• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

scaling antennas

davev8

Gold Star/Marvin Award Member
Apr 26, 2011
163
42
38
59
east cost lincolnshire England
Screenshot at 2019-06-02 15-19-50.png
on 11 meters I have often made a 5/8 wave based on the dimensions in the screen grab you can see it has a ring made from 6 feet copper tube ....now If I made a 20 meter 5/8 wave I can scale up the radiator that off the top of my head is 41 feet ish and radials at 16 or 17 feet ....but Will the length of the ring still be 6 feet ? Or is there something better to match it ? thanks
 
  • Like
Reactions: Christopher17

I've made a couple, for 10 and 2 metres. I scaled to the frequency which seemed to work.
so you are saying i need to scale the matching ring as well ,,,,,i did not know as they are both 5/8th wave end feed ..i think maybe the impedance may be the same for both at the feed point ... which if it was the ring i would think could be the same size for both ...
 
so you are saying i need to scale the matching ring as well ,,,,,i did not know as they are both 5/8th wave end feed ..i think maybe the impedance may be the same for both at the feed point ... which if it was the ring i would think could be the same size for both ...

The antenna doesn't see the inductance itself, it sees the reactance the inductor adds to the antenna. To get the same reactance on an antenna scaled to a different frequency requires a different inductor. Luckily, all you have to do is scale the ring with the antenna to compensate for the needed change in reactance.

So, in easy terms, yes you need to scale the ring with the antenna if you want a match.


The DB
 
going to try something like this, building my first 5/8 wave , assuming there a specific place to tap the ring and would most likely be frequency specific as to the tap location.?
 
The antenna doesn't see the inductance itself, it sees the reactance the inductor adds to the antenna. To get the same reactance on an antenna scaled to a different frequency requires a different inductor. Luckily, all you have to do is scale the ring with the antenna to compensate for the needed change in reactance.

So, in easy terms, yes you need to scale the ring with the antenna if you want a match.


The DB
Thanks DB
 
going to try something like this, building my first 5/8 wave , assuming there a specific place to tap the ring and would most likely be frequency specific as to the tap location.?
yes just make a sliding connection and make permanents when corect ...mine have always been temporary antennas made out of scrap ..a fiberglass hammer shaft is good to replace the wood in the photo ....if i remember i think 1/3 from the antenni end of the ring may a good starting point ...but you soon notice if you are sliding it the wrong way ...
 
  • Like
Reactions: Christopher17

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated