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Determining antenna requirements (fire truck)

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rrnewuser

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Hello,

We have two radios - a Motorola Astro P25 (MHLN6432E) and a Vertex VHF (FTL2011).

So we need two antennas on a new vehicle we are installing these in ... or could we use a single antenna and just sacrifice the ability to transmit simultaneously on both ?

What are some good (small, but high performing) antenna choices for these two radios ? Should I stick with manufacturers accessory items, or are there third party options that would be better ?

Again, we're looking for antennas that will do everything an antenna on a fire engine should do, but hopefully not two meters long...

Thank you.
 

mmckenna

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The Motorola part number you listed is for the control head only, and isn't enough information to tell us what band the radio is. The fact that it is Astro/P25 isn't enough to tell us which band either.

IF the radios are two separate bands, you can use a diplexer to combine them onto one antenna. If they are the same band, you would need two separate antennas unless some very specific requirements were met regarding separation of frequencies.

Ideally you would want to use two separate antennas. Any equipment that combines two radios on to one antenna will result in some signal loss in both directions, transmit and receive. The cost of these sorts of units usually ends up costing more than just installing two antennas anyway. So, the cost savings and the improved performance sort of makes this a choice that only is useful in very limited situations. If there is anyway at all to install two antennas, one for each radio, that would be your ideal choice.

As for who makes the stuff, There is no magic in the antennas, they are all governed by the law of physics, and no manufacturer has figured out a way to cheat this yet. In reality, companies like Motorola don't make their own antennas, they are made by a third party, so unless you really need the brand name, it's cheaper to go with one of the big name antenna manufacturers. Laird, Larsen, Antennex, Etc. Etc. Etc.

The specific antennas you need will depend on the bands you will be using. The Vertex will likely need, at minimum, a quarter wave VHF antenna, which is only 19 inches long (about 1/2 meter). The Motorola will need an antenna, but that will depend on which band it is.
 

12dbsinad

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Ideally you would want to use two separate antennas. Any equipment that combines two radios on to one antenna will result in some signal loss in both directions, transmit and receive. The cost of these sorts of units usually ends up costing more than just installing two antennas anyway. So, the cost savings and the improved performance sort of makes this a choice that only is useful in very limited situations. If there is anyway at all to install two antennas, one for each radio, that would be your ideal choice.
Very good advise here. I second what mmckenna posted. Seperate antennas unless it is not at all possible. You always loose when you combine radios to 1 antenna.

As for who makes the stuff, There is no magic in the antennas, they are all governed by the law of physics, and no manufacturer has figured out a way to cheat this yet. In reality, companies like Motorola don't make their own antennas, they are made by a third party, so unless you really need the brand name, it's cheaper to go with one of the big name antenna manufacturers. Laird, Larsen, Antennex, Etc. Etc. Etc.
One antenna tries to cheat the laws of physics, its called the VHF Phantom. Those things are horrible. UHF and 800 ones work but IMO not nearly as good as quarter waves... but VHF ones are terrible. Very high VSWR thru the narrow bandwidth they offer and as far as performance, mine as well thread on a dummy load.
 
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1/4 wave on top of a fire truck will be all you need. 18-19 inches for that VHF. You didn't specify band for the Moto. UHF, again a 1/4 wave will do it, if it's 700-800mhz, a gain antenna is still under 18 inches.
 

RodStrong

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Assuming you aren't aware, the FTL-2011 is a wideband only radio, and is no longer legal to use to transmit on public safety frequencies. If this makes no sense to you, send me a PM and I'll explain it further. Good luck.
 

cmdrwill

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And you need at least 38" between antennas, or more separation.

One antenna we use: Comtelco A1511A
 

ff-medic

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Put an antenna on for each radio and space as far as possible. If one antenna antenna becomes damaged or broken you still have the other antenna(s) for the other radio(s).

Antennas get bent, broken from accidents, bad weather, flying debris and some other reasons. For Public Safety you do not want to cheat yourself on your communications.

Another thing is that if you do not install antennas properly a back feed will occur and you could damage or destroy the radios electronics. Essentially.... You could potentially fry your radios. My preference is the longer the antenna the better the results. Sometimes length by just a few inches greatly assists transmissions and receiving, which in rural terrain or during bad weather you may need.

