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Author Topic: 5 watts vs 3 watts  (Read 11546 times)
KI5WW
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Posts: 73




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« on: January 30, 2014, 02:23:29 PM »

I have always had some interest in qrp cw work. In the past i have used mfj 90 series transcievers. Six of them to be specific , Single band rigs. . I have always did my qrp work in the shack using a varible voltage power supply. Those radios run very well at 15 volts as per the manual and will do 5 watts all day with thT voltage. When voltage is brought down to 12 volts the power will decrease to three watts in short fashion. So ive always ran them at 5 watts. Now my question. I recently purchased a HB 1 B. i want to take it out camping, fishing, etc real soon. I want to use the internal battery. It is Li, and full charge is 12.7 max is what i get. At that  voltage power out on 40 meters is three watts. So, will i notice a big difference going from 5 watts to 3 watts?  When i go portable with the HB1b?  By the way, i really do like the rig.
Thanks
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W1JKA
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Posts: 1679




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« Reply #1 on: January 30, 2014, 02:38:46 PM »

It has been my experience and that of several other QRPers that I know and have QSOed with that you will not see any noticeable difference between 3-5 watts, however you very well could notice a sometimes big difference in your contacts due to your antenna especially portable if you use the same type of antenna all the time due to every different location having different ground conditions. Experiment with your antennas and don't be concerned about the 2 watt difference.
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W7ASA
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Posts: 233




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« Reply #2 on: January 30, 2014, 02:59:03 PM »

3 Watts to 5 Watts is well less than 3 dB.  So increasing to 5 Watts gains you less than one half of one division on the receiver s-meter.



All that extra power   Wink   would not even be noticeable on the receiving end.


73 de Ray
W7ASA ..._  ._



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WB0FDJ
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Posts: 143




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« Reply #3 on: January 30, 2014, 03:34:15 PM »

This spring I was lucky enough to find an old Argonaut 509 in excellent condition. I was surprised to find that, at some point, the finals were replaced and it can do over 5 watts. I guess I'm a traditionalist because I've never run it more than 2.5-3 watts and in day to day activity I don't see any difference from the five I used to run
.
Now I feel kinda guilty running a whole 5 watts!   Grin

The antenna you use portable will probably be the deciding factor but don't let that dampen your enthusiasm. I've taken the FT-817 out with only an "OK" antenna and first time out worked Greece, at 2.5 watts. You might want to visit the HF Pack website where they've done some antenna shootouts and have posted their results.

Enjoy!

WB0FDJ Doc
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WB6BYU
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Posts: 13253




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« Reply #4 on: January 30, 2014, 07:45:47 PM »

Quote from: KI5WW

... will i notice a big difference going from 5 watts to 3 watts? 



It depends - are you planning to spend your time having fun making contacts or worrying
about whether you're doing it exactly right?  In the former case you won't notice any
difference at all, except that you'll be outdoors in the fresh air.  And you might be a bit
tired depending on how far you've hiked to get there.

My old Argonaut 505 and HW-8 have racked up a lot of miles in my backpack.  Both put
out something like 2 - 3 watts, depending on band and battery voltage.  My pocket
40-40 rig for ultra-light work runs about 1 watt, which allows me to carry a smaller
battery.  All three have made international contacts on wire antennas.

The important thing is to have an efficient antenna.  I use a half wave dipole strung up
on whatever local supports I can find - sometimes the best I can do is my walking stick
(but I've worked long path half way around the world with an antenna 3' off the ground.)
The choice of antenna alone will make more difference than the difference between 3W
and 5W.
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KI5WW
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Posts: 73




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« Reply #5 on: February 01, 2014, 02:47:41 PM »

Thanks everyone for the input. Funny, packed every thing up for practice and looked at the forcast. Cold, windy chance of snow. But there's still the Super Bowl. Cul
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W1JKA
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Posts: 1679




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« Reply #6 on: February 01, 2014, 05:12:29 PM »

Re: KI5WW

Other than winning a bet my favorite part of the Super Bowl is seeing how many QRP contacts I can make during the half time dog and pony show.
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WB2WIK
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Posts: 20595




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« Reply #7 on: February 02, 2014, 03:51:05 PM »

Not much difference.  Propagation, operator skills and the antenna system to all the work.

However...a lot of hams (especially newer ones) have a hard time dealing with weak signals; this could be due to local noise issues, but often are due to operator inexperience in dealing with weak signals!

