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Author Topic: Antenna tuning help  (Read 1113 times)
W9ZIM
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Posts: 159




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« on: July 15, 2017, 11:17:53 AM »

I have an LNR Precision Trail Friendly antenna that I'm attempting to tune, and I need some help.  I raised it into operating position, plugged it into my Bitx40 transceiver using an Elecraft W1 SWR/watt meter, and tuned to around the center point of my operating privileges (which is about 7.250MHz), and keyed up.  It showed an SWR of 3.0, so I nipped a little off the end per the instructions and keyed up again.  It still showed 3.0.  So I nipped off a little more, and still 3.0.  So I nipped off a little more again -- by this time I had removed about 2" to 3" from the radiator -- and the SWR went up to 3.5!  I was under the impression the antenna was shipped too long, and that trimming the end would lower the SWR.  Do I misunderstand antenna tuning theory?  Am I going to have to replace the radiator with something even longer than the "factory default" and start again?
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KE6EE
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Posts: 1849




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« Reply #1 on: July 15, 2017, 12:57:07 PM »

You might begin as if you were using an antenna analyzer and sweeping the band to determine where the low SWR point is on 40M.

You don't know whether 7250kHz is above or below the minimum SWR point. You also do not know what the minimum SWR is.

So test the SWR say every 50kHz from the low end to the top and draw your own curve. That gives you a useful first impression. A better, possibly more useful curve, would benefit from data points closer together, like 25kHz or even 10kHz.

If you need to add a few inches or feet to the wire, no biggie. A well-sealed splice won't affect the performance or durability.
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KB3UWC
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Posts: 24




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« Reply #2 on: July 16, 2017, 03:55:25 PM »

 How are you modulating The signal. The bitx40 is a lsb radio only and has no carrier to power a meter. Somewhere i saw a mod, to enable a tone, for tuning. You need to use another rig with cw, rtty or even am. to operate your meter. Or use a antenna analyzer.
 Steve KB3UWC
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KE6EE
Member

Posts: 1849




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« Reply #3 on: July 17, 2017, 11:06:55 AM »

The bitx40 is a lsb radio only and has no carrier to power a meter.

One would assume that if the OP has gotten SWR readings he has figured out a way to
produce RF output with a sideband transmitter.
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AC2RY
Member

Posts: 282




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« Reply #4 on: July 17, 2017, 01:24:05 PM »

I have an LNR Precision Trail Friendly antenna that I'm attempting to tune, and I need some help.  I raised it into operating position, plugged it into my Bitx40 transceiver using an Elecraft W1 SWR/watt meter, and tuned to around the center point of my operating privileges (which is about 7.250MHz), and keyed up.  It showed an SWR of 3.0, so I nipped a little off the end per the instructions and keyed up again.  It still showed 3.0.  So I nipped off a little more, and still 3.0.  So I nipped off a little more again -- by this time I had removed about 2" to 3" from the radiator -- and the SWR went up to 3.5!  I was under the impression the antenna was shipped too long, and that trimming the end would lower the SWR.  Do I misunderstand antenna tuning theory?  Am I going to have to replace the radiator with something even longer than the "factory default" and start again?

I would start with adding good ground and countepose. Without them SWR meter will not show anything useful.
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JS6TMW
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Posts: 1181




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« Reply #5 on: July 17, 2017, 04:39:43 PM »

A friend had a similar problem with the LNR Trail Friendly. They are supposed to ship too long, so we tuned his using his analyzer when set up in my backyard by trimming about 6 inches. But then in a different setup he found it had changed and had to add wire back on. He ordered a replacement which DID ship too short. Apparently it is a touchy little beast. My suggestion is to follow the other suggestions!
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W9ZIM
Member

Posts: 159




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« Reply #6 on: July 18, 2017, 02:57:39 PM »

The bitx40 is a lsb radio only and has no carrier to power a meter.

One would assume that if the OP has gotten SWR readings he has figured out a way to
produce RF output with a sideband transmitter.

Yeah, I key the mic and give my callsign.  Ha!

Anyway, thanks for everybody's input.  I haven't had a chance to mess around with it since my initial post... too busy.
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KE6EE
Member

Posts: 1849




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« Reply #7 on: July 18, 2017, 04:34:33 PM »

Yeah, I key the mic and give my callsign.  Ha!

I think you missed the point. You need a continuous signal, AM, RTTY, CW or tone-modulated
SSB.
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W9ZIM
Member

Posts: 159




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« Reply #8 on: July 18, 2017, 05:51:27 PM »

Yeah, I key the mic and give my callsign.  Ha!

I think you missed the point. You need a continuous signal, AM, RTTY, CW or tone-modulated
SSB.

You can still see peaks with voice. If I need something consistent then I use a smartphone app to generate a tone into the microphone.
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WZ7U
Member

Posts: 576




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« Reply #9 on: July 18, 2017, 06:54:08 PM »

Do it like the big guns do and whistle into it.  Grin






it was a joke, sheesh
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================================================
WZ7U ~ originating from CN86jc +/-

Yet another imperfect being created by THE perfect God. Thank you Jesus!
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