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eHam Forums => Elmers => Topic started by: WX2S on January 17, 2013, 07:50:15 PM



Title: How much of a help is 6 DB?
Post by: WX2S on January 17, 2013, 07:50:15 PM
The reason I'm asking is that it'd be easy for me to put in a 500W amp but much harder to put in a 1500W one. I'd need to run a 250V line from the cellar, and I'm out of circuits on the breaker box.

73, WX2S.

ED: Oops, make that 4.7712125472 dB.  ;)



Title: RE: How much of a help is 6 DB?
Post by: K6AER on January 17, 2013, 09:04:47 PM
If your signal is just above the noise level at the other hams location 6 dB is a big deal.

If your signal is 30 dB over S9 at the other hams location they probably wont notice the difference.

Most hams have a high noise level operating from the city or the burbs. I have noticed when I call CQ at 100 watts my return rate is about 50%. When I cal CQ at 1200 watts four to six stations on average return the CQ call.

Running a 240 volt 30 amp line to your shack is no big deal. Don't let that be the basis to make your decision.


Title: RE: How much of a help is 6 DB?
Post by: KA4POL on January 17, 2013, 09:54:41 PM
An antenna is still the best amplifier. Would you have room for improvement at that end?
5 dB can make the difference, but how often?


Title: RE: How much of a help is 6 DB?
Post by: K7MH on January 17, 2013, 10:09:18 PM
One thing to consider is the difference in the cost of buying a 500-1000 watt amp that you can use on 120V that you already have and the cost of a 1500 watt amp plus the cost of putting in it's own 240V line, especially if you have to upgrade your electrical service to accommodate a 240V line.
The most can be gained from better antennas. If maxed out on antennas, then an amp is the next performance increase.
I think most would agree that the first 500 watts is the most significant difference.
I use an AL-811 amp on 240V and I am pretty much fine with that. With it an a 2 element quad, I have worked every big deal dxpedition since I have had them, about 7 years. Only 2 or 3 that I couldn't but I never was able to hear them anyway.
I had an AL-1200 sitting here I bought used from a friend for about 3 years and never did a thing with it as I didn't have a 240V line for it and wasn't concerned enough to bother with it so I sold it. I had a 240V line put in this  last August when I had some other wiring done in the kitchen and garage.
The AL-1200 was big and HEAVY! I really hated having to move it around from time to time and I don't miss it.

The AL-80B is a really good bang for buck value and I might consider that sometime.


Title: RE: How much of a help is 6 DB?
Post by: K2DC on January 18, 2013, 04:14:27 AM
  For bad band conditions or a massive pileup, 6 dB may be no help at all.  But in most conditions, the first 5-600W makes all the difference.  And you culd go a little farther.  The AL-572 or AL-80B will both do about 1 KW on 110V.

73,

Don, K2DC


Title: RE: How much of a help is 6 DB?
Post by: AA4PB on January 18, 2013, 05:05:13 AM
Adding a 220V circuit may not require upgrading the panel box. There are "piggy back" 120V breakers (i.e. two breakers in the size of one) that you can move two 120V lighting circuits to. That frees up a spot in the panel for a standard two-pole 240V breaker.


Title: RE: How much of a help is 6 DB?
Post by: AA4HA on January 18, 2013, 05:12:08 AM
Antenna gain also benefits your ability to receive signals as well. Look at some of the antenna radiation profiles to make sure that the gain is at a takeoff angle that is beneficial to your desired operation. A cloud burner with positive gain straight up in the air would not help you with DX work but you would be the big stick for a few hundred miles around.

It is weird for me to say "positive gain" but there are lots of antennas (compromise designs) that are very negative in their gain (losses?).

I have seen problems on commercial VHF/UHF systems where a customer wants to increase their coverage area so they replace the 3 dB omni with a 9 dB omni up on a tower. Suddenly they have dead spots all over the place as the new antenna does not have good "null fill" characteristics or downtilt.

With antenna gain, just realize that it too is a compromise, you do not get something for free. An antenna will get gain by changing the antenna pattern to a smaller main lobe (in elevation and/or beamwidth).


Title: RE: How much of a help is 6 DB?
Post by: G3RZP on January 18, 2013, 06:57:29 AM
I find that LF band CW DXing is where the difference comes in. It's been said that 160m Dxing is 'on the edge' and it's true - 3dB can make the difference there.

