Post by bostonradiodj on Feb 27, 2011 4:04:07 GMT -6
Hello;
I am new here and must say I think this forum is FANTASTIC! While I can't give too much information about myself for reasons that relate to the theme of this board..I own a very large company that caters to the Amateur/CB Radio community on a semi worldwide basis. I am also an unlicensed FM broadcaster, and have been for many years. My current rig is 100% professional quanlity studio equip, Tugicom 25 watt stereo exciter, homebrew 500 watt pallet amplifier. As for antenna..I tried them all over the years and this is what I settled on. I took an Antennacraft 3 element yagi that is made for the 6 meter amateur band and scaled it for my operating frequency (92.1). The antenna is mounted at a 45 degree angle to simulate circular polorization (which it really doesn't, but works far better than horiz. or vertical). The antenna only weighs about 5 pounds assembled. it is NOT very broadbanded, so it must be tuned to your operting frequency. It's very easy with the Gamma Match that comes with the antenna. The scaling of the antenna changes the factory ratings some. I estimate about 7db forward gain. It can be turned with a simple, inexpensive TV antenna rotor. It works great if you want to concentrate your signal in one direction. As an example, with no amplification and just 25 watts from the exciter I can easily cover 15 miles (in stereo) in the direction the antenna is pointed. That is with an antenna height of 45 feet from ground to top of longest element.
Just thought I'd throw that out there as an alternative.
Also...Coax...
Browning makes some cable called BR-400. VERY low loss at VHF. Same size as RG-213 but much lower loss. Accepts standard PL-259 or N Connectors. It's a bit pricey (about $1.Ft. US) but very good.
I've also mentioned using a directional antenna to those who have uneven coverage areas. One can use a simple fixed position two element yagi pointed in the area of the weakest coverage to improve that area. The other directions won't suffer much because the 2-element yagi isn't highly directional and still leaves plenty of signal in the other areas.
Your idea of the 45 degree tilted antenna is used often at vhf on the ham freqs. Not quite horizontal, not quite vertical, it's an attempt to be able to communicate with others using either antenna polarization... works well as a compromise!
My transmitter is 15 watts and have a 1/4 wave ground plane mounted on the roof, (about 45 feet). It's above the rooftops around me, but I have a peculiar problem. I check my signal on my truck's radio as I drive around. To the south and southeast I have a fairly strong signal up to 8 or 9 miles. The other day I had a fringe signal in an Office Depot parking lot about 15 miles from home. However, to the north my signal starts to fade in and out less than two miles away. I live in an urban area just south of downtown. A few blocks to the north is a park, and about two miles away are the office buildings. I have a couple of businesses that like to play my station, but the signal is sometimes "iffy", although they are only a few blocks away. Any idea what's up?
Post by bostonradiodj on Feb 28, 2011 2:50:56 GMT -6
Terrydec..
Your signal is strong 8-9 miles to the south and southeast, but fades quickly to the north. Is that correct? The businesses that want to play your station are to your north, I assume. Is the 'park' in between your TX'er and the potential listiners location? There can only be 2 reasons for this to happen IMHO..there is something in between your TX'er and the north plane to divert your signal from that direction. I ask about the park because a few years ago we had an amateur customer that was having similar problems on 2 meter simplex. Come to find out he was located close to a park, and baseball field..and the large metal backstop behind the homeplate was messing with his signal lobe. Secondly, while in theory a 1/4 wave antenna SHOULD ratiate equally well in all directions, I have seen some of the lesser quality antennas over the years NOT provide uniform 360' coverage (I am referencing VHF Amateur antennas, but the theory would still apply, I guess) What you can do is set your car radio 2 Khz above or below your TX frequency and drive around in a circle. This will in effect reduce the sensitivity if the receiver and you should be able to tell quickly if it's the antenna or something external. If you have approx. the same amount of 'bleed over', at the same distance from the TX'er in all directions the antenna is ok. If you have noticibly MORE bleed over to all directions but to the north, the antenna isn't radiating equally 360'. I hope I conveyed what I was trying to say clearly..sometimes my thoughts don't transfer well to the computer! Let me know how you make out. Good Luck.
You communicated very well. I'll try your suggestion. I've also thought about turning the antenna slightly and seeing if that makes a difference. I bought the cheapest one, ($70), and I've considered springing for the $100 model from eBay Unfortunately the landlord will only allow his worker on the roof and I have to pay. Still, it might be worth it.
Post by HighMountainRadio on Dec 14, 2017 18:53:16 GMT -6
Greetings From High Mountain Radio 99.9 FM !
Thanks for the tip about tilting the antenna at 45 degrees angle, I never heard of this little 'trick' and I have been around radio a very long time ! Operated a FM pirate station back in 1970 using a converted old military FM transmitter used in the military as a relay station for telephone traffic.. :-) It was all vacuum tubes and used an 829B transmitting tube in the final RF amp stage which produced around 40 watts out to the antenna.. The antenna was a homebrew groundplane made from welding rods.. LOL ! It worked very well..
I was going to experiment with 'circular polarization', building my own antenna, MUCH cheaper than buying one ! I have tried both horizontal polarization as well as vertical polarization and vertical worked quite a bit better.. I am anxious to try the tilt approach now ! I will also be building a 5 element yagi and vertically polarize it and shoot across town and into adjacent town which is my main desired area of coverage.. Been on the air quite some time with 5 watts and half decent coverage.. Of course, sporadic on-air times to avoid that dreaded visit..
Great forum !! Thank you !!
Regards, 'Spooky'
"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"
