Batboard

Hello Everyone,

I'm working on a system design and I am hoping to get some holes in my knowledge filled in. This is my first radio system design and I'm having trouble finding some information that may be common knowledge, so please forgive the perhaps obvious questions.

The radio system is for Operations and Maintenence (O&M) for a small light rail line. My first step is to specify the frequencies desired for my radio system so that the FCC application can be filed. The O&M radio needs to only be half-duplex. Another team is working on the train to base communications.

I'm going to ask for 2 channels, a total 4 frequencies. I will ask for frequencies in the same range as the Vehicle team. One channel will be used for Ops and the other for Maint. I plan on specifying the Motorola CDM1250 Mobile and the HT1250 Portable and the Orbacom (IPC) TDM-150. These radios are analog FM radios and should work together, correct?

I'm noticing on the HT1250 and CDM1250 radios a variable channel spacing of 12.5/20/25 kHz. This is the distance between carriers correct? What bandwidth is each channel?

Thank you all for your help,
Brad

You said it is a "light rail" system so I assume it operated by a local government transit authority or is it privately owned? If government do you plan to license in the Public Safety service or Business?

What frequency band UHF or 800? New UHF systems should be licensed for "narrow band" 12.5 KHz channel spacing 11K2F3E emission.

Since you seem totally unfamiliar with the licensing process, it may be worthwhile to pay the extra fees for the Frequency Coordinator to assist with the application preparation or for you to work through a licensing consultant.

You mention the mobiles and half duplex operation but do you plan to use a repeater or use half duplex for mobile to base with simplex mobile to mobile talk-around?

Hi K2Hz,

thank you very much for the reply,

the system will be run by a local transit authority and should be licensed as Public Safety... I know down the road we must submit an FCC 601 form, and this info should be included, I'm guessing. We are very early in the project but I've heard that a frequency coordinator will be consulted.

This system will be in UHF, around 450 Mhz. I'll look into the narrow band 12.5 kHz spacing and 11k2f3e emission requirements.

mobiles and half duplex operation but do you plan to use a repeater or use half duplex for mobile to base with simplex mobile to mobile talk-around?

I'm a little hazy on the differences between the configs you mention above. Will the repeter configuration disallow the simplex talk around? What are the pros and cons.

I'm really lacking some practical information on trunking radio design etc. Do you have any recommended reading?

Many thanks!

I am not sure I understand what you have in mind. Now you mention trunking? That would change everything and greatly increase the complexity, not to mention equipment expense, if you want trunked rather than conventional.

My question about what you had in mind with "half duplex", which implies a base on one side of a frequency pair and the mobiles on the other, is whether mobile to mobile communication would be via the base operating as a repeater or mobile to mobile would involve switching to simplex on the base TX frequency. If there is a repeater involved then normal mobile to mobile communication would be via the repeater with switching to simplex talkaround an option for the users for short range communication.

The FCC filing must be done through an authorized Frequecy Coordinator and the engineering detail required to prepare the application yourself is substantial if you are not very familiar with the process. Errors or an incomplete application can result in a lot of wasted effort and money and delay to the project.

If your equipment vendor can not help with this process, I think you are going to need a consultant.