So I went and bought one of these cute little Tecsun radios that have the signal strength dbu meters in them. Why?  I guess because I felt like it at the time :)  I've always wanted to take one of these out and compare the dbu numbers to actual field strength readings in volts (well, mv anyway).  Theoretically, if these radios are built with any decent quality control I should be able to determine what dbu = what mv, etc. and if this holds even slightly accurate from radio to radio ya'll could use the info for some non-scientific field strength readings.   Seems to me there was an outfit selling Tecsun radios that came with a chart that did this, actually (at a rather steep markup if I recall).  So, anyway, something to play around with. 

At first I thought I had received a radio for a different country.  Only tuned to 1620 (which worked for me since my station is at 1620) and the ad sad AM tuning 520-1710. but I discovered when I changed the AM tuning step from 9 to 10 KHz, it also changed the band for AM from 522-1620 to 520-1710, also changed FM from 64-108MHz to 87.5 - 108 and changed the temperature from C to F.  Thsi wasn't mentioned in the instruction booklet (although I admit I had to read it with my reading glasses AND a magnifying glass).

Anyway, experiment results to come  :)

Tim in Bovey. 

Hi Guys: Test on the talking house ver 5.0 using the wire antenna in  a brick house.

Test was done on june 3,2015 from 11:00 am to 11:50 am est 86 degrees clear & partly cloudy.

No additional ground was attached to tx in test.

Test setup - Tx unit was 4 feet 4 inches of floor to bottom of tx.

The wire that come with the transmitter is a 18 awg stranded alumium wire at 118 inches or 9 feet 10 inches  long.

Test 1 - Was done with original 18 awg stranded wire antenna setup was 2 feet 10 inches was in a vertial position and approx 6 feet 2 inches in a horizontal position.

Range result of test 1 -  1/4 mile range fairly strong, But did hear up to a mile away, But some spots where spotty.

Test 2 - Tx & Antenna placement was the same setup as above.

Used 12 awg solid copper wire antenna in this test.

Range result of test 2 - 1/4 mile was a little stronger, Spotty in spots 1 mile range a little weak.

But did show stronger signal in spots using solid copper wire.

Conclusion - I have found with Talking house / iam radio tx that the antenna should be mounted outdoors in the clear and should be in a full vertical position to give you maxium range.

I havemounted the antenna in a vertical position and did do better in range.

I notice when i mounted antenna in a horizontal position the range was not as good.

This is what i found doing the test at my location.

As doing so many test on different am tx i have found each tx acts so different from each other and you have to be set up and test at you location and make changes for you to get maxium range or your area.

station 8

Is there such a thing as Carrier Current FM?  I remember clock Radio's that had those antenna's that used the electric cord as an antenna.  Now I do remember messing with AM Radio's back in the day that if I put a transister Radio on top of a lamp cord it would carry the AM signal further.  Now I know AM follows the earth and that to make a full wave on AM you need a really long antenna.  But if there is a way to do FM carrier current as part 15 it may be something I'd be interested in as the current would follow the power line and we have one that goes all around the neighborhood and its so close to the house I can almost touch it (something I'd never do).  But point being that I've even considered carrier current on AM but it might be more than I could do since I'm not skilled in high voltage.  I was hopeing that all it was is a tuner and it used the 3rd prong as an antenna.  It something I was curious about as far as carrier current FM.  Could I somehow use say a SainSonic AX-05B and run carrier current FM?

I picked one of these up used on e-bay for a good price.  It's the right size for what I want to use it for, and it is Part 15 certified.  It is also RSS210 certified in Canada - RSS210 is pretty much identical to Part 15 but for one small caveat.  RSS210 cannot be used for broadcasting - for that, you need to use BETS.  The basic technical requirements for BETS are the same as in RSS210, but BETS allows 4 times the field strength of RSS210 in the FM broadcast band.

And here is where it gets complicated.  There is no BETS certification.  You can only get RSS210 certified transmitters.  If Industry Canada stops around to inspect your broadcasting studio, you have to show BETS compliance only.  If your transmitter is RSS210 certified, then by default it is BETS compliant, and you are also allowed to increase your field strength up to 4 times that of RSS210.

