- Posts
Hello all Hope you all are having a good summer. Well I had some rich blood in me so to speak and I saw the Broadcast Vision Transmitters on e bay and decided to get one. I got the metal black 3001 version. It is very small and a nice unit! I put it up in my closet on the top self hooked the wall wort up….put it in mono and turned it on. I drove around my block and was blown away by the reception. I was figuring I would hear the thing about out to the end of my driveway….but no I heard it three houses away from mine and a little bit further down the road until it finally went completely static. Now I have not modified this thing at all. It is currently set to 87.9 FM and the telescopic antenna is fully extended out. Do you guys think this is o k? Can the power on these things be turned up or down? I saw on some other auctions that they were only putting out 1 milliwatt? Do i need to be worried about this or just enjoy it as is?? I just want to be legal that’s why I was so excited because this transmitter has the sticker on it:)The audio sounds great! However it does get a little distorted on some songs. It could be my processing though. I am still tweaking on that.
When I first powered it on I set it to 106.9 FM there was no audio but when I turned my receiver all the way up I heard the 50,000 watt FM at 105.3 bleed over into my transmitter. Is this normal… considering that this is a part 15 compliant device? I changed frequencies at this point to 87.9 and did not hear any bleed over from any other local stations. By the way when I was testing this I was in my truck under my carport.
Any advice, stories, and suggestions are welcomed. I want to make sure everything is right. I don’t want to be worried of compliance issues or anything.Look forward to hearing from you guys.
Total posts : 45366BEV’s own ads say it has a range of 25,000 sq. ft., i.e., approx. 1 square mile — Ridiculous!! It would be in violation of FCC rules, and, further, I saw no designation anywhere which claimed it is Part 15 certified.
The ONLY FCC (U.S.) range and bandwidth criteria on frequencies within the FM BCB for determining the legality of a Part 15 FM broadcast band signal is pretty much engraved in granite. Word-for-word, it reads:
“15.239 – Operation in the band 88-108 MHz.
(a) Emissions from the intentional radiator shall be confined within a band 200 kHz wide centered on the operating frequency. The 200 kHz band shall lie wholly within the frequency range of 88-108 MHz.
(b) The field strength of any emissions within the permitted 200 kHz band shall not exceed 250 microvolts/meter at 3 meters. The emission limit in this paragraph is based on measurement instrumentation employing an average detector. The provisions in 15.35 for limiting peak emissions apply.”
… For a reasonably clear stereo signal, this works out to about 200 ft.
Total posts : 45366Thanks for that important information. What I guess I am confused about is on the bottom of the transmitter it has an FCC approved certification on it. It says FCC ID # M3R FM3001 Below this it reads of course this device complies with part 15 of the FCC rules and regulations etc….. So I am now curious as to how they being a US company got away with a patent on something that does not comply with the rules set fourth??
Any thoughts on this???
Thanks
Total posts : 45366Well, in that case, it simply means that it was certified as tested. There are any number of ways the signal can be attenuated for testing and certification, like antenna mismatching. That means staying legal is up to the operator. If, for example, you did anything to boost the signal gain outside of the testing parameters (and we don’t know what they were), it might come to a place where it is in violation in the strictest sense.
But here’s the other side of that coin: The FCC has not issued enforcement orders on anything like your home FM broadcasting unit. They have bigger fish to fry, as in those who buy those 5 watt blasters on eBay. If they catch you with one of those, they will issue a NOUO in relatively short order.
FWIW, and this is a no-fault opinion, I think you’re probably about as safe with your unit as can be expected, what with its Part 15 certification and all. If you get a 1000 ft. to a good receiver, then good for you. In your case, the very worst thing that would happen is they tell you to shut it off … but I think it’s unlikely.
Total posts : 45366Regarding the bleed over of a strong transmitter into adjacent frequencies. That’s more a statement of the quality of your radio, rather than anything else. I know that my car radio will allow a little bleed over 200 Khz adjacent to the strong signal, but that strong signal disappears 400Khz over (no matter how strong it is). My weak Part 15 FM signal could not be heard 200 Khz over.
As for the BroadVision transmitter, I had several of them. They are Part 15 certified. Receiving the signal 3 houses down is not uncommon, depending on your lot sizes of course. You should get 200 feet or so range to an ordinary radio (and up to 600-800 feet range to a good car radio).
