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   Home   Help Search  
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Author Topic: Want t buy AMP but I want to hear the difference  (Read 10716 times)
N3OX
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« Reply #30 on: April 28, 2009, 08:59:50 PM »

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

Yep, and even if a S-meter was a perfect 6dB-per-division lab grade logarithmic received signal strength indicator, the *DIFFERENCE* that 6dB worth of power output increase makes to copy is still something that hinges entirely on the current signal to noise ratio and the ear/brain system of the listener.

In the next years to come I expect there will be more radios with received signal strength indicators in actual dB, because it's easy to calibrate out the nonlinearities like onset of AGC in firmware if you want, and that'll be useful

But in any situation where half a dozen dB matter to the quality of copy on HF, you're going to be measuring some desired signal and some external noise floor as things fade and change.

So even that meter won't tell you what you really need to know about how much "X" dB of amplification matters.

I think something that *IS* important is that we use deciBels instead of whole Bels because one Bel is not a fine enough grain in human perception.

1dB is.

So 1dB probably isn't worth losing much sleep over, but if you can find a few of them laying around, some people in marginal conditions will probably notice, and if you've got a whole Bel worth of difference like going from 100W to 1kW, it's going to show no matter how good the signal.  You can hear the loudness difference between a signal with 50dB signal to noise and one with 60dB signal to noise.  It doesn't really matter to *copy* one bit, but it'll be noticed.

Having a realistic idea of how much difference new antennas or amplifiers are going to make is the key to spending money wisely on your station upgrades.

I think S-unit comparisons are probably more harm than help there.  

'Course, the economy could use some stimulatin, so go ahead and buy that amp anyway!

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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Posts: 21837




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« Reply #31 on: April 29, 2009, 08:48:38 AM »

>RE: Want t buy AMP but I want to hear the difference       Reply by N3OX


I think S-unit comparisons are probably more harm than help there.<

::Yes, I agree.  It simply doesn't matter.

I start many contacts running a kilowatt, and if the other station is pretty strong, I take the amp off line.  I usually don't even mention this.  If, on the next transmission my contact says, "Gee, what happened?  I can hardly hear you now?" then I put the amp back in line.  If he doesn't mention anything, then I know it wasn't needed.

Isn't that simple?

WB2WIK/6

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W3LK
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« Reply #32 on: April 29, 2009, 02:01:23 PM »

<<I think something that *IS* important is that we use deciBels instead of whole Bels because one Bel is not a fine enough grain in human perception.

1dB is. >>

Someone has written that 1dB is the difference in volume between the sound of  mouse peeing on a blotter and the same mouse peeing on a tin roof.

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
KA5N
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« Reply #33 on: April 29, 2009, 03:45:49 PM »




One reason I like contests is that everybody is S9!!

Allen
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W7ETA
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« Reply #34 on: April 29, 2009, 05:34:13 PM »

When my wife and I took a BMW for a test ride, we were both impressed with how quiet it was at 70 MPH.

A few months after we bought it, I brought it in for 1K fluid change and check up, and mentioned the speedo seemed to be off, cause cars and trucks were flying by us when I did the speed limit.

Turns out, there wasn't anything the dealer could do, cause BMW designed that motorcycle's speedo to always read 110% of actual speed--I got stuck with a loose S meter in my mc.

When the speed limit was 70, I was doing around 63 and people were passing me doing around 80!

Seems as if there isn't any requirement that a speedo be accurate.

Accurate S meters based upon dbs would be nice also.

73
Bob
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WB2WIK
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« Reply #35 on: April 29, 2009, 06:11:29 PM »

Who needs an accurate S-meter?

I  don't get it.

If your noise level on HF is S8 as it can often be, so it takes an S9 signal to be readable, do you actually give that station a "59," even though he might only be 30% copy?

It's all silly.

"59" in contests is a given.  Might as well extend it to all operating, and just give everyone a "59," and get it over with.  ;-)
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N9AOP
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« Reply #36 on: April 29, 2009, 07:43:58 PM »

Dan,
Your post made the most sense of any of them in this thread.  Anyway I always liked the military way of reporting what you hear:
weak-barely readible
weak-readible
fair-readible
good-readible
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W7ETA
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« Reply #37 on: April 30, 2009, 07:15:56 AM »

Hang around in the 75 DX window and one hears reports of 3X9, S8 noise level, 5X9, way over S5 noise level, and 5X3, S1 noise level (receive antenna).
73
Bob



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N3OX
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« Reply #38 on: April 30, 2009, 07:36:55 AM »

"5X3, S1 noise level"

My flag has such low gain on 160m that the reports I would give in the vicinity of S0 to S8 don't even move the meter.

You move my meter, you're very likely to get a "599 big" or similar.

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

Monkey/silicon cyborg, beeping at rocks since 1995.
N4ATS
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Posts: 1305




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« Reply #39 on: April 30, 2009, 09:10:34 AM »

It's all irrelevant, the bottom line is, when the meters are slamming 1.5 KW, the warm air coming up out of the fans and the LEDS are flashing, it just flat out looks and feels better no matter what the "S" meter on the other guys rig says.
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N9DG
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« Reply #40 on: April 30, 2009, 11:16:13 AM »

"Who needs an accurate S-meter?"

Precisely, just read signal strengths directly in dBm and be done with it. I have really grown to like directly reading signal strengths in dBm. As such I never configure my Flex and PowerSDR to ever display S-Units (even though it has the most accurate S-meter scaling available today in ham radio).

It is just so much easier to read the change in signal strength directly in dB and to simply forget about doing all that silly gymnastics of convering S-units to dB and back..
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WA9UAA
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« Reply #41 on: April 30, 2009, 03:15:48 PM »

I propose a new system, especially with the newer rigs, where the noise could be sampled and the received signal, sampled then the difference displayed; thus, a relative S/N reading being used rather than an 'absolute' value. This is really what Steve is talking about doing by ear.
73,
Rob WA9UAA
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W9OY
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« Reply #42 on: April 30, 2009, 03:41:24 PM »

K8AC, you are wrong in your submission.  The Flex 5000 and the Flex 3000 self calibrate to S-9=50mv.  They also use 6dBm S units.  The flex radio is done in software so the AGC is an equation.  As such it reads out in 1dBm steps from MDS until the radio blocks about +5 dBm.  The radio uses one of the DDS channels are its signal generator and that chip is specified to be within 0.1 dBm across its bandwidth

73  W9OY
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W4KVW
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« Reply #43 on: April 30, 2009, 06:36:48 PM »

SOMEBODY's Wheaties got WET it appears!

Clayton
W4KVW
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WB2WIK
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« Reply #44 on: April 30, 2009, 07:03:58 PM »

>RE: Want t buy AMP but I want to hear the difference  Reply  
by W9OY on April 30, 2009  Mail this to a friend!  
K8AC, you are wrong in your submission. The Flex 5000 and the Flex 3000 self calibrate to S-9=50mv. They also use 6dBm S units. The flex radio is done in software so the AGC is an equation. As such it reads out in 1dBm steps from MDS until the radio blocks about +5 dBm. The radio uses one of the DDS channels are its signal generator and that chip is specified to be within 0.1 dBm across its bandwidth

73 W9OY<

::Interesting reply, but this can't be accurate, either.  S-9 = 50mV?  I doubt it.  Probably 50uV.  S units cannot be 6 dBm, but they could be 6 dB.  dBm is an absolute value, while dB is a ratio.  There's a big difference.

WB2WIK/6  
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