On the HF bands, it's not so necessary, although it helps bust a pile up rather faster than a 100 watts does.


Title: RE: How much of a help is 6 DB?
Post by: K5LXP on January 18, 2013, 08:18:19 AM

500W to 1500W = 4.77dB
Being a "big gun" instead of a "little pistol" = priceless.

 ;D


Mark K5LXP
Albuquerque, NM


Title: RE: How much of a help is 6 DB?
Post by: AA4PB on January 18, 2013, 08:24:51 AM
Poor propagation to good propagation = 20dB.
Propagation is the "great equalizer"  :D


Title: RE: How much of a help is 6 DB?
Post by: WD4ELG on January 18, 2013, 08:40:16 AM
Maximize your investment in your antenna before spending any money on an amp.  Once you can't get any better, then get the amp.

I can't do any better than my hex beam and wires (restrictions), and my radio is top of the line (for me, anyway, as I have maximized by skills with it), so I got a THP 1.2kFx on a 120V line, 750 watts.  It DOES make a difference, esp on 160 and when there are pileups on the higher bands.  I am not a big gun, but I am not the last one to get through either.


Title: RE: How much of a help is 6 DB?
Post by: WB2WIK on January 18, 2013, 08:57:57 AM
  For bad band conditions or a massive pileup, 6 dB may be no help at all.  But in most conditions, the first 5-600W makes all the difference. 



Think about that, though.  If the first 500W makes all the difference and you start out with 100W, that's a 7 dB difference.  500W to 1500W is about a 5 dB difference.  Actually, that second ratio is just about as big as the first one.

If 7 dB makes a big difference, so does 5 dB. ;)

If the service panel is maxed out, it's easy to add a subpanel and run a line.  Just don't exceed the max rating of the original panel (usually difficult to do unless it's a really old house with a lot of really new electrical appliances).


Title: RE: How much of a help is 6 DB?
Post by: K0OD on January 18, 2013, 09:51:34 AM
Two points about the almighty dB:

Don't let anyone tell you can't hear a one dB difference. My Flex radio is unique in having a lab quality S-meter. I can definitely detect such difference in band noise level. Also, I can adjust my tuner to well under 2:1 just peaking band noise by ear.

As for the difference in about 10 dB, look at the huge differences in the scores of high power and low power stations in the CQWW contest. Even when you adjust for the generally better antennas used by HP vs LP, you have to conclude that HP helps... a lot!

After a lot research years ago, I concluded that a single dB of transmit power helps CQWW scores by several percent.


Title: RE: How much of a help is 6 DB?
Post by: N6AJR on January 18, 2013, 11:15:54 AM
 ran 500 watts or so fro a long time, and it does help.

if you look at received signals as a  picture, look at it like this. at 5 or 10 watts you are below the  main batch and can only be seen above the " noise" level if there is a break in the noise.  At 100 watts yo are using the same power as a majority of hams and the picture looks like level line of "grass" and you are one of many , each making a little spike  that appears as the "grass". at 500 watts or so, you stick up above the grass as a spike here and there, with your fellow  500 watts users.  At legal limit you are sticking up above the noise  and really stand out.  This make it easier to be found and worked.

I ran 500 watts for a while but finally broke down and paid an electrician $500 bucks to run 2 220 v lines back to the shack. one was for a dedicated 220 v line and the other was used for a  set of 2 more 110 lines for the shack.  I put 3  220 v outlets in the shack from the one circuit, as I don't use more than 1 at a time, but 3 outlets on 3 different walls  me and I don't have to plug and unplug amps when I change radios. so I have one 220 and 2 existing 110 lines and then 2 more new 110 lines, so I finally have enough power in the shack.  ( Almost :)  ). See how much it costs in your area to have an electrician run lines for you.


Title: RE: How much of a help is 6 DB?
Post by: M6GOM on January 18, 2013, 12:17:45 PM

500W to 1500W = 4.77dB
Being a "big gun" instead of a "little pistol" = priceless.


I got that much and more by changing antennas. Best antennas working the best they can first and then the power.

No point putting out 1.5kW if you can't hear anyone.


Title: RE: How much of a help is 6 DB?
Post by: KU3X on January 18, 2013, 01:37:12 PM
All good information above. But to condense it: 6 DB = 1 S unit.
If you are an S 5 on the receive end of your transmission, adding 6 DB will make you an S 6.  If you're S 3, then you'll
be an S 4. Simple math.

