Vertical antennas

[nevesjerry]

Hello. Wondering if someone in the group can help me with question regarding Vertical antennas for coverage between 100khz and 30 MHz. I have tried in the past to build an vertical antenna to cover the above range of frequencies by winding about 100 feet of wire on a wooden dowel and then connecting a lead in coax cable for lead in. It works but not that great. I suspect it has something to do with the proper connection of the coax cable. Let's say the coax lead in cable has has PL259s at both ends. How do I attach a SO239 plug to the end of the wire at the end of the Dowel? I know the wire should be attached to the center of SO239, but what about the ground on the SO239? Should there be another wire in the wooden
Dowel?? For instance I have an RF Systems 6 feet passive vertical antenna that performs quite well compared to the ones I have made. It just intrigues me how the commercial antennas such as the RF Systems is put together. I suppose I could open it up, but then it would be ruined!!
Any ideas??? Maybe they use some sort of balun at the bottom of whip??
Thanks so much for any possible ideas or explanation.
Regards to all, Jerry

 

[Blackswan73]

Google "broomstick antenna"

 

[prcguy]

A very short whip 3ft or 6ft long like your RF Systems vertical on the lower HF bands has a very high impedance and any signals (voltage) that is picked up will be literally snuffed out trying to drive 50 ohm coax. These short passive antennas have a broad band transformer with a very high impedance input around 5,000 ohms and a 50 ohm output. Signals or voltage picked up by the whip is transformed to a lower but usable voltage but the key is there is now enough current available to drive the low impedance coax.

Active versions of these short vertical antennas use a FET and are configured as a common drain or source follower, which provides a very high input impedance and current driving capability with no voltage gain. Sometimes these active antennas have an additional amplifier but unless they are designed by someone who really knows their stuff they can overload easily.

Your "broomstick" antenna is resonant at some specific frequency and its usefulness will peak there, otherwise a bunch of wire wrapped around a wood stick is basically a waste of wire and a stick. Without a counterpoise or ground radials the coax feeding it becomes half the antenna and its length will change the resonant frequency of the wasted wire and stick.
prcguy

Hello. Wondering if someone in the group can help me with question regarding Vertical antennas for coverage between 100khz and 30 MHz. I have tried in the past to build an vertical antenna to cover the above range of frequencies by winding about 100 feet of wire on a wooden dowel and then connecting a lead in coax cable for lead in. It works but not that great. I suspect it has something to do with the proper connection of the coax cable. Let's say the coax lead in cable has has PL259s at both ends. How do I attach a SO239 plug to the end of the wire at the end of the Dowel? I know the wire should be attached to the center of SO239, but what about the ground on the SO239? Should there be another wire in the wooden
Dowel?? For instance I have an RF Systems 6 feet passive vertical antenna that performs quite well compared to the ones I have made. It just intrigues me how the commercial antennas such as the RF Systems is put together. I suppose I could open it up, but then it would be ruined!!
Any ideas??? Maybe they use some sort of balun at the bottom of whip??
Thanks so much for any possible ideas or explanation.
Regards to all, Jerry

 

[VernM]

Nice job of clearly answering him, "pcguy."

 

[ka3jjz]

Actually I used a broomstick antenna with a L tuning network and a el-cheapo capacity hat made out of an aluminum pie plate for quite a while. Not pretty, but it worked. Mike