Broadcastvision FM Transmitter Lab & Field Tests & Review

Interesting set of measurements and comments, Tim.  Nice work.

Below is a NEC4.2 analysis based on your measured data, showing how the field present at a horizontal distance of 3 meters from the transmit antenna varies with the height above ground of the receive antenna.

These variations are produced by the changing r-f phase and amplitude present in the reflection of radiated fields from the earth, due to changing angles and path distances of the reflection.  Those changing reflections combine in the receive antenna with the direct field from the line-of-sight path between the transmit and receive points, to cause the variations seen in the plot.

The input power in this NEC analysis was set to produce a field of about 24.5 mV/m at a horizontal distance of 3 meters from the transmit antenna, and a height of 2.13 meters (7 feet) above the earth -- as per your test setup.

For the 6 mS/m earth conductivity assumed for the NEC study (about average), it took about 25 mW of applied power to produce the field you measured.  That power is fairly close to the power you measured at the antenna output connector with your wattmeter.

Always nice when theory and practice support each other.

Makes you wonder how they go this thing certified.

The BroadcastVision I had (an earlier model) had slightly less range than my Decade MS-100 (which was BETS-1 certified, 100uv/m @ 30 meters).  Still probably well above the Part 15 limit, but well below the model you tested.

Suspected it would be over but not that much! Wow!

Even here in Canada it's way over.

As for the power supply I just throw out the ones that come with the transmitter.

I use what I have here, a switching one yes but one that doesn't hum....they're not all the same. The block style ones are the absolute best.

The Decade MS-100 which I use mostly now is a A/C 16V supply and no hum as the power supply is on board and better quality.

Now that I think about it the Broadcastvision maybe had a LITTLE more signal strength that the Decade MS-100 but not that significant.

Was also surprised at the 20mW output as that can explain the range you got.

The most you can get from the Decade operating at max output is, according to spec. 1.1mW and I was told that when set at BETS-1 the approx. setting is turning the RF out adjust to max. and turn back 4 turns.

Thanks again for tests!

Mark

Makes you wonder how they go(t) this thing certified.  The BroadcastVision I had (an earlier model) had slightly less range than my Decade MS-100 (which was BETS-1 certified, 100uv/m @ 30 meters). ...

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Other things equal, both theory and practice show that the e-m far fields existing at every distance and height AGL from a transmit antenna are dependent on the propagation and operational environment for that installation -- regardless of the physical setup and procedures used to certify that transmit system.

The fact that a given system may comply with Part 15/BETS-1 limits in a test lab does not automatically mean that it will do so when installed and operating elsewhere.

I would expect there to be variation between the lab and real life installations, but, as in this case, a difference of 100 times? 

Are we to believe that the certification testing required is so inapplicable to real life that virtually all tested and certified transmitters are in real life many times over the limits? And that doesn't account for the C. Crane, which came in under the limits after teting 11 different units!  If, when tested under the same "real life" test conditions would that mean the C. Crane was, say 100 times BELOW the limit in their certification tests?

All the certified transmitters I've tested were rather substantially over the limits in the field, with the exception of the C. Crane. 

Are we looking at a fault in the certification system and requirements, where the specified testing is not providing results that provide the wanted results in the field?  If the FCC intention is to limit radiation to 250 uV/m with these transmitters when in use, perhaps their test requirements should reflect real life?  Either that or the law should be changed so that using an unmodified, certified transmitter is defacto defense in the case of a violation.

The idea is that these various test labs should have virtually equal and comparable test rooms, where the same device tested from lab to lab brings the same results, with a very very small margin for variation in the results. 

Either that or the manufacturers have figured out that it wouldn't take long for people to stop buying FM certified transmitters if they ALL had a real, true practical range of a few feet.  We often mention that a legal FM transmitter will have a range of a couple hundred feet.  But what's that coverage when it's in the middle of someone's house? A typical citizen would soon quit buying/using transmitters that don't reliably get to the street in front of their house. Maybe manufacturers actually submit "test units" to get the certification, then sell the public units adjusted for more coverage. After all, the number of people "caught" being over power with these units is probably statictically zero when compared to the number of units sold. 

And in most cases the people manufacturing the units are not the people selling them. Broadcastvision doesn't have a factory churning these out, they're clearly made by Waio, as that is who the certification is granted to. 

Perhaps it's time I try to talk with a couple reps from these various testing labs. The certification application for the BV transmitter is 72 pages long. Test setup photos show the antennas are at least 3 meters apart. Can an RF isolated room actually result in a lower field strength than open outdoor space?  And to the result of 100 times?

Something seems fishy here.  I have questions that only FCC people (not field agents, but internal people) and lab owners can answer!

