500 mW Rubber Duck Simulation

OK I'm legally Blind, but from what I saw that would mean IF the SainSonic WAS putting out 500mW it would have gone 3 miles!!  Well that would be INSANE!!  I'd say at best mine MAY and that is a BIG MAY put out 100mW which proves that at High its putting closer to 100mW and low 15 Nano Watts.  OK so it looks like we should only shoot for 100mW into a rubber duck.  500 mW is too scary for the FCC and it even would scare me just a bit.  My old transmitter YEARS AGO before I knew what part 15 was put out 3 miles so I may have had 500mW ERP.  God I don't think we need anything close to a Watt.  We are not trying to be a commercial station here. We are only a bunch of hobby broadcasters. If we were to have went to the FCC asking for 500 mW they would have told us to grow up and act our age not like a spoiled brat. Thanks for saving us from pure making fools out of ourselves. Well knowing is the best thing right?

Don't let him hear about this.

Hey Carl and I think WDCX (can't remember) I'd like to talk about this some more.  Can you guys call me on the Rockline because I'm afraid if I go on Teamspeak the same time I'm live streaming on my station.  I want to talk where we don't have trolls so they don't get the wrong idea here.  Plus I don't want everyone to know outside our ALPB group just how we are going to try and get things done.  You never know they could call the FCC and tell them a bunch of bad stuff about us and get them pissed at us before we even get off the ground.  Our goal is not to piss off Uncle Charlie or be what the CB world calls a 10:30 or Alligator station lol.  We want to be all 10:8 here lol.  Anyway I can't remember what the hams use to call it but it sort of reminded me of those old days where people ran linears on CB and we had those names for them.  We can call a station that is under part 15 a 10:9 station which means can't be heard.

Unless you are on dial-up I don't think the TeamSpeak stream will have much if any effect on your station streaming.

I have two station streams running all the time.  I've never noticed a problem when TeamSpeak is active.  I'd say give it the acid test and see what happens.

Other people need to mind their own damned business!!!

This is America and I still believe in all the amendments that cover free speech.

You know? Sooner or later those trolls are going to find themselves on the wrong side of the law and then they can all shut the hell up!

Making excuses to cover their asses that they have those rights because of this or that, isn't going to fly after a while.

That is no different than me saying the guy up the road broke the law so that gives me every right to impersonate a police officer.

Bruce.

You have a point Bruce.  OK I'm going into the meeting room now.  All Pro FM's I'll talk to you there.  Hopfully WDCX will be there.  C ya Pro FMers.

Just throuwing out some random thoughts as I read through this. 

I just realized last night that I'm fully equipped to also make accurate readings of the actual output of these Part 15 transmitters.  Not just field intensity but actual output from the transmitter. I have a Coaxial Dynamics watt meter that I usually use for ham radio work, but I have slugs that let me read power output on the FM band at either full scale being 1 watt, or full scale being 100 milliwatts, so I can actually read down to .001 watt if necessary.  

I was looking at the Sainsonic website this morning and I'd be amazed if half their stuff was actually legal, unless they're relying on really crappy antennas to get the output down to legal. 

When you test with a rubber duck, exactly what are the specs on that rubber duck? They're not all the same of course and are designed and built to match a given frequency or band. Whether it's a ham handie talkie or a Part 15 transmitter, an antenna made for a specific frequency will radiate much more than one way out of the ballpark.  I can actually test antennas to tell you what frequency they are resonant at. 

If you are hoping to sway the FCC for more power I suggest you petition for greater field strength, not output power.  e.g. go for 250 uV/m at 10 meters, or 100 uV/m at 10 meters, or some such. From a technical standpoint it's going to be tough to use power output as a specification, as a given amount of power can have a huge variation in coverage/field strength based on the design of the antenna and location of the installation. 

To make a good FCC presentation you can't use random values e.g. "rubber duck into a car radio" from a technical standpoint means nothing.  You can't determine you want x amount of power because you'd like to cover, say, a mile and a half. That same amount of power could cover much more or way less depending on the antenna and installation. 

