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Author Topic: Gain vs Power---which does more?  (Read 18547 times)
KB0OYA
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« on: July 21, 2003, 11:56:26 AM »

Question for you folks. My brother and I disagree.

Two identical recievers set up. Same relative geographical location and same transciever power outputs---100 watts. Also both are connected to beam antennas on towers. (Assume identical cable losses)

#1 has an antenna that because of it's size and construction has poorer gain characteristics than the other one, but the tuner is connected to a 1kw power amp.  

#2 has no power amp connected but it's antenna has substantially better gain.  Assuming the gain figures are actual---not the manufacturers spin on what they say they are---which transciever will put out the best signal---under normal conditions?

In a nutshell, is one better off with more gain or more power? And why? Is there a reference article or graph someplace that shows this.

Thanks in advance---STEVE, KB0OYA
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WB2WIK
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« Reply #1 on: July 21, 2003, 12:36:52 PM »

Your *transmitted* signal depends upon e.r.p. (effective radiated power) focused towards a target receptor.  If the two antennas have the same radiation angle above the horizon and have identical e.r.p., the signal received at the other end of the path will be identical.  The e.r.p. may be developed using lower power into a higher gain antenna system, or higher power into a lower gain system.

However, remember that antenna gain comes from focusing energy in one direction while losing it in other directions; it can come from narrowing the vertical, or the horizontal, radiation pattern, or most commonly, both.   This plays a role in how your signal will be received at the other end of any given path, and it's difficult to accurately predict true e.r.p. at specific angles because of unknown variables such as earth conductivity/reflectivity and exact antenna height above that conductive/reflective layer.  As such, there is truly an "optimum" height above ground to achieve the best results for propagation at any given frequency and any given propagation distance, and there is *no* optimum height that works best for all frequencies and all distances.  If there were such a magic height, we'd all be using it.

Of course, added antenna gain increases station effectiveness far more than added power does, since the gain is useful for receiving signals as well, and in most cases added gain means narrower radiated lobes which can greatly help in reducing interference.

Given the choice between higher power or a better (higher gain) antenna, I'd always go for the better antenna, first!

WB2WIK/6
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KB0OYA
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« Reply #2 on: July 21, 2003, 01:15:28 PM »

Thanks for the reply.  Yours, by the way, is almost identical to the perspective I have. I have a Mosley beam at 70 feet and use an Icom 746 as my primary set-up.  I opted out of buying an amplifier in favor of buying one of the best beams I could afford in terms of performance.  My brother uses a good rig from TenTec, but opted instead to use a lesser cost (and performing) beam antenna on top of a 35' tower---a set-up that left enough money over to buy his amp. It is his contention that we are about apples and oranges with the two set-ups with the edge going to him as this cycle diminishes and signals get "iffier".  I believe if the incoming signal can't be heard whether it be band conditions in general or signal strength from their end---it doesn't matter how powerful you are---from this end.  A contact not made because you can't hear them or one not made because they can't hear you is a wash.  Power then becomes unimportant.  No amount of power will overcome bad band conditions, but signal directivity (gain) can make a huge difference.  For that reason the quality of the antenna---regardless of cost--will always take precedent over an amplifier--regardless of cost--with me.
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WB2WIK
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« Reply #3 on: July 21, 2003, 01:19:12 PM »

OYA, I agree with you.

When I tune around a "marginal" HF band such as 15m and 17m have often been lately, I often jot down the frequencies and callsigns of the strongest signals on the band, and then tune back to listen and find out what they're running (if they say).

Nine times out of then, the "big antennas" are generating those big signals, regardless of their power.  As the bands fade into dust, the "big antenna" guys are the very last signals on the bands, and often they're not running much power.

WB2WIK/6
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KE4ZHN
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« Reply #4 on: July 24, 2003, 01:10:27 PM »

Ita always nice to have an amp available to help in marginal conditions, but antenna gain rules! Steve is right on the money in his explanation. Amps wont help you hear a weak one! The antenna is the single most important part of your station. When the band is right, even QRP will do a heck of a job on a good array, but you can be running a full gallon on a junk antenna and get nothing but frustrated! The ideal situation of course is to have both, a good antenna and a decent amp for rough conditions. But if you are on a tight budget put every dime you can into the antenna system, you wont be sorry.
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KB2FCV
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« Reply #5 on: July 31, 2003, 03:43:36 PM »

Don't forget, you can have all the power in the world into that less-gain antenna... but you still have to be able to hear em' to work em'!
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W8JI
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« Reply #6 on: August 07, 2003, 12:39:17 PM »

Actually the replies indicating GAIN is important on receiving are NOT correct, unless you have a receiver that is not into external noise floor.

See:
http://www.w8ji.com/receiving.htm

The correct factor for receiving is directivity, not gain. A negative gain antenna can have high directivity and be a better receiving antenna than a higher gain antenna, as long as the directivity of the lower gain antenna is higher and the response is aligned with the desired signal.

This means a 2dB gain yagi, with low gain because of loss, can be better (or worse) for receiving than a 10dB gain antenna.

This is why Beverages, even though they have negative gain, receive much better than yagi's on the lower bands.

You should NEVER consider gain directly for receiving, but it does apply to transmitting as long as the main lobe is in the correct direction. Directivity is the key for receiving, and loss does not factor into directity.

73 Tom
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W9WHE
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« Reply #7 on: August 15, 2003, 02:59:52 PM »

9 times out of 10 the "big signals" have BOTH a big antenna and a big amp!
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BUCK
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« Reply #8 on: August 31, 2003, 11:52:40 AM »

One more point about antennas vs amps for gain.  The antenna works both ways.  You'll pull out weaker signals with a good antenna but you'll just be wasting electricity with a big amp and a poor antenna.


If you are operating on 75 meters and only have room for a dipole, then an amp is probably the best way to go.  But if you are operating 20 meters on a dipole and would like to choose between an amp and a beam, I would personally choose the beam as it will amplify my transmit and I can hear the weaker signals better.  Of course, that wouldn't stop me from putting an amp next in line on my budget.

Buck
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WA9SVD
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« Reply #9 on: August 31, 2003, 03:18:53 PM »

I also vote for "antenna first."  It WILL improve both receive and transmit capability.
  But if you already have the best possible antenna in YOUR situation, and can still hear stations that can't seem to hear you, or just barely hear you, then an amplifier may help.  You have to consider the expense, potential interference, etc. if you go that route, however. (And PLEASE, if you DO decide on an amplifier, use it only when necessary!  If you are already S-9, there's NO reason to use the amp!  The rest of us will really appreciate the consideration.  I can never understand the 40+ reports, because both sides insist on using "legal limit" amps. Even without the amps, the signal would still be tremendous.)
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