FCC Rule Part 15.219 Power

Carl,

Yes, what you cited is RF or AC power being applied to the final amplifier but remember that the amplifier also converts the DC power applied into the RF output power. Technically, the two contributions need to be summed when applying 15.219.

Neil

When you modulate with am both the output power and dc input power draw actually doubles at peaks of 100 percent modulation but it's all wasted since you only need half of it. Hi Hi... I have always understood proper engineering practice to state input power at zero modulation on am. If you watch a scope on am you will see the output power amplitude as a certain level on the scope with no modulation and with these conditions if you have a wattmeter in line to the antenna you will read the power output for the DC I x E input power. Now if you modulate the amp with 100% modulation the scope will show double the output power on peaks and no power in the valleys. The I x E input meters will show no change as also the wattmeter on the output will show no change as these read average power (They can't keep up with fluctuations (unless your modulation was 1 cps Ha Ha)). One last thought even a modulated oscillator has an audio amp somewhere in it and it's draw does not count for power input . Only the power input to the final stage counts to the FCC. You don't look at total power draw on a transmitter, only power input to the final amplifier. I could probably run my old RCA BTA-250L am broadcast transmitter at 100mw input (Hmm..2000 volts times .00005 ma = .1 watts = 100 mw (can I cut the power to .00005 ma on those big 810 tubes? and would the 828 modulators cooperate?? Lets see I think the whole transmitter draws about 1500 watts or more for the mains but even so it could be a legal part 15 transmitter (all 1500 lbs of it) if I limit the final current to .00005 ma. Dave

Hi Neil

Your Correct in everyway... When I call the FCC I was tryingto get a answer to Why Realistic
was puting on their Walkie Talkies input power 100mw output 50mw..Yet when I measured the input power
to the Final it was around 207mw ans this is with mo modulation at all...Now I also had their 300mw Walkie talkie that said 300mw input power and 150mw output power. Well this thing was drawing in the neighborhood of 630mw DC input power to the final. I could not under stand why they had double the DCinput power on everything they sold. Yet on the Boxes it said 300mw input power. Well It was the FCC
that told me those were measured on AC input power and not DCinput power. Then they said it about half
the DCinput power for ACinput power then I found it in one of my Engineering books.

Yes I meant P= V^2/impedance Which in most cases is 50 ohms.

Anyways I wanted to meantion something else Iuse a 12 volt regulated power supply it put out 12 volts not no 13.8 volts.

Anyway with Ramsey AM25 if you take out R33,R34 like they say...I set the Transmitter to 1710 and in to a 50 ohm dummy load this thing outputed 5 watts full bias... I found the only way to get a 1 watt signal with
a correct bias was to use a 4.7 ohm resistor not wire wound and bias has to be almost all the way
turned up to get the watt output. Now if you can find a 3.7 ohm resistor it will get closer to the halfway point on the biasing. The transmitter will put out a good solid 1 watt RF..Now this if you live out of the USA...

Do not stick a 12volt supply on that transmitter with no R33,or R34 you will burn up your transmitter.
That transmitter cannot handle 5watts output with those small heat sinks or even 2.5 watts which would be
the half point bias...

Put a 3.7 ohm resistor not wirewound either...Make sure it a 2watt resistor too. 4.7 ohm resistor will work
but you will have to turn your bias almost all the way up to get the one watt output. Put a 50 ohm dummy load on a good watt meter and adust it that way...This is for everyone in Foriegn Countries who can run 1 watt RF output... Ramsey even told me that they have had many transmitters come back blown up due to the Modulation Transistor burning up... Well taking out R33,R34 hook to a 12 volt source at the half bias point still produces 2.5 watts output,and the Audio transistor cannot handle it....

So put a 3.7 ohm,or 4.7 ohm Resistor in the place of R33,R34 and you should be ok. A 3.5 ohm will work too.