I would say the people making and selling current FM transmitters do not help the cause.  I'm amazed that Sainsonic has an FCC approved transmitter that with no modifications can transmit at .5 or .1 watts.  Just press the button! And it works on odd or even FM frequencies. How is it possible to be type accepted when there is not even a slight attempt to make illegal operation as easy as the press of the button?  This is, of course their "long range" AX-05B.  Then I see the AX-7 which claims 1 or 7 watts out, and yet claims to be FCC compliant.  Really? At a watt?  That's gotta be a really crappy antenna or design to bring a WATT down to 250uV/m at 3 meters.  This little bugger has a cooling fan, a telescoping antenna, opeerates out of the box outside the US FM band, and again with a press of a button gives you 7 watts out?  And the FCC passed this?  Their other transmitter that I looked at goes down to .1 watt to be legal.  Yet this one claims to be legal at a watt? Any engineer of FCC rep looking at all this would be thinking "What the hell?"

Careful use of watts is interesting. In the 2 meter ham band (144-148 MHz) you can talk to the international space station with 5 watts FM and a yagi antenna. With 25 watts and a yagi you can bounce signals off the moon.  From my cabin 50 miles away I can hit the local 2 meter ham repeater with a handie talkie at one watt into a matched rubber duck.  Now, I would be on the ground in the woods, the repeater antenna is about 250 feet above ground on a tower on top of a hill.  A clear example of how antenna and local conditions can have an effect on coverage. I know a guy in a small town in Montana who ran a small FM at 10 watts that got out 45+ miles into my car radio, although in this part of Montana it was pretty much wide open range, no not much to stop the signal.  He had a tuned antenna on top of his 1 story office. 

Just trying to show variables. An FCC petition, as far as I'm concerned should be asking for an increase in field strength, NOT power output.  And testing should not be done with non-standard materials -- like rubber ducks and car radios.  For general purposes just to see what might happen it's one thing, but you can't ask for, say .500 watts or a watt, period based on predicted coverage with a non standard, unknown antenna. A rubber duck is not a standard, nor is a car radio. 

I don't think you would be too far off the mark in accomplishing your goals and making a good argument to ask for the same rule they have in Canada.  The engineering work has already been done. It would be a substantial increase over what we have now. 

Just a few random thoughts. 

Tim in Bovey

... I have slugs that let me read power output on the FM band at either full scale being 1 watt, or full scale being 100 milliwatts, so I can actually read down to .001 watt if necessary.  ...

Another consideration -- the accuracy of Bird and Coaxial Dynamics wattmeters typically is +/-5% of the full scale value for the sampling element in use.  So the error range when using a 100 mW element would be +/- 5 mW, and that applies to all measurements made using that element.  This means that measurements made at the low end of the meter scale reading are increasingly inaccurate (worse than +/-5% accuracy).

* Signal reflections from the earth and nearby conductors can produce significant +/- variation from the free space field.  Below is a graphic showing the variation of field intensity related to height above the earth, for the conditions stated.

I'm Curious what the deal is with the SainSonic AX-05B I have because at Low power which on mine claims -48dbm which I figured out to be 16 nanowatts can't even transmit 20 feet without fade out and by the time I get outside my house I have to hold my hand on the tip of the antenna on my Digital boom box. This thing is well under the limit. If I had to rely on low power I'd return that transmitter because it can't transmit out of a paper bag. On High (Which claims to be 500mW) will transmit nicely outside my house and on my boom box I get a nice signal to 800 ft or about that. On a car Radio it can still be heard past 800 feet with fade at times to about ¼ mile and drops off to fff quickly. I suspect that the 500mW claim is an exaggeration at best (A blatant lie). No way is the high setting getting 500mW I've seen 100mW go further than that so I'd say since their low setting is -48dbm that the high setting is closer to 50mW and I'm really giving them credit on that one. In reality it probably puts out 50mW at best case scenario. Maybe the FailSafe one puts that out, but the FailSafe clone (SainSonic AX-05B does not have enough beef to put that sort of signal out. That AX-7C 7 Watt transmitter from what I watched at testing their was a guy on youtube that on the telescoping antenna got out 20 miles (Ouch) and said that was too far for even his comfort. Plus that 7 Watt transmitter will injure a common person that puppy was reported to get Hot enough to cause severe burns. I'd say even if that transmitter was legal its a piece of junk and an example of Chinese junk imported to the USA. The AX-05B is as cool as can be never gets above the temperature around it. I'd be curious if you do test it what you would find as far as field strength and power of this unit. Being on disability I don't have the dough to spend on numerous transmitters. It was a miracle I got this one. I'm trying to win the Whole House FM Transmitter 3.0 so I can see what that one does. 800 feet for me would be OK I have houses near me and I'd get listeners from the bar near by and the library which you can just cross the street and get there. There is an elementary school within 500 feet that parents could hear my station while they wait for their children. So I don't really need to spew out gobs of field strength to get the listeners I want. I looked at that 0-1 watt transmitter if that was the one your talking about. I'd make the signal fade out right at the bar which is about 700-800 feet and that would be on the car Radio and on the boombox I'd make it fade out after 600 Ft and that should be about the same as the Whole House FM Transmitter 3.0. You may ask why I didn't just buy that instead? Its $125 (Can't afford that). So every time they have the giveaway I try and win that one.

