Legal limit at antenna or shack?

[Tom WA3KLR]

Below I have attached the Definitions and Transmitter Power Standards sections from the latest edition (10/01/2010) of Part 97, fresh from the FCC website.
http://www.access.gpo.gov/nara/cfr/waisidx_10/47cfr97_10.html

The relevent excerpts:

97.3 Definitions
b. (6) PEP (peak envelope power).
The average power supplied to the antenna
transmission line by a transmitter during
one RF cycle at the crest of the
modulation envelope taken under normal
operating conditions.

97.313 Transmitter power standards.
(a) An amateur station must use the
minimum transmitter power necessary
to carry out the desired communications.
(b) No station may transmit with a
transmitter power exceeding 1.5 kW
PEP.

To me, the meaning and measuring point is quite clear.

There is no limit on effective radiated power however, as Bill KD0HG already mentioned.  The frequency considered in this thread is 29 MHz.   You can put up as big a beam antenna as you want, and overcome the transmission line losses.

[Bill, KD0HG]

On the technical side, if the FCC were to challenge one for a possible power violation, what would they do when the transmitter output was a 600 ohm balanced feed feeding a reactive load?

Jim
WD5JKO

They can't measure anything other than what a Bird peak-reading wattmeter can measure.

Now, how many hams today have a transmitter with a link coupling to a balanced transmission line? No one. one out of ten thousand maybe. And Don. Everyone uses a pi-net with 50 ohm line to an antenna or a tuner. Even with a broadcast transmitter.

So the argument is a red herring.

I have a 50 ohm feed to a 9:1 balun mounted at the tower. That feeds my double zepp with an 80 foot 450 ohm transmission line.The gummint agents aren't going to measure power at the 450 ohm side, they'll stick the Bird in the 50 ohm line.

I got into phone a discussion with Johnny Johnson at the FCC may years ago about the PEP thing. He said something like, "We're not going to jeopardize the safety of our personnel by making them clip calibrated meters into someone's rig to measure high voltage x amps plate input. PEP is the way to go." (My way or hit the highway)

So...If anyone wants to use a link coupled 600 ohm line to their antenna to evade the regs, go for it. No one cares.

[Jim, W5JO]

Some one should ask an FCC engineer how they measure power.  The last I knew the measurement was performed off air within some proximity of the transmitting antenna using speciality equipment.  I don't believe they use a bird or any other type of meter.

[WD5JKO]

Everyone uses a pi-net with 50 ohm line to an antenna or a tuner. Even with a broadcast transmitter.

Anyone want to fact check that statement? What about guys running BC-610's, lots of vintage military gear, home brew stuff with link coupling, and especially those with push pull finals using a swinging link?

So...If anyone wants to use a link coupled 600 ohm line to their antenna to evade the regs, go for it. No one cares.

Well here is a better reason; how about minimizing losses with a long transmission by using open wire feeders. This goes with Jon's original post that started this thread.

Jim
WD5JKO

[k4kyv]

Some one should ask an FCC engineer how they measure power.  The last I knew the measurement was performed off air within some proximity of the transmitting antenna using speciality equipment.  I don't believe they use a bird or any other type of meter.

Reportedly, they use the proximity measurement as a reference, then physically insert instruments to measure the actual transmitting power, and compare the field strength at the known power to the initial  proximity measurement.

One of the FCC people at the Forum at Dayton stated, right after they adopted the output power standard, that if they had their way, the rules on transmitting power would have included "as read by a Bird 43 wattmeter". So what  would they do in the case of a link-coupled transmitter, feeding a couple of random JS dangling wires to a link-coupled antenna tuner, with no 50-ohm coaxial line between transmitter and tuner?

Roger, N4IBF (SK) once had an FCC inspection of his BC-610.  A neighbour had repeatedly made a nuisance of himself complaining to the FCC because Roger's AM signal interfered with his AM broadcast receiver while he was trying to listen to the ball game. The field engineer knew the guy was a kook and kind of thought the whole thing was a joke, but during the inspection, he measured the power output from Roger's transmitter.  You guessed it.  He inserted a Bird wattmeter in the coax line Roger had between the BC-610 and the coax feeding his antenna  system.

[Steve - K4HX]

I just want to hear how loud you would be with a 10 kW rig!  I can dream can't I?

