Antenna Tutorial
The Antenna Farm — Your Two-Way Radio Source
Welcome to our Antenna Tutorial. We’ll try to make this as quick and “no brainer” as possible.
Page Outline
Antenna 101:
An antenna is an electrical device which converts electric power into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an oscillating radio frequency electric current to the antenna’s terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified.
Antennas are essential components of all equipment that uses radio. They are used in systems such as radio broadcasting, broadcast television, two-way radio, communications receivers, radar, cell phones, and satellite communications, as well as other devices such as garage door openers, wireless microphones, bluetooth enabled devices, wireless computer networks, baby monitors, and RFID tags on merchandise.
Ok now that we have the boring technical jargon out of the way, let’s get to the meat of the matter — “which antenna do I need”? I’m glad you asked...let’s examine the fundamentals and then take a look at some examples of two way radio antenna connections so you can easily determine what type connector you currently have on your radio or what connector you need for your new purchase.
Mobile Antennas (vehicular mounted antennas):
Before we get started please remember one important thing: 99.9% of two way radio failure is due to either the antenna being improper (meaning it’s not made for the frequency used) or the antenna has not been tuned properly to accommodate the transmitting frequency. Your antenna is the most important part of your two way radio system however it is often the most overlooked component. Getting the antenna right is 100% critical to not only achieving good performance but also maintaining the life of your equipment. If you are a complete novice when it comes to two way radios and antennas you would be wise to take a few minutes and read the material provided here. A few minutes of reading may save you a big headache in the future; not to mention money.
With regard to antennas the basic rule of thumb is, the taller (or larger) the antenna is, the more db gain it produces. However for right now let’s just keep things simple — again, the taller the antenna, the more db gain it will produce. The more db gain, the better the performance. Now there are exceptions to this rule, but only in some unique circumstances (which is explained here). So, if you want to “reach out and touch somebody” (meaning you want to reach out as far as possible with your two way radio) then you want the tallest antenna with the most db gain you can afford or tolerate. You may however want to take into consideration your garage at home that you plan on parking your vehicle inside for antenna height; not to mention the McDonalds drive thru window.
Second rule of thumb when it comes to vehicular mounted antennas is fundamental: mounting location of the antenna. The best place on any vehicle to mount your antenna is on the very center of the roof of the vehicle. For optimum performance one would mount the antenna on the center of a metal roof. If you don’t have a metal roof (such as fiberglass or plastic) then you would want to use a “no ground plane” antenna. No ground plane antennas are specially constructed to work in situations where there is not a suitable “ground plane” available. A ground plane being a metal surface positioned around the base of the antenna that the radiating signal reacts with.
Example of a good ground plane antenna situation. Example of a no ground plane antenna situation. This rule of thumb for “no ground plane” antennas applies equally to non-metallic roofs as it does to antennas mounted “out in the breeze”; such as mounting your antenna on a mirror mount. There are also ground plane discs available that will add a suitable ground plane to a non metallic surface. Click here for an example of no ground plane antennas.
Next thing one needs to consider is the frequency or frequencies that one needs to transmit on. Let’s use for example a VHF radio with a transmitting and receiving range of 136–174 MHz. Now let’s say that you transmit on 152.2500 MHz. In that case you would make sure that whichever antenna you decide on is made for transmitting on that frequency.
To calculate which antenna is going to suit you the best when operating on a number of different frequencies: take the highest frequency you transmit on and the lowest frequency you transmit on, add those 2 numbers together and then divide the result by 2; this will give you your “center” frequency. For example; let’s say you transmit on 152.2500, 154.6500, 155.3250, and 155.7500 MHz. Take your highest frequency (155.7500) and your lowest frequency (152.2500) and add these two numbers together = 308. Divide by 2 = 154. Your center frequency is 154.000 MHz. (NOTE: we are NOT concerned about receive only frequencies — only the frequencies you actually transmit on.)
The above example works for picking out virtually any antenna available no matter the frequency. However, there is also another very important factor to consider: how wide of a range of frequencies do you use? Does the difference between the highest and lowest transmitting frequency exceed the antenna’s operating bandwidth? If so, you need a “wideband” antenna.
Ok, so let’s name some antennas here and what purpose they serve:
- High Gain Antennas: Offers high gain performance and usually includes a tunable whip.
- No Ground Plane Antennas: Can be used where a suitable ground plane is not available.
- Wide Band Antennas: Offers the user the opportunity to operate over a wider range of frequencies than can be achieved using a standard antenna.
- Quarter Wave Whips: Standard antennas that are pre-tuned for a certain frequency range and are also very affordable.
- Glass Mount Antennas: Made to mount on a window.
- Phantom/Disguise Antennas: Very small and as “incognito” as possible.
- Field Tunable Whips: Can be cut to length to accommodate its given frequency range.
