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Author Topic: Want t buy AMP but I want to hear the difference  (Read 10727 times)
AE5RE
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Posts: 14




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« on: April 26, 2009, 08:22:57 PM »

I am looking for some help. I want to buy an amplifiers but before I made my final decision I would like to hear the difference between:
1.-100W and 600W  SSB and RTTY
2.-100W and 1000W SSB and RTTY
3.-600 and 1000W  SSB and RTTY
If any of you can help I will really appreciate it.
Please answer to this post or e-mail me. My e-mail is correct on QRZ.com
73
AE5RE
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KB9CRY
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Posts: 4283


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« Reply #1 on: April 27, 2009, 03:08:08 AM »

Get on the air and ask.
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K8AC
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Posts: 1912




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« Reply #2 on: April 27, 2009, 05:30:05 AM »

The value of the amp appears when signal levels are marginal and/or when that little extra bit of power makes the difference between copy and no-copy at the other end.  If you're a DXer, it might make the difference between being copied OK and not being copied at all by a station in Asia.  If you're a contester, it might make you the one who stands out from the crowd at any particular moment, when it matters most.  If you just care about how far it moves the other guy's S-meter in the S-meter sweepstakes, then save your money.  
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AE5RE
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Posts: 14




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« Reply #3 on: April 27, 2009, 06:10:52 AM »

If some on you reading this post has an amplifier and is willing to help please reply to this post or drop me an e-mail to set the date, time and band so I can hear the difference when you are TX with and without amplifier. 73 TNX.
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WB2WIK
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Posts: 21837




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« Reply #4 on: April 27, 2009, 09:21:07 AM »

Let's just make a sked...what bands can you operate, and what times?

I can adjust my output power to anything from a couple of watts to 1500W just by turning a knob, so this "test" could be really easy...

WB2WIK/6
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K6AER
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Posts: 5743




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« Reply #5 on: April 27, 2009, 09:32:57 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. For signals above S9 it is an S meter chase.  

Mobil stations love it when you are running an amplifier for their noise level can be quite high. Call CQ with 100 watts a few mobiles will come back to you even with a 4 element monobander up high. Turn on the amp and call CQ and they come out of the woodwork.

Now mind you, unless you live in a quiet location most 100 watt to 100 watt stations will be pretty square as to each others receive ability and EIRP. For the path margin to improve both stations need to run amplifiers. Your running an amp will help the other guy but not your receive.

The exception is if you can hear much better than a normal station such as being in the county and the other station is in the city and has a high receive noise level.

When the band is dead I always call CQ with the amplifier on. You have no idea how many DX stations have come back to my call and thought the band was dead. I live in rural Colorado and my noise floor is generally S1.
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KH6AQ
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« Reply #6 on: April 27, 2009, 11:52:37 AM »

600 watts your signal will increase 1.3 S-units.

1000 watts your signal will increase 1.7 S-units.

If you run 100 watts and the other station runs 100 watts your signal strengths will be indentical. So say you here a guy who is 57 calling CQ and he is running 100 watts. You call him and he will give you 57. Kick on the 1000 watt amp and he will give you 59.
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K8AC
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Posts: 1912




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« Reply #7 on: April 27, 2009, 12:44:52 PM »

"600 watts your signal will increase 1.3 S-units.
1000 watts your signal will increase 1.7 S-units."

This is just plain hogwash.  Somewhere in history, it was published that an S-unit is 6 db.  A modern day Icom S unit (and most others) is 3 dB or less, and don't expect the scale to be linear.  You can certainly calibrate most S meters to read somewhere around 6dB per unit, but they don't come from the factory calibrated that way.  A 100 to 600 watt increase is 7.8 dB.  Chances are good that the observed S meter difference would be 2-3 units.  The increase from 100 to 1000 watts would be 10 dB, which is likely to show up as 3-5 S units difference.  It will depend on the individual receiver, how its S meter is calibrated, whether or not the scale is linear, etc.  You'll probably get more meaningful information from K6AER's suggestion to simply apply a known level of attenuation at the receiver end (many transceivers offer a stepped attenuator switch).  As I said before, where the difference will really matter is in situations where the S meter might not even be reading anything for a station with 1,000 watts output.  A 1,000 watt signal might be at the noise level while the 100 watt signal may not be audible at all.  That type of situation is the reason to buy an amp.  

