Diplexer and splitter

[Driverj30t9]

Anyone know of a good quality diplexer and also a splitter for a transmitting radio and two scanners? 50 ohm impedence with high isolation that covers 20mhz to 2 ghz for recieving at least?

Want to get both a diplexer and a splitter so I have more options and just to try them. With a splitter I can listen to just one radio at a time at least if I choose to.

If there rated for say 20mhz to 1000mhz is that rating just for transmitting, or both transmitting and receiving?

 

[AK9R]

What frequency is the transmitter operating on? In order to effectively block the transmitter from injecting high levels of RF into the scanners, the filter that blocks the transmitter will need to be tuned to a specific frequency or a narrow range of frequencies.

 

[jonwienke]

Your best bet is to have separate antennas for the scanner(s) and transmitter. If you use a diplexer, the scanners will be unable to hear anything in the transmitter band. Separate antennas will (if sufficiently separated) allow the scanners to monitor every band covered by the antenna, including the one used by the transmitter.

 

[Driverj30t9]

I would be transmitting on 27MHz, but when I get my technicians license I'd like to be able to transmit on the allowed bands for said license also. Or at least some of them. Seems like it would be pretty tricky to do CW while driving. If you can even put up big enough antennas for those lower bands while mobile.

How do I go about tuning the filters?

Also how can I protect the scanner front ends from the transmitting antennas?

Yeah, installing some extra antennas for the scanners is an option. I want to install this setup on my semi-truck though, just not sure where I would install the scanner antenna/s. Maybe on the front of the hood, but that would might reduce what they could pick up with a big trailer behind me. Higher would be better but not sure where I could install them.

Or I could use a diplexer and a scanning cb radio or ham radio when I get my license, I like the radios that scan better because it's the best of both worlds and I don't miss transmissions on other channels that way.

Any recommendations on antennas for this type of setup?

 

[mmckenna]

I would be transmitting on 27MHz, but when I get my technicians license I'd like to be able to transmit on the allowed bands for said license also. Or at least some of them. Seems like it would be pretty tricky to do CW while driving. If you can even put up big enough antennas for those lower bands while mobile.

You are better off with separate antennas. The diplexers/triplexers, etc. are not fine enough to just slice out the amateur spectrum and leave the rest for your scanner. The amateur grade diplexers are pretty broad, so you'd end up with a scanner that was pretty deaf anywhere near amateur bands.

Install a dedicated scanner antenna for your scanner(s).
Install dedicated antennas for your transceivers.

How do I go about tuning the filters?

To do it right? Expensive test equipment.

Also how can I protect the scanner front ends from the transmitting antennas?

Separate antennas with as much space between the scanner antenna and the transmitting antennas as you can get.

Yeah, installing some extra antennas for the scanners is an option. I want to install this setup on my semi-truck though, just not sure where I would install the scanner antenna/s. Maybe on the front of the hood, but that would might reduce what they could pick up with a big trailer behind me. Higher would be better but not sure where I could install them.

It's really the better way to do it. Dedicated antennas will work better than trying to force a bunch of equipment to share one.

Where you end up mounting your antennas will depend on a number of factors. To make any sort of sensible suggestion would require knowing what frequencies, what power levels, how many antennas, what else is on the roof, what your skill level is, what your budget is, how comfortable you are drilling holes, etc…..

Or I could use a diplexer and a scanning cb radio or ham radio when I get my license, I like the radios that scan better because it's the best of both worlds and I don't miss transmissions on other channels that way.

Uniden does make a CB with a built in scanner, but it's sort of a limited scanner. You'd still need two separate antennas, though, one for CB, one for the scanner, and don't forget about the GPS receiver in it.

Any recommendations on antennas for this type of setup?

Depends entirely on what radios you are running, what frequencies you want to use, etc.

Larsen NMO-150-450-800 is a good choice for an all around scanner antenna, but it doesn't perform on VHF low band, which you might want.

For CB, it's hard to beat a half wave/no-ground-plane antenna(s) on the mirrors.

For your amateur radio stuff, it entirely depends on what bands you want to use.

 

[cmdrwill]

Quote:
Originally Posted by Driverj30t9
Also how can I protect the scanner front ends from the transmitting antennas?

mmckenna
"Separate antennas with as much space between the scanner antenna and the transmitting antennas as you can get. "

I also will suggest one of the RF limiter devises to protect the poor scanner's frontend.

You will not have enough space on a car or semi to get good isolation.

 

[Driverj30t9]

That's to bad. It would look cool to having a diplexer and splitter mounted to the dash, but what gives the best performance is more important.

So I guess people must use a diplexer or splitter more for transcievers wirh dedicated frequencies that are far away from each other on the radio spectrum.

Uniden does, good to know, I know at least one model of cobra is a scanning cb too.