Total posts : 45366I get stumped on stuff like that all the time. Thank goodness for the internet!
Most agree that the expected legal range for the field strength limit of 250 uV/M is going to be around 200 feet on an average receiver.
One way to look at that is to see the transmitter in the center of a circle with a 200 foot radius
Area of a circle = pi X radius squared
3.14159 X (200 X 200) = 125,663.7 square feet
For reference, square mile = 5,280 X 5,280 = 27,878,400 square feet
Square root of 25,000 = 158, so the manufacturer has either put the transmitter in the center of a square 158 feet on a side or if in the center of a circle:
3.14159 X something squared = 25,000
25,000/3.14159 = 7957.75
Square root of 7957.75 = 89.2
So with a circle with a radius of around 90 feet, not 200, the manufacturer in this case seems to be within accepted part 15 limits, but I agree, at first glance, a range of 25,000 square feet sounds way out of line.
Great marketing ploy 🙂
Total posts : 45366Ken is right, of course, about the quality of a radio receiver having much to do with how adjacent signals are handled, but there are antenna issues I have found…
Part 15 is so weak compared to the upper-kiloWatt full power stations, if their signals are near yours on the dial..
Your transmit antenna very likely receives a huge dose of kiloWatt energy that can back-flow into your transmitter and actually appear as noise on your signal.
The radio tuned to your signal also is receiving more power down the antenna from the adjacent signal than from yours, so it may leak in.
This also happens on AM if stations are nearby both on the dial and within a mile or so.
A very good practice to avoid this, if possible, is to find a frequency whose next-door-on-the-dial stations are far away geographically.
Total posts : 45366Thanks guys for you comments on this. I learn something new everyday:) Driving around the neighborhood today, the signal does go about 800 ft or so in the car and then totally disappears even when I am on the other side of the street their is some static with trees and all the houses. I feel better about the legal issues regarding my transmitter.
I was wondering those of you who have Broadcast Vision transmitters….Do you have problems with the audio being a little distorted and flat sounding? I am trying to tweak it and get it to sound as normal to the other local stations that I can. The audio also sounds a bit low. If I turn it up on the back of the transmitter It gets a little too distorted. I am using a Breakaway Audio Processor on my computer and then it goes through my mixer and then out to the transmitter. I have tweaked the settings on the processor but it still sounds a little to flat and distorted on some songs. One more thing I noticed is a little bit of hum…. I am assuming this is caused by the power supply that came with it? It is very very low I can only hear it when in between songs. Can I eliminate this completely though?
Thanks again for your help and guidence!
Total posts : 45366Yes, given enough time and detective work, plus a handful of capacitors, chokes and perhaps a couple of ferrite toroids, you should be able to push that down to at least below audible, which is all we care about 🙂
Please to be enjoying one of our earlier entries:
Total posts : 45366I was thinking 5×5000, not 5000×5000. Sorry, my head gets tired very quickly when I try to do math inside it 😉 A square 200×200=40,000.
Area of a circle=; πr sq’d
Total posts : 45366I was thinking 5×5000, not 5000×5000. Sorry, my head gets tired very quickly when I try to do math inside it 😉 A square 200×200=40,000.
Indeed, Area of a circle = π r square = 3.1416×40000 = 125664 sq ft.
What type of inexpensive receiver, other than a car radio, would y’all recommend for listeners outside the house range? I’m thinking Sangean, Sony 7600, Blaupunkt, Grundig, C Crane.
Total posts : 45366Both offer inexpensive pocket radios that pull in weak signals well and are also easy on the batteries – check your favorite product rating site.
External loops will make a big difference. If a radio does not have an external antenna connector option, a few turns of wire around the radio at right angles to the antenna core will serve as the ANT connection and the ground can be clipped to an earphone ground or negative battery terminal.
http://www.eskimo.com/~nanook/radio/2007/01/am-medium-wave-box-loop-antenna-for.html
http://members.cox.net/rwagoner/columns/am_antenna.html
http://www.iw5edi.com/ham-radio/?how-to-build-a-tuned-loop-antenna,118
Total posts : 45366The BroadcastVision is Part 15 compliant, which means that the signal won’t be getting into the aviation bands (unless it’s been modified).
