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Author Topic: Antenna vs Amp for more TX power?  (Read 4048 times)
K7RNO
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Posts: 279




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« on: March 08, 2014, 11:44:19 AM »

I just found this on the Elecraft reflector and wanted to know what the common understanding is in this group here:

"Once you can put up dipoles at
least 1/2 wavelength high and in the clear, it starts to get more
expensive to add to your antenna system than it does to add power.
So, assuming you can hear the station(s) you want to work, you'll
often get more from adding an amplifier than you do making a better
antenna. "

Is this generally correct?
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73,
aRNO
NAQCC #6870, SKCC #11131
KE4JOY
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Posts: 1384




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« Reply #1 on: March 08, 2014, 11:55:09 AM »

I guess that's more or less a fair statement as the next improvement over a wire antenna would be a beam or quad  which would involve a tower and rotator etc.

That being said I would still rather if was a dollar for dollar thing have the better antenna.
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N6AJR
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Posts: 9921




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« Reply #2 on: March 08, 2014, 12:16:46 PM »

I don't agree, I had a fellow I knew who put up a wire "beam" for 40 meters on his roof.

 He used 2x2 inch stick about 2 feet long and mounted them on his eves and center of the roof.  He put up a reflector wire in the back of his house, a 40 m dipole in the middle of the roof and  then a director on the front of his house. He ran the coax along the peak then down from the peak of the roof and into his shack. I don't remember the exact length of his wires but say the dipole  driven element was 33 foot on each side then the reflector was 35 feet on each side, and the director was about 29 feet on each side.

His house  roof peaks pointed about74 degrees on the compas and from the west coast. He heard most of the states and did OK into northern EU off the front and did  some Japan Australia and such off the back.  it only cost him about 20 bucks for wire and he had the sticks. so yea you can improve your antennas for less than an amp. Also a good antenna also hears better too.

est setup is to use the best you can then add more gain with power.  But in truth the dB gain you get from an amp is the same dB gain as you get from the antenna on transmit., but the amp does not help you hear better  so if you cant hear em, ya cant work em, and antennas hear better than amps.
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AA4PB
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Posts: 12985




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« Reply #3 on: March 08, 2014, 12:22:15 PM »

The key to that statement is "assuming you can hear the station(s) you want to work". The benefits of antenna changes include reducing noise and interference (assuming a directional antenna that can be rotated), improved take-off angle for DX, and increased received signal strength - that's in addition to the improved transmit signal.

Personally, I'd much rather have 100W with a 3 element Yagi at 60 feet than a 1500W with a dipole at 30 feet.
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W1JKA
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Posts: 1815




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« Reply #4 on: March 08, 2014, 01:59:26 PM »

Re:K7RNO

 I spent $63.00 on the best amp there is for my K-I a homebrew Hex beam. I would say the answer to your question is No.
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W8JI
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Posts: 9296


WWW

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« Reply #5 on: March 08, 2014, 06:28:22 PM »

I just found this on the Elecraft reflector and wanted to know what the common understanding is in this group here:

"Once you can put up dipoles at
least 1/2 wavelength high and in the clear, it starts to get more
expensive to add to your antenna system than it does to add power.
So, assuming you can hear the station(s) you want to work, you'll
often get more from adding an amplifier than you do making a better
antenna. "

Is this generally correct?


The true answer is complicated. It seems the vast majority of people either do not understand the difference between receiving and transmitting requirements, or just want to give a simple answer that can be wrong half the time.

On receiving, unless you get way down into system noise, the only thing that matters is the ratio of signal-to-noise. This is set by the pattern of an antenna and how it responds to the signal compared to noise. Receiving has almost nothing to do with gain or loss, until the system internal noise starts to determine noise floor.

Let me give you an example. My house is in a quiet location. I can take a 2 foot tall antenna and limit on external noise on 160-40 meters. A two foot vertical pretty much receives everything a 30 foot or a 60 foot vertical receives, all I have to do is have a preamp.

This is why people can use very lossy, very poor gain antennas, to work extremely weak signals on lower bands. My best receiving antenna up to 20 MHz have negative gain!

For transmitting, the effective radiated power at the desired directions and angles is all that matters. This is entirely different than receiving requirements.

Let me give an example with a beam. You can have a lossy beam that has poorly constructed traps, but has a clean pattern, and it can receive as well as or better than an antenna with more gain but a worse pattern. The lossy antenna will not transmit as well, but it can hear just as well or better.

So you see, this complicates the answer quite a bit.

If I was on 160 meters through 80 meters (and maybe 40 or 20 meters), a good vertical would transmit very well. It would not be good for receiving. If I wanted to improve things, I would add a receiving antenna system (that could be inexpensive) and an amplifier.

If I was on 40 through 20 meters, a good dipole up 60-80 feet would be a first step. If I wanted to get louder I could add a beam antenna of some type, and that would also help receiving a lot, **or** I could just add a small amplifier and a cheap receiving antenna system.

On 20 meters and up beams are small enough and easy enough that they are a good first step. That certainly is not true on 160, and not likely true on 80 or 40 unless you just want one or two directions.

It is a very complicated question and answer that depends on the environment, the band, and what you want to do. If someone gives you a simple answer, it will only be correct for the specific condition they are thinking of.