TIB

... Can an RF isolated room actually result in a lower field strength than open outdoor space?

Such rooms attempt to eliminate e-m reflections from the transmit system under test, to the extent practical.  The goal is to approach free space conditions for the fields it measures.

However VHF field measurements made in an open, outdoor space in the real world necessarily will have a reflection from the surface of the earth between the transmit and receive antennas.  That reflection can either add to, or subtract from the line-of-sight radiation from the transmit antenna, depending on the relative r-f phases of those two signals at the receive location.

This situation also exists for typical, installed "Part 15 FM" setups, except usually with many more sources of reflection, and even obstructions in the line of sight paths to receivers.

So it is possible and even probable that a Part 15 FM setup could comply with FCC §15.239 when measured in a test lab, but not when used for its intended purpose in the real world.

... And to the result of 100 times?

Not likely 🙂

Something seems fishy here.  I have questions that only FCC people (not field agents, but internal people) and lab owners can answer!

Those answers would make very interesting reading.

I’m going to be careful with my wording or I may be attacked. Our spokesperson for the New Radio Revolution has discussed with an agent of the FCC their stance on Hobby Radio (since we’re looking to open a new service for Hobby Broadcasting). They have mentioned at present there is an allowance of 250 uV/M @ 3 meters from the antenna (This we know) and the fact that the 150 Ft range is an estimate range to an average receiver and an average height to which most users would be operating. When we asked about operating at the 24^th floor and getting a range of 1 mile or (often more) still being legal the agent said that as long as the transmitter is not modified those ranges are possible under extreme conditions. A remark about changes in the FCC’s stance was uttered and this actually can go for or against our cause in a separate Hobby Radio Service.

Actually several years back the NAB has done a study of several FM Transmitters and came up with the conclusion that most were over 250 uV/M @ 3 meters(You’ll find this using Google). This came after some NPR stations got interference from some of the users who were not watching where they were operating. Plus there was a church that had a part 15 station that got interference from a Serious XM Radio with a built in transmitter and guess who was swearing and acting like a jerk on air… Howerd Stern of course. And so the limits were harshly enforced for a time to stop the obscene content of FM Radio.

I have to ask the question that with the onset of Blue tooth receivers built into car Radio’s and blue tooth transmitters and the bad reputation of FM transmitters not getting ranges that you can get with a blue tooth device has the use of these transmitters dropped in such numbers that this is no longer an issue and the FCC is not as concerned? In my humble opinion based on what we see here the FCC may start taking FM transmitters on by a case-by-case basis. We’ve read phrases like “If they are not interfering with anyone let them be.” This is what seems to be the practice in most cases.

Case in point I had a listener who told me that he was operating on 105.9 transmitting The Legacy in his area(using a Decade MS-100 certified transmitter). However there was a station just outside his contour that came in from time to time. Well someone complained about him even though he felt he was running legally. A station owner (or so he thought) finally contacted him as his number was announced over the air in place of mine and he was informed that the FCC was after him because of his interference. Again nowhere was Pirate Radio, Over part 15 mentioned. The phrase Interference was however mentioned several times. How many times I’ve said even ON AIR make sure a blank frequency is above and below yours and check after 6 o’clock for a temperature inversion. People are hard headed and thus get NOUO’s. So now I have to put this in my promo’s after every 4^th song so that these people GET IT. I feel bad for him, but I told him wait for a while and go AM. He did see strange vehicles in his area but as of yet the FCC didn’t break down his door. He did turn off the transmitter as I suggested and says he’ll put up a 10 foot antenna and go AM later. He said something about Odessa I think was where he said he was but I could not understand as he seemed excited.

Because of my Album Rock station I do have listeners who rebroadcast my station to help break people FREE from the everyday drab. And I’m loving the fact they are doing so.

I suppose we’ll find out when it comes time for the final submission of our petition but I feel that there is a relaxing of the rules and I hope that the 250 uV/M rule is thrown out the window and replaced with 100 mW (at least) just like AM and be done with it. Everyone can buy a Watt meter as even Radio Brandy sells a Workman Watt//SWR meter that can measure that sort of power.

Now I hope I don’t get attacked for my listeners rebroadcasting my Internet station. But I do hope within time we come up with a truce with the other broadcasters who don’t like Hobby Radio.

Very interesting points what Rich and Timinbovey have posted.

I guess the next step to get answers as I don't think that Broadcastvision/Waio are sending one unit for testing and mass producing the others differently, is to actually talk to the people at the test labs. I'm sure that the test facilities in the USA are approachable.

Tim, are you interested enough by what you have seen to investigate further?

You are the one qualified to do this as you are the one with the expertise and the test equipment.

