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Marc, I applaud the effort, but you've got the "gain" thing incorrect. Gain is a relative measure: something over the reference. And decibel is a logarithmic unit. "my antenna has 1db gain" translated to English means "intensity of the field created by my antenna is 1.26 times higher than the intensity of the field created by <what exactly???>". 0 dB = no gain over whatever reference you are using 1 dBi = 1 decibel over isotropic antenna ("i" is for isotropic) 1 dBd = 1 decibel over half-wave dipole ("d" is for dipole) Half-wave dipole has 2.15 dBi gain, that is 2.15 dB over isotropic antenna, and the intensity field is shaped like doughnut Quarter-wave monopole over ideal ground has 2.15 dBi gain, and the field is shaped like the upper half of the doughnut 1/2-wave and 1/4-wave antennas often called "no gain" or "unity gain" because they have 0 dBd gain (who might have thought...). Manufacturers and resellers may specify dBd or dBi. When they just specify dB it is better to assume that dBi is stated.

Hey folks... I have been seeing a lot of antenna related posts lately. Some info I have read lead me to create this post. I want to try to help people understand design types and how antenna SWR and Gain are impacted. I am not going to get too technical, because I don't want new people to feel lost or leave with more questions than answers. As an FYI, while the concepts apply to all antenna types, I will be focusing on vertical antennas, such as what we use on our vehicles. First, lets discuss basic antenna standards and why antenna length matters. The best way to describe how basic antenna length is relevant, is by comparing an antenna to a speaker. Pretty much everyone understands that a speaker vibrates to make noise. We also understand that small speakers do a better job at making very high frequency sounds (tweeters) and really big speakers are better for making very low frequency sounds (like a sub-woofer). Antennas are the same way. The lower in frequency, the bigger (or longer) the antenna. The reason for this is because, like a speaker, antennas resonate (or vibrate) the best at one very specific frequency. As you go higher or lower in frequency, you are moving away from the antennas resonant frequency This becomes important for several reasons. One is because the closer the antenna's resonate frequency is to the frequency you want to transmit on or receive on, the more range and fidelity you get. Another reason is because the energy that gets sent to the antenna must go somewhere. If the antenna is not at the correct length to vibrate at the desired frequency, that energy gets wasted by being "reflected" back into transmitters, as well as desensitizing receivers. Any energy that gets reflected back into the radio is typically identified by the Standing Wave Ratio (SWR) or the ratio of transmitted (forward) energy vs. reflected (reverse) energy. Here is why we watch SWR. If your transmitter is putting out 50 watts, and your meter says you have an SWR of 1.7:1, that means only 45 watts of energy leaves the antenna and 5 watts goes back into the transmitter. A high SWR not only causes power loss, but it also generates heat as well as applying reverse electrical energy to the parts. If enough of a percentage gets reflected back into the transmitter, it breaks. It is very well documented that with the current technology we have, the threshold is an SWR of about 3.0:1. So, now that we understand, on a very basic level, why antennas need to be a specific length to work the best, and also have a basic understanding of what SWR is, lets discuss antenna design. So, what's the standard? An isotropic antenna. This is a theoretical antenna that radiates equally in all directions with the same intensity. Basically, a perfect sphere. The antenna is said to have a power gain of 1 in the spherical space all around it and has an efficiency of 100%. The concept of an isotropic antenna is often used as a reference antenna for the antenna gain. What is antenna gain? Glad you asked! There is a lot of science behind that... so I am not going to bore you with science. Instead, lets talk about food! Everyone loves food and its pretty easy to understand. So, the concept of gain is this... you only have 100% of your energy available. There is no such thing as an antenna magically giving you more power. You know the perfect sphere radiation pattern mentioned earlier... well in the real world, the closet we have ever come to creating that, actually looks more like a doughnut. Imagine a perfect doughnut. Sounds yummy right? Well, you only have 100% of the doughnut. What do you do if you want the doughnut to be wider, say... to fill a box better from side to side? I mean, its a whole doughnut. Easy... you squish it from the top and bottom. Then the doughnut gets shorter from top to bottom, but the food has to go somewhere. So, it spreads out wider or "gains" width in sacrifice of height. Well the more you squeeze from the top and bottom, the wider it gets, but loses height until the doughnut is perfectly flat and the 100% of the doughnut as been spread as far as possible. The squished doughnut thing makes sense, right? Antennas that have "gain" do the same thing. They squish the radio energy doughnut, forcing it to be wider to cover more distance, but at the sacrifice of signal height. This means that while you can transmit and receive further side to side, you lose elevation. Lets imagine you are at the bottom of a hill