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Author Topic: Drinkin' Beer & Wonderin' About Amps  (Read 4452 times)
AF6D
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« on: June 19, 2011, 03:20:33 AM »

There's nothing like having a weekend to sit up with fellow hams and throw stuff against the wall. Purely hypothetical, but we've been discussing running two phased Yagi's on receive, but separating the antennas on transmit and running two 1500 watt amps -- one to each antenna.

Now then, first: the legal. Is it? I can't quite tell by reading the regs.

But second, wouldn't it be the same as running one amp into two phased Yagi's that yield about a 3dB boost?

Please don't take this question ultra-seriously. It's just one of those fun questions at 3am. Like what if you didn't phase the Yagi's and pointed one east and one west with a separate amp on each while calling CQ...

The stuff we come up with.
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W6RMK
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« Reply #1 on: June 19, 2011, 08:26:10 AM »

You're talking about a phased array..
The rules say 1500W PEP from the station.  So your two kilowatt amps would bust the limit, if operated by the same person.  However, if you had one, and your buddy had the other, and you happened be phase locked together, maybe it would be legal: technically it's two different stations.  (this technique is used in broadcast, by the way)  I don't know how a "simultaneous transmit" station works, legally.. Probably it's really 1500W at one frequency, so W1AW transmitting FMT on multiple bands simultaneously is legal (or they have a waiver).  And, a multi-multi contest station is clearly transmitting more than 1500W at one time, but they're different signals on different bands.

There's also a lot of discussion around the lunch table about where's the reference plane for that power measurement?  At the output jack on the amplifier?  At the antenna feedpoint? In the far field, integrated over a sphere?  That gets into a discussion of "active antenna tuners" with a lot of REV and FWD power between amp and antenna.

In other radio services, the limit is set on the Effective Radiated Power or a similar measurement (so a big amp and lossy feedline is the same as a small amp and good feedline).  For historical reasons, the limit for amateurs is set with something easy to measure.  Back in the 20s, it was input power to the rig (since that's what people could measure)..then it was DC power to the final stage: again, easy to measure, and you don't have to argue about filament and exciter power.. so it's closer to "radiated RF power" which is what they really want to regulate.  Now, it's PEP measured at RF (SSB and measurement technology allows it).




A lot of enforcement is based on the "rude rule" -> if you're rude, they find a rule to bust you on. 

It's better than running one amp into two phased yagis.. you've got twice as much power.  (unless the one amp is a 3kW amp.. then it's exactly the same)
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KD8DEY
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« Reply #2 on: June 19, 2011, 10:42:56 AM »

I just hope that "Beer and Amps" don't produce a tendency to QSY to 27.185 and start callin "Yee Ha"
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AF6D
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« Reply #3 on: June 19, 2011, 01:48:42 PM »

I just hope that "Beer and Amps" don't produce a tendency to QSY to 27.185 and start callin "Yee Ha"

HA HA HA HA HA. That got me going! I haven't been on CB since the 70's Good Buddy. "Breaker, Breaker one nine. We got us a convey." DX was so much fun back then. I had an egg beater antenna and a 400 watt amp in my Opal GT and I'd geek around town working Australia and getting the attention of the police...

@W6RMK -- you threw me for a minute there. I have a friend that just moved up to Fresno and he's W6MRK.

Sittin' around at 3am suckin' suds can yield many wonderful topics besides the meaning of life. My wife was gone for the weekend with the kids - a Father's Day present? - and well, you know.

I wasn't aware that this techique was used in broadcasting, so it must obvioulsy has some benefit. It is a moot point for me because I have an Ameritron 811H running on 110v. I don't have 220v down here in "the cave." My basement. But that would be an obvious thought, too. Running  a Henry 3k would do the same power output into a phased array, would be more econimical -- and would be just as illegal. Or is that "unlawful?" When I was in the police academy we were taught that "illegal" was a sick bird. 8=)

Personally, I like contesting days where I deliberately run QRP at 25 watts PEP. It makes it tough but I do get contacts. And once someone hears you and another hears you a pile-up begins. To me that is much more kewl than running legal limit and ESSB that splatters. It sucks that I have a Yaesu FT-2000.

