Copper Pipe? UHF J pole

[Planeguysexploration]

I quickly threw this together using various materials in my basement, I built it to recive~420mghz on my scanner, it dosen't seem to have worse quality than my RH 77ca, but only in the UHF band. It can't really pick up other bands very well. Do you think copper pipe would work in larger builds? Also tell me if I did anything wrong.

 

[prcguy]

Tell you if you did anything wrong......

Well, lets see now. First, the choice of antenna in my opinion is wrong, you would probably be better off making a 1/4 wave ground plane. No, you would defiantly be better off with a 1/4 wave ground plane as you would not have made so many mistakes. Next, what is that speaker wire doing connected to the antenna? Speaker wire is not balanced antenna line and is super lossy at HF and this is a UHF application. How did you determine the connection point for the feedline, or non feedline in this case? Its usually up higher, maybe half way or so on the shorter pipe and determined with an antenna analyzer or transmitting and adjusting for lowest SWR. You can't just pick a spot to connect the feedline. What you have is simply a shorted feedline by connecting both at the bottom of each vertical pipe. The copper J pole instructions call for having copper pipe bends and a short copper pipe joining the two vertical sections, why is there a bent aluminum thing holding it all together?

I think I'll stop here and hope you explore the 1/4 wave ground plane. A J pole has way too many variables and unless you have an antenna analyzer or transmitter and SWR meter it will never work right, even if you built it exactly like the instructions you followed. Even if you build it perfect and tune it perfect, its maybe slightly better than a 1/4 ground plane with about 5X as much work and cost.

Sorry to be so hard on you but if your going to do a project, build it exactly like the instructions and don't change out parts or do anything different. Otherwise you will not have anything close to what the project is supposed to be. Other types of antennas at lower frequencies can be diddled a bit without ending up with a useless lump of metal in the end but seldom with a UHF or higher frequency antenna.

 

[Planeguysexploration]

Tell you if you did anything wrong......

Well, lets see now. First, the choice of antenna in my opinion is wrong, you would probably be better off making a 1/4 wave ground plane. No, you would defiantly be better off with a 1/4 wave ground plane as you would not have made so many mistakes. Next, what is that speaker wire doing connected to the antenna? Speaker wire is not balanced antenna line and is super lossy at HF and this is a UHF application. How did you determine the connection point for the feedline, or non feedline in this case? Its usually up higher, maybe half way or so on the shorter pipe and determined with an antenna analyzer or transmitting and adjusting for lowest SWR. You can't just pick a spot to connect the feedline. What you have is simply a shorted feedline by connecting both at the bottom of each vertical pipe. The copper J pole instructions call for having copper pipe bends and a short copper pipe joining the two vertical sections, why is there a bent aluminum thing holding it all together?

I think I'll stop here and hope you explore the 1/4 wave ground plane. A J pole has way too many variables and unless you have an antenna analyzer or transmitter and SWR meter it will never work right, even if you built it exactly like the instructions you followed. Even if you build it perfect and tune it perfect, its maybe slightly better than a 1/4 ground plane with about 5X as much work and cost.

Sorry to be so hard on you but if your going to do a project, build it exactly like the instructions and don't change out parts or do anything different. Otherwise you will not have anything close to what the project is supposed to be. Other types of antennas at lower frequencies can be diddled a bit without ending up with a useless lump of metal in the end but seldom with a UHF or higher frequency antenna.

Thanks, as I said I sorta threw this together and have no real experience making antennas. I'll try out that quarter wave ground plane.

 

[prcguy]

Ok, but please consider VHF/UHF and higher freq antennas as very sensitive to any changes in size including length and width, etc. They are not like a bird house project where you can change the angle of the roof, make the entry hole a little bigger or smaller, paint it a different color, etc. But even a bird house will fail if you make the entry hole too far out of spec for the type of bird your trying to attract.

