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Author Topic: Want t buy AMP but I want to hear the difference  (Read 10714 times)
K3JVB
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« Reply #15 on: April 27, 2009, 05:37:50 PM »

Do Some on air tests with another, using an amp.
I think with your eyes closed, you will hear a difference in audio. And it may not match what you think the S meter will be.

Yesterday, I was on 20 working barefoot. I was giving some points to Florida contestors.

I had no issues making contacts. On the other hand, in a pile up, it can be the difference of being heard.

But for the most part, I think the antenna is as important as power. Maybe more so.

40 and 75 meters power is a little more important, depending on the absorbing behavior of the atmosphere.

Amps have there place. But when conditions are UGHHH
legal limit may not get the job done.
73


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WB2WIK
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« Reply #16 on: April 27, 2009, 05:38:32 PM »

Now you heard the demo.  Sorry the band was just barely open (it's still very early here in CA) but I gave you what 100W-500W-kW sounds like so hopefully you can make an educated decision.

Thanks for the QSO.

73

Steve WB2WIK/6
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WB2WIK
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« Reply #17 on: April 27, 2009, 05:41:17 PM »

RE: Want t buy AMP but I want to hear the difference  >Reply  
by K3JVB on April 27, 2009  Mail this to a friend!  




But for the most part, I think the antenna is as important as power. Maybe more so.<

::DEFINITELY more so!  The antenna is the most important part of the station, besides the operator.  Power is very secondary.  But when you already have the best antenna you can possibly install, power does make a difference and can be a very worthwhile addition to most any station.

A 240V line to the shack is a worthwhile upgrade for those who don't already have one.

WB2WIK/6  
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K6AER
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« Reply #18 on: April 27, 2009, 05:58:41 PM »

You can very defiantly use an input attenuator to simulate the effect of an amplifier being used at the other end if the signal is week. AGC will move the signal level up and down the scale but it has little effect on the carrier to noise ratio of the signal.  If the signal is 10 dB above the receiver noise floor and you switch in 10 dB of attenuation your signal disappears into the noise floor.

Now I give you that if the noise is external and you switch in 10 dB of attenuation both the signal and the noise floor will drop 10 dB until you reach the receiver noise floor threshold. It has been my experience that most hams suffer from a high noise floor environment and the ham adding an amplifier to his signal at the other end will help greatly to your listening ability.

I always love hearing the statement that hams make when they say one receiver is quieter than another.  Both units have their noise floor jump up 3-6 S units when the coax is connected. The receiver noise floor is limited buy the antenna environment not the design.

Most of the new radios can not use their super dynamic range (100 dB) for the antenna noise floor is 20 dB higher than what was measured in the lab dummy load antenna.
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AE5RE
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« Reply #19 on: April 27, 2009, 07:28:17 PM »

Steve,

  Thank you very much for your help. Band was not open but it was a very good test. With 1KW you were just above the QRN/QRM  (S 5-6) but I was able to understand. With 100W I could not hear you at all. I have no too many options where I live due to community restriction. For DX, I think I have the best antenna for my location. I have a lot of problems to break through a pile up, the amp is the best and expensive option left for me right now. I wished I could move to a far form the city, maybe in a few years. 600W should be enough. Tnx agn.
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KM3F
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« Reply #20 on: April 27, 2009, 11:44:21 PM »

The question as asked demands an involved answer that the  author is not prepared to understand.
He wanted to hear the difference under a specific set of conditiones we can not explain to him by the usual methods.
I can get the same results by changing from a poor antenna to a good one without the use of an amplifier, just to try to prove a point.
For example a dipole to a beam on 20 meters.
Said another way, no signal level and poor copy to a Q5 copy and several or more S units on the same signal without an amplifier.
Putting an amplifier on a poor antenna often results in being heard but YOU OFTEN STILL CAN'T HEAR THE DX STATION and keep asking for repeats.
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AA4PB
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« Reply #21 on: April 28, 2009, 05:32:45 AM »

If the signal is 10 dB above the receiver noise floor...
--------------------------------------------------------
The problem there is that on HF we are hardly ever dealing with the receiver noise floor. The limiting factor is external noise being picked up by the antenna. Switching in a 10dB attenuator will attenuate BOTH the signal and the external noise by 10dB thus there will be no change in the signal to noise ratio. On the other hand, raising the transmit signal by 10dB will not increase the noise thus you get a 10dB improvement in signal to noise ratio. Signal to noise ratio is what determines how well you can copy a signal. Switching in and out an attenuator will not do a good job of demonstrating how much difference power will make.