But the thought of running  two 811H's into twin Yagi's pointed east/west while calling CQ is still interesting. I could do bi-directional with the SteppIR that came down with the divorce and change in QTH. Short path / long path at the same time. Sadly, I run a Yaesu FT-2000 and I swear now that the 5000DX is out people finally admit what I've known for several years -- it's as deaf as the guy that owes me money. I have to admit that I don't turn the HF on like I used to... it is just plain obvious that I cannot hear.

I have a friend with a remote atop an 8,000 foot mountain at a repeater site running a Kendwood TS-480 and a RemoteRig. We WiFi 2.4GHz up to him from my QTH at 6,3330 feet in the mountains (still not bad!) and he hears so much more than I. It's DX, so I know that it isn't the altitude. He's running a 40m-10m vertical groundplane (that will load up on 80 and 6 -- that has to be rebuilt each winter because of ice and broken elements) and beats my Alpha Delta DXCC fan dipole in the clear between two trees about 60 feet above ground. I'm still high above the invcersion layer and my results should be the same as his. But nope. He whoops me on receive and makes conact after contact with 100 watts. He has the added benefit that the CODECs used in the RemoteRig are effective DSP's. I run a ClearSpeech that works. But when I hear what he hears over the telephone I want to choke him out!

That's what got me thinking about trying to get my SteppIR back up. I put my FT-847 back on an antenna switch last night to do an A/B comparison with the FT-2000 and they are about even. This suggests to me that either both suck on receive or my antenna sucks more. No amp will fix that.

But back to the point -- 750 watts PEP in two directions would be legal?
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AD4U
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« Reply #4 on: June 20, 2011, 08:59:35 AM »

WAY back (1960's??) there was an article in QST about a HAM who fed two yagis (one horizonally polarized and the other one vertically polarized) with one rig feeding two separate amps, whose combined output totalled the maximum legal power - back then.

This guy was testing to see if running two yagis at the same time with opposite polarization enhanced his signal.

Unfortunately I do not remember if it worked or not.

Dick  AD4U
« Last Edit: June 20, 2011, 11:30:45 AM by AD4U » Logged
N5KBP
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« Reply #5 on: June 20, 2011, 11:45:37 AM »

I just hope that "Beer and Amps" don't produce a tendency to QSY to 27.185 and start callin "Yee Ha"

HA HA HA HA HA. That got me going! I haven't been on CB since the 70's Good Buddy. "Breaker, Breaker one nine. We got us a convey." DX was so much fun back then. I had an egg beater antenna and a 400 watt amp in my Opal GT and I'd geek around town working Australia and getting the attention of the police...


Opal GT. Now that brings back memories. I had one with a base loaded cb ant mounted in the fender cowling and a cobra 148gtl laying in the floor board. Used to work all over the world in the late 70's. The Opal was a lot of fun especially since I am 6 foot 3. It was a ball to slide down into the seat.
Marty
N5KBP
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AF6D
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« Reply #6 on: June 22, 2011, 07:01:53 AM »

My Opal GT has the 5 foot tall Egg Beater center mounted in the roof! I looked like something out of the freakin' Jetsons! LOL. With a Cobra 148GTL with all the modifications and a 400 watt amp I worked the world. That's when I got bitten as a ham. I loved my Opal GT and it was a chic magnet no less! When not mobile I'd sit on my base station modified for extended range and I'd stay up until the sun would come up as I worked the grey line on 10 meters that I didn't know about yet.

My first radio was a National Radio with 18 tubes. Knowing nothing about loading coils or traps I fashioned a loaded folded dipole and strung it between the trees. I used red/white striped bell wire and wound "coils" over wooden dowels. It worked damn good and I'd DX AM broadcast stations with it. By using the main tuner and the sub-tuner I could actually get up to 50MHz and regularly used it to listen to Los Angeles County Sheriff back when they were on 39MHz. I used slope detection in the AM mode.