OK. Build your 10 kW rig with a link output and run open-wire to the antenna. Then invite the FCC over. Go ahead. If you don't do it, we will call your manhood into question.     

 Gosh Steve, my post was technical and you made it personal. Where is the moderator when we need one? 

On the technical side, if the FCC were to challenge one for a possible power violation, what would they do when the transmitter output was a 600 ohm balanced feed feeding a reactive load?

Jim
WD5JKO

[Opcom]

To answer Don's question about what they would do faced with a TX that expressly had no 50-Ohm port and otherwise nothing but a pair of high voltage terminals feeding a balanced line of unknown impedance (my opinion):

At some point before doing enough real science to prove anything, they would make a business decision and arbitrarily find the operator "apparently" liable. That's what they do all the time. Sometimes do not find a fact but instead an "apparent" fact based on circumstances. The lack of evidence does not stop them from high-handedly demanding fines. They also go after third parties who they can't prove knew about what was going on but have deep pockets. If one reads the many enforcement actions reports there's a pattern of fining without real proof. Cop, Judge, Jury, Executioner. In many ways regarding this practice they operate like a robber-baron.

[K6JEK]

Someone way back wanted the specifics of this situation. The antenna is a hex beam 10M mono-bander up 30'. The SWR is 1.0:1 at 28.860 measured at the base of the antenna mast. The feed line is several hundred feet (!) of 15 year old BuryFlex and new LMR 400. Why do I think I'm losing half the power? I measured it with a Bird 43 both at the station and at the antenna. I also checked it with a dummy load at the far end. This also jibes more or less with the 2.5 dB coax loss measured by a MFJ 259B.

I'll have to find my old notes to figure out just how long the Bury Flex is because it's under the house in the crawl space, put there 15 years ago. The 2.5 dB figure is higher than I expected since the loss for LMR 400 and Bury Flex should be about .67 dB/100' at 30 MHz. That suggests 375'.  I estimate 250' pending discovery of old notes.

The coax is above ground most of the way, fastened to the floor joists under the house, on the top rail of a fence most of the rest of the way, on the ground for the last 50'.  Does this matter?

Why on earth is it so long? The lot is only 1/3 acre. Well it goes the long, long way for historical reasons. Changing the route would difficult. Heck, changing just the feed line would be difficult.

What would be easy is getting a big amp and turning up to 11.

I've found the conversation that has ensued fascinating.

[W1ATR]

Some of these arguments sound like someone trying to weasel out of a speeding ticket. Nobody makes type accepted legal limit "transmitters" today. For the last 50+ years, the majority of amateur equipment capable of achieving that output was and is built in the form of a radio/amplifier arrangement, and the amplifier generally has a 50ohm output with an so-239, that's what they are coming for. They may bring a calibrated bird meter, and a few adapters, but that 50ohm jack is what they are looking for. The whole 600ohm connected feed point thing is silly. They are law enforcement, They don't care about anyone's personal niche in this hobby, they only care about the power your equipment puts out. If they walk in on a reassigned bcast tx'er or a homebrew job that they can't connect to, they can ask you to provide them a means of viewing the output power of the transmitter in question. If you go into a rant about balanced output connections, look at my scope, blah blah, and can't provide a usable 50 ohm connection for them, they are going to say "thank you sir, enjoy your day", and they will get in their car and leave. Your NAL is in the mail. Call your lawyer.

Just a further thought; If anyone thinks they have a way to drop their power quickly without drawing attention, your just digging your hole deeper. Don't think for 5 seconds that there won't be a vehicle sitting somewhere close with a calibrated rx watching your signal. The control test they do before hand, and the test they do when they show up better be the same.

Personally, I've never heard or anyone getting a doorbell from the fcc. You have to be tearing up your neighborhood, or a real azzhole on the air before anything more than a simple letter of inquisition appears in your mail box.

Run what your comfortable handling, don't tear up your neighborhood, and don't be a blow on the air, and you will never see an fcc badge or a letter other than your license renewal.      

[K5UJ]

Below I have attached the Definitions and Transmitter Power Standards sections from the latest edition (10/01/2010) of Part 97, fresh from the FCC website.

The relevent excerpts:

97.3 Definitions
b. (6) PEP (peak envelope power).
The average power supplied to the antenna

What is extremely interesting to me about that part is the word "average."