The test he did with Steve turned out to be under pretty ideal conditions (weak signal) to demonstrate the difference.  
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Bob  AA4PB
Garrisonville, VA
KH6AQ
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« Reply #22 on: April 28, 2009, 08:08:36 AM »

K8AC: Everything I said is true. I gave signal strength differences in the industry standard units of 6 dB per S-unit. I did not give the signal strength differences in decibels as this would have less meaning to the questioner.

Next I demonstrated the principle of reciprocity between transmit and receive. Again, signal strength is the same.

By invoking the notion of incorrectly calibrated S-meters, such as Icom, you have introduced a red herring thereby clouding the issue.

Your language is not in keeping with the decorum of this forum.
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WB2WIK
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« Reply #23 on: April 28, 2009, 08:09:31 AM »

Ricardo (AE5RE) I'm actually sort of glad condx were so lousy...when the band's "wide open" signals can be so strong that an amplifier isn't necessary and hardly noticeable when used.

40m became *much* better (condx) about two hours after our QSO...then the east coast stations were coming in S9++ and that may have not been a very good time for a test.

I could hear you with your 100W, but then my noise level here is normally pretty low, and my limitation is mostly "QRM" from activity rather than noise.

I do live "in the city" (of Los Angeles), surrounded by millions of noise sources but have mitigated most of them.  I don't have any antenna restrictions at all: My 40m antenna for our QSO yesterday was a 1/2-wave inverted vee at 55 feet.

73

Steve WB2WIK/6
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KB1LKR
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« Reply #24 on: April 28, 2009, 09:18:02 AM »

"Listen to week stations and then add 10 to 12 dB of receiver attenuation. The equivalent of amp on/ amp off. In signal condition below S7 or if your local noise level is high it can be quite dramatic...."

That was my initial thought, but the attenuator will attenuate the noise (QRM/QRN) as well as the desired station, whereas if the desired station were to switch his amp on/off his signal would rise fall while the noise stayed the same.

Best would be some contacts w/ stations w/ 600-1000W of amp they could switch in/out, or if good enough band conditions, switch/dial down from 100W to 10-20W (equiv to 1000W-500W to 100W).
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AE5RE
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« Reply #25 on: April 28, 2009, 09:58:29 AM »

Steve, WB2WIK/S, thank you very much for your time, you helped me to accomplish what I wanted to do, hear the differece between 3 level of power. Also, the condx were perfect for the test. Sometimes you need the amp, once you antenna cannot be improved beyond certain restrictions.
I used a 1/4 WL vertical antenna ground mount with 45 radials on a 180 degree shape. In addition towards the north the ground level goes up about 3 ft my radation to the north from NW to NE is lower in power. I wished I could do 360 degree but I have to live with it for the time being. Thanks to everyone for your comments and recommendations we can put this post to sleep now.
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K8AC
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« Reply #26 on: April 28, 2009, 10:58:05 AM »

WX7G: David - nothing I said to you could be interpreted by anyone else as offensive.  In the interest of brevity, I used a word (hogwash) which would be clearly understood by all.  I could have gone into excruciating detail on why your information was bogus, but elected not to do that.  Here's the Princeton definition of hogwash: "bunk: unacceptable behavior (especially ludicrously false statements)".

Since newcomers visit these forums to learn something, it's incumbent on those who answer questions to do so in a factual manner.  You represent the 6dB per S-unit as an "industry standard".  In fact, there is no industry standard body dealing with such things and there are no ham radio industry standards.  The 6dB per S-unit dates back to information from Collins Radio, who at one time calibrated their meters to that "standard".  And indeed, it was a great idea for someone to attempt to quantify an S-unit.  However, today's manufacturers have made no attempt to follow the Collins path.  You can't deflect that fact with comments about an incorrectly calibrated Icom.  Do some Google searches and read the articles written by technically competent hams who have carefully measured S-meters on all brands and models of rigs over the past 20 years.  You won't find ANY calibrated at 6 dB per S-unit.  

You can easily find dozens of articles in QST and elsewhere that even go so far as to make calculations based on this 6 dB S-Unit myth.  But making the same mistake hundreds of times doesn't establish a new technical truth.  I'm sure you still believe you're right, so I will challenge you to cite the identity of the standard you mentioned so we can all learn something.  Or, find a single case where someone actually measured an S-meter (other than on a Collins) and found a uniform 6 dB per unit calibration.  Why is this important at all?  Well, someone not technically savvy and evaluating an antenna f/b ratio might be led to believe that the 6 S-unit front to back difference he sees is 36 dB, when in reality it could be as small as 7-8 dB, or maybe 18 dB.  And examining the available literature reveals that the calibrations vary wildly by band on a given transceiver or receiver.  Applying an arbitrary definition to a measurement unit that can easily be proved to be false by 100% or more fits the definition of "hogwash" pretty well.  


