The golden rule of antennas and feed lines for listening

[Oldglide]

"Once the signal leaves the transmitter's antenna...your on your own" There is no "Holy Grail" combination of antennas and feed lines and there is no "Best", lot's of "Better". Every situation is different. Electromagnetic wave theory and wave propagation are a science unto themselves. We are dealing with the basic laws of physics which we have no control over. After many years of dealing with antennas and feed lines, I used to DX television and I still DX commercial FM, I've learned to follow 4 basic rules when it comes to antennas and feed lines. 1) Do your research. Figure out what best suits your situation; location, inside or outside, what do you listen to etc. 2) Spend as much as you can for your antenna and feed line as this is the weakest link, it's not unusual to spend more for the antenna and feed line than for the radio. I like to use the 55-45 or 60-40 rule with the highest % going to the feed line. An average antenna with a high quality feed line will work better than a "super" antenna with a crappy feed line. 3) Mount your antenna as high as you possibly can without it being a problem or a hassle, stay away form those power lines! Inside or outside, higher is always better. 4) Remember, some days reception will be great some days it will be crap, Mother Nature doesn't give anyone special consideration. Once the antenna is up don't fall into the trap, "If I do this maybe it will be better", "If I change this maybe....". "Increases in performance diminish greatly with the more money you spend" Sit back and ENJOY!

 

[khoelldobler]

Oldglide is correct in what he is stating... the golden rule is made up of many considerable factors and he describes all of the basics. I follow some GOLDEN RULES when it comes to my scanner antenna / coax / reciever combinations too, starting with "quality shielded coax" to help keep the signal strong between the antenna and the receiver. I would like to add a few more considerations when planning an antenna installation. The following is a portion of my golden rules guidelines when laying out an installation for myself, as I do not do this on a professional level, I do try to follow professional level standards. This gameplan has always worked well for me and it may work well for others.

Signal should and will remain strongest when traveling thru the shortest distance of coax, with the antenna mounted safely and securely at the highest elevation possible, therefor, try to place your antenna (especially if outdoors) close to the reciever, using the shortest run that you can... outdoor obstructions taken into consideration, as high as you can safely to complete the install.

Quality connectors (only sometimes expensively priced) should always be used, with minimal couplings and elbows, and try to eliminate joining two or more coax cables into any antenna cable run... the more connectors and elbows, the greater the loss of signal strength at the receiver. Poor grade connectors and ill-fitting connections lead to signal loss. End connections should, for the most part, be shrinkwrapped whenever possible for strain relief.

Height is a key factor in my rulebook... its a priority to be taken seriously. Baring outdoor obstructions, reach for the sky... as they say "the sky's the limit" but limitations may be present. Use sturdy mast or mounting platforms whenever possible to ensure a safe mounting. I recommend guy wires for high wind and storm prone areas, to be used as recommended by the mounting type manufacturers specs. Along with height, comes the posibility of lightning strike and static charge... ground your antenna system properly for safety.

Be picky... spec out an antenna that will do the correct job, as there are many choices in the market place. Don't be shy... as questions on the RadioReference forums to gain knoweledge. Like Oldglide stated, DO A BIT OF RESEARCH HERE... once your install is complete, you do not want to tear it all down to perform a "do over" project.

Always disconnect the antenna coax from your receiver prior to approaching storms... it just might save your receiver from disaster.

The entire build can become costly, and I suggest saving some money on the side for such a project, as you continue to do research. Just because you see the expenses adding up, is no time to stop and cheat yourself of the quality of some of the materials out there in the marketplace. ALSO, expensive does not always mean better... shop around for that good quality coax and antenna... there are always sales, to be found in many places. Make a list of mfr's part numbers, of the items you feel are best suited for your needs, then go on to track down the best prices for those items. A materials shopping list or check-off sheet will come in handy.

Remember to ask for help from a friend... antenna installations are not always easy. Especially when footing a mast or working on a roof-top. And, someone may be needed as a runner to pass up those required hand tools that you forgot to bring up with you...

I have followed these steps when planning out my personal installs at home, and they have brought me great results. I couldn't be more pleased with my outcome. I currently monitor VHF , UHF, and 800mhz trunked systems on my home scanners... I own several discones and yagi style directional antennas... remember, I am not a professional, therefor, results may vary.


PS I believe that increases in performance can be made by purchasing the best possible quality materials, no matter what the expense. Do your homework, shop around, and try to keep with-in your rational budget or expense limitations. HAPPY MONITORING !!