Everyone uses a pi-net with 50 ohm line to an antenna or a tuner. Even with a broadcast transmitter.

Anyone want to fact check that statement? What about guys running BC-610's, lots of vintage military gear, home brew stuff with link coupling, and especially those with push pull finals using a swinging link?

My Eldico TR-1 uses a swing link output.  Any old handbook has lots of transmitter coupling designs for things like twisted pair from a swing link to a link coupled tuner to balanced line.  The worst thing about the old link coupled output networks direct to antenna is the poor harmonic suppression.  I would not bring the power measuring issue up with FCC though as their solution would probably be to issue a ban on any output network that isn't a pi network into an unbalanced feed.

Someone way back wanted the specifics of this situation. The antenna is a hex beam 10M mono-bander up 30'. The SWR is 1.0:1 at 28.860 measured at the base of the antenna mast. The feed line is several hundred feet (!) of 15 year old BuryFlex and new LMR 400. Why do I think I'm losing half the power? I measured it with a Bird 43 both at the station and at the antenna. I also checked it with a dummy load at the far end. This also jibes more or less with the 2.5 dB coax loss measured by a MFJ 259B.

I'll have to find my old notes to figure out just how long the Bury Flex is because it's under the house in the crawl space, put there 15 years ago. The 2.5 dB figure is higher than I expected since the loss for LMR 400 and Bury Flex should be about .67 dB/100' at 30 MHz. That suggests 375'.  I estimate 250' pending discovery of old notes.

That was me.  300' of Bury Flex with 100 w.  out of tx gives you 58 watts to the load on 29 MHz with a 1:1 vswr (load matched to feedline).  New LMR-400 gets you about 63 watts to the load out of 100.  Sounds like balanced line is not an option.  You have to either live with losing 40 to 50% of your power in your feedline, or invest in really good but costly hardline or figure out a way to shorten the feedline run.   A lot of this has to do with how much of a perfectionist you are--not caring is cheap and easy.    I tend to let things like this bug me, but I'd be more concerned with such a loss on the low bands where not being piss weak can matter.

The way you route the feedline (above ground) mattered only because it told me what routing options are available, whether or not you have to deal with jacket degradation from direct burial, water contamination in the dielectric, digging damage, and whether or not easy splicing is an option with two males and a bullet.  A "bullet" is a short section ending in jacks.  A "barrel" is two males end to end. 

Bury-Flex loss 100' run 29 Mhz 1:1 vswr is 0.765 dB, not great not bad.  Your problem is the frigging length of your run.  That's what's eating up all your RF.  This is why FM broadcast stations on 88 MHz, even if only running a few hundred watts, have 3 inch heliax going up the tower and 250 w. medium wave AM daytimers run 7/8 inch heliax (durability is another reason).   

Lots of hams think 1:1 vswr and/or operating on 160 m. and/or running low power mean they can get by with some ridiculous feedline like 150 feet of 8X or 58U.  And another piss weaker is born 

You can get an amp to double your power to make up the 3 dB loss--that is viable for you -- it isn't so much for broadcasters because they are businesses transmitting continuously and paying the light bill out of revenue so a one-time outlay passive solution is preferred.  I would check your feedline however, for signs of exposure damage and fatigue.  An amp won't keep it nice and new.

[W1RKW]

measuring transmitter power with a 3 ft piece of coax or a 3000ft piece of coax?

[flintstone mop]

Here's a link to various coax cables and their losses.

http://www.w4rp.com/ref/coax.html

You must be using RG8 on 10M.
And then I came from the communication industry, make up the losses with a better antenna with higher gain........VHF and up.
HF........get something higher than 50 feet and no loading coils.

And as Opcom and another reply states no matter how long we try to out buzzard each other on the air, your electric bill will not increase noticeably.
If you want to see a reduction in your electric bill UNplug all the devices that are in "standby" in your house. All TV's in the last 5 yrs, cable modems, cable boxes, satellite receivers, computers, UPS's.
I could drop about $10 a month here if I did that.

And who's checking anyway......it just gets expensive to buy or build anything bigger.
Fred

[WU2D]

Perhaps at one time there was a team of legendary enforcers at the FCC. Those actual power numbers, however interpreted, are there as legal regulations to set the basic limits. When they are actually used for enforcement, usually some number of related incidents and complaints have been filed. The power measurement at that point is simply part of the "evidence"  that can be submitted to prosecute.

