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swr on antenna

swr on antenna

  • anyone?-, neep help

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  • s&w 357, jessy james

    Votes: 2 66.7%

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    3

moonwalker61

Member
Dec 23, 2018
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got new tower set up, with spt 500 penetrator on 11 meter. got swr down to 1:1. But when I turn on the 150 watt linear, swr goes to 2:1 on channel 1 and 4:1 on channel 40. Don't have antenna tuner or antenna analyzer. If I adjust swr with the linear on, then SWR goes up on barefoot mode. Open to any suggestions.
 

using external meter? if it is 1 to 1 with out amp on,, then you are good,, the reading you are getting is from the amp giving out harmonics,,,, the swr meter then doesnt know what to show,,,, in others words with the amp on you will get false readings,,,, if 1 to 1 is what you are getting barefoot then you are fine,,,,,
 
between radio and amp or amp to antenna...… could also be showing high because amps input or out put is not tuned correctly. also showing the reflect from the extra power. not always the spurious emissions from said amp. amps only amplify what is put in. so dirty in dirty out. could be all the above. also don't think you are changing anything adjusting coax length. you are just fooling the meter and/or getting a false reading.
 
The problem is not the antenna, it's the linear.

It's putting out more than just the one frequency the radio feeds into it.

The other frequencies are usually higher than the channel range the atennna is tuned for. The SWR for those frequencies is really high, even though the antenna is accepting the 27 MHz portion of the amplifier's output just like it should.

Say, for example the amplifier is putting out the second harmonic frequency of a 27 MHz channel. That's 54 MHz. If you put an analyzer on the antenna, and check the SWR at 54 MHz you'll probably find that it's ten-to-one, more or less.

The SWR meter can't tell multiple frequencies apart. It simply reads all the reflected power at all the frequencies going up to the antenna. The sum total of them makes it look as if the antenna has a high SWR.

If the reading is low with the barefoot radio, the antenna itself is perfectly okay.

But the amplifier has a headache.

73
 
Yeah what Nomadradio said! I've had guys call me and tell me of the same VSWR problems on mine and other antennas. Problem was the amp was not designed right, and or the radio was transmitting some weird off frequency RF Energy. Due to the golden screw driver effect. But mostly amps not designed right.

Jay in the Great Mojave Desert
 
One experience here I'll share, that happened many years ago. One customer insisted that I send Him a I-10K 5/8 WL GP Antenna for free so that he can test it. I said well we have tested it for a few years now and are happy with its performance. He kept calling me telling me the design was all wrong and he could fix it. Ok I said what type of antenna range you have and what type of equipment do you have to make antenna comparison Field Strength Measurements. And all measurements will need to be calibrated, and in the Far Field, and a few other requirements. The answer I got was disappointing at the least. He said he buddies will use their S-Meter on their radios. Wrong answer.

So finally he sends me a payment for the antenna, and I ship it to him. A few days later he calls up and says he doesn't need to use all the tuning parts, as the design is all wrong. And the VSWR is way off. Got him to install all the needed parts per the instructions, but still have a high VSWR. The transistor amp this guy designed and built had a bad matching input and output impedance matching circuit. When the amp was removed the VSWR was almost a 1 to 1.0

There are out there.

Jay in the Great Mojave Desert
 
One experience here I'll share, that happened many years ago. One customer insisted that I send Him a I-10K 5/8 WL GP Antenna for free so that he can test it. I said well we have tested it for a few years now and are happy with its performance. He kept calling me telling me the design was all wrong and he could fix it. Ok I said what type of antenna range you have and what type of equipment do you have to make antenna comparison Field Strength Measurements. And all measurements will need to be calibrated, and in the Far Field, and a few other requirements. The answer I got was disappointing at the least. He said he buddies will use their S-Meter on their radios. Wrong answer.

So finally he sends me a payment for the antenna, and I ship it to him. A few days later he calls up and says he doesn't need to use all the tuning parts, as the design is all wrong. And the VSWR is way off. Got him to install all the needed parts per the instructions, but still have a high VSWR. The transistor amp this guy designed and built had a bad matching input and output impedance matching circuit. When the amp was removed the VSWR was almost a 1 to 1.0

There are out there.