My love of antenna design was born back then as well. Seeing what I had done my neighbor, a SK now, gave me a block of wood and 5 metal rods from which I made my first quarter wave ground plane by drilling into the block of would at 45's and epoxy gluing them in place. I connected the radials and direct soldered the coax. It worked okay but I found that I could take a CD radio antenna and shorten the 5/8 wave vertical element and get killer low band reception. Back then, in the 70's, low band was still really popular.

This past brings me here wondering about phased Yagi's pointed either in one direction or bi-directional. Does one amp running through a power divider have more or less punch than phased antennas each with their own amp.
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WB2WIK
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« Reply #7 on: June 22, 2011, 10:15:59 AM »

I had an Opal GT in 1971!  I bought it brand new while in college, found out I really couldn't afford it, and sold it after about a year but it was a lot of fun.  Mine was a metallic green with flat black highlights.  Never put an HF antenna on it, though.

Anyway, back to "legality" and using separate amps to drive antennas...I actually think this is legal, since FCC imposes no e.r.p. limitations on any band except 60 meters (for U.S. hams), and amplifiers are restricted to 1500W PEP output, but I don't see why two (or ten) amplifiers running to different antennas at the same time would be unlawful.

This actually was (maybe still is) done by a few HF contest stations back in the 70s and 80s when I was actively M/M contesting.  The rationale was to "keep a frequency clear," mostly, not to be any stronger anywhere.  We actually did this a few times, operating from the NY area.  We'd have a beam NE towards Europe, to run Europeans; then another beam SW, aimed mostly at our major competitor in TX, just to keep him away from our frequency.  Drove both amps with the same exciter.

The strategy worked fairly well and did help keep the frequency clearer for us, so we could hear more answers when they came.  I always suspected many contest stations did this, although only "confirmed" (verbally at a meeting at Dayton) that one did.

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W6RMK
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« Reply #8 on: June 22, 2011, 12:14:26 PM »



Anyway, back to "legality" and using separate amps to drive antennas...I actually think this is legal, since FCC imposes no e.r.p. limitations on any band except 60 meters (for U.S. hams), and amplifiers are restricted to 1500W PEP output, but I don't see why two (or ten) amplifiers running to different antennas at the same time would be unlawful.


First.. .two 750W amps feeding identical signals to two antennas.. clearly ok.  meets the 1500W limit.

But, the other scenario.. multiple amps, totaling more than 1500W..  My gut feel is that if they're the *same* signal, you'd be violating the intent of the reg, but perhaps not the letter.  It all revolves around where you draw the box around "transmitter".   One exciter feeding multiple amplifiers might be one transmitter.

97.313 (b) No station may transmit with a transmitter power exceeding 1.5kW PEP.

So... can a station have multiple transmitters?   One needs to look at Part 2 which has the big master list of definitions to figure it out.

2.1...
Station. One or more transmitters or receivers or a combination of
transmitters and receivers, including the accessory equipment, necessary
at one location for carrying on a radiocommunication service, or the
radio astronomy service.


--

basic advice here..
If the answer you might get is bad, don't ask the question.
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WB2WIK
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« Reply #9 on: June 22, 2011, 02:16:31 PM »



First.. .two 750W amps feeding identical signals to two antennas.. clearly ok.  meets the 1500W limit.

But, the other scenario.. multiple amps, totaling more than 1500W..  My gut feel is that if they're the *same* signal, you'd be violating the intent of the reg, but perhaps not the letter.  It all revolves around where you draw the box around "transmitter".   One exciter feeding multiple amplifiers might be one transmitter.

I don't think so, but someone can post the question to the FCC via their general query address and get a response (usually).  The response can take weeks, but I've found there usually is one.

My interpretation: Unless the two signals were always in phase, doing this doesn't increase power output.  Where they happen to be 180 out of phase, they can actually cancel each other.  And also, again, it's perfectly lawful to run multiple transmitters on multiple bands at 1500W output simultaneously from the same location, even using the same antenna if you can work that out.  W1AW does it several times a day (but so do lots of contest stations).  And there's no e.r.p. limit (for American hams, anyway) on the HF bands except 60m.

But it's an interesting question and someone really interested can just post it to Friendly.  I think the address is info@fcc.gov but I may be wrong -- haven't used it in more than a year.



