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   Home   Help Search  
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Author Topic: How much of a help is 6 DB?  (Read 9795 times)

Posts: 835

« 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.  Wink


73, - Steve WX2S.
I subscribe to the DX Code of Conduct.

Posts: 4608

« Reply #1 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.

Posts: 2409

« Reply #2 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?

Posts: 427

« Reply #3 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.
« Last Edit: January 17, 2013, 10:14:00 PM by K7MH » Logged

Posts: 1551


« Reply #4 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.


Don, K2DC

Posts: 14303

« Reply #5 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.

Posts: 2375

« Reply #6 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).

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f

Posts: 8080

« Reply #7 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.

Posts: 5249


« Reply #8 on: January 18, 2013, 08:18:19 AM »

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


Mark K5LXP
Albuquerque, NM

Posts: 14303

« Reply #9 on: January 18, 2013, 08:24:51 AM »

Poor propagation to good propagation = 20dB.
Propagation is the "great equalizer"  Cheesy

Posts: 136

« Reply #10 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.

Posts: 21749

« Reply #11 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. Wink

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).

Posts: 2909

« Reply #12 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.

Posts: 9930

« Reply #13 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 Smiley  ). See how much it costs in your area to have an electrician run lines for you.

Posts: 1050

« Reply #14 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.
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