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Author Topic: How much power do you need?  (Read 3306 times)

gil

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How much power do you need?
« on: August 04, 2016, 08:07:33 AM »
A discussion is raging on the Elecraft reflector about crowd funding a 1500 Watts amplifier! That is an awful lot of power and money... How much is enough? Most amateur radios output 100W. CB radio 12W at the most. Let's look at some numbers and radio feats:

Remember Voyager One? The probe is now at the edge of the solar system after 37 years of travel at five light-seconds, more than twenty billion kilometers away! We are still receiving telemetry from its 14ft dish antenna. How much power does Voyager use? 23 Watts.

The long-distance amateur low power record is held by KL7YU and W7BVV using one micro-Watt over a distance of 1,650mi on 10m between Alaska and Oregon in 1970. ONE MICRO WATT!

I routinely made contact from Florida to Eastern Europe including near the Black Sea using 5W. I once made a 5200mi contact to Estonia on 1.3W. Ray heard me fine on more than one occasion 820 miles away using 100mW. I have made a few 1200mi contacts with my DC20B on 20m at 500mW, same with my Rock-Mite 30.

Don't throw away your 100W radio yet, but you might think twice before spending a fortune on an amp. Amplifiers sell for one main reason, contests. It's all about smashing the competition. The FCC rules that minimum power should be used to establish good communications, which unfortunately can't be enforced. Amps have major drawbacks, mainly current draw and weight. Low quality units with little filtering, mostly cheap CB amps, spatter the bands.

Military manpack radios practically all output about 25W SSB. That number seems to be the bees' knees for reasonably reliable voice communications. My RT-320 has confirmed this so far. Using Morse code with CW 5W gets you practically anywhere.

When the conditions are as bad as they are now, nothing goes through.. Whether you can receive a communication or not depends on the noise level and signal strength, assuming the ionosphere does reflect your signal back to Earth. The key element is your antenna. Sure you need a bit of power, but usually not that much. Reduce noise and losses... You don't need 1500W, hell, you really don't need 100W either. If there was a small 100W radio that fit in my cargo pants pocket and drew 50mAh on receive I'd buy it, but I have a better chance finding a unicorn. Power isn't free.

After a small to medium disaster radio chatter increases. First responders and Hams get to work, the noise level increases. After a major disaster however, few stations will remain on the air. Those who have solar power and low current draw radios will operate much longer, if not decades for some... Anyone using a generator with a boat anchor radio, even by modern standards, will soon be off the air. Noise generated by grid powered appliances will disappear, so even low power signals will be heard.

Here are the numbers that matter IMHO for HF:
  • 25 Watts SSB, 10W minimum.
  • 5 Watts CW, 2W minimum.
  • Less than 200mAh on receive, ideally 50mAh max.

Wire antennas work best, half waves, dipole or end-fed.

Don't be the guy who can't get his signal down the block without a $2K amplifier or bugs everyone with his 1500W screaming 59 until red in the face...

Comments?

Gil.

cockpitbob

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Re: How much power do you need?
« Reply #1 on: August 04, 2016, 08:22:56 AM »
Most people would be better served by putting up a better antenna.  What's the point of blasting 1,500W if you can't hear the barefoot 100W station trying to reply?

For me, the only amplifier I would consider is a 25W-50W amplifier for my KX1 that puts out only 2-3W.  But even that's a mismatch of philosophies because the KX1 is intended for hiking and while a 25W amp won't weigh much, the batteries to run it for any reasonable period of time would be too heavy for hiking. 

Jim Boswell

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Re: How much power do you need?
« Reply #2 on: August 04, 2016, 11:15:10 AM »
     Cockpitbob has a good point. These days most hams put too much emphasis on their transceiver because that part of their station is plug and play. In the old days the rule was spend 60% of your budget in the radio gear and 40% on the antenna. HOA and antenna restrictions cause problems for hams in newer subdivisions. You have to consider younger hams and the limitations they have living in apartments.
     When you talk about the Voyager, consider the gain of the earth antennas. NASA used the VLA system to complete the mission. The VLA system has about 200Db of gain. With the VLA you can hear a cell phone on Jupiter.
     Portable opps makes for a totally different conditions. When you consider the VHF and UHF bands where portable opps goes you can do just about anything, handheld antennas, rover stations, that kind of thing.
     The Hf bands just require so much more antenna due to the wavelengths involved. When you compact the antennas you lose bandwidth. I sum up antennas with this statement, most antennas longer that 1/4 wavelength can have gain, any antenna smaller than 1/4 wavelength loses signal and bandwith.
     You are right hams think they need too much power and because of that are "polluting their own world". I just don't see the need for any ham to use an amp over 500 watts. If the band is open, make the contact per the rules, with minimum power needed.
     When I use my Icom 703 or Tentec Argosy people are so amazed I can make a contact at all. QRP CW stations are kind'a common, but low power SSB stations are a real minority.

gil

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Re: How much power do you need?
« Reply #3 on: August 04, 2016, 12:11:12 PM »
I think the Yaesu FT-817 has changed the perception of low power SSB a bit, but some people won't believe it works even if you show it to them, and they have to self-justify spending thousands on rarely needed equipment...