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[jackj]

I agree with what has been stated except for the blanket statement that higher is better. It can be better, it can be worse and it can be uneconomical. Trunked systems are like cell phone systems, they reuse the same frequencies over and over. Adjacent towers do not use the same frequencies but ones 2 or 3 sites over do. It is possible to get your antenna height so high that you are picking up more than one tower's control channel. That's bad. Simplex frequencies are reused also. It is possible to get high enough to pickup co-channel users from other areas. Again, that can cause problems with interference.

You WILL reach a point of diminishing returns. Raising your antenna height means a longer feed line. At some point, depending on your feed line, any increase in received signal strength is lost in increased feed line loss. A higher antenna will not give much greater range in a lot of cases. The limiting factor with range isn't the free-space signal loss, its the horizon. Raising the antenna means the horizon is further away but at some point the increased distance won't be worth the expense.

A higher antenna is more expensive. It means not only a longer feed line but more expensive feed line to keep your line losses low. It means a more expensive support structure, you can get 20 feet at the gable end of your house pretty cheaply. 40 feet means a tower of some type. A tower means guy wires and guy wire anchor points or a bracket. You will reach a point were the expense will increase but the returns will vanish. Only you can decide how much money and effort you want to invest in your hobby.

 

[khoelldobler]

I agree with what has been stated except for the blanket statement that higher is better. It can be better, it can be worse and it can be uneconomical. Trunked systems are like cell phone systems, they reuse the same frequencies over and over. Adjacent towers do not use the same frequencies but ones 2 or 3 sites over do. It is possible to get your antenna height so high that you are picking up more than one tower's control channel. That's bad. Simplex frequencies are reused also. It is possible to get high enough to pickup co-channel users from other areas. Again, that can cause problems with interference.

You WILL reach a point of diminishing returns. Raising your antenna height means a longer feed line. At some point, depending on your feed line, any increase in received signal strength is lost in increased feed line loss. A higher antenna will not give much greater range in a lot of cases. The limiting factor with range isn't the free-space signal loss, its the horizon. Raising the antenna means the horizon is further away but at some point the increased distance won't be worth the expense.

A higher antenna is more expensive. It means not only a longer feed line but more expensive feed line to keep your line losses low. It means a more expensive support structure, you can get 20 feet at the gable end of your house pretty cheaply. 40 feet means a tower of some type. A tower means guy wires and guy wire anchor points or a bracket. You will reach a point were the expense will increase but the returns will vanish. Only you can decide how much money and effort you want to invest in your hobby.

valid point, regarding height... a higher antenna is more expensive, but may capture signals from a greater distance, or may help to enhance pulling in a nearby weaker signal. A higher antenna may pull in the adjacent towers, which can come in handy if my nearby tower is down, if those towers share the system I am monitoring, and attenuation on my reciever can be tweaked for this. Many newer scanners can be customized to eliviate or reject some noise. Line of sight and distance play crutial roles, and height is a factor for many of us, especially for those of us who might reside in city environments. A long feed line with a filter for interferance / intermod could work too, however, band filters installed in-line act as a slight reduction in overall gain as do all added conectors.

Obstructions with-in the signal path can be overwelming. It all depends on what you wish to monitor, type of signal, type of transmission system, band width, distance, transmitted signal strenght power, weather and atmosphere conditions... all critical to the final outcome of what's being monitored. Personally, expense is not my limitation, as I spend what I have to in order to better enjoy my hobby of scanning.

Longer feed lines will surely degrade signal and db gain to the receiver, but my rule of thumb is to prepare myself with coax that will overcome that diminishment right from the start, taking into consideration the requirements needed for what I intend to monitor. knoweledge of Mathmatics and understanding antenna and coax ratings in terms of loss in feet per run are instrumental. I myself would also start with a higher gain antenna to compensate for the lengthy run of coax required for the height in my scenerio. Like I stated, results may and will vary, and expense is part of the hobby in order to find that sweet spot. Everyones outcome, pertaining to thier environment, geographical area, and budget will be different. Finding a working, suitable balance can be a hit or miss and as stated, it all depends on what level you want to take yourself to. My add-ons to the golden rule were merely add-ons that I stated have worked for me... soley me... they are a part of the guidelines that have been proven to work best for me in my area. Again, preparation, and research, resources and knowledge, along with budget factors will bring you the final result... I hope these key factors bring you the results you are looking for.