and your buddy is at the top. If you don't squish the doughnut, he can hear you because the doughnut is at its full height. But if you squish the doughnut, people further away at your level will now hear you, but your buddy who is very close at the top of the hill will not. So, gain has a trade-off. If you live in a hilly or mountainous area, you may want to avoid high gain antennas, so as your elevation changes, you are less likely to lose touch with someone. Compare that to being on the water, in flat(ish) desert or talking aircraft to aircraft, you may want a very high gain antenna, because there will be no significant elevation differences. Now, from here, we could talk about the benefits of stacked phase element antennas, takeoff angles and a bunch of other stuff. However, unless you have a more advanced understanding of antenna propagation and design, and plan on getting into some high-tech stuff, it will likely cause more confusion. Not to mention, for what we are doing... those items are almost not relevant when it comes to helping you pick the correct antenna for your application. So, let talk about how gain and SWR can really be confusing and how numbers can trick you into making a mistake. Remember when we discussed antennas needing to be a specific length to resonate at the desired frequency? Well, many high gain designs cause the antenna to properly resonate at only small segments of the frequency spectrum. Basically, what these means is (as an example) instead of being resonant and having good SWR across 100 megahertz, the antenna design may cause the antenna to only be resonant and have proper SWR at 10 small groups of frequencies inside that same 100 megahertz range. Watch the two videos linked below for a better understanding. In the first video, I have a Diamond NR7900A mobile antenna. It has 3.7db gain on VHF in the 140MHz-160MHz range, and 6.4db gain on UHF in the range of about 440MHz-500MHz. You will see that while measuring the SWR (or the antenna and cable resonance) you will see that in the VHF segment, the SWR varies somewhat quickly, but only has a single swing, from high to low and back to high inside of about 20MHz. When I switch to UHF and test the higher gain portion of the antenna, you will see the the SWR bounce up and down a few times as I sweep about 30MHz. This shows that the higher the gain, the more the antenna design may actually make it so the antenna is not usable on your desired frequency. Of course this all varies by brand and model, but the principle is still universally true. https://www.youtube.com/watch?v=Rh6w46VM_Ng Now, in this second video, we are looking at a UHF 1/4 wave antenna. This antenna is considered to have a gain factor of 1, and any number times 1 equals itself... so effectively, no gain. You can see that we sweep over 50MHz and while the SWR wavers a little, the SWR is stable compared to the high gain antenna and 100% safely usable through the whole spectrum, never going over 1.4:1 from 440MHz to 470MHz. Again, reinforcing the idea that the closer the antenna is to the desired resonant frequency and the less you squish the doughnut, the broader the usable frequency range will be, the broader the geographical coverage will be, the less risk of losing power due to poor SWR, and less risk of damaging your transmitter. https://www.youtube.com/watch?v=P5GiPLzVzbg So, to wrap this up, I want to discuss antenna tuning. Some antennas may need to be cut to the proper length to resonate on the desired frequencies. This is typically done with antennas that either have no loading coils (1/4, 5/8, 1/2, 7/8 wave length antennas for example) as well as some bottom loaded antennas. A bottom loaded antenna is an antenna that has a whip that is not the correct physical length to be resonant on a desired frequency, but the coil of wire on the bottom makes the antenna electrically the correct length. General speaking, for VHF and UHF, I recommend staying away from antennas with coils in them if they have been physically shortened for looks/clearance reasons. These antenna work, but are not very good performers. That said, there are some antennas that are "pre-tuned" at the factory to perform correctly in the indicated frequency range. These are typically gain antennas that have a collection of coils and capacitors on the antenna to help create the phasing and properly stack the elements. These are referred to as LC networked antennas. If you have an antenna that has stacked phasing and/or LC networks and you can't get a good SWR... unless the manufacturer provides directions on how to properly do so, do NOT trim the antenna to try to achieve the proper resonance, as you will only damage the antenna. The coils, capacitors and whip elements are precisely cut to work together. If you do not get a good SWR, either you need to pick a new location to install the antenna, the antenna is not properly grounded or the antenna is damage and should be replaced. If you do trim a stacked phasing and/or LC network antenna, in most occasions, the antenna never gets to the proper length regardless of how much you cut the whip and you end up tossing the antenna in the trash. If you get it tuned to a target frequency, it's usable bandwidth will be so small that the antenna will not have any real value. I have seen some people try to tune high-gain antennas, get them tuned to about 1.7:1 or even 1.9:1 and as soon as they tune 10KHz in one direction or another the SWR skyrockets. I hope this helps with some of the antenna questions.

