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Author Topic: Power Level  (Read 2153 times)
KR4TH
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Posts: 47




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« on: October 10, 2012, 08:17:14 AM »

I am running 100 watts out on cw on 40-10, on a 40 meter dipole and making most contacts on the first call with 57 to 59+ reports.  I am considering running reduced power.  I have worked several stations running 30-35 watts, even Europe dx on 10 and 15 and been surprised at their signal strength

Have you noticed a level of output that seems to significantly reduce power to a more difficult level of communication.  I am not looking to go qrp.  There seems to to be the most common power outputs, 5, 100 and full power.

Your observations will be appreciated

Jerry
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WX7G
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Posts: 6214




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« Reply #1 on: October 10, 2012, 08:34:54 AM »

Due to the law of reciprocity if you and the station are running the same TX output power you will each produce the same power into your receivers. That is, if you each run 100 watts, and he is S-7 at your QTH, you are S-7 at his QTH.

If you know his TX power, your TX power, and his signal strength at your QTH you know your signal strength at his QTH. So, you might assume that the other station is running 100 watts. And assume that S-5 or lower may not result in a QSO. From this you can tell if he will come back when you call. If he is S-5 and you are running QRP he might not come back. If he is S-9 he will hear you. The "secret" of QRP is to call only strong stations.
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AC5UP
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« Reply #2 on: October 10, 2012, 08:36:20 AM »

FCC Part 97 says we should run the least amount of power necessary to make a Q and IMHO that's both good practice and compliance with the license terms.

As for the question, a 'reasonable' amount of power is dependent on band conditions, time of day, time of year, and the characteristics of a particular band. There is no hard & fast answer. I've run 50 watts SSB on a 100 watt transceiver due to a power supply that lacked the moxie needed to deliver full current and did quite well on 20 Meters and up. On a good day 30 watts was more than adequate. Try the same thing on 75 Meter 'fone and you'll probably be disappointed.

Your mileage may vary.

What I'd suggest is that you try running 50 watts as your default power level. If you're making Q's without repeating yourself that's all you need. If not, you can always go full power. If that doesn't work then maybe it's time to give it a rest for the day.

If I had a soapbox I might mention something about how on eHam there are always new threads about the 'best' antenna and the 'best' amplifier but rarely any mention that a good band opening will beat the best of the best any day. Like any other game of chance, being in the right place at the right time has its value.
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WA3SKN
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« Reply #3 on: October 10, 2012, 08:43:31 AM »

Propagation conditions, time-of-day, antenna height all play a part along with power.  So just how much frustration are you willing to put up with?
I worked 14 years with QRP SSB because it was what I had at the time.  Md to New Zealand with less than a watt output on the audio peaks.  Md to Birmingham Ny with 39 MICROWATTS on the audio peaks! (Calibrated meter!)  How much of a challenge are you up for?
Why not start with normal power and then just lower your output?  Very educational!
73s.

-Mike.
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AC5UP
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« Reply #4 on: October 10, 2012, 08:47:46 AM »

Due to the law of reciprocity if you and the station are running the same TX output power you will each produce the same power into your receivers. That is, if you each run 100 watts, and he is S-7 at your QTH, you are S-7 at his QTH.

That's true, but assumes equal antenna capability.

'Spose two 100 watt stations are both running dipoles on 20 Meters. One dipole is perpendicular to the other station while the second dipole is off axis by maybe 30 degrees or more. Does the concept of reciprocity still work? What if the two dipoles are perfectly parallel to each other but one is at 35 feet and the other at 20 feet? The lower antenna has a higher angle of radiation and might line up with the skip angle better (or worse) than the pattern of the dipole at 35 feet.

It's also very possible these same two stations might Q for hours on end one day and not hear each other for the next week or better even though nothing has changed at either station... Every day is like a fresh roll of the dice.
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WB6BYU
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« Reply #5 on: October 10, 2012, 09:39:11 AM »

My Ten-Tec Argosy is rated at 50 watts output, and I typically ran it at about 25 watts.
I got a number of 579 reports from European stations that were barely above my noise
floor (and I have a quite site in the country, on the west coast.)

I've worked DX on 2 to 5 watts as well, though I might have had to wait for the band
to be a bit better.

For Stateside work on 40m when the band is open, I don't notice any difference in the
number of casual contacts I make running 5 watts or 100:  there are almost always
stations to work.  When conditions are more difficult, higher power is more useful.


The best thing to do is to try it yourself.  Try making contacts at 10 or 20 or 30 watts.
If you always get good reports, try lowering the power and see what happens.  If you
get lost in the noise too often, increase your power until you find a level that feels
comfortable to you.  And you can always change it - even in the middle of a QSO if
conditions get noisy, or if signals seem particularly strong.  You may find that your
comfortable power level changes from band to band, or with time of day.  But in
the end it is what is comfortable for YOU, and that is a matter of personal preference
that only you can decide.
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W8JI
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Posts: 9296


WWW

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« Reply #6 on: October 10, 2012, 09:46:28 AM »

Due to the law of reciprocity if you and the station are running the same TX output power you will each produce the same power into your receivers. That is, if you each run 100 watts, and he is S-7 at your QTH, you are S-7 at his QTH.

People always confuse reciprocity in power loss from the transmitter to the receiver with readings on S meters, and ability to copy the other fellow. There is a very significant difference between the power loss between the input from one antenna to the other being identical in both directions, and S meter readings and readability.