I will take a look at RF limiters.

Well I"ll have to figure out how to set everything up then with an extra antenna for the scanners.

Do you know if using one antenna for two or more radios radios reduces the signal strength that each radio receives?

If I get the scanner antenna installed it will be interesting to see how well it picks up 27 mhz, I've only picked up a transmission once on 27mhz when using the rubber duckies or my telescoping antennas.

 

[jonwienke]

Before you spend money on a limiter, get or borrow a watt meter and dummy load. Connect the dummy load to the output side of the meter. Connect the scanner antenna lead to the input side. Then key up each transmitter on a range of frequencies to see exactly how much RF would be hitting the scanner.

I've hit my 436 with 500mW with no damage, but you should probably keep things under 250mW to be safe. If the needle doesn't move at the meter's lowest power setting, then you have nothing to worry about.

 

[Driverj30t9]

Wow, doesn't sound like it takes a lot of wattage to do damage.

Sounds like a good time. I"ll give it a try.

 

[jonwienke]

With a 25W radio and antennas about 3 feet apart, I get about 500mW of RF into the scanner antenna on some VHF frequencies, but it's mostly around 250mW. That hasn't damaged my 436, but it's an awful lot of signal to dump on something designed to handle microvolt-level signals. On UHF and CB, the meter needle barely moves. The amount of RF coupling depends heavily on each antenna and the distance between them. Antennas tuned to different bands will have less RF coupling than ones tuned to the same band. The best thing to do is test before you key up with the scanner connected.

 

[mmckenna]

Do you know if using one antenna for two or more radios radios reduces the signal strength that each radio receives?

Yes.
When splitting one antenna to two radios, if the signal hitting the antenna is strong, you likely won't notice. On weaker signals, you might have more of an issue.
You can overcome that loss by using a preamplifier, but that will also increase the signal strength of things you may not want, like the other transceivers.

How many scanners are you going to install?

If I get the scanner antenna installed it will be interesting to see how well it picks up 27 mhz, I've only picked up a transmission once on 27mhz when using the rubber duckies or my telescoping antennas.

The physically shorter antennas are going to be very poor performers on CB, so it's not surprising that was your experience.
To receive CB well on a scanner, you really need to look for an antenna that is designed for CB, although that can often hamper other bands.

 

[Driverj30t9]

Doesn't sound like it will be to many mW on my cb then but your right that would be good practice to test everytime anyways.

I have a pre-amp but it doesn't have the right connector, can always get more or maybe an adapter will work.

I plan on running two scanners for now. Kinda surprising how much I was missing with just one.

Yep, makes me wonder what I'm missing on the lower bands. My scanners only start at 20mhz.

 

[Driverj30t9]

I guess it's like shortwave radio, cw and digital modes and skip. Never hear anyone talking skip. Still have much to learn.

 

[wrath]

Yes.
When splitting one antenna to two radios, if the signal hitting the antenna is strong, you likely won't notice. On weaker signals, you might have more of an issue.
You can overcome that loss by using a preamplifier, but that will also increase the signal strength of things you may not want, like the other transceivers.

How many scanners are you going to install?



The physically shorter antennas are going to be very poor performers on CB, so it's not surprising that was your experience.
To receive CB well on a scanner, you really need to look for an antenna that is designed for CB, although that can often hamper other bands.

Buy an old CHP car take the 102" whip and ball sell the car and shazam CB antenna for your scanner ,in the good old days you could hit radio shack at the mall(malls and radio shacks are what happened before the internet).

Sent from my SM-T810 using Tapatalk

 

[mmckenna]

Buy an old CHP car take the 102" whip and ball sell the car and shazam CB antenna for your scanner ,in the good old days you could hit radio shack at the mall(malls and radio shacks are what happened before the internet).

The CHP hasn't used those antennas in a long time. They switched to base loaded whips mounted in the center of the roof.
They were also tuned for the 42MHz range, so a bit short for CB.

Great antennas, though. I've got an old 102" whip sitting up in the rafters in my garage, just can't stand the thought of tossing it. When I use CB (rarely) I prefer the Larsen NMO-27 base loaded whips. I'm sort of hanging on to it just in case I ever decide to mess around on 10 meters.

 

[Driverj30t9]

I was thinking of maybe putting 102" whips on there. How do I know if the mount I get will be sturdy enough?

Buy an old CHP car take the 102" whip and ball sell the car and shazam CB antenna for your scanner ,in the good old days you could hit radio shack at the mall(malls and radio shacks are what happened before the internet).

I"ll just order another workman 102" whip. Much easier. We had a radio shack up until about two years ago at our mall. There gone now though. I guess not a huge loss because I get all my stuff online anyways.

Don't have a real good understanding of impedence and radiation resistance and all that yet, but I hope to get the antennas resonant on 10m, 11m, and 2m.