I have a neighbor (well, about a mile away) who was using a terrible antenna system (G5RV as an inverted vee, up only 20' above ground at its apex) and having a hard time working anybody; so, I visited him.  I tuned across 20m CW and heard lots of stuff, and said, "Hey, let's call this guy."  He said, "What guy?"  He didn't hear the signal, at all.  Just noise to him.  I heard a signal just fine, from Japan.  It was probably 319 or so, but very, very readable.

Zilch, to my neighbor.  I tuned in very carefully, selected his CW filter and turned up the volume.  "You really don't hear this guy?"

Nope.

It can take some experience to copy weaker signals.
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K8AXW
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Posts: 3839




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« Reply #8 on: February 02, 2014, 07:56:39 PM »

WW:  I have read the same question many times from those operating 1500W and want to go down to 100W.....and from those who are running 10W and want to go to 5W and now yours down to 3W.

I have also read the same answers for each question and they usually start by comparing S-units, db or in other similar scientific and mathematical terms which then begins with "The difference is "only" this or "only" that.

Let me explain this as simple as I can make it.  HELL YES IT WILL MAKE A DIFFERENCE!  It's a proven fact more power is better.  Can you make contacts?  Sure!.  Can you make lots of contacts?  No doubt.  Can you work DX.  Sure.  We've all read about it here time after time.

But, the bottom line is that power, using the same antenna, will do it better.  This is a proven fact.  Otherwise, why would anyone buy an amplifier.  Why would most of your transceivers sold  put out 100+ watts?  Why is it that QRP operators normally wind up at the bottom of the pile? 

But to your question.  If you get better service from a 3W rig because it's smaller, lighter and uses less battery power or lets you use smaller battery(s), then this is what you want to do.  These reports are facts.  No question.  But the fact of the matter is, it's more difficult and less reliable than running more power.  In some cases even a couple more watts will make the difference.

Whenever you ask the question "Will 3w do as good as 5w?" then you're asking someone to blow smoke up your butt, and you'll get it here!!

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WB6BYU
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Posts: 13253




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« Reply #9 on: February 02, 2014, 09:53:57 PM »

Quote from: K8AXW

Whenever you ask the question "Will 3w do as good as 5w?" then you're asking someone to blow smoke up your butt, and you'll get it here!!




But that wasn't the question that he asked:


Quote from: KI5WW

...So, will i notice a big difference going from 5 watts to 3 watts?...




Sure, there will be some times when a station will be able to pull him through at 5 watts but not
at 3 watts, but in practice, not all that often.  More likely the other station either can't copy him
at either power level, or copies him well enough in both cases, so there isn't a big difference,
which was his question.  If you're trying to bust a pileup on a rare DX station using 3 watts to a
Miracle Whip, increasing your power to 5 watts won't improve your chances much.  When chewing
the rag on 40m and signals are 20dB over S9 with the noise floor at S4, then reducing your signal
to S9+18dB isn't going to make it more difficult for the other station to copy your signal.
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W1JKA
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Posts: 1679




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« Reply #10 on: February 03, 2014, 02:51:00 AM »

Read TWICE, respond once. Carpenters use a similar technique when cutting a piece of lumber to a particular length. In my case I have to read three times and most of that between the lines. Wink

Re: KI5WW, BTW I broke even on the Super Bowl, I bet on both teams to lose.
« Last Edit: February 03, 2014, 03:06:39 AM by W1JKA » Logged
K1WJ
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Posts: 455




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« Reply #11 on: February 06, 2014, 01:07:01 PM »

Why would you run 3watts when you could run 5watts? I would think you would need a good reason, like to conserve on battery power or something of that nature. Double power factor does make a difference for the receiving station.
3w to 5w is not quite double, but as you progress 1w to 2w, 2w to 4w, 4w to 8w, 8w to 16w, 16w to 32w, 32w to 64w & so on - it does make a difference...........If you are a mud duck at 3watts - might as well go for 5watts.....73 K1WJ
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AA4PB
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Posts: 12847




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« Reply #12 on: February 06, 2014, 01:24:23 PM »

But he does have a good reason. He said he wants to use the internal batteries (that put out 3 watts) rather than having to lug around a separate external battery that can provide enough voltage to get 5W output.

For general operating, he won't notice the difference between 5W and 3W.
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KB4QAA
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Posts: 2373




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« Reply #13 on: February 11, 2014, 08:14:49 AM »

Of course the OP can compensate for the lower power by improving his antenna system!
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AA4PB
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Posts: 12847




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« Reply #14 on: February 11, 2014, 09:33:23 AM »

The nice thing about improving the antenna is that it improves receive as well as transmit - all for the same cost.
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