Amplifier band specifications

[Pele]

I maintain a radio system that includes multiple above ground simulcast transmitting sites, as well as an extensive underground distributed antenna system. It is a trunked system that runs in the 490 MHz UHF commercial band. We have several channels Above and below 495 MHz.

Our above ground system uses Motorola Quantar base stations. I notice that there is a different part number for the Power Amplifiers, Exciters, and Receivers dependent of if they are a Range 3 or a Range 4 unit. The cutoff for Range 3 and range 4 is around 495 MHz. This complicates things since we have to stock multiple types of parts.


Additionally, in the underground distributed antenna system, we have Bi-Directional Amplifiers. They are manufactured by several different manufacturers including Allen Telecomm (Defunct), Decibel (Defunct), Kaval (Defunct), PowerWave, Sinclair, and Andrew... (Hodgepodge of parts, dependent on age and/or replacement date.)

I've noticed that these too have a separate amplifier for high and low range. They use diplexers and filters to route the correct frequencies to the correct amplifier.

Is there a significance to 495 MHz? Why is all the active RF equipment divided at this point?
Is it possible to get an amplifier that will do between 488-502 MHz in one package?

Trying to reduce points of failure here.

 

[code3cowboy]

Have you looked into EMR Corp products? I believe they have some BDAs that serve the T Band. You may also want to look at Minecom.

If you are talking about the system I think you are, I once spent a day just riding along enjoying the sights and listening in with a scanner. The coverage was impressive.

 

[Pele]

^

Hopefully you were just visiting, because this is HARDLY paradise.

 

[W2NJS]

I think you'd have a much better chance of receiving a competent reply to your questions if you were to pose them at
http://batboard.batlabs.com.

 

[ChartofVirginia]

Pele,


To answer your main question, just as in Microwave there are very minute tolerances with frequencies this high in operation. Microstrip layouts for inductance and mostly SMD components allow for reliable operation but call for tighter bandwidth ranges so performance of the devices is maintanined.

With these tolerances means a change to the tuned circuit and also means new ranges of component values. 488-495 may be 44-68pF where 495-512 is 58-77pF and so on with the performance of the equipment in mind.

That Quantar PA ranges 3 and 4, is reliable as it was designed to operate within set limits given and it will do this under continuous duty with the stability needed to perform to FCC spec's and your requirements without failing.

Unlike subscribers, most infrastructure equipment is designed to a higher standard leaving little room for degredation in performance unlike a mobile or portable where 10% or even 20% is to some manufacturer's acceptable.

To go in the other direction there are devices out that can do what you ask, just make sure you have accurate equipment and the required bench tools to do an alignment on the PA when the frequencys change as these too operate on their specific frequency range only. So for 488 you will need to retune the PA, for 496 you need to retune and so on. That can make for a dissapointing moment when someone forgets to retune or uses the wrong bandspilt and cannot get the performance expected out of the PA until retuned.

Oh, not recommended to retune these in the field, but sometimes it will work.

CoV

 

[radiofan1]

www.TxRx.com