Gil

cockpitbob

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Re: How much power do you need?
« Reply #4 on: August 04, 2016, 12:16:39 PM »
I think the Yaesu FT-817 has changed the perception of low power SSB a bit, but some people won't believe it works even if you show it to them, and they have to self-justify spending thousands on rarely needed equipment...

Gil
The day I received my used MFJ-9420 (20 meter SSB QRP rig) I plugged it my antenna and immediately hit a California station. 

My philosophy is with QRO you can work who you want.  With QRP you'll make plenty of contacts, but not necessarily the ones you want.

gil

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Re: How much power do you need?
« Reply #5 on: August 04, 2016, 04:35:02 PM »
I wish I had one of those 9420s! Almost bought one before leaving Florida, for the boat.
Gil

RadioRay

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Re: How much power do you need?
« Reply #6 on: August 04, 2016, 05:19:00 PM »
The best 'amplifier' you can have is the antenna.

Remember that the USA standard of one kilowatt came from the days of spark gap transmitters and extremely poor receivers on the bands below 600 meters.  Unless you're a commercial broadcaster, or operate on 80/160 during thunderstorms, why do that? When I lived in Virginia, I had large, wire antennas in the tops of  110 ft trees, fed with open wire line. Needless to say, QRP was quite effective. I had a small amplifier for QRP rigs (The Backpacker) and it helped when someone lived in a high noise area and needed it due to THEIR local noise. My local noise was essentially zero.

However, I've had people quite agitated when they realized that I was using a veru inexpensive radio station. One pair of guys calling their friend in Belize, I heard both ends, and relayed for them.  After doing that, Beliezian staiton and I had a great SSB conversation - QRP to him.  When the other guys heard that I was QRP SSB (Ten Tec 505) I was accused of lying, including this classic line:

"I got thousands of dollahs of gear here and a big amp.

They ain't NO WAAAY that you'ze twakin' to my friend wid
some dinky little QRP', when I can't even hear him!!!
 


Yes - we are and you're welcome for the help with the relay of traffic.   Basically, we had propagation and Mr. 'I got It All' did not - that's all - no amount of credit card debt would change that on this band at that time.

THERE IS NOTHING WRONG WITH BIG STATIONS, if that's what a person enjoys.  Also, there is nothing wrong with small stations, which I happen to enjoy. Gil and I had a sked for two years from over 800 miles.  Much of the time he ran 2-3 Watts into a simple wire out the window at moderate height. Lost skeds due to poor contacts could be measured on the fingers of one hand. That is VERY reliable.

From a ridgeline, with a good, wire antenna - it's easy to work the world on 5 Watts CW/data.  I've done well under similar conditions with a 20 WattSSB manpack.  As Gil commented though - if there wasa 50 Watts, radio and power source that was Small, Lite and had a small power drain: I'd jump.  However, increased power means increases in all of the above PLUS larger physical construction due to heat sink and etc.

How much power? 

With a dipole:
CW/data: 1-10 Watts is plenty
SSB Voice 20-30 is usually enough

So - the 'standard' 100 Watt rig and a dipole - a very capable station.
« Last Edit: August 04, 2016, 05:42:28 PM by RadioRay »
"When we cannot do the good we would, we must be ready to do the good we can."  ~ Matthew Henry

gil

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Re: How much power do you need?
« Reply #7 on: August 04, 2016, 06:07:49 PM »
Hello Ray. When I think about our skeds back then we indeed had very few days without contact, and you used your Sierra while I had either my MTR or K1, 5 to 6W, not to mention the indoors Buddistick "episode" at 2W and our 100mW tests. We were at the top of the solar cycle, but still. Today we probably would have to move down to 80m on the same path.. I don't know what Utah-France is going to look like when sun spots return.. Right now it's Europe only for me, single-hop up to 1300 miles.

The military manpack power ratings do show what works. If it didn't, those radios would output 100W, not 25. The whips BTW were used mostly for short ground wave contacts. The fact that they occasionally work skip is another proof that QRP works. Use a resonant wire antenna with 25W on an open band and it will most likely go through.
 
