Scanner & Two-Way Radio on one antenna

[n9upc]

Greetings to all,

Have an installation issue that I am running into at my apt. I have been allowed by my landlord to put up 1 antenna only on the outside of my apt. (It is a big step, trust me.) So I am checking in to see which type of antenna I want to mount outside. I am thinking about a dual band but then I have another issue I am running into.

The apt building I live in is all concrete thus trying to get a signal inside is a chore in or itself (hence getting permission to put up and outside antenna) and I want to run a scanner as well as a two-way radio.

Now I have thought about using an antenna switch but I was looking to see if there was any other device that would allow me to use a scanner and radio coupled into 1 antenna. I have looked on-line at Tessco and found combiners and splitters for running one radio into multi-antennas. But, I need the reverse of 2 radios (scanner & radio in this case) into one antenna.


Any help?

[tvsjr]

Not if you want transmit capability on the radio and general coverage on the scanner. With very specific frequencies in-band or splitting per band (say the radio on VHF and the scanner on 800 via a diplexor), maybe, otherwise no.

Either use an antenna switch, or consider lying. I suspect the landlord doesn't know much about antennas. Either put two fiberglass sticks up and don't tell him they're two separate antennas. Or, show him a picture of a discone (big and ugly), then a fiberglass stick. Offer to run two sticks instead of one discone.

[mike m]

Depends on the tx power, but some type of simple limiter will do the trick if you keep your tx power around 10 watts or less.

I know that the US Coast guard uses these on their copters to protect sensitive receiver front ends: http://cp.literature.agilent.com/litweb ... 2-9295.pdf.

They work very well with 10 watts tx power directly into their avionics receivers.

If you need more power than 10 watts then I'm sure you could get creative and use some notching and bandpass filtering to lower the tx power even further.


Mike
here is a nice article below if you want to build a limiter yourself.
http://www.edn.com/filtered/pdfs/conten ... 486567.pdf

[thebigphish]

Not if you want transmit capability on the radio and general coverage on the scanner. With very specific frequencies in-band or splitting per band (say the radio on VHF and the scanner on 800 via a diplexor), maybe, otherwise no.

Either use an antenna switch, or consider lying. I suspect the landlord doesn't know much about antennas. Either put two fiberglass sticks up and don't tell him they're two separate antennas. Or, show him a picture of a discone (big and ugly), then a fiberglass stick. Offer to run two sticks instead of one discone.

I agree with terry on this one. Use an antenna switch if it really comes down to brass tacks. We're talking about A SCANNER, if it was a mission critical installation, it wouldn't be in your apt, and it wouldn't be on a scanner anyway. If you are going to run one, or the other, which will have priority? That's right, probably the mobile unit. I would say run an antenna relay (a la MTR2000 style with a PTT relay option) which isolates the scanner from the loop when you key down, or run an antenna switch which can be manually thrown. On my mobile unit, when you pick up the mic from the hub, it mutes the RX of the scanner WAY DOWN so that people on the other end of my mic aren't barraged with background audio, only my melodious voice - ha...that can be also modified so that when you unground your mic or keydown or whathaveyou, it cuts out the antenna feed to the scanner, and prevents your big powerful finals from cooking your ratshack scanner. The scanner is for whacker-fackter, and chances are you won't be doing anything THAT important on it, other than listening...if it's important enough to talk about on your channel, it will be on your mobile right?

You have to determine which one takes priority, and in this case...i'd say the mobile.

[wa6jbd]

I've lived in places with similar restrictions. What I've done is install a discone on the roof. That takes care of antenna performance issues across the spectrum of interest. Then, I use a coaxial 4 port transfer relay and a resistive splitter (like you get from Mini-Circuits). The relay is driven via a sequencer, like what the VHF and microwave hams use for their transverters.

What you end up with is this: The discone feeds a splitter, which feeds the scanner, and the transceiver. When you hit the PTT on the transceiver, the sequencer causes the relay to switch first, routing the transceiver directly to the antenna. The splitter get's it's input port terminated into it's transceiver port, effectively isolating the scanner. When that's done, the sequencer then keys the transmitter. Unkeying, the process is reversed. The transmitter unkeys first, then the relay switches.

It's a lot of hardware, but it works, keeps the scanner safe, and allows both radios to receive. Using a discone even takes away any band issues, so the system is more limited to what the radios are capable of.