And I cant figure it out. on 99.9 I have a random diapole taped to it. It performs better at full length than correctly tuned at 1/4 wave.
And I cant figure it out. on 99.9 I have a random diapole taped to it. It performs better at full length than correctly tuned at 1/4 wave.
The full height is about 3 1/2 Feet when fully folded out.
now 95.7 Antenna tuned to 1/4 wave does not go as far as 99.9 antenna fully folded out (also about 3 1/2) goes just about as far as 99.9 . I Simply just dont get it. Why does it matter to tune the antenna if the range is better just by folding it completely out?
It may be that your transmitter works better with the load presented by the "untuned" dipole than with one of the proper length. The impedance of the dipole depends on its length at the operating frequency. Not all transmitters are designed to give optimum performance with a 72 ohm load and it could be that your transmitter transfers more power with another impedance.
For example, I use a transmitter with a built in whip antenna. I can set the range by adjusting the length of the whip. This range has more to do with the antenna match to the transmitter than the actual radiating length of the whip since the whip is short (19 inches maximum) with respect to a 1/4 wavelength.
Neil
The Ramsey FM 25B transmitters are built to take abuse, no you can't pick one up and throw it across the room and expect it to still work.
I mean as far as a mis-match between the transmitter and antenna.
Mine operated two years with a make-shift dipole antenna that by theory should not have worked at all.
Here's what it was made of:
1) 75 ohm cable tv coax 50 feet in length.
1) 75 ohm to 300 ohm balun
(the kind with spades on one end and f - connector on the other end)
2) lengths of 12 guage awg automobile wire cut for 97.7 fm
The wires were soldered onto the spades of the balun, the balun screwed into the coax and the other end of the coax connected to the Ramsey fm 25 b.
Nothing was tested for swr or matched.
The dipole was mounted at a angle on my deck at 3 1/2' off the ground.
That's it!
Range with Ramsey variable turned wide open was nearly a mile and a half in a east to west figure eight.
With power turned down it just barely covered the park.
This antenna should not work this well but then again, as many other users of the Ramsey FM 25B will tell you, this tx is very forgiving.
It must be, considering it has a telescopic antenna mounted right above the transmitter. I hate to see how much rf is reflected back into the circuit.
🙂
I use a coaxial dipole on my Ramsey 30B. Its a simple antenna.
1. six feet of RG-58 coax w/BNC male connectors at both ends.
2. A BNC double female barrel connector
3. A snap-on ferrite like the ones used on computer video and power cords.
4. A 40 inch "rat-tail" antenna (supplied with the transmitter)
5. Two cable ties
Assemble rat-tail antenna, barrel connector and coax in series. Measure from the insulator on the rat-tail to the tip and adjust to just short of a 1/4 wave long (see formula below). Then, measure slightly longer than 1/4 length from the insulator down the coax and snap on the ferrite using the cable ties at either end of the snap-on to keep it in place where you need it. Use the loose end of the coax to connect to the transmitter. Less than 10 mw input produces about about a 1/2 of a mile listening area on the car radio. I operate with less than 5 mw for my purposes. The transmitter is capable of going up to 35 mw.
Suggestion: try to hang the antenna so that the angle where the rat-tail and the coax join is between 120 to 90 degrees to each other. Coax length between rat-tail insulator and the ferrite is 1/2 of the dipole and the rat-tail is the other half. The RG-58 coax can be any length, but remember there is diminishing signal lost in the coax if its too long.
Formula: 2916 divided by frequency (MHz) equals length in inches.
2916 divided by 101.5 MHz = 28.73 inches
Give this a try. Its and it works.