I might pay $1000 to gain 10 dB on transmitting with an amplifier. I might have to pay $10,000 to gain just 6 dB with antennas. It might just cost $200 to gain 20 dB better S/N on receive, and it might cost $10,000 to gain 6 dB if In do it with a big transmit antenna.

The only correct answer is it all depends on the band, the location, what you have to start with, and what you want to do. With so many variables, there can't be one answer.

There is one thing for certain though. Anyone claiming a transmitting gain of 1 dB equals a receiving gain of 1 dB is probably wrong in virtually all real world cases, and a whole lot of people think that.

73 Tom       

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AA4PB
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Posts: 12985




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« Reply #6 on: March 08, 2014, 06:42:44 PM »

Tom, if my antenna has a measured gain of 1dB on transmit doesn't it also have a measured 1dB gain in the receive direction? The difference however is that 1dB of antenna gain on receive doesn't necessarily mean that you will have a 1dB improvement in received signal to noise ratio. On receive it's the signal to noise ratio that matters. It is possible that and antenna that has less gain can improve the signal to noise ratio.

 
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W8JX
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Posts: 6465




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« Reply #7 on: March 08, 2014, 06:54:11 PM »

I just found this on the Elecraft reflector and wanted to know what the common understanding is in this group here:

"Once you can put up dipoles at
least 1/2 wavelength high and in the clear, it starts to get more
expensive to add to your antenna system than it does to add power.
So, assuming you can hear the station(s) you want to work, you'll
often get more from adding an amplifier than you do making a better
antenna. "

Is this generally correct?


You have gotten complex answers to a simple question. The key here is if you can hear them you want to be able to work them and to that the answer is yes. A amp will help you especially on lower HF bands. 1000 watts will give you a 10db boost. Going to 1500 will only give you about 1.5 dB more. Sure a beam can help some on high bands but then there are those running beams and 3000+ watts too.
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W8JI
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Posts: 9296


WWW

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« Reply #8 on: March 08, 2014, 07:02:42 PM »

Tom, if my antenna has a measured gain of 1dB on transmit doesn't it also have a measured 1dB gain in the receive direction? The difference however is that 1dB of antenna gain on receive doesn't necessarily mean that you will have a 1dB improvement in received signal to noise ratio. On receive it's the signal to noise ratio that matters. It is possible that and antenna that has less gain can improve the signal to noise ratio.

 

Signal level change is reciprocal, but signal-to-noise almost never changes at the same rate.

Yet when you read comments and articles, almost everyone thinks signal level change = signal to noise change.

We had a case with a noisy low band two-way site. Because the noise on the horizon was so high, it established noise floor. A bigger antenna picked the transmit signal to mobiles up the expected amount, but the base station couldn't hear the mobiles one bit better.
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G3RZP
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Posts: 4844




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« Reply #9 on: March 08, 2014, 11:30:05 PM »

Stir in to the mix that there are times when a lower antenna does better. Back in 1986 in the Bermuda Contest, I was on 20m SSB with a 5 element monoband yagi at 62 feet, running the West Coast stations. I could also use a G5RV at 25 feet, and that enabled me to chase off the East Coast stations who had my signals about 3 points down on the Yagi as compared to G5RV. The West Coast couldn't hear the G5RV.... I find that the height is a disadvantage to Caribbean on 10 metres when the band is open, although it's fine for CP, OA and the like.

For the LF bands, separate receive antennas are really necessary for DXing. If you are running an amplifier, make sure that there is some protection for the receiver from those separate antennas - my 160m tuned loop had 80volts rms across it when I had 400 watts into the vertical 70 feet away!

73

Peter G3RZP
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NO9E
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Posts: 436




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« Reply #10 on: March 14, 2014, 07:54:03 AM »

As W8JI writes, the story is not that simple.

In economic terms, one should look at current limits to radio enjoyment and cost of actions to increase it by some amount.

Let's look at a cost of a better antenna. If the current antenna is low wire and tall trees are around, the cost is low. When tall trees are not available, the cost increases. When in a HOA location, the cost of a better antenna can be > $100k (new house).

Change from a dipole to a hexbeam when enough space is available costs $1-2k (antenna, rotator tower). Change from a single beam at 70ft to phased beam can cost >$10k. 

The cost of an amp varies too dependent on what kind of job one does. With lots of time on hand, a cheap option works well. For a busy guy where trouble with an amp can cost him thousands in lost contracts, a high end amp is the best deal.

When one uses a simple radio and is interested in SSB, the best deal is having a radio with a good speech processor and equalized audio.  The difference can easily be 6 db.

At my location the biggest limit to radio enjoyment is noise from neighbors transmitted over TV cable and from powerlines. One option is a new property (at a cost of > $100k + likely hell from wife).

Ignacy, NO9E
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NO2A
Member

Posts: 824




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« Reply #11 on: March 14, 2014, 10:52:50 AM »

By all means a bigger better antenna will always win,if you can do that. If you can`t an amp will certainly help. Lately I`ve worked quite a few stations running my AL-80A with an 80m dipole on 12 meters. Since this band is marginal at times,it makes a huge difference. On 17m,after calling cq I got a responce from a UA0 station. He was very weak,but I could tell it was a UA0. After he could tell I was having difficulty hearing him,he increased his power to qro levels. I don`t know how much he was running, but his 229 signal went up to 559 with no fading whatsoever. But as mentioned,this only helps if you can hear them. I was running qro also. Quite simply,if you need the boost use it. If nobody has a problem hearing you then save the electric.
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