1/4 Base Antenna

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dripline2025
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1/4 Base Antenna

Post by dripline2025 » Wed May 05, 2010 2:37 pm

Hi,

I want to make a 27 mhz 1/4 base antenna but I have no idea how to make it.Any body that can help me please what kind of metal i need ,what is the lenght etc. means I need drawing or diagram how to make it.Thanks please help me .

Larry V

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Stretch
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Re: 1/4 Base Antenna

Post by Stretch » Wed May 05, 2010 3:47 pm

Ask Finch. Member here, he's a whizz on all that :)
Mitch Rogers

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Re: 1/4 Base Antenna

Post by Finch » Wed May 05, 2010 3:55 pm

Hi,
Any metal so long as it conducts electricity. Aluminium tubing would be best for this application.
The vertical element should be 2.75 meters long. You will need 4 ground plane radials each 2.75 meters long. Connect the centre conductor to the vertical element and the braid to the 4 radials. The radials should be 90 degrees apart.
Because you can't solder to aluminium the easiest way is to get a small screw and put the bolt through the aluminium tube and have the nut on the inside and clamp the wire in.
You don't have to have the radials, but if you don't have them the performance will suffer.

I'll draw up a diagram a little later.
-Alex

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Stretch
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Re: 1/4 Base Antenna

Post by Stretch » Wed May 05, 2010 3:58 pm

Told you :)
Mitch Rogers

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Phantom
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Re: 1/4 Base Antenna

Post by Phantom » Wed May 05, 2010 5:08 pm

Trust me - a good ground will dramitically improve your performance

dripline2025
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Re: 1/4 Base Antenna

Post by dripline2025 » Wed May 05, 2010 5:13 pm

What is the size of the aluminuim tube? it is 1/2"? thanks for help Finch and Stretch, I'll wait for the drawing thanks again.

dripline2025
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Re: 1/4 Base Antenna

Post by dripline2025 » Thu May 06, 2010 7:50 am

To all thanks for helping me.

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rredbeak
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Re: 1/4 Base Antenna

Post by rredbeak » Tue Nov 30, 2010 12:14 pm

the postings here will make a great homebrew antenna.

Some facts about your quarterwave that you might like to know.

The 4 Ground radials should be lowerred to 45 Degrees,the top one [radiator] should be vertical . This Configureation will give you 50 Ohms impedance giving a great match to your radio,BUT,always check swr.

With the 4 radials lowerred to 45 degrees gives you a transmitted angle of takeoff to 45 degrees ABOVE the horizion giving good distance locally and great dx.There is a imaginary quarterwave under the ground during transmit that determines angle of radiation. The Quarter wave is a truly outstanding antenna.

To LOWER the angle of transmit takeoff above the horizion.BUT to get lower take off angles you need Longer antennas.
For example,half wave,5/8 wave,.64 wave [otherwise known as 3/4 wave] all get lower as the length increases. So the .64 is around 11 Degrees above the horizion giving massive dx opportunities.

Im NOT saying get a .64,only,telling you how longer antennas work.

Your quarterwave is most excellent on BOTH local and dx.

Now you know more about your system you'll enjoy it more knowing what to expect and WHY others can talk to dx station that [possibly] you may not. Yours will work dx the bigger ones cant due to shorter skip bounces [hops]. Its proportional.

Cheers Rod
I LOVE AOR scanners, but cant afford the newer ones LOL. So Uniden is it.

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rredbeak
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Re: 1/4 Base Antenna

Post by rredbeak » Wed Dec 01, 2010 3:57 pm

Just an add on.

It might sound confusing 90 degrees apart and 45 degrees down.

CORRECT,4 radials spaced 90 degrees apart,BUT all 4 sloping down to 45 Degrees. This gives 50Ohms load. OIF yopu lowerred them straight down it would be 70 Ohms load,not a perfect load so 45 degrees lowerred please and your radio will love you LOL. CHECK the Swr.

Cheers Rod
I LOVE AOR scanners, but cant afford the newer ones LOL. So Uniden is it.

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Azoic
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Re: 1/4 Base Antenna

Post by Azoic » Sun Jan 30, 2011 12:35 am

Someone should also point out that a 1/4 wave antenna MUST be tuned in SITU....that is, if you tune it at 10 foot in the air, and raise it to 50 foot, the SWR will raise exponetionaly thus making what was 1.5: 1 at 10 foot, 150:1 at 50 foot. If you wish a 1/4 wave vertical to be mounted at 50 foot in the air, it MUST be tuned...50 foot in the air....and thats why the 5/8 and .64 exist. Tuning issues are negated by the additional length and proximity to wavelength. The best 1/4 wave antenna for 27 Mhz is still the 1/2 wave.
You don't have to have the radials, but if you don't have them the performance will suffer.....Finch
One point on this comment....the 1/4 wave is a groundplane antenna, also known as a MONOPOLE, without the radials, the antenna will NOT mirror the vertical and be a true dipole. The SWR will be so high even a tuner wont correct it, and the reflected power will be so detrimental to performance that NO signals will be heard at all. The radials on a 1/4 wave antenna MUST always be fitted, only the ANGLE to ground may be altered, the SWR is affected by the deflection angle, and is attenuated to the vertical. The higher the band the antenna is used on, the the more critical the angle becomes.

Check the ARRL Antenna handbook for proof, chapters 1,3,7,9,11,14,16, 27-29, and 33 all explain it more.

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Spectre
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Re: 1/4 Base Antenna

Post by Spectre » Mon Oct 22, 2012 2:42 am

Despite this being a rather old thread I just wanted to clarify the above post a little, the radials of the 1/4 wave antenna act as a counter poise to the radiator, this balance can also be achieved by substituting a very short mast OR a motor vehicle.

I built a 1/4 wave antenna from army surplus HF rods back during the 90's, it worked almost as well off a 1m grounded mast as it did mounted on my car's roof rack... the biggest difference over the use or deletion of the radials is it's effect on the radiation pattern, radials lower the pattern that's why the 5/8 wave GP's were so popular as base station antennas. their ability to land more signal at the horizon than over it, the 1/4 wave has an inherently higher angle of radiation than longer wavelength antenna and thus was quite popular for DX :wink:
Equip: Uniden 57XLT, 780XLT, 895XLT, Realistic Pro-2020, Pro-2025 & Pro-2040

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