Legal limit at antenna or shack?

[K6JEK]

Getting on 10, I've discovered my very long run of coax provides almost 3 dB of attenuation.

Would I be justified running 2X the legal limit in the shack knowing that it was 1X at the antenna? Has this question been answered by the FCC?

[W7TFO]

Under amateur regs, they specifically relate to carrier Watts, but I'm not sure just where one is supposed to measure them.....TX output, antenna input, direct, indirect?

Under part 73 broadcast, the type of line is called out in the engineering submissions, and considered in the transmitter power output vs. antenna input power.

Interesting point.

73DG

[Tom WA3KLR]

The .pdf edition of Part 97 I have is from 2005.  
Section 97.313 "Transmitter Power Standards"
Power limits refer to transmitter power.

If they allowed for transmission line loss, it would read, "as measured at antenna feedpoint".  But it doesn't.

[WD8KDG]

Ain't nobody watching, no longer required to have a means of measuring TX power. 

Craig,

[W7TFO]

Ain't nobody watching

Oh yeah, well this damned thing never sleeps....

73DG

[K6JEK]

The .pdf edition of Part 97 I have is from 2005.  
Section 97.313 "Transmitter Power Standards"
Power limits refer to transmitter power.

If they allowed for transmission line loss, it would read, "as measured at antenna feedpoint".  But it doesn't.

Shucks.

[Opcom]

sematics depending on the equipment. Most people measure at the input to a coaxial cable that carries the juice out to the antenna. Hre is wherethe link coupled balanced folks may have an advantage. I would not want to argue that point to the FCC though.

As for the power meter, it might be hard to explain the 8KW increase in consumed power for 3 minute intervals while claiming to stick to 1500W.

[W7TFO]

Prolly easier to replace the lossy coax with some good stuff.

73DG

[K5UJ]

K6JEK, no one can give you a decent answer to your question if you never provide some specifics about the installation.  What 10 m. antenna are you using?  how long is the feedline run?  Is it laying on the ground then making a 90 degree bend to go up to the feedpoint?  Do you have a dipole suspended so the feed is dangling down?  Beam on a tower?  Vertically polarized dipole or monopole?  How is it supported?  Ground mounted? \?\?\?\?  
How do you know you are losing 3 dB in the line?  How did you measure it?  If the line is truly dissipating half your tx power you are going to have to replace the line with something else.  That's the only decent solution.

Rob

[Jim, W5JO]

The rule says "transmitter power", nothing else.  So, given the way federal officials look at things, I would not run more than the legal at the transmitter.

[WD5JKO]

Jon,

  I heard you briefly last night on 10m. You were strapping into Texas.

So, if your feedline was RG-8/U it takes 300' to get 3 db loss at 29 Mhz.

So, if your feedline was LMR-400 it takes 450' to get 3 db loss at 29 Mhz.

http://www.timesmicrowave.com/cgi-bin/calculate.pl


  So I see your concern, and to VHF and UHF this is a big deal. But for 10m with good coax and reasonable length, the loss is insignificant. Even if it were 3 db, that is 1/2 an 'S' unit. When 10M is open the signals are usually S9 + 20db or higher. Here you could lose 10 db, and still be S9 +10 db.

 Also having a 3 element Yagi at the end of the coax with 8 dbd gain has a huge way of overcomming a db or two of feedline loss.

Jim
WD5JKO

[Bill, KD0HG]

Getting on 10, I've discovered my very long run of coax provides almost 3 dB of attenuation.

Would I be justified running 2X the legal limit in the shack knowing that it was 1X at the antenna? Has this question been answered by the FCC?

The regs don't specify a lawful effective radiated power, which I think this is all leading to.

There's a lot of other losses in an antenna system in addition to feedline loss; resistive loss, ground losses in a vertical, RF absorption by nearby objects,  the FCC isn't permitting anyone to run 15KW into an antenna system with 10 db of inherent losses.

My two centavos.

B

[Opcom]

The rule says "transmitter power", nothing else.  So, given the way federal officials look at things, I would not run more than the legal at the transmitter.

