Can someone advise me on how to tune an antenna. Let’s just use a dipole as an example. How would I calculate the length ?

I don’t use the antenna calculators online, they are always wrong or only somewhere near your frequency.

I want to cut and tune to frequency so it’s bang on, or very close. I’m currently using a nano vna to see the resonant frequency’s.

I know what you mean about those calculators. Here's how I did it.

Start with a calculator and find the length for the frequency you want to tune to. Add 2cm to each side.

On the nanovna check the resonant frequency. It should be below your required frequency.

Cut 1cm from each end of your dipole and re-test. The resonant frequency will have moved towards your required frequency.

Rinse and repeat with smaller reductions as the resonant frequency gets closer to your required frequency.

Stop cutting when you hit it.

Hope that helps.

It's very easy, have a look at the instructions here http://www.gareth.net.nz/nrgworkshop/ha ... aerial.htm

This is from the original NRG UK website.

Why does it says that a dipole outperforms a 5/8 wave vertical?

Bton-FM wrote:Why does it says that a dipole outperforms a 5/8 wave vertical?

5/8 has less gain. Dipole has more gain.

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Electronically wrote: ↑Sat May 02, 2020 1:05 pm

Bton-FM wrote:Why does it says that a dipole outperforms a 5/8 wave vertical?

5/8 has less gain. Dipole has more gain.

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Then why does it say that the 5/8 wave has a higher gain in all articles about them?

Bton-FM wrote:

Electronically wrote: ↑Sat May 02, 2020 1:05 pm

Bton-FM wrote:Why does it says that a dipole outperforms a 5/8 wave vertical?

5/8 has less gain. Dipole has more gain.

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Then why does it say that the 5/8 wave has a higher gain in all articles about them?

All I know is from experience 5/8 is crap. Only thing 5/8 is good for is folk with down low locations.

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Good formula is f/142.5= L4 mts
exsample 98/142,5 = 0,687719298245614 mts (687mm)

For best match you need tool.. like antenna analyser or NANOVNA

OR minimum SWR Watt meter like diamond SX200 to adjust swr d lowers is possible,... lower then 1.2!

Yeh I tried using it with nanovna but can’t get it any lower than about 20db.

Why all the hate for the ⅝-wave? With ¼-wave radials (at least three of them) and a base match coil, I see around 2.8dBd gain - so usefully beating the dipole - and a radiation characteristic that's really useful on low sites. The ⅞-wave is much better - correctly matched, it performs much like a "full wavelength" aerial without the matching issues. My 144 MHz amateur band mobile aerial is a ⅞-wave and it really works well when mag-mounted to the car roof.

Albert H wrote:Why all the hate for the ⅝-wave? With ¼-wave radials (at least three of them) and a base match coil, I see around 2.8dBd gain - so usefully beating the dipole - and a radiation characteristic that's really useful on low sites. The ⅞-wave is much better - correctly matched, it performs much like a "full wavelength" aerial without the matching issues. My 144 MHz amateur band mobile aerial is a ⅞-wave and it really works well when mag-mounted to the car roof.

5/8 is useless waistes alot of your power. 1/4 wave is better than 5/8. So between a 1/4 and 1/2 I would take them as my choice any day.

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XXL wrote:Yeh I tried using it with nanovna but can’t get it any lower than about 20db.

That's about 1.2:1 SWR which doesn't sound too bad, depending on mounting location and coax length.

for coverage, reaches only dipole, real gain. 2 way 4 bay 8 bay. I use antena analyser because is faster.. before I use calculator for close tune and after that fine tune +- to get 1.1 1.15... with AA i get less then 1.1.. but need extra of time...

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

I can confirm that a jpole is what your looking for. But if I was you I would do what Albert says put plastic over the top of your poles as it protects against rain. From my experience using a jpole the swr went up a bit when it was raining but once the plastic was over the top of the poles the swr was dead when raining. Between the jpole and nrg vertical hi gain they both do the same.

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I used to really like the colinears. It's easy to get ~6dB omni gain. Look at Harry's design:

http://sm0vpo.altervista.org/antennas/6dbvhf0.htm

It's easy to build and really works well.

That's a single-slot colinear. I like multiple slot, end-fed versions on the top of high towers (or plumber's shops in Crystal Palace back in the 80s!)

Albert H wrote:I used to really like the colinears. It's easy to get ~6dB omni gain. Look at Harry's design:

http://sm0vpo.altervista.org/antennas/6dbvhf0.htm

It's easy to build and really works well.

That's a single-slot colinear. I like multiple slot, end-fed versions on the top of high towers (or plumber's shops in Crystal Palace back in the 80s!)

I've built one of those before Albert they do work very well. I just recently built a 1/4 with ground planes. to my surprise the power coming out of antenna was phenomenal. When I had 100 Watts coming out the amp then once out of antenna it was like 300 odd Watts very strong. I tried it with a normal ariel I wasn't getting that strongest in areas. But once teh 1/4 wave was in place my goodness it was strong in those areas brilliant I really like 1/4 wave

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rigmo wrote: ↑Sun May 03, 2020 9:07 am for coverage, reaches only dipole, real gain. 2 way 4 bay 8 bay. I use antena analyser because is faster.. before I use calculator for close tune and after that fine tune +- to get 1.1 1.15... with AA i get less then 1.1.. but need extra of time...

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

rigmo wrote:

rigmo wrote: ↑Sun May 03, 2020 9:07 am for coverage, reaches only dipole, real gain. 2 way 4 bay 8 bay. I use antena analyser because is faster.. before I use calculator for close tune and after that fine tune +- to get 1.1 1.15... with AA i get less then 1.1.. but need extra of time...

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

Why do folk assume the 5/8 wave antenna is good. You actually lose power. I know those ariels says 4.8db there is no chance that's happening mostly likely around 3db if anything.

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Electronically wrote: ↑Sat Jul 04, 2020 8:51 am

rigmo wrote:

rigmo wrote: ↑Sun May 03, 2020 9:07 am for coverage, reaches only dipole, real gain. 2 way 4 bay 8 bay. I use antena analyser because is faster.. before I use calculator for close tune and after that fine tune +- to get 1.1 1.15... with AA i get less then 1.1.. but need extra of time...

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

https://www.a****f.com/en/5-8-fm-transmitter-antenna/

Why do folk assume the 5/8 wave antenna is good. You actually lose power. I know those ariels says 4.8db there is no chance that's happening mostly likely around 3db if anything.

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3dB gain instead of 4.8dB gain is still double the ERP (twice as much power)

......so you are not losing power, you are gaining power. :tups

teckniqs wrote:

Electronically wrote: ↑Sat Jul 04, 2020 8:51 am

rigmo wrote: https://www.a****f.com/en/5-8-fm-transmitter-antenna/

Why do folk assume the 5/8 wave antenna is good. You actually lose power. I know those ariels says 4.8db there is no chance that's happening mostly likely around 3db if anything.

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3dB gain instead of 4.8dB gain is still double the ERP (twice as much power)

......so you are not losing power, you are gaining power. :tups

Yea but it states 4.8db but why if its only around 3db and yea it doubles but I don't see any difference because the 1/2 wave vertical did more coverage. Just my opinion. 1/2 vertical was around 4.2db which I believe is what most folk should be aiming for if I'm honest. I know most folk will disagree but I believe this is the case unless I'm proving wrong.

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