Mobile Antenna Mounts:
Ok, now that you know what kind of antenna you need; you need to pick out a suitable antenna mount. Let’s look at the options:
- Permanent Hole Mounts: You drill a hole through your roof, trunk or wherever seems like a good place.
- Thick Surface Mounts: Same as permanent hole mounts but used where the thickness of the material drilled through exceeds standard vehicle thickness.
- Magnetic Mounts: Just plop it on top of your roof and go!
- Trunk Lip Mounts: Fasten to the “lip” of your vehicle’s trunk. No holes drilled.
- L Bracket Mounts: Uses a simple L shaped bracket to mount an antenna just about anywhere.
- Mirror Bracket Mounts: Clamp down to most any tubular shaped metal — popular with truck drivers.
- Universal Lip Mounts: The most convenient way to mount an antenna without drilling holes while still achieving a clean look.
- Luggage Rack Mounts: Attaches to most luggage racks — another “no holes” mounting solution.
<Quick Note About Mounts> Antennas have different bases — meaning where the antenna physically screws down onto your mount. The majority of antennas we sell are what’s known as ‘NMO’ type mounting. There are 4 major mounting types:
- NMO — This is the most widely used mounting type. Images: NMO Base | NMO Mount | NMO Combo
- PL-259 — Common with amateur radio antenna products. Images: PL-259 Base | PL-259 Mount | PL-259 Combo
- N — Commonly found on antennas that are 1200MHz or above. Images: N Base | N Mount | N Combo
- 3/8 x 24 Thread — Most common with some CB antennas. Images: 3/8x24 Base | 3/8x24 Mount | 3/8x24 Combo
Radio Antenna Connections
Now you might ask yourself: “what kind of connector do I have on the back of my radio”? Let’s look at the most common connections. (NOTE: if all else fails you can search our connector section of the website.)
| Connector | Image | Description |
|---|---|---|
|
SO-239 (UHF Female) |
 |
About 5/8" in diameter with outside threads and female pin hole. The most common connection found on most two way radios. |
| Mini UHF Female |  |
About 5/16" in diameter with outside threads and female pin hole. Commonly found on Motorola two way radios and some Vertex and Kenwood models. |
| BNC Female |  |
About 5/16" in diameter and looks like a round barrel with little knobs on each side. Commonly found on scanners and WiFi devices. |
| N Female |  |
About 1/2" in diameter with outside threads and female pin hole. Commonly found on 800/900/1200 MHz and higher radios and some amateur radio gear. |
Note: If using the information provided above you are still unable to determine what connector you have on your two-way radio or transmitting device, please refer to the connectors category on the website.
Base Antennas:
Before we get started please remember one important thing: 99.9% of two way radio failure is due to either the antenna being improper or not tuned properly. Your antenna is the most important part of your two way radio system however it is often the most overlooked component.
With regard to antennas the basic rule of thumb is, the taller (or larger) the antenna is, the more db gain it produces. Again, the taller the antenna, the more db gain it will produce. The more db gain, the better the performance (click here for more information on gain).
To calculate what antenna is going to suit you best: take the highest frequency you transmit on and the lowest frequency you transmit on, add those 2 numbers together and then divide the result by 2 to get your “center” frequency. Use this center frequency to select the correct antenna. (NOTE: we are NOT concerned about receive only frequencies.)
Ok, so you know what antenna you need. Now you might ask yourself: “what kind of connector do I have on my antenna”? Here are the most common base antenna connections:
| Connector | Image | Cable Termination |
|---|---|---|
|
SO-239 (UHF Female) |
 |
Your cable would need to be terminated with a PL-259 connector. |
| ‘N’ Female |  |
Your cable would need to be terminated with a ‘N’ Male connector. |
| ‘N’ Male |  |
Your cable would need to be terminated with a ‘N’ Female connector. |
| 7/16 Din Male |  |
Your cable would need to be terminated with a 7/16 Din Female connector. |
| 7/16 Din Female |  |
Your cable would need to be terminated with a 7/16 Din Male connector. |
Ok, that should be enough for you to get started picking out a radio, antenna and mount combination. If you are still unsure of what to look for please feel free to contact us.
*Note: Exception to the “bigger the antenna the better” rule:
In regards to mobile antenna operation, a tall high gain antenna is not necessarily a better choice if you operate in an area with a strong repeater system located on a high mountain or hill top and you operate below it in a valley. In that case a 1/4 wave or “unity” gain antenna may serve you best.
In regards to base antenna operation: if you operate a multi-story hotel or a large outdoor work area, a unity gain antenna would serve you best. They cost less, and they “shower” down a signal better than a high gain antenna. A unity gain base antenna centered at or near the center of your work area would not only give you ample coverage but will also keep your over-the-air conversations from reaching the next town 50 miles away.