With commercial entities it is different. The FCC is more pro-active here. Broadcast stations have always been checked regularly. And since the FCC started selling frequencies, you can guess who has the most vested interest in enforcement. Remember the whole deal is related to - are services impacted? Are you interfering with a commercial (money making) enterprise? Did you take down part of a cell site with a harmonic of your repeater or your phone booster which has gone into feedback? Are you messing with the FAA frequencies? Malicious interference on these frequencies is taken seriously. Hams and CB'ers with their various issues are in the noise.

[k4kyv]

The relevent excerpts:

97.3 Definitions
b. (6) PEP (peak envelope power).
The average power supplied to the antenna

I'll hafta pull out my copy of the regs to review the full text of the paragraph, but looks like that answers the question posed by the initial poster.

Another scenario I could imagine would be someone with a transmitter that did put out more than the legal limit.  The OP wanted to comply with the letter of the law but not modify or mis-tune his transmitter, so he inserted an rf attenuator made up of non-inductive power resistors in line to reduce the power output to the legal value.  Broadcast stations do that all the time, particularly to bring DAs precisely into compliance, or when the antenna turns out to be so efficient as to bring field strength up beyond calculated values. What is the difference between a resistor network, and 100ft. of extra crappy coax that does exactly the same thing?

There is no reg that states that one must have a 50-ohm unbalanced output. And the FeeCee repealed the regulation that used to require "means to accurately measure power" when they changed the power regs, in response to numerous commentors who brought up the issue of amateurs' capability of measuring output power.  They added some B.S. statement to the effect that amateurs could determine power output by "means other than accurate measurement" (whatever that is supposed to mean). They also stated in the R&O that the FeeCee would assume the burden of measuring the power output of a transmitter in the event of a station inspection if the op couldn't do it. Not having a 50-ohm link somewhere in the transmitter/feed line system would not in itself be legal justification for a NAL, unless they had some other convincing evidence that the rules were being broken, such as several  KW input to a 3CX15000.

The only QRO transmitter I have ever had in nearly 50 years that uses an SO-239 or 50/75-ohm balanced output is the Gates BC1-T, and that one originally comes with a ceramic Dolly Parton insulator feeding through the top of the cabinet. I JS'ed an SO-239 on top of the insulator myself to accommodate the unbalanced L-network I used to employ outboard because the transmitter wouldn't fully take the load without it.

[K6JEK]

Thanks, Rob for your careful analysis of the crazy situation I've created for myself.  The routing is historical.  There are all manner of patios, walkways, trees, lawns, power lines and other obstacles in the way of a more direct route.  These could be overcome but not as easily as writing a check for better coax.

Ham fest season out here is over. Otherwise I'd be trolling around for some cheap hardline or Heliax.  If  Heliax fell out of the sky I'd put on my coveralls and crawl under the house (and I do mean crawl) to replace the 150' section of BuryFlex then the 100' of LMR400 and be in like Flynn.  I see 1/2" Heliax on eBay going for about $1.50/foot sans connectors

I've never worked with either Heliax or hardline. Installing connectors not to mention paying for them would be an education. 

Thanks,

Jon

[Opcom]

Wouldn't the expensive hard line last almost forever compared to 'regular' or even LMRnnn coaxial cable? It might be worth a one time expense if the loss was reduced enough and you plan to use it for 20+ years. I quit pulling old coax off defunct installations because it was always rotten in some way or another.

The topic of power measurement and interpretations of the wording of the regulations was discussed in great detail before but revisting it might not add anything new.
http://amfone.net/Amforum/index.php?topic=25835.0


looking at the EB page, there do not seem to have been many actions lately. I guess the spectrum is all cleaned up!
http://transition.fcc.gov/eb/AmateurActions/Welcome.html

[k4kyv]

97.3, (b)(6) PEP (peak envelope power). The average power supplied to the antenna transmission line by a transmitter during one RF cycle at the crest of the modulation envelope taken under normal operating conditions.

That should clear up the original question. "Antenna transmission line" means the transmission line that runs from ATU up to the antenna, NOT the line linking the plate tank circuit to the final stage of the tuning network, even when the tuning network is built in sections with the last stage located at the base of the tower, remotely from the main box. In other words, the ultimate point in the chain between active device (tube or transistor) and radiating element (antenna) where it is practical to insert a power measuring instrument.