Yes, to them the transmitter is 'that box', even if the feed is welded and non-detatchable from it and the only connector is at the antenna base. I'd agree. My solution to the rule in the presence of higher powered stuff is to find a way that if it is inspected by someone smarter than myself it is compliant. That could be anything from an attenuator between the ricebox "vfo' and the TX, or a stop on the front panel variac, or any number of 'stoppers' to keep the set legal. I doubt they will pick a fight over a small discrepancy but 3dB over 1500W will be trouble.

The way they inspect, also, at short notice, is designed to reduce the possibility of the operator materially changing things and cheating the inspection. I'm sure there are ways to cheat them, but I myself won't take the chance. (see 'smarter than me', above)

It is a happy coincidence that a 100W transmitter will only drive a GG 3CX3000 to about 1500W.

Replace that cable! It's almost free energy anyway! The smart people here told me to use a balanced open feedline to reduce loss. My 2 cents there.

[k4kyv]

Transmitter output power or input power to the antenna? A matter of semantics. Isn't this being a little picky and splitting hairs over nothing? Give yourself the benefit of the doubt.

Since the rules are non-specific on this detail, I would define power output as whatever the meter reads at the very last point where I could physically insert a measuring instrument before the rf reaches the radiating part of the antenna. Furthermore, if it is a homebrew transmitter you designed yourself, the "output terminals of the transmitter" are wherever you define them to be. At my station, the feedline running out to the tower and tuning network at the base of the tower are all components of the transmitter, not the antenna. With open wire tuned feeders, the OWL and ATU are interactive with the PA tank circuit, making them all integral parts of the transmitter's output network. Just as a transmitter can have an outboard VFO, speech amplifier or power supply, it can also have an outboard tuning network. Not all amateur transmitters in use to-day consist of nothing more than a black box feeding a run of co-ass.

In any case, don't worry about it. Unless you are doing something to actively generate complaints, the likelihood of being inspected is about the same as that of winning the PowerBall.

[Detroit47]

Run what ya brung as long as you don't piss off the neighbors.

John

[WD8BIL]

-
(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.

Where's the problem? This is quite clear! Your transmitter cannot put more than 1500W PEP into the antenna system. Asking where your transmitter ends and antenna system starts doesn't cut it.

[k4kyv]

This is quite clear! Your transmitter cannot put more than 1500W PEP into the antenna system. Asking where your transmitter ends and antenna system starts doesn't cut it.

Maybe quite clear if you are running a ricebox directly to a coax-fed antenna. Otherwise, in what section of the rules is there any specification or definition of "transmitter power" that spells out precisely where the transmitter ends and the antenna system begins?

In a DX-100, the output network is inside the main box.  With a ricebox, the output network is an optional accessory (so-called "transmatch") that you pay extra for, and runs outboard to the unit.  You could place it right beside the box, or use a long piece of coax and place it in a waterproof enclosure on the side of the tower.

It's one of those vaguely defined areas in Part 97 like "minimum power to carry out  the desired communication (how do you define that?), "good amateur and engineering practice", and "minimum bandwidth to transmit the information rate". Better left a grey area until someone at the FCC decides to make an issue of it.  I would not recommend contacting anyone at the Commission and asking for a definition.

[Steve - K4HX]

Nonsense.

Rice box autotuners are internal to the box.

No transmitter I've ever seen comes with a 50 foot piece of coax, open-wire line or any other transmission line.

The concept and definition of Effective Radiated Power (ERP) is well established in FCC regs. If the FCC wanted to include the feedline and antenna system in the equation, the term ERP would have been used not Transmitter Power.

Bottom line is you can run any power you want, as long as you don't get caught.   

[k4kyv]

No transmitter I've ever seen comes with a 50 foot piece of coax, open-wire line or any other transmission line.