Also Thelegacy raises a good point about getting the legal power to 100mW power(or whatever) as this is easy to measure with an affordable watt meter that anyone can get and measure for compliance...simple!

If the FCC checks they measure the output of your tranmitter. Certification is easier also. A simple measurment between antenna and ground.

Mark

There is still a significant difference in what Tim measured for the Broadcastvision, and other certified transmitters such as the Decade MS-100, or even the Whole House 3.

I don't know if the FCC will relax the rules or not.  I think it's a good idea to make certification easy to measure, as it is with AM.  Whether that means 15 nanowatts, or, as in the case of Canada, a microwatt (this is actually in the BETS-1 rules, along with the expected field strength that such power will generate), or something more - who knows?

I think these test are having one good outcome - at least we now know that most certified FM transmitters are well over the current legal limit.  Never mind the Chinese specials that are advertised as anything from 1/2 watt and up, and that seem to be favored by those on the Part 15 (!?) Facebook page.  I guess the moral of the story is - use FM at your own risk, even with a certified transmitter.

I think field strength should be abolished and it should be measured output power taken from circuit board antenna to ground, say 1mW or whatever.

Some other places have this rule...China included. By the way the Chinese transmitters can't even be used there legally!

Much simpler and end user can easily comply.

Tim tested the CM-10 not the MS-100 but the MS-100 has the RF adjust that can be precisely set and is set there when sent out.

The MS-100 max only gets to 1.1 mW as per specs and asked about this and the approx position for BETS-1 is about 4to41/2 turns back from max.

The one microwatt power needed to get the max field strength is with the most efficient antenna like a center fed dipole proper lengths or a ground plane.

A telescoping antenna is not the ideal antenna. I think if the MS-100 was only 1 microwatt with the attached antenna even adjusted for the right 1/4 wavelength wouldn't get near the allowed field strength. You need at least 1/2 a milliwatt or more to do this. We are using a 1/4 wavelength not the ideal full wavelength antenna.

Mark

#6 is a great post, because it asks a lot of questions, and I'd been thinking about some of this stuff after reading yesterday.

It could be just an error in setting the power in that one unit.. but for practical reasons, a fitness club is going to need a signal that can cover thousands of square feet indoors, and do it clearly around a room full of machines with motors and their controllers, and to headphone radios and phones of different kinds, with varying reception.

In the real world, that would take more power, and with the transmitter is mounted on a wall or other area just above the patrons (as BV's recommended install), indoors in that large space, it's probably not going to cause too much of a ruckus outside very far.

Plus the fact that most gyms are located in shopping centers, malls, or by themselves in a strip center, likely not surrounded by homes, just other businesses, and how many of those others are going to be concerned with FM reception of more distant stations? If you were listening to a distant station while driving through the area, how long would the gym's transmitter affect your radio as you went past?

Given all these factors, I'd have to think in the real world that a gym's transmitter, even if over the limit as stated in the rules, placed on a good frequency, has very litle impact on the surrounding world outside of the gym.

I don't need to know why there are inconsistencies in the test results, it's not a mystery to me, and I don't have to know, if you know what I mean.

The problem is when the transmitter is not used in a gym.

... I think field strength should be abolished and it should be measured output power taken from circuit board antenna to ground, say 1mW or whatever. ... Much simpler and end user can easily comply. ...

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The cost of the hardware needed to measure the r-f output power of a "Part 15" AM/FM transmitter accurately easily can exceed the cost of the transmitter producing that power.

Also note that the accuracy spec of commercial r-f wattmeters is based on a fixed load impedance (typically 50 ohms, non-reactive) -- which very rarely exists for installed Part 15 AM/FM systems.

David I think it's good that we finally agree with each other. Maybe that's why some other websites we're saying all along use FM at your own risk and really try to sway folks away from FM. It's because of the fact that in a large city where you are noticeable by other stations and ham operators  you could be given a NOUO.

I don't believe that manufacturers are all in a conspiracy to defraud the government. There is a lot more going on behind the scenes than we understand as I suspect. Thinking that all manufacturers are out to get the government by cheating on their test is not practical I don't believe that's what's going on at all.

 that's not to say that some manufacturers aren't cheating. I think the reality is that the 250 micro volts per meter rule that the FCC has set is actually being relaxed but has not really been put on the books officially 2 portray this in writing. I have my reasons to believing this what is the major lobbyists that they have to deal with.

If Donald Trump wins and he is a businessman I'm curious to find out what the outcome would be in all of this. Would he allow for hobby Broadcasting or is he a pay all the royalties you must pay type of guy even though it cost you a hundred percent of your income?

I can't imagine Hillary Clinton's view on hobby broadcasting or even if she knows anything about it.   I suppose whoever wins will find out soon enough.