With the legal stuff out of the way, I was very impressed with the sound quality of the Whole House 2.0.  I really couldn't tell the difference between it in mono mode and my Decade MS-100.  I used a quality USB AC adapter (not one of those dollar store el cheapo's) to power it via its USB port and I noticed no hum (you can also use batteries or plug the USB into a computer, but I didn't attempt either).  I do all my audio processing external to any transmitter I use, so I didn't even bother to use the AGC.  Much has been made about this transmitter being prone to overmodulating, but I didn't find that was the case.  The input control on the Whole House is fairly coarse, so I just put it on the setting where it started to distort, and then backed off the volume on the audio chain side.  In doing that, I was able to get a clean, undistorted signal transmitted that was as loud as anything else on the FM band.

Now, the Whole House comes with an antenna extension kit for countries other than the U.S. that may have more liberal rules. In another review, with that kit installed, the field strength of the transmitter was 1000uv/m at 3 meters - exactly the maximum allowed in BETS.  I don't have the required instruments to measure field strength, but I did notice a definite signal increase with the antenna lengthened, and it appeared to approximate the range obtained by my BETS compliant Decade transmitter.

The build quality of the Whole House is definitely not up to the standards of the Decade, or my other FM transmitter, the Landmark FM-350 (both Part 15 and RSS210 certified).  It is made out of lightweight plastic, and looks and feels cheap.  But then, it costs a fraction of the Decade and the Landmark.  I noted that the LCD panel was not fitted on straight, but I don't know if that was a vagarity of my particular unit, or standard across the product line.  I also don't know how long the transmitter would hold up under continuous 24/7 transmitting - you certainly wouldn't want to give it a bump of any kind.

It was fun to test this out, but I don't think it will replace my Decade.  I wanted to put a transmitter on a window sill, but the lengthened wire antenna is very long, and it just won't fit vertically extended (my townhouse complex doesn't allow any sort of outside antennas).  I think I'm going to put my Decade on the 3rd floor on top of a dresser overlooking the window and see what kind of range I can get there (it's pretty poor right now on the first floor).

All in all, the Whole House is a great transmitter for those who want to get into FM microbroadcasting on a limited budget, either in Canada or the U.S. (those in the U.S., of course, can't use the antenna extension kit legally).  New ones go for about $150 on e-bay at a buy-it-now price, and the seller also usually has several on auction that go for anywhere between $100-$150.

I'm probably also going to sell the one I have in the near future.

Yes I have one, what? An AM C-Quam Stereo kit already assembled by Chris Cuff himself and fully operational! See images below.

This area in the photo above is where the RF output stage is. That transistor is the output transistor Chris Cuff used, but this transmitter only has a distance of 20 feet from the antenna.

Here is a photo of the kit below. Output stage is in upper left corner.

I do not know if you can ID that output transistor because I have fallen on a dead end with IDing it. It does not cross reference to anything. The numbers on it are 1034-01

The output on a 100 foot wire is limited to maybe 20 or so feet.

I have an Realistic TM-152 AM Stereo receiver, it does pick up the AM stereo pilot quite well.

The problem is this transmitter does not cover anywhere near the part 15 allowed in the USA and I have no clue how to get the output up to allowable part 15 AM range.

Any ideas what I should do?

Bruce.

The RF output power adjustment in the AMT5000 part 15 transmitter from sstran.com has creative applications.

The RF power control of course was designed so the user can adjust for precisely 100 mW, but it has other uses besides.

For strictly indoor AM listening I back the RF power down to 36 mW (minimum power) which is just exactly enough to cover the interior without reaching other neighborhoods, although at such a low level it provides a real DX challenge for distant listeners.

While dabbling in the yard 36 mW is slightly more fragile for portable listening but still useful, although I usually crank up to 100 mW for solid yard coverage.

The high side reaches nearly 400 mW but getting up there would be wrong so I prove my trustworthiness by never doing it.

I hear about people struggling with other transmitters and I have to ask myself, "Why? Why do they torture themselves?"

I figured I'd share this video with the group, I found it to be pretty interesting it is not C-Quam but it uses the Magnavox system: https://www.youtube.com/watch?v=4xYwuUYz5t0

Imagine building that kit.

Bruce.

