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Corvette
New member
Username: Corvette
Post Number: 1
Registered: 3-2019
| | Posted on Wednesday, April 01, 2020 - 5:36 pm: | 
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total length is correct i think i made it 248 in.,swr starts out in the uper 3 adjust the length shorter the best i can get is on 20 and 40 is 1.7 and channel 1 is 2.0 any more adjustment the swr just goes up. adjust the ring and wire very little help. did not extend the length. what should be the next move to lower the swr. |
Tech833
Moderator
Username: Tech833
Post Number: 2454
Registered: 8-2002
| | Posted on Saturday, April 04, 2020 - 4:15 pm: |
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How long are the ground planes? Also, if you have access to an MFJ or similar antenna analyzer that will tell you the resistance and reactance of the antenna, please use that and let us know what the values are. That will give us an idea what is going on there.
Your radio 'Mythbuster' since 1998
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Buckeyefan
New member
Username: Buckeyefan
Post Number: 1
Registered: 3-2020
| | Posted on Thursday, April 09, 2020 - 7:40 am: |
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I am encountering the same issue as Corvette with my new Maco as well. I don't have access to aa analyzer, so I will be following the post to see what tips I can try. |
Corvette
New member
Username: Corvette
Post Number: 2
Registered: 3-2019
| | Posted on Sunday, April 12, 2020 - 11:43 am: |
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the ground plane rod is 104.0 in. that is with the (4) in. slid in to the larger tube. per instructions. i donot have a analyzer with the way the 259 con. is set up the entire antenna ohm. pegs out any where you check it. stillno idea of what to do to get the swr down. |
Tech833
Moderator
Username: Tech833
Post Number: 2457
Registered: 8-2002
| | Posted on Sunday, April 12, 2020 - 11:05 pm: |
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The Sirio 827 is the aluminum antenna with 8 short radials. I have never played with one of those, so I have no explanation for your results. Keep experimenting, that's what it's all about.
Your radio 'Mythbuster' since 1998
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Ke0koy
Junior Member
Username: Ke0koy
Post Number: 19
Registered: 12-2018
| | Posted on Monday, April 13, 2020 - 12:01 pm: |
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Tech833, if you were replying to my Sirio experiment, I think you put it under the wrong post. I did check out that link and thought it was very cool. Nice work on that! I have a friend with the Imax and GP kit, I'll share that with him.
Since I'm here, I should comment on this post.
Ive seen this issue before. Consider (for those of us with an analyzer) doing an SWR sweep of any coax with a dummy load at the end. Because most coax cables are not exactly 50+j0 ohm, there will always be a tiny amount of reflection (unless you make the antenna or load 52-j6 or whatever the coax really is). This can be seen on an SWR sweep as little dips in the already low SWR every half a wavelength. When a coax is 1/2 wave (or multiple), the input impedance is closest to that at the antenna end. One might assume that the impedance transformative effects of the coax shouldn't affect the SWR as the impedance rotates around a constant SWR circle, but that only happens when there is a perfect match. Being there is likely a slight mismatch even with a 50ohm dummy load (again, depending on the coax), the impedance is going to deviate from that constant SWR circle and start messing with SWR. For coax odd#/4 wavelength, the mismatch is exaggerated at the coax input the most. If you make your coax 1/2 wavelength or multiple of (electrically), you should be able to get that SWR down lower next time you try tuning at the antenna. This also has the advantage that the common-mode path on the coax shield will have an almost infinite impedance on account of it being an end fed half wave!!! Good luck! |
Ke0koy
Junior Member
Username: Ke0koy
Post Number: 20
Registered: 12-2018
| | Posted on Monday, April 13, 2020 - 12:30 pm: |
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I forgot to mention how to find an electrical half wavelength without an antenna analyzer. Since a half wavelength of coax will transform the impedance full circle back to what is at the other end, a half wavelength open-ended coax will present an infinite impedance at the input end (but ONLY if the other end is open and its a half wave long).
Connect the radio to the SWR meter, a tee to the antenna port of the SWR meter, and a dummy load to one side of the tee with the coax to be cut on the other side of the tee. As you trim the end of the coax off (keeping the conductors from touching during the tests), when you reach a half wavelength, the only load the SWR meter will see is the dummy load. When that happens, the SWR drops to nothing. Take another inch off to account for the tee and stop there. If the open-ended coax is not a half wavelength, it will appear as a reactive component in parallel with the dummy load raising the SWR. Sure, its a downright cruddy way to do this, but at 11m, it will certainly get you close enough! |
Dale
Senior Member
Username: Dale
Post Number: 2382
Registered: 12-2002
| | Posted on Saturday, May 09, 2020 - 11:00 pm: |
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according to ya swr numbers higher on 1 id say try lenthing the antenna another inch or so.. also try moving the wire around the ring..when measuring make certain ya going end to end
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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