Adjust your power using a watt meter till you hit the 1 watt output....
Ramsey Transmitter will do 1 watt Ok if you take these precautions.

Sean

Hi Carl

I do Amateur Radio also... I also been a electronic Engineer for many years. I saw some of your other post. If you really want to find the True output impedance of the Rmasey AM 25 you will need a QRP SWR/Watt Meter...Then try the different loads on it and you will get different SWR readings. If it is a true
50 ohms out put when you stick a 100 ohm resistor on that SWR meter you should get a reading of 2:1.
Anyways I have a watt meter that shows the low watts ,but SWR it cannot read. I call Bird Meters and they were completely useless at these wattages. They have one that works in this frequency range ,but is
set up for a 10 watt scale. The meter itself run around $800.00 then you need the different elements
that you stick into those meters. If anyone is interested the Meter is the 4410A,and the element you need
is the 4410-2...Very expensive meter,and the element cost too... A good oscope will do the samething you just have to do the math to calculate your wattage. For that price you can have a nice oscope that works in this frequency range.

My watt meter goes from 50mw to 10watts so that not bad. So I can get a pretty good ideal what I am putting out.

Anyways Power is not an issue on a good signal...When I took my Ham license many years ago they said to gain 1 S singnal on a receiver meter you would have to double your power.

So say you have a S signal of 5 ,and your transmitter putting out 50 watts then to go up one S singnal
yu would have to jump your power up to 100 watts to see any difference.. Some would tell you to go to 200 watts to see a S signal of 7 on the meter.... Now I am talking about the receiving meter you see on most ham radios that goes from 0 to 40...Some may go to 60... For the most part they go from 0 to 30..
Really more on CB Radios have the 0-30 meters. Anyways it really takes a really huge jump in power.
I know Ramsey say you get a full 100mw output and believe me that illegal and I have in different post told how to bring the Ramsey into FCC compliance. Anyways let Say you have a 25mw out put out of Ramsey or
SSTRAN then only way your going to hear a difference is to jump that power up to a 75mw output.
Rangemast says they get around 90 to 95mw output. So with that transmitter you may hear a difference over
the SSTRAN or Ramsey AM25..Now if you run the Ramsey with a 100mw output you out do the Rangemaster,
but you will also be very illegal...I know the input DCpower runs from 360mw to about 400mw.. I have checked it many times with a 50 ohm load on it. Anyways here the Deal if you get 25mw out of the SSTRAN
and get 95mw out of a rangemaster. The S signal will only jump up two units. So distants receivers that are
only getting a reading of 1 S unit may jump up to a 3 S unit.. Now you being in ham radio that not much of a change. Either way the signal is still going to have alot of static on it. It not the power but how well your antenna Works. That means a SSTRAN Transmitter with a very effective antenna could perform as well as
a Rangmaster or even better. Remember Rangmaster is only using a CB wip antenna...A well designed
AM Broadcast antenna could out perform a CB Whip antenna anyday since they were never designed to work at such a low frequency. Believe me CB manufactures look in everyway to make thos fiberber glass perform
best a 27MHZ,so making it work in the 1 Mhz range has it losses. You are forcing an antenna to work way out of it range. Look at the CB Whips you can see the wire wraped around the fiber glass. The spacing of each wrap around that fiber glass whip is calculated where it should be to give that CB whip a broad enough
band spread to work over the entire CB band....Those antenna's are truly set up for 27Mhz even if you try to trick them into working at 1Mhz range. This means you can construct an antenna that really more for the lower bands. Anyways With a good antenna you could make up those 2 S units a Rangmaster would have over most transmitter a distant receivers. Some transmitter output 50mw and Rangemaster only being at 90 to 95 mw would not even give you 1 S unit difference. This is the reality of the situtation. I have been a engineer for 27 years and Started in Radio Broadcast at the age of 13 years old. I had my ham license at a very young age also. I had many people teach me what I just now told you. Rangemaster is a good transmitter,but SSTRAN or Ramssey transmitters set up correctly could possibly out do Rangemaster.
This means have a good antenna system...Experiment in everyway you can. If you can't get them to work
like that then go spen near $1000.00 for a transmitter. Buy the way Procaster is Good,Talking House transmitters are good.. There is alot of good Transmitters on the market.

