Is there an fm antenna for fm broadcasting 87.5-108 transmit that does not need any tuning over the 88-108 band. It must be a pain to have to re tune to different frequencies if you have to change locations on the dial transmitting taking down the antenna each time to tune it.
So looking for an antenna 200-300 watts with minimal swr tuning.
Also do they make an antenna swr tuner/matcher for the 88-108 band?
I know they make swr meters but an swr tuner would be great. I have tried looking but just seem to have the swr meter.
Post by HighMountainRadio on May 21, 2018 6:16:26 GMT -6
Greetings from High Mountain Radio !
Although an antenna tuner can be built for the FM broadcast band, I would not waste my time, antenna tuners merely present the transmitter with a nice happy 50 ohm impedance but that does not change the fact that the antenna is still not matched properly and therefore not 100% as efficient as it could be !
Here is what I suggest, a 'folded dipole' type of antenna. It has a quite broad bandwidth and really nice gain ! This is what I use, although keep in mind, it is somewhat directional, but that was my goal here. Truthfully, even though it IS somewhat directional, my other 3 directions do not suffer any significant signal degradation at all !
"Knowledge Is Always Made More Valuable By Sharing It With Others !" Always Remember To Be Kind ! True Greatness Often Has Very Humble Beginnings ! Help A Kid Out Today ! *** High Mountain Radio *** "Broadcasting From Somewhere High In The Remote Appalachian Mountains"
With any transmit antenna you will be limited by its bandwidth and how well your transmitter can handle higher SWR.
Your best bet is to tune it up between two frequencies you know will be used most, or tune it to the middle of the FM broadcast band and hope for the best.
The larger the antennas elements the wider the bandwidth usually is, and there are antenna designs which have a wide bandwidth to begin with but keep in mind the wider the bandwidth usually the less gain the antenna will have over a traditional dipole. Discone antennas for example have huge bandwidths but make terrible transmit antennas because they have substantial negative gain, but work great for reception because.. no tuning required.
Even if your SWR goes up to 2.0:1 you are still putting almost 90% of your signal into the air and listeners aren't going to notice a difference with that tiny bit of power loss. Many antennas will cover a large portion of the FM broadcast band and still be below this range for SWR. The real issue is will your transmitter handle it okay without shutting down or damaging the output transistor since the mistuned antenna has to push RF somewhere.. often in the form of heat, but usually anything under 3.0:1 SWR is somewhat in the safe zone until things start heating up too much and power losses become a real issue. I also would stay away from an antenna tuner if you can since you are so close to the tuned antennas frequency to begin with as tuners have their own RF losses and can over complicate a simple situation.
Nothing beats a properly tuned antenna, especially one with focused bandwidth for the frequency of use, but in a pinch you can get away with a little mis-adjustment, otherwise antennas like rubber duckies on walkie talkies would never work across a large band segment.
Post by HighMountainRadio on May 27, 2018 17:10:36 GMT -6
Greetings dss56 !
I agree with Kage, 100% ! I do not know of any commercially available antenna tuner that will cover the FM broadcast band. If that is what you prefer to use, one would have to be constructed which is easy enough, but as Kage mentioned, there is nothing like a properly matched antenna !
The 'folded dipole' type of antenna has a fairly broad bandwidth compared with other types. I use a 3 element folded dipole yagi that has around a 5.5 db gain across the entire FM broadcast spectrum. I have it tuned to 99.9 MHz and can change operating frequency up or down the band and still maintain a very acceptable VSWR. I have attached a picture of it's gain plot and a pix of the antenna itself. If I can assist you in any way, don't hesitate to message me !
73... Spooky...
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"Knowledge Is Always Made More Valuable By Sharing It With Others !" Always Remember To Be Kind ! True Greatness Often Has Very Humble Beginnings ! Help A Kid Out Today ! *** High Mountain Radio *** "Broadcasting From Somewhere High In The Remote Appalachian Mountains"
Thanks for the advice on the tuner. Maybe I meant a good swr meter as I have one on the way should have in a few days. Also im almost done with my adjustable dipole antenna.
Made of a pvc tee and 3/4 inch copper with a 3/4 to 1/2 inch fitting at the end for 1/2 inch to slide in or out to adjust to different freqs.
I will be mostly on the lower end of the band so it will be adjusted to 90mhz and has a band with of about 4mhz so it should hopefully cover 88 to 92mhz there are some open slots that seem to be quiet hopefully going for 88.8mhz.
My design is just a copy of a commercial made dipole that cost $150-$200+ and made of aluminum that is marked with frequencies to adjust the end for different freqs.
I will set it all up on the ground and do some testing to adjust the swr. Will be using rg213 coax. Antenna will be up approx 30feet and a 75foot or less of the rg213 to the swr meter and jumper to the 25 watt CZE-T251 . The transmitter has built in swr and temp sensor to detect bad swr or temp and will sound an alarm and shut down the transmit. Hope to only use 10-15 watts to cover a 2 mile radius.
Well all this is in progress and hope to get the antenna done this week then order the transmitter and coax.
Anyone have any input on this> 25W FM Radio Transmitter Broadcast Wireless Stereo Station CZE-T251?
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