OK I've always checked 96.3 to be sure its Blank and 95% of the time it is.  However Yesterday I was off the air around 6PM on FM.  I desided to scan and see what DX conditions I was gonna get because there was a huge temperature inversion.  I picked a station 152 miles away on FM on 96.3 in Jacksonville, NC.  So the moral of this story is if you know the temperature is gonna invert you may want to go off the air once say hr or hr 1/2 to be sure your frequency is still not occupied.  Remembe it is possible for your transmitter to transmit further during a temperature inversion so if you have a station comming in on your frequency you could get a NOUO for jamming a used frequency.  Plus its just a good way to play nice on FM to do this practice when you know there is gonna be a temperature inversion or Rain as this too will cause distant stations to come in.

I hope this helps all part 15 FM Broadcasters.

Best Regards.

Am I missing something? How does a certified unit that operates from 88.1 to 107.7 run on 87.9?

As I posted in another thread, I've been researching the sensitivity of various FM receivers.  Any statement with regard to the range of a Part 15 FM transmitter that doesn't take into account the specifications of the receiving equipment at the other end - and the most important spec is sensivitity - is just meaningless.

Although I've just started this task, I have some reasonably accurate numbers on high end home receivers, and good car receivers can approach, at least in FM sensitivty, the specs of those home receivers.

So let's do some analysis on the current Part 15 FM rules, which allow a field strength of 250uv/m at 3 meters.

The best home receivers (along with the best car receivers), have a useable mono sensitivity of around 1uv, a mono sensitivity with 30-50 db quieting of 1.5uv, and stereo sensitivity of 15uv with 30-50 db quieting.

Field strength is linearly proportional to the distance between the transmitting antenna and the receiving antenna.  So, the field strength of a legal Part 15 signal at 200 feet (about 60 meters) would be 12.5uv/m, line of sight.  However, the signal level at the input to the receiver would be around 5uv (math for this factor done elsewhere on the Part15.us site).  That's easily within the ability of these receivers for a mono signal - a stereo signal would likely be too noisy, and the receiver would either switch to mono automatically (most car receivers do this) or you would have to switch to mono mode manually.  In fact, you would need a field strength of around 40uv/m to receive a quiet, stereo signal with separation - that would translate to a range of 18.75 meters or roughly 60 feet.

Moving to 400 feet, the field strength of a legal Part 15 signal would be 6.25uv/m.  That would translate to an input signal of around 2.5uv.  You would still hear a mono signal with full quieting on the best home and car receivers.

Moving outwards to 800 feet, the field strength would be 3.125uv/m, and an input signal of 1.25uv.  You would be able to hear a mono signal, but it would be weak and could be noisy.  You would still have full quieting for a mono signal at 600 feet (with a field strength of 4.69uv/m  and an input signal of 1.875uv).

It is likely that any discussion with the FCC and the NAB and others about increased field strength for Part 15 FM will focus on the potential for interference.  So it is imperative that we look at the maximum ranges that any field strength can produce.  But that's not going to be the typical range that most people will get - most will not have McIntosh home receivers, although it is likely that they will have a reasonable car receiver.  I would like to propose that we define a new term - useable range - which also defines a typical home receiver and its sensitivity, and takes into account obstructions (i.e., if your antenna is indoors, a signal has to travel through walls to get to it, reducing its field strength, not to mention other buildings and even topographic features that might get in the way).  It's the useable range that we, as Part 15 broadcasters, are most interested in.  And we likely have to define both the useable mono range and useable stereo range.

Moving along a bit further, the Canadian maximum legal field strength for FM is 1000uv/m at 3 meters.  You merely multiply the above ranges by 4 to get the Canadian equivalents.  For example, at 600 feet, with the U.S. maximum, you can easily receive a mono signal with full quieting on a high end home or car receiver - in Canada, that translates to 2400 feet.  You would be able to receive a very weak and potentially noisy mono signal at 3200 feet.  And a stereo signal with quieting and separation at about 240 feet.  But just a word of caution for Canadian readers - those numbers are for line of sight.  In the real word, the further you get from the transmitting antenna, the more likely there will be obstructions between it and your antenna (trees, buildings, hills, etc.).  And those obstructions will attenuate the signal field strength and reduce the range.