Procaster is FCC Certified.
Talking house is FCC Certified
And there is two others also,but I do not have their name right off hand.
Talking house Transmitters have a built in ATU Antenna Tuner unit. So it will tune anything you stick
on it. Stick a real good antenna on it and it will make sure you are really tuned.
Anyways It not the Transmitter it your antenna that needs to be good.

Thanks SKW40

I have been trying to follow this thread and have found it to be confusing to say the least. Neil has posted correct information, but it seems to have gone by the wayside as the thread progresses.

MEASURING DC INPUT POWER TO FINAL RF STAGE:
The power equation is P = E*I . "I" is the DC current flowing to the final RF stage ONLY. One way of measuring this on classic grounded-emitter RF stages is to insert a 10 ohm resistor between the DC power supply and the final RF stage with a fairly big bypass cap to ground on the output of the resistor to ensure no RF current is present through the resistor. Then measure the voltage ACROSS the resistor and calculate I = (Eresistor-in - Eresistor-out) / R. (In this example, R = 10).
"E" is the DC voltage measured at the RF-bypassed output side of the 10 ohm resistor.

"AC" INPUT POWER TO FINAL RF STAGE
Forget about this term entirely! Just stick with DC INPUT POWER as referenced in the FCC rules and virtually all texts on radio transmitter theory.

RF OUTPUT POWER
Since the transmitter output is RF (AC at the transmitter frequency), output power must be stated in terms of RMS power. The relevant equations are:
Prms = Irms * Erms
Irms = Ipeak *.707
Erms = Epeak *.707
Prms = Ipeak *.707 * Epeak *.707 = Ipeak * Epeak *.5

MEASURING RF OUTPUT POWER
The most meaningful point to measure the power is at the feed point of the antenna, AFTER all the tuning circuits that may be inside the transmitter or external in the form of a loading coil. This measurement point will show the actual power output after all transistor and tuning circuit losses.

There are some problems to overcome. First is that hanging a meter or scope probe at the antenna will detune the transmitter and will drain some of the power off to the meter or scope. The second problem is how to measure the antenna current? The ground loss resistance is the "load" on the antenna and varies widely depending on many ground system factors.

One solution is to use a dummy antenna that approximates your estimated ground resistance. 20 ohms has been tossed around as a "typical" value, but for random Part 15 installations, it may vary from a very good 5 ohms to a poor 100 ohms. To make a dummy load, solder one end of a 30pf NPO ceramic capacitor to one end of a 20 ohm resistor. Connect the dummy load as follows: (1) break the connection to the base of the whip or copper pipe antenna, (2) connect the free end of the capacitor to the output of the transmitter or the output of the loading coil, (3) connect the free end of the resistor to the transmitter ground point.

Now all measurements can be taken at the low impedance junction of the dummy antenna capacitor and resistor without de-tuning or loading the output significantly. You can use a scope or a peak-reading diode detector circuit feeding a DVM. When viewing the RF waveform on a scope, the peak voltage is half of the peak-to-peak voltage you see on the display.

Output power measurement procedure:
1. With a scope or peak-reading diode detector/DVM connected between the junction of the dummy antenna capacitor and resistor and transmitter ground, TUNE THE TRANSMITTER for highest peak reading.
2. Calculate the output power delivered to the load resistor R using the equation P = E^2 / R, but since you are measuring PEAK voltage you need to convert the measurement to RMS power:
Prms = Erms^2 / R
Prms = Epeak *.707 * Epeak * .707) / R
Prms = Epeak * Epeak * .5 / R

Overall transmitter efficiency is Prms divided by DC Input Power.