CCR is a common one for "Cheap Chinese Radio" which includes Baofengs, Wouxuns, and such. I think having a list would be good!

I wish we all lived closer. I would love to sit down and chat with many of you. There is a lot of knowledge and experience in this group. I would definitely bring some doughnuts.

Marc, I must add that I am a also very technical person, being a broadcast engineer, but that doughnut analogy of yours is spot on. A flattened doughnut will spread its contents outward from the center point - just like a stacked vertical antenna array - no doubt about it. Now... uh, where are those doughnuts? In my world, 12 dB = one dozen doughnut balls. Mmmm. I'll take those with RC Cola please.

Marc, I'm a technical type myself and I did pick up on the misstatements but I also wasn't going to nit-pick a great analogy apart over what, in the great scheme of things, were fairly minor points. It was, and still is, a great non-technical write-up of a very technical topic.

Much obliged sir! Will remove. Great people on a great forum.

Cheap Chinese Radio. I never would have guessed. I realize such an endeavor can quickly get out of hand. I wasn't thinking of an all inclusive list like those referenced above, just those you're likely to encounter in these threads. Thank you, Tom

New mic just came in and everything is good now

I'll add my 2 cents for Corey and JohnE regarding the 90 degree coax connectors. I am retired from the cable tv industry and I will tell you that we started using the 90's for cable management benefits but soon found out that we were experiencing far too many signal failure and signal strength loss issues to continue on with them. We ended up doing a massive rewire to remove all existing 90 degree coax fittings in the plant. My hands experience with those issues says I will never install a 90 degree fitting in any of my radio coax connectivity. Too many opportunities for failure and equipment loss. Craig

Thanks for the writeup Marc, very good. ..except I have to agree with Axorlov, a quarter-wave antenna has a gain FACTOR of one, not a gain of 1dB. A gain factor of one, is in fact, zero dBd, or 2.15 dBi. An antenna that is rated for 3 dBd gain would have a gain factor of 2, thus a 10 Watt transmitter going into a 3dBd gain antenna would produce 20 Watts ERP. (effective radiated power) Each 3 dB of gain represents a doubling of power. Each 3 dB of loss equals a halving of power.

Setup: Duracomm 14amp power supply, ed fong gmrs antenna approx 12ft high on roof mounted to vent pipe, 50 ft of rg8x. I had a midland mxt275 running through this setup already with no problems Test: requested radio checks through the linked net, I can hear the repeater tone after rx. One of the mics is a dtmf and tones come through fine. Also tried simplex to handheld with no luck. Also tried monitoring using mygmrs.com homepage live stream web link to repeater network. Tested: I have a tk880-1 ver2.0, a tk880-1h ver1, a kmc27, a kmc28, 3 mic cables (2 aftermarket, 1 oem) I swapped back over to the mxt275 and it still works just fine. Will go back into programming and check everything again, I'm pretty new to all of this so I may have messed up somewhere. New mic should be arriving today from ebay to try as well.

While I understand this, starting out I did not. I appreciate your description. It should make it easy for anyone to understand. People must understand, you cannot make energy appear or disappear. It can be lost by converting it to heat (via line loss or SWR). While many want to "squeze the most" of out their radio by getting high gain antennas, they must first evaluate their operating conditions. Cases where no gain (1db) would be ideal may be mixed use (both simplex to another radio and repeater usage) as well as high elevation changes where you drive or ride (such as here in Ohio, most of PA, mountainous areas). Places you might get away with high gain antennas include the great plains, FL, places you can see straight for miles and miles. I would like to add, for the above reasons, if you don't want to think about it and have great consistent all over use while driving, wheeling, riding, etc, perhaps stick with no gain antennas. Remember, even if you can get 30 miles simplex, the other station must also be able to respond to you for communication to work. Even if you can squeeze that extra distance, the other party may have a no gain antenna and may not get back to you. Keep in mind, for GMRS 1/4 wave antennas are approximately 6" (462.00MHz = 6.39", 467.00MHz = 6.32") and provide wide bandwidth and 1db gain.

To clarify further for you guys, that 200' limit is the cutoff for requiring FCC/FAA filing and paint/lights. You can go above 200' if you want to deal with the hassle.