Quote
If you know his TX power, your TX power, and his signal strength at your QTH you know your signal strength at his QTH. So, you might assume that the other station is running 100 watts. And assume that S-5 or lower may not result in a QSO. From this you can tell if he will come back when you call. If he is S-5 and you are running QRP he might not come back. If he is S-9 he will hear you. The "secret" of QRP is to call only strong stations.


That is not an entirely correct view, because it assumes noise floor, noise figure, bandwidth, S-meter calibration, and operator ability is the same or similar on each end of the path. This is rarely the case.

For example, a typical rural location, on HF, can have 20-30 dB less noise than a typical urban location. That alone can be equivalent to a 100-1000 times effective radiated power change for the distant station.

Making things more complicated, directivity (pattern) generally establishes S/N ratio on receiving, while gain in the direction and polarization optimum for a path determine absolute level at the far end.

On 40 meters, running 1500 watts, I can work stations with a few watts and indoor antennas. I can work low power mobiles in Japan or Australia on 160. I often have to run about ten times their power, or more,  to have an "equal" copy. If someone operating from here runs 100 watts, the perception is always like the transmitting antennas are nearly dummy loads.

As a matter of fact, I can hear Europeans almost all day and night on 40 meters in winter. They cannot hear me, even though I am at 1500 watts, unless they are in very quiet locations, unless I wait until most signals are far out of my local noise.

This entire issue is complicated, but the important issue to remember is antenna directivity and noise floor determine receiving ability, while absolute radiated power determines transmitting levels. This means there are no set universal simple rules, and receiving can vary 30 dB or more with location and antenna, which is far more than transmitting normally varies.

73 Tom
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NR4C
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Posts: 310




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« Reply #7 on: October 10, 2012, 09:56:45 AM »

If you are running 100 watts now, note that 25 watts is only one (1) "S"; unit less power. And remember, you're only supposed to use the least power required to make the contact.

...bill  nr4c
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WB2WIK
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Posts: 20636




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« Reply #8 on: October 10, 2012, 10:03:49 AM »

Operator ears are a really big variable.

I work lots of stations that read "S0," or whatever the ambient noise level happens to be, and not 1 dB above that, on CW.

Good headphones, concentration, using a really narrow filter, tuning the signal to quite a low pitch (often well below the standard 600-700 Hz) and using lower speeds all helps.

I've had lots of shack visitors tell me, "There's nobody there!  Are you making this up?" when I'm working a weak station. Wink
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AC5UP
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Posts: 3927




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« Reply #9 on: October 10, 2012, 10:12:02 AM »

One of my favorite tricks for shack visitors is to tune WWVB @ 60 kHz (not a typo!) in AM mode. That's the NIST 'atomic clock' station.

On a good day you might hear the noise floor go higher and lower, but to the untrained ear nothing is heard. Then I flip modes to CW or FSK. Booop, booop booop, booop, booop... Sounds like super-slow CW (it's data) and comes up out of the nothingness like magic.

Whoa.......... Who Knew?
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WX7G
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Posts: 6214




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« Reply #10 on: October 10, 2012, 10:14:21 AM »

Due to the law of reciprocity if you and the station are running the same TX output power you will each produce the same power into your receivers. That is, if you each run 100 watts, and he is S-7 at your QTH, you are S-7 at his QTH.

That's true, but assumes equal antenna capability.

'Spose two 100 watt stations are both running dipoles on 20 Meters. One dipole is perpendicular to the other station while the second dipole is off axis by maybe 30 degrees or more. Does the concept of reciprocity still work? What if the two dipoles are perfectly parallel to each other but one is at 35 feet and the other at 20 feet? The lower antenna has a higher angle of radiation and might line up with the skip angle better (or worse) than the pattern of the dipole at 35 feet.

It's also very possible these same two stations might Q for hours on end one day and not hear each other for the next week or better even though nothing has changed at either station... Every day is like a fresh roll of the dice.



The two stations can trade antennas and the received signal power does not change.
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G3RZP
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Posts: 4845




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« Reply #11 on: October 10, 2012, 10:16:53 AM »

I've had QSOs where the amplifier was an absolute must - working Heard Island on 160, or Johnston Island on a dead 20m band. OTOH, I haven't had a working amplifier for 6 years and I've worked all the new countries that have come on.

But thinking of buying one, mainly to cover 160. I'm getting too old to actually get one built despite having the bits.
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N4NYY
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Posts: 4818




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« Reply #12 on: October 10, 2012, 01:27:31 PM »

I am running 100 watts out on cw on 40-10, on a 40 meter dipole and making most contacts on the first call with 57 to 59+ reports.  I am considering running reduced power.  I have worked several stations running 30-35 watts, even Europe dx on 10 and 15 and been surprised at their signal strength

Have you noticed a level of output that seems to significantly reduce power to a more difficult level of communication.  I am not looking to go qrp.  There seems to to be the most common power outputs, 5, 100 and full power.

Your observations will be appreciated

Jerry

Jerry,

I have run 5 watts and when conditions permit, I have talked around the work on it. Most of it will be on 10-15.
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NO2A
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Posts: 825




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« Reply #13 on: October 10, 2012, 03:01:54 PM »

Often it`s necessary to run qro,not cause your signal is weak,but because the other guy`s noise level is bad. I often here this from European hams. "Sorry om,please repeat,the qrn here is bad."I don`t usually have a problem hearing them,however. Location does matter.
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KR4TH
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Posts: 47




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« Reply #14 on: October 10, 2012, 04:30:43 PM »

thanks for your good comments, I will experiment with power levels

Jerry
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