The feedline connection on an antenna can also be very critical and for a 1/4 wave ground plane you can simply solder brazing rods or house wire right on a connector then use a factory made coax assy to connect to your radio.

Thanks, as I said I sorta threw this together and have no real experience making antennas. I'll try out that quarter wave ground plane.

 

[mmckenna]

Do you think copper pipe would work in larger builds?

I made a 6 meter dipole out of 1/2" copper pipe once.
Made a few 250+ mile contacts with about 7 watts.

Like most ham radio things I build, I play with them for a while and then take them apart and do something else with the pieces.

 

[Planeguysexploration]

Tell you if you did anything wrong......

Well, lets see now. First, the choice of antenna in my opinion is wrong, you would probably be better off making a 1/4 wave ground plane. No, you would defiantly be better off with a 1/4 wave ground plane as you would not have made so many mistakes. Next, what is that speaker wire doing connected to the antenna? Speaker wire is not balanced antenna line and is super lossy at HF and this is a UHF application. How did you determine the connection point for the feedline, or non feedline in this case? Its usually up higher, maybe half way or so on the shorter pipe and determined with an antenna analyzer or transmitting and adjusting for lowest SWR. You can't just pick a spot to connect the feedline. What you have is simply a shorted feedline by connecting both at the bottom of each vertical pipe. The copper J pole instructions call for having copper pipe bends and a short copper pipe joining the two vertical sections, why is there a bent aluminum thing holding it all together?

I think I'll stop here and hope you explore the 1/4 wave ground plane. A J pole has way too many variables and unless you have an antenna analyzer or transmitter and SWR meter it will never work right, even if you built it exactly like the instructions you followed. Even if you build it perfect and tune it perfect, its maybe slightly better than a 1/4 ground plane with about 5X as much work and cost.

Sorry to be so hard on you but if your going to do a project, build it exactly like the instructions and don't change out parts or do anything different. Otherwise you will not have anything close to what the project is supposed to be. Other types of antennas at lower frequencies can be diddled a bit without ending up with a useless lump of metal in the end but seldom with a UHF or higher frequency antenna.

Alright, tried out the quarter wave ground plane, seems to work better, hope I didn't mess up as bad as I did on the first.

 

[Planeguysexploration]

Also, is there any way to make a good coax cable, I don't have any.

 

[mmckenna]

Also, is there any way to make a good coax cable, I don't have any.

Cheaper to buy it than the parts/headaches involved in making your own.

For scanner use, TV antenna/Cable TV coax will work just fine.

 

[prcguy]

No good easy way to make acceptable coax. What kind of radio are feeding and what kind of connector is on it?

Where are you located?

Also, is there any way to make a good coax cable, I don't have any.

 

[Planeguysexploration]

No good easy way to make acceptable coax. What kind of radio are feeding and what kind of connector is on it?

Where are you located?

I'm using a Uniden sr30c, it uses a BNC, obviously I'm not using this to transmit, just on my scanner. I found some TV coax that works good.

 

[Planeguysexploration]

I'm using a Uniden sr30c, it uses a BNC, obviously I'm not using this to transmit, just on my scanner. I found some TV coax that works good.

Also, in western NY

 

[Thorndike113]

For scanner use, TV antenna/Cable TV coax will work just fine.

I actually use close to 100 feet of mostly RG6 coax (about the same thickness as LMR400 or RG 8) coupled with some regular better quality cable TV coax (all 75 ohm) just to be able to get it in the house, hooked to my 50 Ohm scanner. The antenna I am using is an 11 foot commercial VHF base antenna and that combo of coax actually works better than 50 Ohm RG8 or RG58 coax. It helps to cut out interference and improve the signal. I did a bunch of testing before I went with it. It is NOT for transmitting, just receiving.

 

[mmckenna]

I actually use close to 100 feet of mostly RG6 coax

Yeah, RG-6, RG-11, there's even some hams that use old CATV hard line with good results. I'm running RG-6 for an end fed wire antenna in my back yard.