the WH 3.0. it was a HUGE jump.  I also did this with the CM-10, but just in quick test in the front yard when I first got it, not out in the field, and not at proper height, etc... but again, even with the CM-10 as soon as I plugged in the audio cable the RF output made a HUGE jump. Even on an uncalibrated meter, set up wrong, this HUGE increase is readily apparent.

I did exchange emails with an engineer at Potomac, concerned about what seemed to be unlikely high field strength numbers for a "certified" transmitter and he said I would be surprised at the number of labs and engineers that call them having a hard time believing that so many Part 15 devices (not specifically hobby transmitters) turn out to be well over legal limit!

TIB

Interesting.....wouldn't it make sense to test for certification with an audio cable and A/C power cord as it would be used? Who uses a transmitter just turned on without audio? Think the test facility techs would know this.

These tests you're doing are bringing to knowledge what was never thought of before!

Then maybe certification is just the transmitter and intentionally doesn't include accessory cables?

Mark

this is why when a rangemaster or procaster is place high up even if the ground isn't connected they still get much much more range than a ground mounted system over radials, it's why a talking house does so well from the top floor of a building and not so well on a first floor.

the power and audio leads will and do radiate and it is very hard to sufficiently suspress radiation from those power and audio leads

OK if the tests are done with audio cables and we all know no two companies audio cables are the same. I can buy GE audio cables from Walmart which have 3.5 mm male ends on them and connect it to my transmitter which does cause the Patomac FIM-71 to jump to a higher reading. Joe Smith can buy the very same transmitter and have everything the same on his transmitter and go to Best Buy and purchase Monster cable because he has more money than I and wants the best. He goes home and plugs his audio cable into his very same transmitter I have and he just so happens to have a Patomac FIM-71 around his house lol. Anyways he tests the transmitter and gets a higher reading maybe 20-30 times higher than I did. So knowing there is such a margin for an error, does the FCC take all of this too under their consideration before they deem the transmitter unworthy or its presence on US soil? Sometimes I do wish someone who works for Uncle Charlie would pipe in and say Hey guys this is what we do and give us a idea of what is blatantly against FCC regulations and what they may frown on a little but will pass by the skin of the teeth. I think but don't quote me that they simply use a dead carrier. But that is not how a Radio station adjusts their transmitters. They inject a 440 Khz tone at 50-100% modulation to see if the transmitter is putting out what it should. So I'd like to know if injecting a tone on air would cause the transmitter to deviate wider than the 200Khz allowed for FM? If so that too should be illegal. Do they take spurs and harmonics under consideration as well? Maybe I don't know but maybe they overlook field strength if the transmitter is unbelievably cleaner in emissions than others of its type.

Speaking of FM Transmitters it looks like TAW Global is up to some other tricks as they are coming out with a yet stronger transmitter than the Whole House FM Transmitter 3.0 and get this sit down for this one. Its output is 1.2 Watts and is getting FCC certification to be sold in the USA. What? That is TWICE the power of my SainSonic AX-05B already a gray area transmitter. Now this is out of the box NO secret power switch flipped or two button combinations pressed to get this power. When I followed the link on Hobby Broadcaster that talked about this transmitter the FCC's site is being redone talking about some changes in part 15. DID THEY CHANGE THE RULES WITHOUT OUR KNOWLEDGE? Somehow this is doubtful. But there is something rotten going on here with this. Now my Sainsonic gets out ¼ of a mile on a Car Radio in Stereo till rock solid quick drop off like a cliff. Your talking about a transmitter that will go over a mile now on a Car Radio and possibly a mile on a boom box. How far is this transmitter going to bleed the entire dial on FM? You know people are going to rush out to buy this new transmitter and every person why ever wanted an FM transmitter will now have one and set up their own neighborhood station. I guarantee you the FCC won't give 75% of the part 15 population a NOUO. Is this their way to try and force the FCC to increase the rules by deceptive and underhanded practices as to get the public so their not worried about their transmitter and then spring a transmitter at the New Zealand power level? Plus its interesting that FM user is now carrying their new transmitter when it comes out. We're gonna have fun now.

they are complete garbage, i have a rack mount harris MS-15 agile exciter that can adjust from well below part 15.239 levels up into full blown pirate and have an optimod 8000 for it. had it on the spec analyzer in the nanowatt range and it didn't have so much as a blip anywhere up to 650 mhz. it's cleaner than even a part 73 setup qat part 15 levels and that is probably 35 year old technology now. and on top of that it is built like a sherman tank. good ol amaerican engineering when things were still made here.

Interesting.....wouldn't it make sense to test for certification with an audio cable and A/C power cord as it would be used? Who uses a transmitter just turned on without audio? Think the test facility techs would know this.  etc.

All of the text below is speculation ...

Maybe the certification testing needed to prove compliance with FCC Part 15 in practical use was not sufficiently defined in the reference(s) used by compliance testers.

Added to this is the possibility that the FCC may not fully have understood/vetted the test data submitted to them before issuing a Part 15 compliance certificate for a given device.

I've also thought this, like kc8gpd said, it could be hard to stop the increase the field strength caused by plugging cables in.

I've seen the schematic with chokes on the audio input that was posted by Carl last week, but even plugging something in would create a capacitve connection with the circuit and might radiate and increase the efficiency of the supplied antenna. A transmitter with a wire antenna and something plugged into it is working like a dipole with the transmittera t the feed point.

I agree about not having feuds with other sites. I dont' knwo how important the argument is since I've only read about it here and wasn't around then, but in general it seems there's more fightin' to be done about the rules, consolidation that allowed local radio to be taken away from listeners, and good things like making the most of Part 15 for individual fun and maybe for community service.

The net is wonderful, but not for your immediate community. It was tried with NeighborNode, but that failed, I guess people weren't used to using the net to commune with their neighbors.

Thelegacy.....Where did you see this about a "new" wholehouse? Nothing on their site.

Transmitters can be certified for applications other than part 15. Part 15 is just an unlicenced catagory.

Did this say no licence needed? was it part 15 certified?

It could be getting certified for sale in the USA but maybe not for unlicenced use.

Mark

It wasn't Part 15 certified - Part 73 (? - too lazy to look it up) I believe.  Requires a license.

There are probably better transmitters out there for that application.

good things like making the most of Part 15 for individual fun and maybe for community service.

Kindly note that no FCC NOUOs likely will be issued to the operators of unlicensed AM/FM transmit systems actually complying with Part 15 -- regardless of the "individual fun" those operators experience, or the "community service" such operators believe may be provided by such systems.