It's not about looks : it is about being able to communicate especially when talking on simplex , and radio traffic to EMS and helicopters.


FF - Medic
 

sloop

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I am a member of a volunteer fire department. My advice to you is don't do it yourself! Myself and two others in the department are fully capable of installing both radios and antennas...BUT...we don't! Our department (as well as others in our county) contract radio installation / maintenance out mainly for the warranty and insurance (maintenance as well) that the installers offer in case something goes wrong. It is a lot cheaper than replacing a radio if you have an oops moment. Also I would hate to think that someone was injured because the radio system I installed 'went south' because of something I did or did not do not to mention the possible liability since I am not a 'certified' installer.
 

scannermanner1

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that's interesting because our Fire Department has been using their Motorola radios for well over 5 years & have not had one problem

but do not get me wrong because I am worried about my Yaesu 75watt radio causing front end damage to my scanner with its external antenna!
 

rrnewuser

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Ok, an update to this thread ...

We decided to ditch the vertex because of the wideband issue.

We will now be using a Motorola Astro/P25 radio that runs in the 480 mhz range, and a kenwood TK-790.

So, given the comments above, we will be getting two antennae, and put one on each side of the truck.

Are both of them 1/4 wave, 18" tall ? Anything more specific than that ?

Thanks.
 

mmckenna

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Ok, an update to this thread ...

We decided to ditch the vertex because of the wideband issue.

We will now be using a Motorola Astro/P25 radio that runs in the 480 mhz range, and a kenwood TK-790.

So, given the comments above, we will be getting two antennae, and put one on each side of the truck.

Are both of them 1/4 wave, 18" tall ? Anything more specific than that ?

Thanks.
Radio antennas are a tuned device. They resonate at specific frequencies. Like a tuning fork, they have a natural frequency they operate best at. Same is true with your antennas on top of the fire truck, they need to be a specific length to work properly.

There are some specific formulas that can be used for figuring the length of a quarter wave antenna based on it's intended operating frequency. Those work great on paper, but the exact length depends on the base design, the ground plane, other near by items (lights, speakers, anything conductive), so figuring this out with a calculator or me telling you how long they should be isn't the proper way of doing it.
-I will say that a 1/4 wave antenna for 480MHz is going to be around 5 inches. A 1/4 wave antenna for VHF is going to be around 18 inches.-

This might get you close enough, but close enough isn't a good way to do radios for public safety use. Guessing this isn't a responsible way to go about cutting antennas

If (and only if) you know the -exact- manufacturer and model of the antennas, you can check on the manufacturer website, they'll often have cutting charts that will usually get you close.

If you don't have that information, or you just want to do this right, you need to get the whole truck, with the radios installed, to a radio shop that can either:
1. use an antenna analyzer to properly tune the antennas.
2. at least use an SWR meter to check how well they are radiating the RF.

-or-

You can get a SWR meter that is designed to work on VHF and UHF (one designed for CB isn't going to work right) and you can tune them yourself. Unless you have done this before, it can be a headache. Not impossible, but not a lot of fun if you don't have some exprience.

The good news is that 1/4 wave antennas are quite broad banded, and getting them close (using the cutting charts for the -exact- model antenna) works fairly well.

Not tuning the antennas properly can affect performance and damage the RF amplifier stage of the transmitters. If the antennas are not tuned right, they won't properly radiate the RF energy from the radio. RF energy that cannot be radiated will get reflected back into the radio. The radio will handle a bit of reflected power, but if it's too much, the radio won't. The radio will end up turning that reflected energy into heat, and heat kills electronics. Damaging the RF amp stage of your radio will cause it to fail (-always at the worst possible time-) and the radio won't put out enough power to function properly. Basically you'll end up with a radio that might receive just fine, but won't transmit worth a darn. Repairing this will cost in the hundreds of dollars.

If this was amateur radio or another hobby radio service, I'd say go for it and try it on your own. Since this a fire service and peoples lives may very well depend on your radios working properly, I'd strongly suggest going to a radio shop and getting this done correctly.
 
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ff-medic

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Ok, an update to this thread ...

