I found an online calculator for antenna lengths based on frequency. Can this be used for FM? I don't have an SWR meter so I was trying to get by with this.
If I adjust the telescoping legs and the top antenna to a quarter wavelength, where should I assume the length starts? At the beginning of the piece before the bend or after the bend? And for the top antenna, would the length start where the BNC connector plugs into or where the antenna bends?
Below is the picture of the antenna I'm using to help illustrate what I'm talking about.
As long as you use a calculator tailored to VHF freqs you are ok. Don't use one for HF freqs.
You may have to settle for a calculator for a vhf j-pole, and remember that the main radiator is a half-wave length instead of the quarter wave you are using.
The lengths start at the coax connector. Every length of metal past it becomes antenna.
Just IMHO:
I wouldn't operate without an SWR meter. Seriously, I think you are "flying blind" without one (I'm really not trying to be a "smart-alek" with you) :-)
Post by Ozone Express Radio on Nov 20, 2010 21:44:02 GMT -6
Not to knock your antenna, but honestly, I had one of those, and I never could get it to actually do much more than be a problem.
I have a 25W HLLY transmitter, which is actually a pretty decent unit, but I run it through a 5/8 wave Comet antenna with LMR400 feeding it. The SWR is very low and it broadcasts a signal clearly for 5-6 miles in one direction and around 10 in another in very tree covered terrain from a somewhat low elevation.
I always run an SWR meter inline on the lead out to the antenna. Its cheap insurance knowing what is going on and keeping the transmitter "unfried." For less than 20 bucks you can pick up an SWR meter.
Thanks for the replies. Do you have any recommendations on where to get an SWR meter? I bought one at the ARC thrift store for about 20 bucks and sold it for about $115. Whish I'd have kept it now...
Post by Ozone Express Radio on Nov 21, 2010 20:36:14 GMT -6
The Meter in the link above is for 144-220 Mhz. Not the correct range for FM broadcasting. It also doesn't state what its impedence is either. Lots of them for CB or HAM use are 52 ohm.
Have a look on e-bay. A search using the term "SWR Meter" came up with 6 pages of everything from new to used, and all price ranges too.
Yes, the link provided is for an swr meter that is listed as an amateur radio device.
The frequency range shown does not mean it will not work properly on a lower frequency. In fact it means that the device is accurate enough for that higher range of freqs, and will work just as well at a somewhat lower freq (FM band).
I personally have used an earlier model of that same meter on FM, and it worked quite well.
Yes, it is for 50 ohm equipment, as nearly all communication equipment is made with 50 ohm output impedance.
Of course, one can look around on e-bay. There are bargains to be had but you generally get what you pay for. Caveat Emptor!
I would also recommend a different antenna. I've had a quarter wave dipole with the ground radials, and a homemade copper J-Pole. I would highly recommend the jpole, it's worked the best for me and isn't too hard to make.
