View Full Version : Antenna and power
kk4fpx
03-24-2015, 05:33 PM
Hello everyone, haven't been here for a while. My question is.... I have an Arrow 4 element beam for 2 meters. It is rated at 150 watts, Do you think I would hurt anything if I ran 300 watts thru it ? :cool2:
N2CHX
03-24-2015, 05:46 PM
Hello everyone, haven't been here for a while. My question is.... I have an Arrow 4 element beam for 2 meters. It is rated at 150 watts, Do you think I would hurt anything if I ran 300 watts thru it ? :cool2:
Depends on several factors and the most likely scenario is breakdown of insulation at a high impedance point inside the antenna somewhere.
First, did the manufacturer rate it conservatively? (an unknown, most likely). Second, what kind of modulation and duty cycle would you be using? Third, depends on how well tuned it is. Higher VSWR will increase the chances of something flashing over. Fourth, depends a little on your elevation and relative humidity. and fifth, why would you want to? You're not going to gain a whole lot in the grand scheme of things.
kk4fpx
03-24-2015, 06:25 PM
I'm using a TM-281 Kenwood at low power ( 25 watts ) into a Mirage amp. I bought the amp at an auction for $45.00 mainly for the preamp to work birds with. My elevation is around 4000 feet above sea level and the humidity is high. I check into a simplex net on Sunday nights that's about 60 miles away, thought the amp might get thru better. I originally had a 5 watt ht on it but needed the ht for uhf.
N2CHX
03-24-2015, 06:43 PM
I'm using a TM-281 Kenwood at low power ( 25 watts ) into a Mirage amp. I bought the amp at an auction for $45.00 mainly for the preamp to work birds with. My elevation is around 4000 feet above sea level and the humidity is high. I check into a simplex net on Sunday nights that's about 60 miles away, thought the amp might get thru better. I originally had a 5 watt ht on it but needed the ht for uhf.
Ah, understood. Can you lower the output of the Kenwood at all? If not, you might want to look into building an attenuator to decrease the drive into the amp. It would need some hefty resistors, but very doable. A lot of AM radio stations with older transmitters that couldn't do very low power, use resistors to burn off extra power as heat, to decrease the power to the antenna to meet licensed levels for lower nighttime power. Let me see if I can dig up some formulas for you on that, if you're interested.
kk4fpx
03-24-2015, 06:52 PM
Kenwood is not adjustable High and Low that's all. I noticed several of the Arrow antenna's were rated at 150 watts , so that might just be a ballpark figure.
WØTKX
03-24-2015, 07:34 PM
Arrow antennas are well built, but I wouldn't do it.
Which Mirage amplifier? The 300 watt B-5030 G I'm familiar with does 300 watts with 50 watts drive.
25 watts drive would be less output, and probably OK.
Do you have a watt meter for 2 meters and a dummy load or antenna that can take 300 watts?
Measure what you actually are putting out.
Arrow antennas are well built, but I wouldn't do it.
Exceeding the power rating on an antenna by 100% is a sure-fire way to destroy it. I'd go with "don't do it" as well.
Aw, don't listen to these scaredy-cat old farts—that 150 watt limit is just a scam to trick you into buying Arrow's more expensive antennas. Go ahead and run a kilowatt through the thing, it'll be fine. A little arcing never hurt anyone. Well, not much, anyhow although it's burned down a few houses, maybe...
Waiting...waiting....waiting; isn't anyone going to tell him that doubling his input power equals a 3 dB increase to the antenna and, that the 3 dB increase in his signal would *probably* not make a difference on the receiving end.
Maybe I'm wrong about that, maybe 3 dB gain would make a difference EME or Sat-Comms, feel free to edify me.
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ETA: Doubling you watts is not the same as doubling the length of your pecker; hard to get that concept over to the CB crowd!
kk4fpx
03-24-2015, 08:25 PM
The Mirage is the B 3030 G. It's not listed on their site. It says 30 in 300 out. I was getting almost 100 out with a 5 watt ht and I'm getting 300 out with 25 in, measured with two different meters into a home made Egg beater antenna.
K7SGJ
03-24-2015, 08:50 PM
Waiting...waiting....waiting; isn't anyone going to tell him that doubling his input power equals a 3 dB increase to the antenna and, that the 3 dB increase in his signal would *probably* not make a difference on the receiving end.
Maybe I'm wrong about that, maybe 3 dB gain would make a difference EME or Sat-Comms, feel free to edify me.
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ETA: Doubling you watts is not the same as doubling the length of your pecker; hard to get that concept over to the CB crowd!
I never thought of a 3db gain in pecker length. (other than from at rest to attention) Interesting concept.
The Mirage is the B 3030 G. It's not listed on their site. It says 30 in 300 out. I was getting almost 100 out with a 5 watt ht and I'm getting 300 out with 25 in, measured with two different meters into a home made Egg beater antenna.
13748
A gamma match is usually a variable capacitance device; the difference between a 2Kw gamma match and a 10Kw gamma match was the thickness in the dielectric insulator. Build yourself a heavier gamma match with large components.
http://arrowantennas.com/solid/146-4s.html
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WØTKX
03-24-2015, 09:45 PM
Mel and Kelli have great ideas.