A lot of transmitters come with a 6 to 10' piece of coax between the oscillator stage and the buffer, driver and final.  One example is the Viking I and II /122 combination.  The BC-610 comes with a long cable between the speech amplifier and the rest of the transmitter that includes the driver and modulator.  The Johnson 500 comes with an outboard power supply connected via a long HV cable. So who is to say that part of the transmitter's rf output network  can't be separate from the rest of the transmitter, connected via an rf transmission line?

The concept and definition of Effective Radiated Power (ERP) is well established in FCC regs. If the FCC wanted to include the feedline and antenna system in the equation, the term ERP would have been used not Transmitter Power.

The problem with ERP is that it takes some serious test equipment and technical expertise to accurately measure it. Far beyond anything you could ever expect of Hammy Hambone. Plus, with directional antennas, ERP may vary widely according to the orientation of the antenna. How would it be defined when a beam antenna is in use? Most Hammy Hambones don't even understand what p.e.p. is, other than  "that's what the meter reads in the p.e.p. position". Imagine the average Joe Bloe ham's understanding of ERP. ERP simply wouldn't be practical for amateur radio.

AM broadcast stations measure output power at some arbitrary point between the transmitter box and the base of the tower, usually with an rf ammeter (with shorting switch for  lightning protection) at the dog-house at the base of the antenna. When I worked at the BC station years ago, part of the tuning network was mounted in a plywood box on the wall about 6' from  the main transmitter box, with about a 15' run of 3/4" copper pipe out the wall of the transmitter building and brazed to the base of the tower.

The amateur regulations make no mention of where this measurement is to be made, other than "transmitter power", a term subject to interpretation. If I designed and built the transmitter, I can locate any part of the output network anywhere I want to put it, and use the conductor of my choosing to connect the pieces together.

Maybe modern riceboxes come equipped with autotuners.  The earlier all solid state versions simply had a broadband solid state "brick" for the final amplifier, with some low pass  circuitry between the brick and the coax connector on the back.  It would work fine into a 50-ohm resistive, non-reactive load.  But with significant SWR or reactive component, a manually  tuned transmatch was required, or else the transmitter would automatically reduce power to protect the final.  IOW, the final tank circuit now came as a separate outboard unit that cost extra, whereas the older hollow state rigs included the tank circuit right inside the box. That outboard unit could be located anywhere the operator wanted to put it.

[Steve - K4HX]

All your example are inside the box or power cords. Nice try though. I'm sure it would work with the FCC!  

Further, an external tuner is just that. It's not part of the transmitter.

[WD8BIL]

Even with an external autotuner the output of the transmitter is still the same and easy to find. As Steve implied, I don't think your arguements would go too far with the FeeCee, Don.

[WD5JKO]

Even with an external autotuner the output of the transmitter is still the same and easy to find. As Steve implied, I don't think your arguements would go too far with the FeeCee, Don.

Maybe so, but what if the RF transmission line is open wire, say 600 ohm type, and resonant. Nowhere for Mr. FCC to connect his 50 ohm based meter. After the tuner we got more open wire, resonant lines feeding the antenna. Would he be able to measure W = EI X Cosine theta?? I doubt it.

Jim
WD5JKO

[Steve - K4HX]

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.     

[k4kyv]

Even with an external autotuner the output of the transmitter is still the same and easy to find. As Steve implied, I don't think your arguements would go too far with the FeeCee, Don.

I don't think this is an issue that has ever been brought up before the FeeCee.  Nothing in the rules clearly states exactly what would be an acceptible legal power measuring point and what would not, or whether they consider output from the transmitter legally indistinguishable from input to the antenna, so at this point this whole thing is nothing more than speculation, which would require an official ruling to establish a settled policy.

This is a classic example of whether something is permissible until declared prohibited, or prohibited until declared permissible.  Under our purported form of government, I would give myself the benefit of a doubt and assume the former.  Frankly, under the present state of affairs, I don't think the FeeCee would give a rat's arse. Ask anyone who has ever dealt with Glenn Bastardi.

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.     

Probably wouldn't be wise @ 10 kw.  But @ 1 kW DC input, it might be less to worry about.

[WD5JKO]

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