Jay in the Great Mojave Desert


yup and masking it with coax length does not fix the amp or radios problems.
 
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Ok I was wrong. with amp disconnected, & barefoot only, the CB set at 20 watts, the SWR is 4 on channel 1 & 2 on channel 40. I cant lengthen the antenna anymore, its at the max length. Shortening the ant.only makes the SWR higher on both channel. My Galaxy Melaka has a watt knob on back to adjust wattage, and it's at the max, (20 watts) I can turn it down to1 1/2- 2 watts and get a 1;5 SRW, but not enough to drive the linear. Don't know what else to do. Unless the workman swr-watt meter is not reading correctly. antenna; SPT 500 penetrator. coax rg213. With base set at 2 watts barefoot I cant even get out far enough to get a radio check. Linear is a 150 watt DC. and with linear hooked up SWR is about 8-9!!
 
If changing the power-knob setting on the radio causes the SWR reading to change, this suggests the radio is putting out some squirrelly extra frequencies itself. A check for loose ground screws around the edge of the radio's main circuit board is the first place to look if this happens.

Initially you said the barefoot SWR was 1.1. If that reading has changed, something in the antenna system has changed to cause it, most likely. Or maybe in the radio. Don't know.

Any chance you have one or more coax connectors with a loose connection to the shield inside the plug?

A soldered connection is really the only viable thing to use at the outdoor end of the cable feeding the antenna. The cheaper "crimped" type plugs usually have plastic molded around where the cable enters the rear of the plug. Those are okay indoors, out of the weather and with low power.

But the connector is not waterproof. Rain will get into it and oxidize the connection to the coax shield if it's not properly waterproofed. In extreme cases, rainwater will "wick" into the braid of the coax. Capillary force will draw the water down inside the coax jacket and eventually form a puddle on the operating desk where it plugs into the wattmeter or antenna switch.

DIssolved solids in this rainwater will precipitate when the water dries, leaving a visible crusty surface on the threads of the coax socket where it's connected.

6XfBRt.jpg


But these are common causes of this type of trouble we have seen many times over the years.

73
 
Ok I was wrong. with amp disconnected, & barefoot only, the CB set at 20 watts, the SWR is 4 on channel 1 & 2 on channel 40. I cant lengthen the antenna anymore, its at the max length. Shortening the ant.only makes the SWR higher on both channel. My Galaxy Melaka has a watt knob on back to adjust wattage, and it's at the max, (20 watts) I can turn it down to1 1/2- 2 watts and get a 1;5 SRW, but not enough to drive the linear. Don't know what else to do. Unless the workman swr-watt meter is not reading correctly. antenna; SPT 500 penetrator. coax rg213. With base set at 2 watts barefoot I cant even get out far enough to get a radio check. Linear is a 150 watt DC. and with linear hooked up SWR is about 8-9!!
bad coax …….
 
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Moonwalker6,

I know you said you didn't have much test equipment, but if you have a dummyload, unscrew the coax from your antenna and put the dummyload on it and see what your SWR readings are. If they are flat, then your coax should be ok; if not, then you have a problem with your coax. A dummyload is purely resistive and doesn't have any reactive impedance (capacitive or inductive) so the length of your coax won't give you false readings.

What freq. do you want to tune your antenna to?
What is the minimum length your coax needs to be to reach your antenna?
 
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Moonwalker6,

I know you said you didn't have much test equipment, but if you have a dummyload, unscrew the coax from your antenna and put the dummyload on it and see what your SWR readings are. If they are flat, then your coax should be ok; if not, then you have a problem with your coax. A dummyload is purely resistive and doesn't have any reactive impedance (capacitive or inductive) so the length of your coax won't give you false readings.

What freq. do you want to tune your antenna to?
What is the minimum length your coax needs to be to reach your antenna?
freq. somewhere between 27.165- 27.965-27.405, for 11 meter.38 feet from ground to antenna plus 7feet to go into the window, and I have 50 feet of coax.
 
freq. somewhere between 27.165-29.965 to 27.405, for 11 meter antenna.. 38 feet from ground to antenna plus 7 feet to go into the window so that gives me 5 feet of slack.
 

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