Seven may not be a lucky number, the bigfoot monster might be a myth and my view of input power to the final was mistaken. The comment contributors have been very civil by politely repeating the facts that PhilB finally crystalized, and this thread will be printed and saved in the Part 15 filefolder.

Think how dangerous it would be if people with incomplete knowledge got turned loose with higher power levels.

Hi Carl and Phil

Anyways we did get side track from this Thread. Anyways

DcPowerinput is P=I*E

Now I just brought up everything else since in the 1970's and 1980's Walkies talkies under
Realistic were be advertise as 100mw input power while they were much higher...
I used them as examples since we do not have alot of low power transmitters that
are amplitude Modulated at only 100mw...Radio Shack 100mw Walkie Talkies actually
Ran around 207mw DCinput and not the 100mw they claimed.

One thing I did want to point out RangeMaster Transmitters are running Close to 99mwRF output.
Yet they only have a 100mwDCinput power.
Very effiecent circuits being used in it.

Ramsey AM25 Puts out 100 mw RF ,but it runs from 360mw DCinput power to 400mw DCinput
Power. That only a 40mw difference... I notice it draws the 360mwDCinput if you first turn it on cold.
Yet if you leave it on for about 24 hours it will draw 400mwDCinput...That just 40 mw more due to the
Transmitter being warm up..

Well here the deal Rangemaster is legal with a 100mw output of RF because it fall into the DCinput
Range of the FCC.

Ramsey put out the same 100mw RF,but this transmitter is illegal due to it fall outside of the DCinput
Power the FCC rules have placed..

A 100mw RF out of any transmitter will not go any further. The Distance is determine by how well
The Antenna performs at this point.

Another thing Ramsey claims this transmitter meets FCC Part 15 Rules,and I have many talks with
Them since I own one. They said their people interpeted the rule and they are correct on the
Power rating....Well it just a mess when a company think their transmitter is Legal in the eyes of the
FCC. Right now I am saving up for a legal transmitter...

Well if the FCC ever changes that rule to not exceed 100mw RF output from the Transmitter
Boy that would make thing simple.

Alot of people are using a 100mw RF output anyways if they own a Rangemaster or Procaster
Transmitter.

Well I am sorry this thread went on different subjects. The bottom line is 100mwDCinput is the limit
we have to go by to be legal.

SKW40

SKW40 said "One thing I did want to point out RangeMaster Transmitters are running Close to 99mwRF output. Yet they only have a 100mwDCinput power. Very effiecent circuits being used in it."

99% overall transmitter efficiency is not possible, but here is the important point: the RF output stage transistor efficiency can be close to 99% with a Class E design, but the OVERALL transmitter efficiency will be considerably less because there are unavoidable losses in the tuned-circuit components between the transistor and the antenna.

Follwowing is a repeat of a post I made on another forum on 3/9/2009. There is a line in the analysis labelled "Total Eff. into load". This is the bottom line for overall transmitter efficiency after factoring in a good tuned-circuit loss of 15 ohms.

---------------------------------
POST FROM OTHER FORUM
---------------------------------

Here are more precise efficiency calculations for a transmitter operating near 1600 kHz.

Amplifier Effiency is the efficiency of the RF transistor. It is an indication of how much of the input power is dissipated as heat in the transistor. Less heat dissipation = higher amplifier efficiency. Three example values are shown.

The DC input volts and DC input amps are examples only and are not important except that the product of the two must equal .1 watt which is the maximum allowable input power per part 15 rules.

Rloss is the loss resistance of the tuning circuit. 15 ohms is a realistic value for a transmitter using an on-board toroid coil or small solonoid coil. This includes wire resistance and core loss. The loss resistance can be lowered substantially by using a large high-Q base loading coil. Practicality is inversely proportional to the coil Q!

The transmitter load resistance is the sum of the ground resistance + radiation resistance. This load resistance is the load seen by the transmitter and is the final reference point for overall efficiency. The actual radiated efficiency is very small due to the very low radiation efficiency of a part 15 antenna.

