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1:9 UNUN, why? Icon_minitimeToday at 9:57 am by Razz229

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 1:9 UNUN, why?

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karelgol
Senior contributor
Senior contributor
karelgol


Call Sign : 19-CT-024 / PD0GOL
Posts : 166
Times Thanked : 6
Join date : 2020-05-21
QTH or Location : Steenwijk, JO32bs
Equipment Used : Dynascan AT5555,Yaesu FT-897, CB silver rod as mutiband HF antenna, OSJ-pole for 2m/70cm, MFJ-925
Age : 65

1:9 UNUN, why? Empty
PostSubject: 1:9 UNUN, why?   1:9 UNUN, why? Icon_minitimeSun Jun 23, 2024 4:03 pm

As those who followed my struggles with the silver rod/HFmultiband antenna might know i used a 9:1 UNUN to connect to it. Now i'm evaluating the whole (slow) progress i made and come up with some questions about why????

Reading the manual of the MFJ-925 tuner i found this:
Features
• Automatically matches antennas from 6 to 1600 ohms impedance (SWR up to 32:1)

The CocoaNEC model i developed gives a max inductance/SWR of:
Feedpoint(1) - Z: (325.820 - i 597.660)    I: (0.0007 + i 0.0013)     VSWR(Zo=50 Ω): 28.6:1

Looking back i now have doubts about the use of the 9:1 UNUN. Without it the MFJ-925 should handle it all just fine in my opinion. Maybe even better, as i think the little adjustments the 925 makes will be mutiplied by 9. When on it's own i suppose it could work with less coarse tuning steps.

Or am i missing something (as usual 1:9 UNUN, why? 263a )

73
Karel
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Alan Pilot
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Alan Pilot


Call Sign : 163-CT-220...MW7TTA
Posts : 2550
Times Thanked : 69
Join date : 2019-11-19
QTH or Location : Anglesey North Wales
Equipment Used : Yaesu FT-991A,,Yaesu FTDX-10,,Icom ic-7300,,Anytone AT-D878UV PLUS",,LINCOLN II+.
Age : 15

1:9 UNUN, why? Empty
PostSubject: Re: 1:9 UNUN, why?   1:9 UNUN, why? Icon_minitimeSun Jun 23, 2024 5:27 pm

A dipole yes i would try it but not sure on the silverrod ???.
Watching this or rather waiting for input.
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Victor
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Victor


Call Sign : 26-CT-3228 / M7VIC
Posts : 5829
Times Thanked : 355
Join date : 2019-11-10
QTH or Location : Bedford
Equipment Used : Various

1:9 UNUN, why? Empty
PostSubject: Re: 1:9 UNUN, why?   1:9 UNUN, why? Icon_minitimeMon Jun 24, 2024 5:51 am

As you've already figured out Karel your 9:1 transformer works best when the antenna presents a 450 ohm load at the frequencies of interest, (so requiring a specific antenna length).

The problem with just simply using a 'tuner' is that you have to account for losses in your feedline and most get around this by utilising a remote tuner at the antenna end to avoid such issues. Others (like myself) utilise ladder-line feeders to circumvent such losses that would be presented with coaxial cable but even then it isn't a magic cure-all often requiring additional or less feedline lengths to avoid extremes.

The last thing you'd want to do is burn out your MFJ tuner when presented with such extremes a mismatched antenna can present nor introduce massive losses on your feeder making your actual antenna fairly useless. You'll also want to avoid common mode current issues and the easiest way to get around that is the introduction of a 1:1 common mode choke between your transceiver and ATU.

Try to think of your antenna experiments as a 'whole' antenna system with everything from the back of your rig to the tip of your antenna being inclusively important.

If this helps any I'll provide a link (although to a commercial site not endorsed by myself or CT) that provides some additional information when utilising antenna impedance matching systems :-

https://www.hfkits.com/antenna-tuners/


There's much more information out there besides and worth exploring more but you may find yourself having to trawl through misinformation, myths or hype plus it's always best not to make quick assumptions of your own.

I wish you all the best with your antenna experimentation and although it can be frustrating at times just ensure that you're enjoying yourself.

(I think I've had more fun with antenna experimentation since becoming a Ham than anything else! 1:9 UNUN, why? 1f44d )

73
Victor

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1:9 UNUN, why? Empty
PostSubject: Re: 1:9 UNUN, why?   1:9 UNUN, why? Icon_minitime

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