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Author Topic: Amp/Ant  (Read 2643 times)
AE5QB
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Posts: 267




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« on: February 15, 2013, 07:56:43 AM »

My friends and I are having a discussion about antenna systems vs power.  Is the following statement true or not?

"A big amp will cover the effects of a p-poor antenna on transmit, but it does nothing to help the p-poor antenna on receive. Therefore, if you have a poor antenna system, you are just polluting the airwaves with RF, as those who can now hear you, will never be heard by you."

Conclusion:  Unless you have a super good receiving antenna, throwing more power into the mix is just a waste of time, money, and bandwidth.
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K6AER
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« Reply #1 on: February 15, 2013, 08:25:36 AM »

Only true in some cases.

If the person has a high noise floor and is having a hard time hearing you, by you using an amplifier, you enable him to complete the QSO.

Most hams live in a city or suburban areas and as a result of the many microprocessors in a typical home have very high noise floors on receive.

Having a 10-14 dB stronger signal doesn't mean you signal is polluting the air waves. It is a matter of settin you station up properly. I have heard many broad band splattering signals running just 50 watts.
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AA4PB
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« Reply #2 on: February 15, 2013, 08:43:25 AM »

Receiving is all about signal to noise ratio. You can have the highest gain antenna in the world and you still won't be able to copy if it's picking up a lot of noise. For example, if the antenna increases the received signal by 6 dB and also increases the noise level by 6 dB then the signal to noise and the ability to copy remains the same. Sometimes, especially on the lower frequencies, a lower gain antenna can improve receive copy because it decreases the noise level more than it decreases the signal level.

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K8AXW
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« Reply #3 on: February 15, 2013, 08:44:50 AM »

As AER says, "In some cases."

Think of it like this.  You're using a dipole antenna and running 100w.  You HEAR a DX station which has created a pileup.  

Question:  What do you think your chances are of getting the contact with the DX station?

Answer:  Low.

Now, same situation.  Only this time you hear the DX station and you light up the antenna with a KW.  

Question:  Same.

Answer:  Much better.

Another scenario:  Same operating conditions.  You hear a station you wish to contact.  If your signal to him is marginal, it's very possible he might not respond, preferring to work a station where he can enjoy a relaxed QSO without having to "crawl into the signal" to copy.

Whereas, if he's marginal, but you're running some decent power, then the effort is on you and since you want the contact, that's OK.

Conclusion:  You're friends have p-poor analytical skills.

Note:  You're friends are right if you call CQ using a KW and a dipole antenna.

« Last Edit: February 15, 2013, 08:49:24 AM by K8AXW » Logged
WA6MJE
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Posts: 71




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« Reply #4 on: February 15, 2013, 12:07:28 PM »

I am learning the hard way about antenna performance on the receive side.  The metrics for improving radiated emission performance on a transmission antenna is not the same as the theory for receiver performance, since as mentioned here it is signal to noise ratio not just gain that matters.

I now am thinking that I should worry more about the receiver side than the transmission side of things.  More power can help on the transmission side, but just more antenna gain may not help on the receiver side and an amplifier does nothing whatsoever.  A receiver preamp essentially increases both noise and signal with no net effect on hearing an unheard station.  In other words, it may be harder to resolve hearing problems than being heard problems when configuring a station for DX.

So what really bothers me is to look on a reverse beacon network and see many DX stations out in the open that I cannot hear but that can be heard by my colleagues.  I see many of them every day so I now am spending more time understanding the receiver side of antenna theory, and from what I can tell there is a lot less written about that.

Signal to noise ratio is the key, and basically a receiver noise floor has little to do with it.  I have systematically started removing noise pollution from my home, the two biggest offenders were my plasma TV which I gave to my son, and light dimmers I had installed in various rooms.  I am now experimenting with coax, grounding, parasitic verticals and other methods to improve signal to noise ratio.  My goal is to hear more stations that I can see on a reverse beacon and not hear.   Then I will find out if they can hear me, and only then will I consider flipping on my amplifier button.  Turning on and leaving on an amplifier at all times is not necessarily something that has a benefit if DX is your goal.  Generally I can work any station I can hear on 100 watts with great or at least acceptable signal reports.  It is the stations I cannot hear that are the problem. My amplifier is not much of a solution for anything but that marginal contact that you just cannot make without one.  Those are infrequent.

