2 element 40 yagi ---

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We have 40 meter yagi antenna cut for the cw portion of the band. Will this antenna work on the phone portion of the band?
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Posted 2 years ago

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Photo of Jim Gilliam

Jim Gilliam

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The SWR will be higher in the phone portion of the band, and more than likely you will need a tuner to get full output from your transmitter. Generally the more L you add to the tuner the more loss you will have and consequently less power output. This is especially true with a tuner similar to the one used in the flex as it uses lumped capacitors and inductors. Generally the inductors will have a higher loss than a tuner comparable to the Palstar tuner that uses a large rotary inductor. If you can afford it, go with that kind of tuner. You probably won't get the same directivity operating in the phone bands because the relative tuning between the passive and active elements will be changed.

Jim, K6QE

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This is very true as I have a Palstar HF-Auto and have compared the built-in tuners in several different radios to it using an Alpha 8410 SWR/Power meter to check the results.

I am using a Mosley Pro-67C with 3 elements on 40 m tuned for CW/Phone the tuner is required for both ends of the bands for max output.

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fThanks Jim
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Norm - W7CK

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Have you checked the SWR at the upper end of the band yet?  Depending on the Yagi, it may be wide enough to cover most if not all of the band at 3:1 or less.  2:1 - 3:1 isn't too bad as long as you have pretty good coax LMR400 or better.  If you are mainly into cw, you may want to re-tune the yagi for the upper end of the cw or digital portion of the band. That way the SSB portion shouldn't be too bad.   If you don't run an amp, stick with the internal tuner in the Flex.  It will work fine.

Norm - W7CK
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Ria - N2RJ, Elmer

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Some yagis are designed to cover the whole band at a slight loss in performance.

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Charles Fontenot

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As you depart above or below the design frequency of a yagi, front-to-back ratio is the first parameter to suffer, then SWR, then Gain. A tuner can resolve the SWR issues away from design frequency where you can still have reasonable gain, but the F/B ratio will be significantly reduced. The SteppIR yagis do agood job of avoiding the pitfalls of bandwidth limitations of fixed yagi design. Careful design can reduce the ravages of bandwidth pitfalls at the expense of maximum Gain, F/B, and SWR. Even at a single frequency you can not achieve max Gain, max F/B, and perfect match. Pick one of the three to maximize, you can't have 2 of the 3, much less all 3. How many times have I heard on air statements that someone has an antenna designed for max Gain AND max F/B AND an impedance of 50+j0 ohms at a certain frequency. Too many times. I always ask for the NEC file for me to verify such a statement, but have not reveived any such files as yet.

So in the real world we use antenna tuners and low loss heliax to use our yagis at the ends of the band ranges and are generally satisfied with the results. Or use frequency agile yagis like the SteppIR antennas.