Here's a link to one of many online calculators to derive the dB difference between two power levels: http://www.crownaudio.com/apps_htm/designtools/db-power.htm .



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KH6AQ
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« Reply #8 on: April 27, 2009, 02:06:34 PM »

Hogwash no. Standard yes. Please don't use such disparaging language.  

It is true that Icom (incorrectly) sets the S-meter on the 756 Pro II and III to 3 dB per S-unit.

The Elecraft K-3 is calibrated to 5 dB per S-unit.

The industry standard is said to be 6 dB per S-unit.

The industry standard for S-9 is 50 uV.
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K8AC
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Posts: 1912




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« Reply #9 on: April 27, 2009, 02:21:45 PM »

First you tell the guy what he'll see on the S-meter using numbers to one decimal place.  Then you admit that Icom uses 3 dB and that makes your numbers off by 100%.  I submit there are NO current rigs that are calibrated to 6dB per S-meter unit, so what conceivable sense does it make to quote numbers based on that?  Sorry, but hogwash hit it the nail on the head.  
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AE5RE
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Posts: 14




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« Reply #10 on: April 27, 2009, 02:34:04 PM »

I am not interested on how many S-units. I need to hear the difference. As someone suggested I can use the attenuator but that's like using a simulator for me but the idea is very welcome. I want to hear the "real" thing.  WB2WIK has offered his help and I really appreciated.  I will report back my subjective findings and decision.
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K8AC
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Posts: 1912




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« Reply #11 on: April 27, 2009, 04:29:45 PM »

If you completely ignore S-meter readings, even your subjective evaluation can be wrong - here's why: AGC systems on today's transceivers/receivers work rather well.  You can tune to an S9 signal,crank in 6 or 12 dB of attenuation and very likely EXPERIENCE NO CHANGE IN VOLUME OF THE RECEIVED AUDIO AT ALL.  Moving from 100W to 1000W output is 10 dB - that's a mathematical fact.  I've just told you (and tried it on my rig to verify) that I can insert 12dB of attenuation and not be able to tell the difference based on audio volume.  

To do any sort of evaluation, you're going to have to know how much the signal level actually changed at the receiver.  If you don't know that, you can't possibly judge whether the 7.8dB increase (100W to 600W) or the 10dB difference (100 to 1000W) means enough to you to buy the amplifier.  By all means run the tests with Steve, but make sure that you have him transmit at a level where you can barely copy and then increase the output by 10dB.  That's where you'll see the big improvement.  If you do decide to use the S meter, you might want to take a look at this rather thorough discussion, complete with visuals:
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm#Introduction

Those who think that an S-unit is 6dB can learn something from the article.  
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WB2WIK
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« Reply #12 on: April 27, 2009, 04:34:58 PM »

Using an attenuator to simulate making a signal weaker is not an accurate depiction of the real deal unless you have a zero-noise environment.

A "demo" of power level change is pretty meaningful if the received signal is not overwhelmingly strong.

I don't go by S-meter readings, especially since I usually operate with my eyes closed (to rest them after staring at multiple monitors all day long).

My first few receivers for ham radio didn't have any S-meters.  They barely had BFOs!

WB2WIK/6
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K8AC
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Posts: 1912




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« Reply #13 on: April 27, 2009, 04:41:40 PM »

After re-reading your original question, I've one more comment.  You should be aware of the RTTY power rating of an amplifier if you plan to use it for RTTY.  It can be quite a bit lower than the CW or SSB output rating and often even then the manufacturer may state a limit for "key-down" time.  For example, an amp that can put out 800w on CW or SSB might be rated at 400W RTTY for no longer than 5 minutes.  The more expensive amps (Alpha and others) can run the legal limit output on RTTY with no time limit.  If you try that with one of the lesser amps, you'll either trip a temperature cutout, destroy the tubes, melt pi-net coil forms, etc.  A particular amp may survive at the manufacturer's RTTY output rating, or may not.  Search the usual places to find out RTTY operators' experiences with a particular model.
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K8AC
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Posts: 1912




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« Reply #14 on: April 27, 2009, 04:45:08 PM »

"Using an attenuator to simulate making a signal weaker is not an accurate depiction of the real deal unless you have a zero-noise environment."

Can't go there - I have a near zero noise environment.
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