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Antenna switching


WRXR255

Question

I have a mobile radio that can do multiple bands, specifically for my needs will be 2 Meter and GMRS.  I also have two mag mount mobile antennas tuned for those bands with PL-259 connector off the radio for the antenna.

Curious if there is a source to buy a ready made switch that would work in a mobile setting that instead of having to pull over and switch the CoAx off the radio from one to the other, I could flip a switch/toggle/lever that could work in a quick and seamless way.

I could build one myself I think, but if there is a source out there already, even better.

Miss the days you could walk into a Radio Shack(tm) and tell the guy you needed a 10 Pico Farad capacitor, and he would find one.  Last time i was ever in one I asked something similar, and he asked if i was needing batteries...

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You want a coax switch. Be sure you get one that is rated up pass the highest frequency you intend to use. Since you're stuck using SO-239 sockets on it you have to be careful to get the right insulator and socket design type.

Most SO-239 sockets for CB radio or HF work may use the crappy red or brown Bakelite insulating material around the center pin. DON'T use those!. These will cause SWR issues.

The better choice is when the material is white. That would typically be Delron or Teflon. While better than the above I would only recommend it for VHF and below.

The best is where the center pin is supported by what looks like a spoked wheel design around the center pin. That gives the interior of the socket mostly air and results in a socket impedance closer to 50 ohms, matching the radio and coax, which will mitigate SWR problems.

https://forums.mygmrs.com/gallery/image/431-coax-switchjpg/

 

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Like @back4more70 I’m using a dual-band antenna that performs excellent on 2M/70CM and good enough on GMRS (Comet SBB-5NMO). This has worked well for me. 

56 minutes ago, WRWE456 said:

It seems like the main issue with dual antennas is if you can keep them separated enough to avoid interaction with each other

I don’t think this would be an issue as you would only have one connected to a radio at a time. I do find the idea of a switch intriguing. Is there much loss through a switch? 

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Wouldn't you prefer a diplexer/duplexer so that there's no manual switch to operate? 2m passes on the low port, and gmrs on the high port?

I've got one in my vehicle, and one on my base mast to switch between 6m, 2m, 70cm. 

Switches are fine too if you prefer a switch. Just throwing it out there.

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It seems like the main issue with dual antennas is if you can keep them separated enough to avoid interaction with each other. I understand that can be a problem. If that is the case a dual band antenna may be a better solution? WRXR255 have you noticed any issues with this in your setup?

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2 hours ago, WRWE456 said:

It seems like the main issue with dual antennas is if you can keep them separated enough to avoid interaction with each other. I understand that can be a problem. If that is the case a dual band antenna may be a better solution? WRXR255 have you noticed any issues with this in your setup?

This is something I have yet to actually attempt yet but was thinking about it last night, as I have just got a new mobile radio to replace one I had with dual band antenna.  That rig was on my last car that got totaled in January taking the rig with it.  So, I was just brainstorming if on the new car a dual antenna setup would be more efficient.  I was also, as I asked the question, thinking the same thing if the two antennas would cause issues with proximity to each other.

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Its pretty common to run a 2m/70cm antenna and a cross repeat radio with no desensing on either band.  Its one radio using the same physical antenna, listening on two bands at once, or transmitting on one band and listening on the other. Using 2 physical antennas wouldn't be much different.

I run a 2m antenna on the rear passenger side, and a gmrs antenna on the rear drive side. They feed into a diplexer (instead of a switch) at the back, then feed into 1 coax going to a single radio. No desensing, interference, coupling, or other issues that I can find on an analyzer or hear in performance.

You will get some desensing on uhf if the frequency separation is <1mhz. I start picking up interference at around 800khz. But the antennas are only 4feet apart.

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For what its worth I use a Alpha Delta switch.  Its a manual switch, there are a couple of different versions depending on frequency.  The version I use is good through 1.3 ghz.   Losses are down in the .1 range.  There is good isolation between in the switch.   They are not cheap, and I got mine through dx engineering.  Best of luck

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3 hours ago, WSAA254 said:

For what its worth I use a Alpha Delta switch.  Its a manual switch, there are a couple of different versions depending on frequency.  The version I use is good through 1.3 ghz.   Losses are down in the .1 range.  There is good isolation between in the switch.   They are not cheap, and I got mine through dx engineering.  Best of luck

I only use Transco switches. No fake specs and extremely low insertion loss.

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11 minutes ago, tcp2525 said:

I only use Transco switches. No fake specs and extremely low insertion loss.

It's not really a switch, but a coax relay. Plus it uses a 28VDC coil voltage. Not something easily available in a motor vehicle. I have a couple of coax relays but they use SMA connectors. Picked these up a long time ago for a project, but never got used.

SMA Coax Relays.jpg

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Fortunately, I have a bunch of these Transco switches. Right now I have two on top of the tower to switch between vertical and horizontal antennas on 2m and 6m. A bit overkill for those two bands, but the price is right and they are reliable. I'm eventually going to do the same for GMRS, switch between a high gain vertical and a stacked set of yagis.

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Hi WRXR255,

I needed an inexpensive coaxial switch for a recent build. My first choice was a Diamond Antenna CX210A from Buy Two Way Radios. Unfortunately, they were out of stock (a common problem with them). So I purchased an Anteenna TW-102:

coaxialswitch-1.thumb.jpg.d02528ad9b6e4f06734c441f98fa8f0d.jpg

Now it is out of stock also. But the blue version (TW-102BLUE) is still in stock.

coaxialswitch-2.thumb.jpg.9063016fdd51d76815f33d99796807d4.jpg

They have SO-239 ins and outs so you can use your existing cables.

As for proximity of antennas, since they won’t be transmitting at the same time, I’ve had good results spacing antennas 1/4 wavelength apart. In this case, use the longer wavelength for your 2-meter frequency (so, roughly 1/2 meter apart).

Kind regards, RGB

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