[Steve - K4HX]

Angels dancing on the head of a pin. Until someone actually does this, it's just more typical bulletin board BS.

[Opcom]

Angels dancing on the head of a pin. Until someone actually does this, it's just more typical bulletin board BS.

Isn't it -all- just typical bulletin board BS?

[Steve - K4HX]

Yes it is!

It's fun to hypothesize but it can become tiresome after a while. I had fun on 80, 40 and 10 meters today. No BB BS there!  

Angels dancing on the head of a pin. Until someone actually does this, it's just more typical bulletin board BS.

Isn't it -all- just typical bulletin board BS?

[w1vtp]

Before this thread, I thought I knew what 1500 watts PEP meant.  Now, I'm totally confused

Al

[Todd, KA1KAQ]

A little time back on the air and you'll be as good as new, Al. I've noticed that too much time spent on line tends to muddle things, but a few hours on the air actually clears the head and puts it more into perspective. Not unlike the sunny day at NEAR-Fest after the rain the day before.

[flintstone mop]

Reading your original post..........and somewhere down the thread you mention LMR400.............ok good stuff, but 375 feet is going to kill you as you get close to 10M.........
And I read the historic reasons for not re-running or shortening the route or root.
When the band is open your 3dB loss will never be noticed.
Fred

[Detroit47]

Jim
WD5JKO

They can't measure anything other than what a Bird peak-reading wattmeter can measure.

Now, how many hams today have a transmitter with a link coupling to a balanced transmission line? No one. one out of ten thousand maybe. And Don. Everyone uses a pi-net with 50 ohm line to an antenna or a tuner. Even with a broadcast transmitter.

So the argument is a red herring.

What if one runs a Globe King 400 which is ballanced output. And can be feed straight into ladder line it don't need no tuna.

N8QPC

[K5UJ]

<<<97.3 Definitions
b. (6) PEP (peak envelope power).
The average power supplied to the antenna
transmission line by a transmitter during
one RF cycle at the crest of the
modulation envelope taken under normal
operating conditions.>>>

Help me out--I am having trouble with the word "average" in there.  In a class C PA a single RF cycle is pretty much the top 20 or 30% of the complete sine wave right, so we have that at the peak or crest of the modulation envelope.  I guess in that case averate = peak.   Maybe my problem is looking at it purely from an AM point--I guess this has to be considered in the context of other modes.

What was so bad about the old way which I think was still in effect when I was first licensed?  (I paid scant attention to it because back then I was light years away from getting close to the legal limit)  Carrier input power to the final.  You have meters for the plate current and plate voltage.  Game over.  What on earth was so difficult?  This seems far more complex.   I vaguely recall a change so SSB was 2 KW input AM/CW 1 KW.  At the time I did not understand the reason for that.  It seems like the old method would eliminate all these problems with feedlines, impedance, watt meters, RF amp meters etc.

Thanks, Rob for your careful analysis of the crazy situation I've created for myself. 

You're welcome Jon, I've bought heliax at hamfests, you have to look it over for damage but you can get lengths sometimes with the connectors on already but probably not 300'.   So you splice a pair of 150' runs.  There's someone on eBay now with new looking 1.5 inch heliax, three 200' runs for $1200 or maybe it's $1600, can't remember.  That's a heck of a lot of do re mi (but it sure would work well ).  Once you  get it uncoiled it isn't too bad but it isn't designed to be worked back and forth like jumpers are.   You lay it out and clamp it into position and that's it.  Cut it with a hack saw, not wire clippers as they will smoosh the cable before cutting it.  A Dremel tool with a cutting blade is helpful for preparing an end to accept a connector.  The connectors can be relatively expensive but again, if you are looking to have a feedline run for 20 years it pays for itself.  I'd take a look at what's available at future hamfests.  Runs from cell phone towers are good.  Some of the towers are getting upgraded to RF units up at the antennas with fiber optic going up the masts so the heliax is getting  removed.  If you wind up buying it new Davis RF is a good vendor with reasonable prices.  www.davisrf.com   If you are only interested in 10 m. during the peak of the solar cycle then all this may be overkill as I think Fred implied.  There's no sense investing in really expensive line if it will sit unused for years between 11 year cycle peaks.

rob