Now CW is a whole other ball game! In ballistic terms we'd mention sectional density. For the same weight, a smaller caliber bullet will penetrate deeper.. Another good example would be a flashlight vs. a laser.. Same power, same energy, widely different results.

Now I might go down to 500mW for fun once in a while with a RockMite, but I'll keep my 5 or 10W CW! No need to go to extremes

Let's not forget our purpose here, to establish communications when everything else has failed, and to continue doing so long term using alternate power sources, meaning low capacity batteries. QRP is not a choice here, it is the only way to stay on the air.

BTW I am attaching a great PDF document here on the efficiency of different modes..

Gil
« Last Edit: August 04, 2016, 06:19:47 PM by gil »

cockpitbob

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Re: How much power do you need?
« Reply #8 on: August 04, 2016, 07:30:04 PM »
Nice article Gil.  Now I've got real numbers for how much more power deficient CW is vs. SSB.  17dB or about 50x better.  So the 2W from my KX1 is about the same as 100W of SSB. 

vwflyer

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Re: How much power do you need?
« Reply #9 on: August 04, 2016, 09:00:54 PM »
I recently came across the ARRL podcast "The Doctor is In".
http://www.arrl.org/doctor
The episode on CW is very good and he does a good job of explaining why CW works so much better than SSB. Definitely worth a listen.

NWARadio

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Re: How much power do you need?
« Reply #10 on: August 22, 2016, 06:54:09 PM »
Reading this makes me want to attempt another RockMite build and learn CW. I'd certainly love a kit that could fit into an ammo can and go.
So long, and thanks for all the fish

cockpitbob

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Re: How much power do you need?
« Reply #11 on: August 22, 2016, 10:54:10 PM »
CW totally rocks.  My best was 10,500 miles to Antarctica with 3W and a simple wire antenna.  Of course the propagation gods were smiling on us that night.  CW has a hidden benefit few people talk about.  When you get older and your hearing starts to suck deciphering noisy voice gets harder and harder.  CW on the other hand doesn't.  No matter how bad the frequency response of your ears is, you can still tell if it was a short or long beep.

My main trail rig is a 3-band MTR with a built in touch keyer with touch pads glued to opposing sides of the box on one corner (so the key weighs nothing and takes zero room).  The battery pack is 3 LiFePo4 3.2V batteries and the antenna is a 63' long end fed half wave.  The whole thing weighs 15oz!  It kills me to bring the slingshot with fishing reel attached so I can get the antenna way up there because the reel/sling almost doubles the weight!

swxx

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Re: How much power do you need?
« Reply #12 on: August 23, 2017, 11:44:43 AM »
In truth I'm supportive of QRP (low power) especially for portable operation and prepping. But IF you have the power, then it can be used, and I must say I found it very satisfying to hear a signal from the other side of the world on 20m at night when I thought the band was closed to propagation with a genuine RST 599 (Readability 5/5, Strength 9/9, Tone Quality 9/9). I asked PWR/ANT? and the answer: 10kW 7ele. WOW. Now that is optimisation at power AND antenna isn't it?! The 10kW is 20dB better than 100W. And the 7ele likely adds another 20dB, well maybe not quite, but who knows, a LOT. And over SSB there is already a gain of up to 20dB. So approaching 60dB advantage, or 10 S points!

For me a survival radio should have the OPTION to decrease power, but should have at least 5 W or ideally 10 W output. Otherwise you can only get through when a) conditions are better - 1W to 10W is 10dB difference, not much when conditions are OK but if below noise or almost inaudible, 10dB is a lot. b) the operator at the other end is 1) not in a noise-free location 2) less than competent 3) not skilled at getting CW out from -10dB or more below noise level. An antenna especially portable, cannot always be easily optimised or enhanced. WHen I'm operating CW mobile, there often is a lot of difference in make or break if I use 50W instead of 10W. But that's in a moving car with car battery being charged by the alternator, not stationary with a 9V PP3 battery!

gil

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Re: How much power do you need?
« Reply #13 on: August 23, 2017, 12:21:38 PM »
Quote
And over SSB there is already a gain of up to 20dB.

I know you meant CW here ;)

Gil.

swxx

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Re: How much power do you need?
« Reply #14 on: August 27, 2017, 08:49:43 AM »
Quote
And over SSB there is already a gain of up to 20dB.

I know you meant CW here ;)

Gil.
Indeed I did mean OVER SSB, CW already has a gain of up to 20dB. :-)