Your analysis of the range of Part 15 FM is accurate as far as it goes. But don’t forget that a field strength of 4uv doesn’t mean that a signal of strength 4uv will be getting into your radio. I believe there were some posts earlier which talked about how to calculate the signal strength given the field strength. It appeared, for a rough rule of thumb, to be about 1/2 the field strength. So that 4uv field strength means about 2uv signal strength, which is close to the sensitivity limits of a good car receiver with a reasonable level of quieting (some may go down to 1.5 uv with some quieting). So that 600 to 800 foot range for a good receiver, and line of sight to the antenna, is probably pretty accurate. I would imagine that a better car antenna would make some positive difference as well (that measurement assumes a 1 meter rod type antenna).
Total posts : 45366If somebody gave me a Broadcast Vision
transmitter cheap I would use it but only
under certain conditions.As I’m sure you know, the FM band is right
next to the aviation band (108 to 136MHz.)I would try to find a radio friend who had
access to a spectrum analyzer and see if
the output is clean. I am very conservative
about this stuff (that’s just me) but if the
thing is putting out any energy in the aviation
band that wouldn’t be good at all.Then if that is OK you rig it to not go too far
and comply with Part 15.239.What this means is a subject of debate. Some
people have said that if the signal is gone about
200 feet away on a good FM receiver then you
are in compliance. Other people have said that
around 800 or 1000 feet is OK for complete fade
out on a really good receiver.If you are looking at 250 uV/m at 3 meters – a little
less than 10 feet – you can extrapolate that out to
some distance. Such as:125 uV/m at 6 meters
62.5 uV/m at 12 meters
about 33 uV/m at 24 meters
about 16 uV/m at 48 meters
about 8 uV/m at 96 meters
about 4 uV/m at 192 metersI guess that’s about 640 feet or so.
You could also take it out to
2uV/m at 384 meters, I guess.
Or 1280 feet roughly. At that
point the signal should probably
be gone or almost gone.It seems to me that’s when most
really good car radios start to lose
it as far as sensitivity is concerned.My car radio is great. It can hear
FM stations 80 to 125 miles away
while driving around town. These
are very weak signals, as would
be a Part 15.239 compliant signal
at 500 or 1000 feet or so.I have done comparisons between
mono and stereo and have found
in my experiments that both fade
out about the same time, but the
mono quality is much better than
stereo as the range goes from
near the transmitter out to some
distance. For instance, if I run
stereo, the signal is choppy on the
car radio sooner than if I am running
mono. In mono, a lot of those deep
fades and nulls do not happen until
the whole signal is gone.Oh well, that’s my 2 cents. I am not a
radio engineer, but just a dude who loves
radio. I’ll say this – a Part 15 compliant
signal might not even get into a neighbors
clock radio next door. MY clock radio is
awful. it has trouble with the local stations.Best Wishes,
Bruce, Dog Radio Studio 2P.S. I just thought of 2 more things.
If you have a really good scanner receiver
that covers the aircraft band and local
fire, etc., you could tune through those
ranges and look for spurious emissions.
This can be VERY tricky, though. If the scanning
receiver is too close (or not well made)
it may overload and
hear your signal on frequencies that your
transmitter is not really transmitting. It
could just be overload in the scanners
RF section. Then you would have to figure
that out.You also mentioned the flat sound of the
transmitter and the little bit of distortion.
I have a really cheap Maxell P-13 Part 15 FM
transmitter that I brought at a drug store
for only 12 dollars. It only transmits on
4 channels, so I don’t use it much.No matter what I do, it will only do 80%
deviation (I have a meter that measures
that.) So basically, it is not as loud as
my other Part 15 transmitters or regular
radio stations. However, using an audio
equalizer and an audio compressor/limiter
I can get it to sound pretty good. You just
have to fool with the settings for a while.
It still has softer audio than the other stations,
though.
Total posts : 45366Yup, you are absolutely right!
I had forgotten about that!
Really good to know.
Best Wishes,
Bruce, Dog Radio Studio 2P.S. Probably about the same
time you were writing your last
post, I added some more comments
to my post with the site’s edit function.
If you have any comments on my
additional input they are welcome.
- You must be logged in to reply to this topic.
