Re: Mobile FM Transmitter Antenna dipole updated
I have the Maxrad myself the coil is in the base, The best part is it looks like a CB antenna but is intended for VHF (aka FM) with a 200 watt rating. The 1/2 wave antenna performed well in my hands on testing. My SWR is < 1.1.1 the meter does not budge. I use it for special events like fairs etc. My antenna of choice is the dipole pictured here.
http://www.radiobrandy.com/FMants.html The dipole has provided me with the best results; My test antenna at 30 feet above ground test on three frequencies 95.1 99.1 104.7 with a 7 watt drive. Each antenna was tuned for the frequency SWR meter barely budged. The frequencies performed better as might expect. All test were conducted using stock car radios from GM & Ford, at 95.1 exceeded 37 mile range noise free. On 104.7 21 miles note: we had a distant station skipping in during test.
We also conducted a test in Las Vegas before 97.5 came on the air. The dipole antenna 30 feet above ground fed by a Panaxis FMX running 350 milliwatts on 97.7 The results really surprised us as the signal was herd 12 miles out noise free. For the record the transmitter was located on the far eastern side of Las Vegas on Hollywood Blvd an herd well into Green Valley.
While I have yet to test the J Pole. Others I know well have reported good results as soon as our test site is relocated I will be conducting on J Poles myself and report back the results. Both antennas use copper pipe allowing maximum energy to be transferred.
Note: The dipole uses a balun resulting in the signal arriving balanced both elements radiate.
Dropping the power to less than 100 milliwatts still provided good results with a solid coverage 2 miles out using a car radio. I did conduct test with a portable Panasonic analog radio with good results a mile out from the transmitter.
The signal was crammed between two 20,000 watt transmitters causing the AFC to jump to the stronger signals in spots.
Dropping the signal down to 10 milliwatts pulled the signal in to just shy of 3/4 miles before noise started to intrude in some spots.
RG-8 from Radio Shack was used on all test, Using Belden would offer better performance. We wanted to test with a cable anyone could get.
Steve
www.Radiobrandy.com
> Steve,
>
> These look more like CB antennas cut down to the exact
> frequency but do the antennas need the loading coils?
>
> I am researching 'J-Pole' and 'Slim Jim' antennas for FM
> transmission... these seem pretty promising and the Slim Jim
> design is said to be 6db better than J-Pole and if set up
> correctly at the proper height and properly shielded will
> produce another 0-6db from what I'm reading!
>
> This will be good when the time comes to buy my first FM
> transmitter as these are the best setups to test.
>
> Have you experimented with any of these antennas? What is
> your experience with FM antennas?
>
> Radiopilot
> <P ID="edit"><FONT class="small">
Edited by RADIOBRANDY on 09/18/05 03:57 AM.</FONT></P>
