In band repeater

[pluto1914]

Hi...

We are trying out something different in our Chief's car.

We are looking at doing in band repeating. We have two UHF mobile radios that we are looking at tying together so when something is Rx'd on one radio it is then TX'd on the other and of course vice-versa. I know CES wireless makes a repeater maker http://www.ceswireless.com/Rm_20%20Repeater%20Maker.htm . Would this work? Anyone attempt this before?

Thanks.

David

[kb1nbn]

That would work.. Or an even easier solution, is if you are using something like a Maxtrac or GM300, just build a repeater cable... (or buy a R.I.C.K.)

http://www.batlabs.com/maxrpt.html

[ekoperda]

Don't forget that you are likely to require a duplexer in the vehicle... otherwise the transmitting radio may desensitize the front end of the receiving radio.

The least expensive duplexers are simply fancy notch filters; thus, it's easiest if your repeater has only one transmit frequency and it's known in advance. Your project will grow complicated quickly if there are multiple transmitters on UHF or if frequency agility is required. Is this for some sort of interop application?

[pluto1914]

It is mainly being used as an fireground repeater, permitting fire ground units to remain on a simplex channel while still being tied to the primary. We are setting up the interface to be bidirectional. We are not looking at covering a large area with this setup.

Basically using this as a pyramid repeater.

[motorola_otaku]

Before you can even get into linking two radios together, you need to look at your frequency spacing and whether your primary channel is duplex (i.e. repeated).

The best possible scenario would be if your simplex fireground channel is on 453 MHz and your primary ops channel is on a 460/465 MHz pair, because that would give you 7 MHz of spacing between the 453 TX and 460 receive, and 12 MHz between 465 TX and 453 receive. If the opposite is the case (453/458 pair, 460 simplex) you could still probably do it but you'd need better filters. Basically what you are going to need is a combination of high-pass or low-pass and notch filters on both radios to prevent one radio's TX from de-sensing the other's RX.

Here's how it would work for the first scenario (460/465 pair, 453 simplex):
Radio 1 (Primary Radio)
-High-pass filter that drops off at around 459 or 458 MHz with (ideally) 40 dB or better attenuation below the pass
-Notch filter tuned to your simplex frequency with (again, ideally) 35-40 dB or better attenuation at the target frequency and a notch width of several hundred kHz max.

Radio 2 (Simplex Frequency radio)
-Low-pass filter that drops off above around 454 MHz, same spec as above
-Notch filter tuned to the 465 MHz TX frequency of the primary radio, same spec as above.


This is just something I drew up on a napkin; others who do this stuff on a daily basis can comment on what filters to look for and how much they will cost.. or if they even exist at all with those specs. And bear in mind that any filter is going to incur some insertion loss; you may need to up the gain on your primary radio's antenna to compensate.

If both your repeater pair and simplex frequency are within 1 MHz of each other, forget it.. ain't happening without infrastructure-grade filtering (i.e. big $$$ and lots of space).

[500e]

Midian make a repeater board

http://www.midians.com/html/products.as ... er/Builder.

We have been using both MR, Tait & Simoco mobiles for in Band X band + multi band repeaters, for years