How to make a good and simple narrow band antenna (50 Ohm match)
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- เผยแพร่เมื่อ 7 ก.พ. 2025
- Each pôle length is lambda / 4
143/2F = Length of each radiator element in meter.
PVC pipe is about lambda / 4 long from the reflector.
Use 50 Ohm coax câble
If the antenna is well done, this kind of antenna can support very high power like 1kW as long as your coax cable can handle it. - วิทยาศาสตร์และเทคโนโลยี
U want to keep the ground element feedpoint and the conductor active element evenly parallel from one another not offset also bye changing the distance at the space between the 2 will effect the impedance...make sure it's around 3/4 -1 inch apart .. ..
This guy is a genius. I've copied his design and tested it. Although many "engineers" claim that this antenna would not work, because of impedance mismatch and no coils, bla bla, I can assure you that I have never had a better performing antenna than the design based on the simple formula of Mr Roosen. Yes the antenna will give you a SWR of 1:75 but I can tell you that having a SWR of 1:75 with a resonant antenna is much more effective than having a SWR of 1:1 with an antenna with a matching system. I have my own theory with the formula of Mr Roosen , the returned power somehow is re-used and emitted again, like exhaust gasses in modern Diesel engine. Call me delusional but how can someone explain that i cover a distance of 2,5km with only 100mw with this antenna almost defying the law of physics ? This is simply fantastic, I never could to that with my 180 Euro pro matching dipole, NEVER EVER. This single dipole is more effective than a bay with multiple expensive dipoles, especially with low power transmitters.
the top pole ... 3/4 lambda!
the lower (ground) pole 1/4 lambda!
swr? .... elongated / shortened upper pole
1/4λ (cm) = 7.200 : MHz
3/4λ (cm) = 21.600 : MHz
446 mhz?
7200:446=16.14 cm
21600:446=48.43cm
you can cut to 50 cm and then small 1 mm cuts to fix r.o.s.
;)
i made one of these but then for the 2 meter band got a swr of around 1.1 low band and 1.4 high band
This is a half wave dipole. Half wave dipoles have an impedance of around 70 ohms. So this is NOT a 50 ohm antenna. This would work halfway well for receiving but if you run a 50-ohm transmitter into this there will be an impedance mismatch resulting in power from the transmitter being reflected back to the transmitter- this is called SWR - standing wave ratio- if SWR is over 2:1 or so there's a chance your transmitter will be damaged by trying to dissipate the RF power that is reflected back into it, and since half or more of your power is not being radiated out of the antenna, the range of your transmission will be less than you hoped for. An SWR of 1.2 : 1 or less is usually considered acceptable for small transmitters. The closer you match the antenna's impedance and the impedance of the transmission line and the transmitter, the closer you get to an SWR of 1:1 in which all the radio power produced by your transmitter would radiate out of the antenna. Using coils, radials, a balun or other matching network you could tune this antenna to close to 50 ohms at your working frequency, but as it is there is going to be a fairly large impedance mismatch.
Billy Wheaton
a very good comment .
@@mohammadalfauomey3443 I believe it's more of a 2ele beam , no VF taken into account , but it is using it's mount pole.
the top pole ... 3/4 lambda!
the lower pole 1/4 lambda!
swr? .... elongated / shortened upper pole
1/4λ (cm) = 7.200 : MHz
3/4λ (cm) = 21.600 : MHz
446 mhz?
7200:446=16.14 cm
21600:446=48.43cm
you can cut to 50 cm and then small 1 mm cuts to fix r.o.s.
;)
I did this except that I zip tied the wires to a T fashioned from pine wood lumber. Unfortunately it didn't do much to improve reception. A later design made from 1/2 inch copper rubbing and a pvc T worked well and brings in stations from almost 100 miles away.
Do you have a picture of this?
whats wrong with 300/1 meters x 0.95 velocity factor then divide 4 for 1/4 waves
U will never have 50 without some type match .... Just staying
GOOD
what brand of shaving cream did you use to seal it?
I use expance mouss isolation that you can find in any store about gardening or DIY store
What is the significance of the factor 0.238333 ? Where does it come from ?
god knows? i use 300/1 x 0.95 velocity factor
👌🏻👍👍👍
Please use proffesional antenna meassuring system, and meassure your design.
Very good demonstration.
Thank you my brother.
GOOD FOR FM?
Hello my friend, I don't understand the formula. What size you need for 94.4 Mhz and what is the diameter of the copper ? Can you layout how you calculate ? Sorry noob here.
Hello with pleasure. Don't worry you welcome. The diameter of the element don't really count. Only the length. So for a frequency of 94.4 MHz that make: (300/94.4)x0.238333=0.76m so each element must be around 76cm ;)
Diameter of copper wire may be around 5 mm
hello. i need transmit in 148.040 What size i need. please
Dipole is not 50 ohms without balun or gamma match
Es una Antena Dipolo Abierto -.
What kind of Cable do you use ... RG58 - RG8 ..?
Thanks i am you Fan..
Hello dear Jhim,
It is RG213
this cable that you used floris, for the line of descent is a RG213?
thanks
Olingka dupaya pancarar jauh harus pakeai apa
a dipole to coax without a balun? and a dipole is around 70 ohms not 50
now if you added groundplanes you could turn it into a unbalanced 50 ohm groundplane
the top pole ... 3/4 lambda!
the lower (ground) pole 1/4 lambda!
swr? .... elongated / shortened upper pole
1/4λ (cm) = 7.200 : MHz
3/4λ (cm) = 21.600 : MHz
446 mhz?
7200:446=16.14 cm
21600:446=48.43cm
you can cut to 50 cm and then small 1 mm cuts to fix r.o.s.
;)
Intelsat17 satlate what hapaning
Where's the matching coils?
+Paul Hicks Hello dear, there is no need for matching coils. ;)
fmbroadcast I've always used a pawsey stub balun on mine. Not sure if it works any better?
Paul Hicks Hi,
I think you should really try this antenna design, it is very efficient ;)
Balun is not necesarry, for current conservation reason.
I already have. It's a 1/2 wave dipole. One of the simplest designs.
I prefer the gamma matched version. They radiate far better.
You'll never get better than a 1.5 : 1 SWR and your coax will radiate, putting RF on the OUTER of the coax - very bad!. You need a balun or a Pawsey Stub to make this work at all well.
music volume dude! better yet talk....
Hi Friend its easier formula 142.5÷Mhz half wave or quarter wave 71.25
Without coils, this antenna is nothing. You never can to build good antenna without coils
No, you don't need coil necessarly. Can you demonstrate your affirmation seriously ?
Its not true that without coils its nothing ! ... it simple half wave dipole. Simple antenna not best not worse