The best advise someone gave you was to put the work into the antenna. The better the antenna the better the
ERP and the better the receive signal on your end.
Junk antenna = junk signal
Good antenna = good signal.


Title: RE: How much of a help is 6 DB?
Post by: WX2S on January 18, 2013, 02:07:34 PM
Thanks, all, for your helpful replies.

My antenna situation is that I am not maxed out technologically, but probably with respect to what I can do and still keep the XYL. :) Towers and Yaagis or hexbeams are not an option. So I run a Hustler 6BTV with a radial system as recommended by DX Engineering. It's so far done the job; I've gotten some decent DX with 100w. Where I could use some improvement is in pileups.

73, -WX2S.




Title: RE: How much of a help is 6 DB?
Post by: KD0REQ on January 18, 2013, 02:22:58 PM
not every entrance panel is expandable, for the simple reason that breakers for some old crud are no longer availiable.  in the case of FPE and Zinser/Sylvania, there is a darn good reason, there are enough insulation, construction, and breaker flaws to rightly label them "arcwelders."

but if you're in for a dime and in for a dollar with non-disaster power distribution, heck, get some piggyback breakers if you can, double up some lighting circuits on them, and go for the pileup buster.


Title: RE: How much of a help is 6 DB?
Post by: K0OD on January 18, 2013, 02:51:14 PM
Quote
But to condense it: 6 DB = 1 S unit

That may have been true 60 years ago. On my TS-850 I came up with an S-unit being about 4.7 dB and only on the middle portion of the scale.  Difference between say S-2 and S-3 was much less. And I was only testing on 40 meters where I was trying to get an accurate determination of the performance of my array of phased verticals. S-meters can vary by band or even by frequency within a band according to one article.


Title: RE: How much of a help is 6 DB?
Post by: WB2WIK on January 18, 2013, 03:11:25 PM

500W to 1500W = 4.77dB
Being a "big gun" instead of a "little pistol" = priceless.


I got that much and more by changing antennas. Best antennas working the best they can first and then the power.

No point putting out 1.5kW if you can't hear anyone.

However, many already have the very best, biggest and highest antennas they can ever install so there's no potential for growth there.

Also, on HF (as opposed to VHF-UHF-SHF+), I've found adding antenna gain can result in not hearing anybody better unless the band and environment are very quiet (low noise).  Often a better "receiving" antenna is one that improves S/N but hasn't necessarily any gain at all.

On TX, the only things that count are power and antenna gain, and placement of that gain at a useful angle for the desired contact.  On RX, the only thing that counts is S/N and it doesn't matter how you achieve it.  Most big-gun DX stations on 160m and 80m don't use their "gain" transmitting antennas for receiving. ;)


Title: RE: How much of a help is 6 DB?
Post by: AA4PB on January 18, 2013, 03:13:37 PM
Regardless of how inaccurate your "modern" S-meter may be, the point is still a good one. That is, 6dB makes only a "little" difference in the received signal. It isn't going to turn a weak signal at the noise level into a "booming" loud signal. It may get you through a pile up however if your signal is 6dB stronger than everyone else. But, you can sometimes get through the pile up with QRP if you get the timing right and/or have propogation on your side.


Title: RE: How much of a help is 6 DB?
Post by: W8JX on January 18, 2013, 03:20:40 PM
Regardless of how inaccurate your "modern" S-meter may be, the point is still a good one. That is, 6dB makes only a "little" difference in the received signal. It isn't going to turn a weak signal at the noise level into a "booming" loud signal. It may get you through a pile up however if your signal is 6dB stronger than everyone else. But, you can sometimes get through the pile up with QRP if you get the timing right and/or have propogation on your side.


I disagree on 6db not making a difference. Granted if you have a strong signal another 6db is not going to do much but if you are in the noise and unreadable or barely readable, 6db can be a real game changer.


Title: RE: How much of a help is 6 DB?
Post by: WB2WIK on January 18, 2013, 03:20:59 PM
Depends on what kind of operating you do, also.

I work a lot of stuff on 10m that's right in the noise.  These are signals that are maybe "32" or so on SSB, or 329 or so on CW.  6 dB makes a hell of a difference; if those signals lost 6 dB, they'd be gone.

I work stuff on 160m that's weaker than that, pretty often.  CW signals that would "honestly" be 229 or 219.  But contacts can be made!  Again, -6 dB from those signals is "gone."