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AA4PB
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« Reply #27 on: April 28, 2009, 01:11:26 PM »

I quite often use the 6dB per S-Unit reference myself. Not because its an accurate number, but because most hams have a good feeling for what an S-Unit is whereas they might not have a good feeling for a dB. If someone says they doubled their power, if I tell them that's only 3dB they are often left wondering. If I tell them thats only 1/2 an S-Unit then they immediatly understand its not very much. I think it can serve a useful purpose, even though the actual S-Meter reference varys from radio to radio, even between bands on the same radio.
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Bob  AA4PB
Garrisonville, VA
N3OX
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« Reply #28 on: April 28, 2009, 04:59:54 PM »

"You can easily find dozens of articles in QST and elsewhere that even go so far as to make calculations based on this 6 dB S-Unit myth. But making the same mistake hundreds of times doesn't establish a new technical truth."

I agree with this...

I also think that radios vary too much to make the "S-unit" a TOTALLY USELESS way to communicate signal level changes in the absence of other info.

We rely on it too much to get a "good feel" for what's happening, but in reality, you just never know.

On my FT-857D, a common, popular rig, there's only something like a one dB change between S1 and S2 and S2 and S3.  I'm sure the FT-897D, another common, popular rig is the same thing.

The only 6-dB S-units seem to be 7 to 8 and 8 to 9 (maybe 6 to 7 is 5dB).  I should run it again to be sure and write it down somewhere I don't lose it this time :-)

AA4PB says " I think it can serve a useful purpose, even though the actual S-Meter reference varys from radio to radio, even between bands on the same radio."

I don't know Bob, I see what you're saying but I think the real consequence outweigh the convenience.

F/B ratio reporting is a good example.

Let's say I've got a friend on 2m who hits me with a S5 signal on my new yagi when I point it at him.

I swing it 180 and he goes down to S1.  That's something like  S5 -> S4 = 3dB, S4 -> S3 - 2dB S3->S2 = 1dB S2->S1 = 1dB

That's a lame 7dB F/B, but I conclude from "4 S-units" that I have 24dB F/B and I publish my nice design on the web.

And let's say a dipole gives S3 while my beam gives S5.  That's a whopping 12dBd gain by S-unit measure, but a rather less whopping 5dBd by real measure.

Now, a careful experimenter with reasonable expectations will say "hmm... 12dBd from an antenna where I expected 5dBd gain, no way"

But it could lead someone with no other test equipment who builds a really big beam that doesn't work to conclude that the design is good...

The internet, the place where new hams are reading and learning on their own much of what they will KNOW for SURE in 10 years is full of crap antenna designs from people who use their S-meters as their only measurement/verification tool.

Is it occasionally good for a "quick, intuitive insight" into what an amplifier power or antenna change might do for you?  

Maybe.

Occasionally.

If you're lucky.

But I think it's going to build bad intuition on average.  In almost every situation where you might *really, really need* an amplifier, for example, instead of running barefoot, you can't even see the meter deflection change when the amp goes on and off.

On the highest bands it's because you're not even in AGC range yet.  On the other bands it's because the noise is so variable ...

Think about the guy that's really, truly marginal copy on 75m.  Isn't he right at the noise level, thereby making his S-meter reading a wild function of time?

I agree with you that few have an intuition about dB measurements.  But I think we should maybe spend more time trying to rectify that problem than by encouraging people to think 6dB S-units are somehow typical.

We should AT LEAST take a big survey of what S-units actually are and average them into the number we choose!!!

6dB is probably an upper bound on the S-unit these days, not even an average value.  Who's got a rig with, say, 9dB S-units?

73
Dan


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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB2WIK
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« Reply #29 on: April 28, 2009, 07:10:01 PM »

I have never used an "S" meter for a signal report in my life (44 years as a ham).

The R-S-T system evolved years before receivers had "S" meters.

If you're loud and clear, you're 59, whether that reads S2 or S9+40.  Who cares?

If you're very tough copy, you might be 33, even if the meter indicates S9+.  Again, who cares?

The only thing that counts in communications circuits is whether we can hear each other.

My first three receivers as a ham didn't have any meters, but they were good receivers.

WB2WIK/6
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