Still not earth shattering numbers, but significantly better than in the U.S.  And the sky hasn't fallen in here yet.  So I do think that there is potential to increase the U.S. field strength maximums if the requests are reasonable, and backed up by solid technical information re potential interference, as well as maximum and useable ranges.

There has been some discussion on this and other sites about unique antenna connections on certified Part 15 transmitters.  Here is what the FCC actually says on this matter:

"The manufacturer may design the unit so that a broken antenna can be replaced by the user, but the use of a standard antenna jack or electrical connector is prohibited. This requirement does not apply to carrier current devices or to devices operated under the provisions of §15.211, §15.213, §15.217, §15.219, or §15.221."

I've found a study out of the Netherlands which actually measured the receiver sensitivity of 10 each car radios, portables and handhelds.  Sensitivity was measured for 20db Signal to Noise Ratio and 46db.  The testers generated a stereo signal that was either directly fed into the receiver antenna jack, or indirectly fed (and then a factor was applied for the losses).  Any radio that could not generate a stereo signal at those levels was rejected and not measured.  At the end, 9 car receivers were included, along with 5 portables and 6 handhelds.

I suspect that the results are probably more accurate and real world useable than manufacturer supplied numbers.  The measured sensitivity was in dbuv, and I converted all of them to uv.  I also did some rounding so they're not exact (but they're pretty close).

Here are the results, which are the voltages applied to the input of the radio to generate signals with the specified SNR's.

Car Radios (9 in Total)

20db SNR: Average 1.3 uv, Best <1.0 uv, Worst 6.3 uv

46db SNR: Average 80 uv, Best 56 uv, Worst 800 uv

Portables (5 in Total)

20db SNR: Average 4 uv, Best 2.3 uv, Worst 5.6 uv

46db SNR: Average 100 uv, Best 56.2 uv, Worst 141 uv

Handhelds (6 in Total)

20db SNR: Average 8 uv, Best 2.3 uv, Worst 28.2 uv

46db SNR: Average 400 uv, Best 200 uv, Worst 1000 uv

Some Considerations

No home stereo receivers were tested, although they more than likely rival the car receiver results.  That has to still be verified.

There was one car receiver that tested very poorly and it somewhat skewed the results.  Most car receivers were around the 1-1.5uv sensitivity mark for a 20db SNR.  A few were under 1uv.

Typically, portables did much more poorly than car receivers, and the handhelds performed more poorly than the portables (although one handheld, the Sony ICF-C1200, rivalled the portables.  Interestingly enough, the worst handheld was also a Sony, so name brands are no protection against bad radios.  The best portable was a Sony, the CFD-S550.  The best car receiver was the JVC KS-FX480, but there was a Kenwood & a Blauplunkt that rivalled it.

I'm struggling a bit right now to make sense of these numbers, as I have no good idea of what a 20db SNR sounds like (nor a 46db SNR either).

It takes a much greater field strength to get that 46db SNR.  If you take the average for the portables - 100uv - then you only would be able to get that type of signal at 3 meters from the transmitting antenna (if you're running at 250uv/m at 3 meters).  Obviously, you can hear that signal much further than that with decreasing SNR - a sensivity of 4uv with 20db SNR (the average for portables) translates to a range of 75 meters or about 250 feet.

Anyway, I just thought I'd throw this out there for discussion.  No major surprises, just more grist for the mill.

FCC OET Bulletin 63 (link below) is titled UNDERSTANDING THE FCC REGULATIONS FOR LOW-POWER, NON-LICENSED TRANSMITTERS.

Page 29 of this document states:

What is the relationship between "microvolts per meter" and watts?

Watts are the units used to describe the amount of power generated by a transmitter.  Microvolts per meter (µV/m) are the units used to describe the strength of an electric field created by the operation of a transmitter.

A particular transmitter that generates a constant level of power (watts) can produce electric fields of different strengths (µV/m) depending on, among other things, the type of transmission line and antenna connected to it.  Because it is the electric field that causes interference to authorized radio communications, and since a particular electric field strength does not directly correspond to a particular level of transmitter power, most of the Part 15 emission limits are specified in field strength.