OK lets talk about field strength and what to ask for. How about 250 uV/m @ 90 meters. That is 305 feet that the signal will go and reach a regular Radio. Remember 250 uV/m will go 10 feet to a clock Radio. So your looking about 315 feet to a clock Radio. And if 250 uV/m goes 800 Ft to a car Radio than 250uV/m at 90 meters will go over 1,000 feet and be legal to a digital boom box. That is about the range I'd need or want. I'm sure with around 1,000 feet you should get neighbors in your area to hear you as your station would cover a few blocks and not likely cause any interference. Remember the 2^nd image for FM is right around channel 7-13 so 500 ft worse case scenario you'd bleed a TV. But a clean transmitter should not do that. What are your thoughts about 250uV/m @ 90 meters?

Well, yes, I know the CD Watt meters have about 5% error, but I'll be reading via cable right off the output of the transmitters.  Since so many seem to be advertising 100mw, 500mw, there's even one advertising a "legal" and FCC approved transmitter they're rating at 1 watt (with a high power switch for 7 watts) it would be interesting to see what they're actually putting out.  I'm betting all these transmitters put out well over what's necessary for 250 uV/m and losing enough to be legal with ineffecient antennas.  Or perhaps they're advertising their input power and the transmitters are so ineffecient that we get legal power out. I don't know, just want to play around and see what I get.

The R-506 is what the FCC uses to determine compliance. Again, I'm betting all these transmitters come in high. Clearly I won't be working in a vacuum but I should be able to be just as accurate as an FCC field agent. 

Tim in Bovey

I almost bought a Tranamitter with 4 power levels.  .01 mW,10 mW (150 feet legal part 15' 100mW and 2oo mW which goes 1'000 feet.  

RE: Reply #11 above:

Well, yes, I know the CD Watt meters have about 5% error, but I'll be reading via cable right off the output of the transmitters. ...

Congrats on your stated ownership of both an FIM-71 and an R-506, Tim. But still, a caveat.

Your CD (Coaxial Dynamics) wattmeter measurement will be most accurate (+/-5%) only at a full scale reading of that wattmeter, and then only if the impedance of the antenna system load matches the impedance of the sample line section of that "thru-line" wattmeter.

The impedance reference of the sample line section in such wattmeters most commonly is 50 ohms non-reactive, and that is the basis for the stated measurement accuracy of that wattmeter.

If the load impedance connected to the output port of that wattmeter varies from this as "seen" by the wattmeter, then measuring error can be worse than +/-5%.

Note that the feedpoint impedance of a self-resonant, 1/2-wave, center-fed dipole in free space is about 70 ohms. The feedpoint impedance of that dipole varies considerably with its height above the earth.

So with such variations, the power shown on the display of a thru-line wattmeter is not a very accurate measure of the power produced by the r-f source (the transmitter), when connected to such radiating antenna systems.

I've already been pondering what the output impedance of these various transmitters might be.  As you say, the CD meter is meant for 50 ohms. I have a variety of 50 ohm dummy loads to use to I won't be testing the transmitters into an antenna for the power output readings.  But still I doubt the various Part 15 FM transmitters are actually designed for a 50 ohm load.  I haven't sought out any tech specs yet that might include such information. 

But for testing purposes I'll be using a 50 ohm dummy load. Which of course will have it's own tolerance I'm sure.  But nonetheless, if I test a handfull of transmitters all on the same setup I'll still have useful relative numbers, e.g. if transmitter B puts out 3 times the power of transmitter A it will be insightful indeed. 

Tim in Bovey

And so it goes.  I would suspect the same errors for the same tests performed with the same equipment by the FCC.

I suppose that puts us on the same page.