Rene - WA6MJE
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W6UV
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Posts: 536




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« Reply #5 on: February 15, 2013, 03:00:29 PM »

Directivity is really the key on receiving antennas. One good example is the Beverage. This is a very directive antenna with negative gain relative to an isotropic antenna (typically -20 to -10 dBi), but it's so directive that it doesn't pick up nearly the noise that a less directive antenna would, hence the S/N is much better.
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AE5QB
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Posts: 267




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« Reply #6 on: February 15, 2013, 06:11:36 PM »


Conclusion:  You're friends have p-poor analytical skills.


 Wink  That's funny!  Maybe the stated position was mine.  LOL.  Anyway, thanks for the feedback, point well taken.  It makes a lot of sense.

Rene, keep us posted on your progress.  I am interested in what you find and I think most hams would appreciate hearing about your investigation.

73,

Tom/AE5QB
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WX2S
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Posts: 689




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« Reply #7 on: February 15, 2013, 08:01:17 PM »

Time for some numbers:

A Yagi will get you about 10 dB of gain over a dipole on both transmit and receive, all other things being equal.

1500W will get you about 12 dB of gain over 100W on transmit only.

So, if you have the option, the Yagi is the better investment. I don't have the option personally, so I'm sticking with my vert.

And, re the "polluting the airwaves" comment, only a lid transmits to a DX he cannot hear or goes QRO unnecessarily.

73, - WX2S
« Last Edit: February 15, 2013, 08:20:07 PM by WX2S » Logged

73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
WN2C
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Posts: 429




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« Reply #8 on: February 15, 2013, 08:15:36 PM »

Basicaly, yes.  If your antenna is not a good receiving antenna but will put out rf.  This is known as the syndrome of 'Gator Mouth'.

wn2c  Rick
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G3RZP
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Posts: 4391




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« Reply #9 on: February 16, 2013, 02:44:21 AM »

But another point to remember is that intelligent operating gives a LOT of dB advantage. That also includes using all the receiver features.
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W5LZ
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Posts: 477




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« Reply #10 on: February 16, 2013, 03:42:03 PM »

Your friends statement is 'right', but it's just carried too far.  It's a fact tht if you can't hear'em you can't work'em.  But a "better antenna" isn't always the answer or even possible sometimes.  Exactly what are you calling a 'p-poor' antenna, and why?  Does running an amplifier mean that you have to have some 'fabulous' antenna?  Of course not.  But it still means that if you can't hear them...
 - Paul
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N6AJR
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Posts: 9891




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« Reply #11 on: February 21, 2013, 09:32:33 AM »

Antennas are  the first place to improve your signal, both ways. a nice tribander at 40 feet is a great start. then add power, the to improve your RX get a loop for RX, like a K9AY or a pixel technolies loop. they allow you to null out noise.  the best  trick is to get a good radio that you can adjust for best signal. I have several rigs and my Orion is the best radio I have ever owned.  I use a TS 2000 for backup, but it is dead on HF compared to the Orion. 
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AB2YC
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Posts: 53




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« Reply #12 on: February 21, 2013, 12:10:23 PM »

Would you rather run a KW into a dummy load or 100 Watts into a Great antenna?

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W6UV
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Posts: 536




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« Reply #13 on: February 21, 2013, 07:44:13 PM »

Would you rather run a KW into a dummy load or 100 Watts into a Great antenna?

I'd rather run a KW into a great antenna.
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AH6RR
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Posts: 803




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« Reply #14 on: February 22, 2013, 08:50:18 AM »

Would you rather run a KW into a dummy load or 100 Watts into a Great antenna?

I'd rather run a KW into a great antenna.

I do Grin
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