Page 29 goes on to develop an equation to calculate the power needed to produce a specific field intensity at a distance of three meters, assuming a transmit antenna system with a gain of zero dBi (an isotropic radiator):

P = 0.3E^2 where P= power in watts and E = field intensity in V/m

Inserting the field limit of FCC §15.239 on the right side of the equation:

P = 0.3(0.00025)^2 = 0.000 000 018 750 watts, or 18.75 nanowatts

Discussion:

There are many transmitters sold for Part 15 FM use that are rated for hundreds and even thousands of times more output power than legally can be radiated under FCC §15.239.

The FCC has issued citations to some unlicensed operators where it can be calculated that the radiated powers used fall into the range of those produced by transmittters commonly sold and used for Part 15 FM.  Here is summary of some of those:

This information is not provided or intended to deter anyone from using/enjoying Part 15 FM, but to give some perspective on the operational realities permitted by FCC §15.239.

Here is a link to FCC OET Bulletin 63:

https://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/o...

I continue to read elsewhere sweeping statements that a legal Part 15 statement will not leave your own property.  Of course, there's no accompanying math or physics to prop up those statements at all.  That's because there are none possible.  Perhaps those who continue to put this msinformation forward believe that if they continue to say it, eventually it will become like fact.

But the truth is that the range of a Part 15 signal is entirely dependent on the receiving equipment and obstructions between the receiving and transmitting antennas.

My recent research on receiver sensitivity revealed that there are any number of car receivers that are capable of receiving signals in the 1-1.5uv range with up to 20db quieting.  A Part 15 legal signal with field strength of 250uv/m at 3 meters has a field strength of 5uv at 150 meters (around 500 feet) line of sight, more than strong enough to be heard by those car receivers.  And for some, that range could extend out to 800 feet or more, line of sight.

There's also no doubt that the typical portable or handheld FM radio has a much more difficult time hearing a Part 15 legal signal.  That same research showed that the typical portable might hear a signal out to about 40-45 meters (around 150 feet) and a typical handheld would be lucky to hear it at 20 meters (maybe 75 feet).

So while it is true that portable and handheld receivers might not hear a Part 15 legal signal 'off your property' (depending on the property size, of course), a good car radio or the best home stereo receivers (other research has showed that they have pretty much the same sensitivity as car receivers) could hear it much, much farther.

QED.

Tonight was to be the introduction of KDX-FM, but I needed to open up the C.Crane FM Transmitter to repair the telecopic antenna's contact with the antenna circuit.

Normal use of the telescoping antenna causes the spring-metal connected at the base of the antenna to break connection with the circuit board, where it was evidentally insufficiently soldered.

But the spring metal piece is shiny metal and does not accept solder, dooming it to never actually staying attached.

Very displeased with this inconvenience I have blacklisted the C.Crane Company for ten years.

I will now go in there and attach a plain wire, screw it.

All the talk about Part 15 FM, 15.239, and experienced signal distance have inspired me to conduct semi-professional experiments for purposes of comparison.

I have already compared three "certified" FM transmitters and found they all produce the same field readings in "dBu" on a spectrum analyzer at 14'7" from the transmitters, using the 14" telescoping input antenna that came with the analyzer.

Those transmitters are C.Crane FM Transmitter 1, Wholehouse 2.0 and Scosche FMT4R.

Setting aside the fact that all three transmitters produce the same field levels when set for U.S. compliance, today's experiment will be made using the Wholehouse 2.0.

At the moment I have these readings.

Wholehouse 2.0 with 3" wire antenna = 31dBu.

How much signal increase occurs by adding an additional 4.5' vertical transmit antenna wire?  Answer: 2 dBu for a total field reading of 33 dBu.

What are some comparative analyzer readings for full power local stations?

88.1 MHz 42 kW located approx. 30-miles south = 26 dBu;

90.7 MHz 100 kW located approx. 6-miles south = 62 dBu;

92.3 MHz 99 kW located approx. 20-miles south = 46 dBu.

Hi all,

  In trying to find an emtpy slot for what will eventually be a Part 15 FM station, I did some searching on the dial. Everyone says that radio-locator is the best way to find an open station, but it's not very accurate.

  I found a site called radiolineup which shows a list of stations in your area and the distance they are to you. I found seven clear stations where radio-locator said there were zero. Also, radio-locator said that 107.9 is open, but it's not - there's a new station there.