True, the doubling of power (from 150 to 300) isn't gonna do much at all. However, he's stuck with the 300 watts output because of the radio. For now. How many feet of RG-58 would it take to attenuate... ;) :lol:
That Arrow antenna has a claimed gain of 9.7dBi. :chin: Even if a bit of a high claim, that's a big help. Typical 10 element Yagi instead would be what, maybe 11-13dBi? Arrow antennas are pretty damn good, so that is decent. all by itself.
Another Arrow Yagi "stacked" with a power divider is "yet another" 3dB, and would split that 300 watts. No more power issues, and gulp, more gain. Of course a phasing harness would split the power and give even more gain if carefully designed.
But hell, the combination of 150 watts and the Arrow should do quite well.
Two of those Arrows with 300 watts would hurt people. Eh?:mrgreen:
Always go for MOAR POWER (gain)!
13749
kk4fpx
03-25-2015, 09:34 AM
Okay all I'll not try the 300 watts. Thanks for the input.
K7SGJ
03-25-2015, 09:45 AM
Okay all I'll not try the 300 watts. Thanks for the input.
A wise choice. Just to give you an idea of what can happen, scientists had a 150 watt tracker on a bald eagle. One of them briefly ran 300 watts, and...........
13751
PA5COR
03-25-2015, 12:53 PM
A well designed 10 element yagi can do 10 dBd my 11 element Flexa yagi states 12.4 dBd
9.7 dBi will be 6 dBd.
wa6mhz
03-25-2015, 03:29 PM
just put a 50 foot run of RG-58 coax between the radio and the amp. U will lose enough dogbones to lower your power output way way down! 'Course Ur RX will be numb then too! (by about the same DB!)
Seriously, I doubt the antenna would be harmed, if U have some decent coax going to it from the amp. RG-8X will probably warm up though I have run a KILLERWATT through mine. Those antennas are probably way underrated, as they never expected anyone to run high power through them.
I would bet U could run a full 1500W into it and it would work just fine!
Nothing on the antenna is really going to break down. The gamma match or T match is probably same the HIGH power antennas have, it is a pretty standard design. I know the tower mounted antennas are good for 1500W, but the arrow is a hand held antennna. Again no one expected any one to be QRO into a hand held antenna!
wa6mhz
03-25-2015, 03:38 PM
After examining that link, I cannot see why it wouldn't handle 300W EASILY! It' not the hand held antenna I was thinking of.
wa6mhz
03-25-2015, 03:40 PM
A wise choice. Just to give you an idea of what can happen, scientists had a 150 watt tracker on a bald eagle. One of them briefly ran 300 watts, and...........
13751
I wouldn't wanna PISS THAT BEE OFF!!
NA4BH
03-25-2015, 04:34 PM
Again no one expected any one to be QRO into a hand held antenna!
You can do it once
http://3.bp.blogspot.com/_qj4XaRCP_50/TI7em9ijKgI/AAAAAAAABDY/qHxI6Kt5700/s1600/Wile+E.+Coyote3.jpg
Mel and Kelli have great ideas.
True, the doubling of power (from 150 to 300) isn't gonna do much at all. However, he's stuck with the 300 watts output because of the radio. For now. How many feet of RG-58 would it take to attenuate... ;) :lol:
That Arrow antenna has a claimed gain of 9.7dBi. :chin: Even if a bit of a high claim, that's a big help. Typical 10 element Yagi instead would be what, maybe 11-13dBi? Arrow antennas are pretty damn good, so that is decent. all by itself.
Another Arrow Yagi "stacked" with a power divider is "yet another" 3dB, and would split that 300 watts. No more power issues, and gulp, more gain. Of course a phasing harness would split the power and give even more gain if carefully designed.
But hell, the combination of 150 watts and the Arrow should do quite well.
Two of those Arrows with 300 watts would hurt people. Eh?:mrgreen:
Always go for MOAR POWER (gain)!
13749
He wold hit every repeater in a 75 mile rang - at the same time!
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WØTKX
03-26-2015, 10:24 AM
100 feet of RG8X would work as a coax attenuator. If you have it laying around, or can get it free/cheap. Some of the cheaper stuff is rated 150 watts at 200 MHz, the better stuff is rated at 360. Pushing it a little. Should get about 3-4 dB loss with that. Of course, measure the power after hooking it up to make sure.
Worth trying if it's cheap/free. Hook up a whole roll of the stuff. :mrgreen:
You'd need the ability to easily switch it out of the circuit on receive.
I never thought of a 3db gain in pecker length. (other than from at rest to attention) Interesting concept.
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Fellow was arguing with his wife and he says to her, "I'm gonna go out and find me some new p*ssy." The wife turns around and replies, "If you had two more inches of d*ck you could find some new p*ssy right here!"
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WØTKX
03-26-2015, 05:02 PM
"May not be long, but it sure is sharp and skinny". ~ Me, the "Stinger" CB "handle".
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