A lot has to do with how well you can hear, which in turn has a lot to do with what your local noise levels are like.  On a "quiet" night on 20m CW -- after 99% of the activity has dissipated and there's almost nobody on the band -- I work a lot of stuff that's literally right in the noise and somehow they hear me, so they must have quiet locations also.


Title: RE: How much of a help is 6 DB?
Post by: N3OX on January 18, 2013, 04:53:44 PM
Here are some files I made a while ago where I mixed steady noise recorded from my radio with the same recording of my voice over the radio

http://n3ox.net/files/6dB/

I mixed the "this is a test we'll keep 6dB higher" part of the voice recording to a level 6dB more than the first part using my recording software.

Then I adjusted the overall levels to different scenarios I've heard on the air.

75m_locals.mp3 is very loud like S9+10 signals.
dx_15m.mp3  is a signal-to-noise situation that reminds me of a decent but not very loud signal from Oceania...
brokencontact.mp3 was mixed down until I couldn't copy the first part at all.

You shouldn't take these too literally as the noise doesn't vary too much and there's no fading, but it might give you an idea.


Title: RE: How much of a help is 6 DB?
Post by: WB2WIK on January 18, 2013, 07:15:28 PM
When the going gets tough, 1 dB makes a difference.

When sigs are 1 dB over the noise, adding 1 dB to the TX power makes copy much more possible.


Title: RE: How much of a help is 6 DB?
Post by: K8AXW on January 18, 2013, 08:47:19 PM
Ed:

If push comes to shove, consider "piggy-backing" or extending the 240V line from your kitchen range or clothes drying to your amp.  It's just that you can't run both at the same time. 

If it's this or nothing..... then I'd try it.  No big deal.



Title: RE: How much of a help is 6 DB?
Post by: W8JX on January 19, 2013, 05:16:56 AM
You know 1000 watts is a excellent compromise between 500It can be done on 120 if need be and gives you 10db over 100 watts. going to 1500 is only about 1.5 db more.


Title: RE: How much of a help is 6 DB?
Post by: WX2S on January 21, 2013, 08:39:29 AM
FYI: I finally got smart and ran some VOACAP predictions at 500 and 1500 watts. The short answer is that the extra 4.77 dB does buy some circuit reliability in DX areas, probably enough to be important. So I think I'll spend the extra shekels and get the big-gun linear to go with my popgun antenna.  ;D

73,
- WX2S


Title: RE: How much of a help is 6 DB?
Post by: W8JX on January 21, 2013, 08:57:51 AM
FYI: I finally got smart and ran some VOACAP predictions at 500 and 1500 watts. The short answer is that the extra 4.77 dB does buy some circuit reliability in DX areas, probably enough to be important. So I think I'll spend the extra shekels and get the big-gun linear to go with my popgun antenna.  ;D

73,
- WX2S


And what about 1000 watts?  It does not have to only be 500 or 1500.


Title: RE: How much of a help is 6 DB?
Post by: WX2S on January 21, 2013, 01:45:57 PM
And what about 1000 watts?  It does not have to only be 500 or 1500.
Selling one?  ;D

Seriously, I didn't check. I'll do so but would imagine that it's somewhere in the middle.

73,
- WX2S


Title: RE: How much of a help is 6 DB?
Post by: WX2S on January 21, 2013, 07:13:20 PM
Well, I did check it. The difference between 1 and 1.5kw is pretty insignificant.

- WX2S


Title: RE: How much of a help is 6 DB?
Post by: NR4C on January 23, 2013, 06:56:52 AM
Money for amp vs antenna......

Remember, an amp, even a 15oo watt amp, will only help the other guy hear you.  If you cn't hear him, you are toast.

Money spent on the antenna system will benefit BOTH you and the other guy.

The five most important aspects of communication by rdio are:]

ANTENNA


Title: RE: How much of a help is 6 DB?
Post by: W8JX on January 23, 2013, 09:23:11 AM
Money for amp vs antenna......

Remember, an amp, even a 15oo watt amp, will only help the other guy hear you.  If you cn't hear him, you are toast.

Money spent on the antenna system will benefit BOTH you and the other guy.

The five most important aspects of communication by rdio are:]

ANTENNA

While there is no doubt that antenna is a factor, a amp can be a deal maker at times especially on 40 and below.