  So, I just wanted to let everyone know about this instead of blindly following what one site or the other said.

Earlier on another thread there was mention of so many different transmitter manufacturers that I decided to start a new thread just for Transmitters so we can get this thing going. Please tell us rather or not the Transmitter has a certification and if so the FCC ID# if possible. Here is a start.

SainSonic AX-05B http://www.sainsonic.com/sainsonic-0-5w-long-range-10km-dual-mode-stereo-broadcast-fm-radio-transmitter-fashion-black.html

FCC Part 15 compliant FCC ID # 2ABT5AX05B7C Low Power -48dbM/500 mW (To adjust power hold down the power button while unit is unplugged then plug power in. Press Down arrow to switch to -48dbM or up arrow for 500mW Click power to confirm. You'll see the highest frequency 108Mhz click to confirm. Then you'll see lowest frequency 88.1 Mhz click power to confirm. Click again and transmitter will say OFF and the desplay will be dark. Now press power and select a blank frequency.

FM Stereo IC with PLL technology 75uS Audio pre emphasis, Limiter and Low Pass filter circuit. Large Digital display with blue backlight. Aluminum Enclosure. 88.1-107.9 Mhz US Factory setting or 76-108 Mhz outside USA. Tuning step 100Khz/0.1 Mhz. Power Supply 9-12 Volt DC (the current load of power supply should over 1A). Stability of frequency +- 0ppm (-10C +50C). Frequency Response 100-15000 Hz. Frequency to noise ratio >70db. Distortion <o.5%. Operation Time: True 24.7. Antenna Design: Rubber Antenna. Output Impedance 50 Ohm. Audio Input Connector: 3.5 mm headphone connector. Mic Input Connector: 3.5 mm headphone connector. Size of transmitter 113*88*38 mm. Transmission Signal: Stereo. Barrier free broadcast on 500mW setting 1,300 Feet (gray area in USA Note: I put that one in).

All specs were from the actually box the transmitter came in. Website says low power is 100mW but the actual transmitter when it arrived and I opened the package says low power is -48dbM (far less than 100mW). Again this is the revised transmitter with reverse threaded TNC connector.

It has came to my attention that we could have a security risk when Carl did his FM tests so we could try and achieve what field strength it would take to get a quarter mile and was hoping the Canadian field strength at BETS level would do it. We wanted to see the difference between the BETS setting and the USA setting. Fear not we don't need to be illegal to get this done. We have members in the ALPB that are in Canada and New Zealand. The question I have is can you members from Canada or New Zealand please test your transmitter at your BETS level FIRST then flip the switch back to the USA level (Since your allowed more than USA level) and test that. We'd need someone to do this on youtube or a FTP server. If you do it on youtube you can have someone on the left channel repeat 1 Watt over and over and the right channel say World Wide so we don't have anyone reporting us for copyright infringement. Then connect your portable to a camera's input and record it wile your walking or driving so we can see when it fades to Mono and the difference. This way the little puppy dog trolls working for the FCC or that other site can't frame us as a Pirate as we all know those people are lurking and just waiting for any of us to f*ck up so they can do yet another article on how bad we all are and how they took down the almighty pirate in praise for part 15 AM. All their doing this for is to try and stunt the growth of the movement to improve part 15 FM and I'm NOT gonna have it. Sorry there is more than one way to skin a cat so you can run around like a mealy little mouse but just like the song said by Jethro Tull – The Mouse Police Never Sleeps. So lets fight harder than ever before. Else I'll recommend we ask for the 1 Watt into an inside antenna and really f*ck up these trolls plans because instead of the 500mW to 700mW that I wanted I'll just say 1 Watt like New Zealand. Plus I'm gonna hang a flag in my yard that says FM FM FM FM FM so there have fun with that. I'm not gonna give up just because some say I should and there are many ways to achieve the same results if one way is not going to work. When a window of opportunity closes a door opens. Just like it took me 7 yrs to fight against my local ISP in order to stop the throttling and techs who didn't know their job so too will I fight for 7 years if this is what it takes to improve micro FM broadcasting. Yes FM FM FM.

On a daily visit to hobbybroadcaster.net I picked up this radio story:

http://www.laweekly.com/music/las-smallest-radio-station-975-kbu-broadca...