Weird 1/4 wave length and SWR cross use

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1hardyanimal

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Durand,Mi.
Hello!
I have a goofy question. My local repeater in Flint Michigan was hosting what I believe is called a “net”, where everyone checks in, socializes, identifies and record is kept of the transmission. Well I was following on my HT, as I cannot yet participate as I do not have my license, until shortly after I test tomorrow morning and then it struck me; what a perfect time with all of this traffic for an antenna experiment! Albeit not a very big or adventurous one, it was a first somewhat successful one.
All I did was take a piece of TIG rod from my garage and stuck it in the magnetic base of an antenna mount that has no load. I hooked this up to my Icom ic-208h as I listened in on the Baofeng HT. Well no surprise, I could receive just fine, and rightfully so I should at any length of wire. SO knowing I cannot yet transmit I decided to just do a simple SWR test. I know that a ¼ wave 2m/70cm is about 19.75 +-“ I was wondering if you guys could tell me why my TIG rod antenna needed to be 25” to get an SWR of 1:2:1 When I tried to make it any shorter it only got worse and I had to start over with a new rod. I tried to loop the coax up and it did not help. I used a Galvanized steel garbage can lid as a ground plane.
My next question is, I have a “Mod 104 SWR and Power Meter” that is made for reading UHF and VHF. Is it possible, and if so to also use this on my CB radio?
 

prcguy

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It could be your garbage can lid was way too small for a ground plane and even though lengthening the whip to 25" is tool long for 2m, it does add more capacitance from the whip to the ground plane, lowering the impedance. An SWR measurement does not necessarily measure resonant frequency of an antenna, its an overall indication of any power reflecting back to the radio for various reasons.

You can make changes to an antenna like change its impedance higher due to a smaller ground plane or bending ground radials down, then slightly make up for it by lengthening the whip and so on. If your trash can lid is less than about 3ft across, then that could be your problem. Otherwise without seeing your exact setup it would be hard to comment further.
prcguy


Hello!
I have a goofy question. My local repeater in Flint Michigan was hosting what I believe is called a “net”, where everyone checks in, socializes, identifies and record is kept of the transmission. Well I was following on my HT, as I cannot yet participate as I do not have my license, until shortly after I test tomorrow morning and then it struck me; what a perfect time with all of this traffic for an antenna experiment! Albeit not a very big or adventurous one, it was a first somewhat successful one.
All I did was take a piece of TIG rod from my garage and stuck it in the magnetic base of an antenna mount that has no load. I hooked this up to my Icom ic-208h as I listened in on the Baofeng HT. Well no surprise, I could receive just fine, and rightfully so I should at any length of wire. SO knowing I cannot yet transmit I decided to just do a simple SWR test. I know that a ¼ wave 2m/70cm is about 19.75 +-“ I was wondering if you guys could tell me why my TIG rod antenna needed to be 25” to get an SWR of 1:2:1 When I tried to make it any shorter it only got worse and I had to start over with a new rod. I tried to loop the coax up and it did not help. I used a Galvanized steel garbage can lid as a ground plane.
My next question is, I have a “Mod 104 SWR and Power Meter” that is made for reading UHF and VHF. Is it possible, and if so to also use this on my CB radio?
 

1hardyanimal

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Joined
Mar 11, 2017
Messages
34
Location
Durand,Mi.
See that is an interesting thing. This is the lid from my dog food can, it is about maybe just shy of 2’ in diameter? And what is funny is the tin the beginning of testing I had it on a wooden stool and was wondering why it was testing so poorly. So I had my son grab the lid and it did only improve a bit. Maybe I will try a piece of garage shelving that is about 2x3’.
As for radials, I will try to find away, perhaps just strip the ends of some wire and wrap them around the ground thread of the magnet base and stretch them out equally in four directions so that they are maybe 19 inches as well from corner to corner? Just recently broke my leg and trying to save money. Going to get my license tomorrow, and would love to get a QSO going while I am stuck on the couch but am blessed with a radio and no antenna just some spotty raw material and time.
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
A 2" dia ground plane for 2m would explain the bad match and it should be ok with a 2X3 ft metal shelf.

BTW, if you are using an SWR meter, then you are actually transmitting and your not supposed to do that until you have a license.
prcguy

See that is an interesting thing. This is the lid from my dog food can, it is about maybe just shy of 2’ in diameter? And what is funny is the tin the beginning of testing I had it on a wooden stool and was wondering why it was testing so poorly. So I had my son grab the lid and it did only improve a bit. Maybe I will try a piece of garage shelving that is about 2x3’.
As for radials, I will try to find away, perhaps just strip the ends of some wire and wrap them around the ground thread of the magnet base and stretch them out equally in four directions so that they are maybe 19 inches as well from corner to corner? Just recently broke my leg and trying to save money. Going to get my license tomorrow, and would love to get a QSO going while I am stuck on the couch but am blessed with a radio and no antenna just some spotty raw material and time.
 

1hardyanimal

Member
Joined
Mar 11, 2017
Messages
34
Location
Durand,Mi.
No, it was 2' (2 foot in diameter) and I was not sure as to weather or not it transmitted on SWR testing, thank you for the clarification...guess all testing is at a standstill until sometime next week...Thank you for your help.
 
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