We decided to ditch the vertex because of the wideband issue.
Price Considerations. Seem like good prices to me :

Vertex Standard


----------------------------------------------------------------------

Vertex VX-2200 VHF 25-Watt Radio [AC061N134-VX] - Amerizon Wireless

-----------------------------------------------------------------------


Vertex VXD-720 Digital Two Way Radio

------------------------------------------------------------------------

◾Mixed Analog and/or Digital Operation by Channel
◾MIL-STD-810) C, D, E & F
◾Narrow and Wide band channel spacing (Analog mode)
◾P25 Digital with IMBE+2tm VOCODER
◾Analog features include CTCSS, DCS, DTMF ANI, 2-Tone (Mulit 2-tone decoding)
◾P25 features include NAC, TGID, Unit ID, Caller ID (LCD versions only)
http://www.vertexhouston.com/p25_portables.htm

-----------------------------------------------------------------------

Vertex Standard VX-7200-G8-45 UHF Mobile Radio, P25 Compatible PSICOMPANY.COM

-----------------------------------------------------------------------

P25 Digital Mode Capabilities:
Expanded Signaling -- Supports selective calling, Talk Group IDs (TGID), Network Access Codes, Individual ID lists and Paging Group lists for flexible communications.

Secure Communications (optional) -- Options available to support both Advanced Encryption Standard (AES) and Data Encryption Standard (DES) as required by APCO Project 25. Additionally, multiple encryption keys can be stored in the radio.

Mixed Mode -- Seamlessly switch between analog to P25 digital mode on each channel based on call type received and on programming for transmit.
http://www.vertexstandard.com/lmr/P25/VX-7200


------------------------------------------------------------------------

Multi-Configurations For Dual-Band CapabilityOne VX-6000 Control Head and two RF Decks on different bands may be networked for dual-band operation. Low Band, VHF or UHF radios may be combined to meet complex communications requirements for multi-agency operations.
Large Channel Capacity For Greater ReachFeatures 250 channel capacity and the ability to program up to 20 memory groups with no limit on the number of channels in each group.
http://www.vertexstandard.com/lmr/Mobiles/VX-6000


Vertex offers a three year warranty.

Vertex is very competitive, and their prices are hard to pass by. IF you do your research and / or know where to shop......you will find some really good prices.


We will now be using a Motorola Astro/P25 radio that runs in the 480 mhz range, and a kenwood TK-790..
Trust me on this. Things are much simpler if you keep to one radio brand - what ever brand you pick. Maintenance, parts, monetary deals and price cuts, and overall dealer satisfaction...and ease of the dealer maintenance and parts ordering.....will be much better.

So, given the comments above, we will be getting two antennae, and put one on each side of the truck.

Are both of them 1/4 wave, 18" tall ? Anything more specific than that ?

Thanks.
Nope. Good deal. One radio = One antenna.

Feel free to review the specifications = Land Mobile Radio | Vertex Standard

Vertex = Rugged - Multi tasking - Very comparable in price and quality with other radio manufacturers. Vertex is my favorite brand of Public Safety Land Mobile Radio.

I have experience with Motorola , Kenwood , Vertex and Bendix King.

Kenwood with volunteer fire service. Motorola at work and in the military. Bendix King with the volunteer fire service and the military. And Vertex ( I personally bought this radio ) with the volunteer fire service, and paid EMS.

I would take a Vertex radio any day of the week.

FF - Medic !!!
 
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ff-medic

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Radio antennas are a tuned device.

VHF/UHF 1/2 Wave Antenna (VHF 144-174Mhz / UHF 450-470) [VHF-UHF-1/2W] - $48.00 : Rugged Radios: Headsets, Intercoms, 2-Way Racing Radios and Communication for Motorcycles, Offroad, Circle Track, Drag Racing, NASCAR, Police, and more...

Amazon.com: Browning BR-PT450 UHF Pre-Tuned Land Mobile Antenna: Electronics

Sears.com


You can get a "Pre-tuned " antenna, it is no big deal. They make them every day.

But after you install the antennas, every once and awhile, wipe them down and keep them clean. Keep the grime off of them as much as possible. In the winter time, and early spring , try not to let the ice build up on them while on a call , so you do not damage or ruin the radio.

FF - Medic !!!
 
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