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AF6D
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« Reply #10 on: June 22, 2011, 11:24:19 PM »

This has become a fascinating topic to me!

It seems to me that if one were running two phased antennas they are either narrowing the H field or the E field. Unless the amplifier was inserted into the 75 ohm feeder for each antenna they wouldn't really be in phase as we think of with stacking, right? One would just have two antennas with separate amplifiers pointed in the same direction. I can easily see remoting U/VHF amps on the tower making stacking possible like this but not from the shack. But then again I'm a complete stacking rookie Smiley Otherwise I guess one would have very long 75 ohm cable runs.

I find it fascinating and revealing that contesters would actually use this technique
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WB2WIK
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« Reply #11 on: June 23, 2011, 08:51:41 AM »



I find it fascinating and revealing that contesters would actually use this technique

Contesters definitely have, and maybe still do.

But again, it wasn't to be "stronger."  It was to help hold a frequency by being strong in multiple directions.
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AF6D
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« Reply #12 on: June 28, 2011, 02:49:24 AM »

I am not a contester but I think the practice is just wrong. But hey... on contest days I don't turn the rig on. I don't turn it on much these days anyway. I am very disappointed with the receive on the Yaesu FT-2000, but that is another post probably never to be started. One day my daughter's cancer will be gone for good, I'll own a home again and put the SteppIR back up with a DX-5000 or something current and better.

One question I don't recall seeing answered was that if one was running one exciter into two amplifiers each feeding a yagi one over the other but not phased as far as cable goes, am I correct that the ERP would increase but that the pattern wouldn't change nor would the gain?
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W8JI
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« Reply #13 on: July 03, 2011, 05:03:21 AM »

This has become a fascinating topic to me!

It seems to me that if one were running two phased antennas they are either narrowing the H field or the E field. Unless the amplifier was inserted into the 75 ohm feeder for each antenna they wouldn't really be in phase as we think of with stacking, right? One would just have two antennas with separate amplifiers pointed in the same direction. I can easily see remoting U/VHF amps on the tower making stacking possible like this but not from the shack. But then again I'm a complete stacking rookie Smiley Otherwise I guess one would have very long 75 ohm cable runs.

I find it fascinating and revealing that contesters would actually use this technique

You don't narrow electric or magnetic energy storage fields, you enlarge them.

You really meant to say you are narrowing the E or H plane of the antenna system, not field. It would be clearer yet to say it alters the pattern.

The cables from the antenna should match the antenna feed impedances. It is only in narrow band combining systems we have 75 ohm cables in 50 ohms systems, because certain lengths act like transformers. In my arrays with wide spacing I use matched lines to a phasing box where they are combined and then impedance stepped back up through a transformer. This widens bandwidth.

I transmit in two or more directions at once at times, and almost always use a narrower receiving pattern than transmitting pattern. Commonly I transmit omni, and receive very directional. Hundreds of people do this in daily operation on 160 meters.

There is nothing immoral or illegal about doing this. It is often the way most stations work on 160 meters.

In the 1980's when working DX on 20, there we so many rude inconsiderate retirees from Florida calling up north, it was difficult to work DX using a beam. My weak signal in Florida would let them start up and ruin my QSO. I installed a trap vertical above my beam, over 130 feet in the air, and used the vertical for transmitting when a Florida station would rudely start up. That solved the problem without disruption or arguments.

73 Tom

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W1ITT
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« Reply #14 on: July 03, 2011, 06:59:37 PM »

Interesting beer topic!  One other complication is that two "identical" amplifiers, even if they are fed in phase will probably not be exactly in phase at their outputs depending on tuning.  I recall setting up a two-transmitter FM broadcast rig into a combiner, and being unable to find the phase control (usually a trombone line section in the driver stage). Finally I called the manufacturer and they told me to detune the driver stage of one transmitter while watching the reject power in the combiner for a minimum.  This would alter the phase through that transmitter.  (I also had to tweak driver amplitude as well.) 
The point is, if you get through another sixpack and decide to try it, you need some way to sample output phase and control it to make this wonderful experiment "valid". I'm not sure what the legal implications would be, but it might be better, in the name of science, to ask for forgiveness rather than permission.
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