Ways to improve efficiency:
1. High amplifier efficiency
2. Reduce R loss (high-Q inductor)
3. Reduce R gnd (elaborate ground radial system)

Increasing R rad would be the single most productive way to increase the radiated signal strength, but the part 15 rules ensure low radiation resistance by limiting the antenna length.

There are two reasons to use the high end of the band for best efficiency.
1. The antenna radiation resistance gets even smaller as the frequency is decreased.
2. The antenna capacitance (roughly 30 pf) is essentially constant over the band, so the tuning coil needs to have a higher inductance as the frequency decreases. Higher inductance causes higher R loss for practical-size coils.

I actually had many emails with the Designer of the Rangmaster. Now at first I could not believe he was getting from 95 to 99mw RF output from his design. He assured me his design was running over 90% or higher in effiency... Then I saw people saying in there testamonials that they were getting 97mw of RF..
Still to me most circuits are either 50% or 78% effiecient due to people using class C bias circuits or class
AB bias. I only recently lood at class D or E Bias Circuits,and I figure Rangemaster is using one of them.
I understand what you are saying. Even if you have a great transmitter your going to loose everything through this Part 15 antenna system. I am a Ham opereator also,and these are some real tight guide lines,and makes it hard to get any distance out of these transmitters.

Then you have to take in the consideration that most am Receiver of top notch Quality at 1610 have a
sensitivity of only 300uv 10 db S/n Ration and at 530khz it drops off to 600uv... Cheap radios are lucky
to see a 1000uv sensitivity with a 10db S/N Ratio... So it also cut the limit of didtsance down too..

With ham Gear we are so use to .1uv to .25uv sensitivity with a 20db S/N ratio so much better than a AM
Radio.

Anyways I understand where you are coming from.

Thank
SKW40

SKW40,

Thanks for the positive reply. Sometimes I feel like I am a one-man crusader trying to make the Part 15 world understand overall transmitter efficiency. There is an aspect of salesmanship and propaganda at play. We should not believe some things just because they are in print on the wild and wooly web. As you know, it is not possible to get overall transmitter efficiency of +90% when you are driving a 20 ohm load through a ~15 ohm-loss tuning network, even with a 100% efficient RF transistor circuit.

Somewhere out there on the web is a document written by someone back in the 80s or early 90s that describes the "ultimate" way to drive a part 15 AM antenna. I can't recall...maybe someone can help here. The recommendation was to use a loading coil about 1 ft. in diameter and space wound (to reduce self capacitance). This would reduce the "~15 ohm" tuned circuit loss to a much lower value, and the overall transmitter efficiency would increase substantially. At least, there is a way to achieve better efficiency. Publishing transistor efficiency at +90% without any qualifications is not relevant.

In addition, I want to add that there is no way to use a Radio Shack or whatever, SWR/Wattmeter to measure a Part 15 antenna. These things are intended to be used in-line with a 50 ohm antenna. Who knows what they will read when you connect them at the output of a transmitter with internal tuning like the Rangemaster. The impedance at that point is several orders of magnitude higher than 50 ohms.

Phil

NEVER mention you are a ham! LOL!!!

HI John

Why not Mention that I do Amateur Radio. I saw you did in one of your Post. Anyways I was just currious why you said that.

Thanks
SKW40

Because there are internet "trolls" out there who seize the opportunity by trying to discredit radio experimenters, hams, etc.. Also, some view hams as arrogant know-it-alls, who try to impress the unwashed masses that they are superior. I know that's not your intent as a newbie out here. 🙂

73, John - WA4JM

Thanks

I have been into Amateur Radio since the mid 80's,but this aspect to radio in pretty new to me.
I tried it back in 1990 ,but not much was happing back then. well at least I was not aware of it since the
internet was not around to look at.

Sean

You are here!!!