How quickly can an antenna be switched?

[prcguy]

A circulator can give about 35dB of isolation and in a marine radar there is always a limiter of some kind in front of the receiver to reflect or absorb the left over transmit power so it doesn't damage the receiver. PIN diodes can be used up to a certain power level as a very fast T/R switch but you need a high voltage like -100v or more to bias the diodes in a high power environment.

A semiconductor switch works at nearly the speed of light - the delay comes from the actuating circuit. I don't know what you are doing bit maybe a circulator might be an alternative, depending on what you're doing?

Think about radar - Kilo/MEGAWatt power going out as a pulse, isolated from the receiver expecting microVolts back! Pulse repetition can vary a lot, but the receiver needs to be activated immediately the pulse has gone out, and minimum range for some radars is a few miles - that's a very short time!

 

[Camerart]

It probably is, but I don't think we're completely understanding your scenario.

How is this different from a repeater?
How will this be utilized?
Is this voice or data?
VHF/UHF or HF?

Hi M,
It's interesting, when on these forums, that one persons clarity is another persons mystery! I am also working on a project, where this happens in reverse, so I can't understand the replies that have been kindly sent to me.

My radio club has a net where we talk over FM a couple of time/week.
Some of the net can't hear others.
My idea is to hopefully, relay messages live between deaf members, using another member's radio.

From what I understand a repeater, is quite an elaborate set-up, where RX is separated from TX by cavities, and much more than I am thinking of.

Is this clearer?
C

 

[mmckenna]

Is this clearer?
C

Yep, that helps.
So, it'll be a person at the radio handling the traffic?
-Listen to traffic from net, verbally repeat for the other station? Sort of like a simplex repeater. Gets annoying for others in range to hear traffic repeated twice, but if it's what you have to do…. You can get simplex repeater boxes that will handle the work for you. T-R switching times are not an issue.

If you were doing DMR, the single frequency repeat will do the same thing:
RX packet on slot 1, immediately TX same packet on slot 2. The DMR radios will handle this rapid rx/tx cycling.

Another option:
You can bypass some of the hardware if you do a cross band repeat:
Radio listens to the net on VHF, retransmits simultaneously on UHF. No duplexers needed.

 

[Camerart]

Yep, that helps.
So, it'll be a person at the radio handling the traffic?
-Listen to traffic from net, verbally repeat for the other station? Sort of like a simplex repeater. Gets annoying for others in range to hear traffic repeated twice, but if it's what you have to do…. You can get simplex repeater boxes that will handle the work for you. T-R switching times are not an issue.

If you were doing DMR, the single frequency repeat will do the same thing:
RX packet on slot 1, immediately TX same packet on slot 2. The DMR radios will handle this rapid rx/tx cycling.

Another option:
You can bypass some of the hardware if you do a cross band repeat:
Radio listens to the net on VHF, retransmits simultaneously on UHF. No duplexers needed.

Hi M,
Ah, good!

As many of the 'old codgers' (me included ) are settled with radios of their choice, I think DMR and cross band repeat, also repeating traffic a second time are not options. Actually, we have a Net controller who does repeat messages if necessary.

This idea is to switch between TX and RX instantly at perhaps 20KHz, so all traffic is immediate. I imagine an acurately timed box, connected to 2x radios, and 1x antenna.
If this is possible in physics, then we all will be doing this in parallel.

I can guess, that this isn't possible, but if it is, then it would be great.

EDIT: I looked up DMR repeat. This looks similar, but if it uses a repeater, then it is not an option.
C

 

[mmckenna]

I can guess, that this isn't possible, but if it is, then it would be great.

It's possible, but not as easy as you think. T-R switching times are not likely what's going to hold you back on this. The choppy audio would sound pretty awful. What you are talking about is sort of a Time Domain Multiple Access. Doing that on analog is going to be hard to impossible to get it to work right. Doing it on digital is possible, but that's what DMR is.

EDIT: I looked up DMR repeat. This looks similar, but if it uses a repeater, then it is not an option.
C

With the right radio, it's not a repeater like you are thinking. It listens to traffic on one timeslot and the when the next time slot comes up, it resends those packets. A 'repeater' of sorts, but not like what you are thinking. No duplexers to tune, just one radio, one antenna, and the radio does all the work.
But it requires everyone to be using DMR. By the time you buy all those new DMR radios, you could probably put up a repeater of your own, or buy the guys that cannot hear the net a better antenna.

 

[Camerart]

It's possible, but not as easy as you think. T-R switching times are not likely what's going to hold you back on this. The choppy audio would sound pretty awful. What you are talking about is sort of a Time Domain Multiple Access. Doing that on analog is going to be hard to impossible to get it to work right. Doing it on digital is possible, but that's what DMR is.



With the right radio, it's not a repeater like you are thinking. It listens to traffic on one timeslot and the when the next time slot comes up, it resends those packets. A 'repeater' of sorts, but not like what you are thinking. No duplexers to tune, just one radio, one antenna, and the radio does all the work.
But it requires everyone to be using DMR. By the time you buy all those new DMR radios, you could probably put up a repeater of your own, or buy the guys that cannot hear the net a better antenna.

Hi M,
Re DMR: Ok, I'll look closer at the DMR system if all else fails.

Re Idea: I don't imagine it will be easy, or we would be using it now.
As for choppy!, strereo isn't choppy, so using this speed also won't be. Instead of RIGHT/SWITCH/LEFT etc, it would be TX/SWITCH/RX etc.
C.

 

[mmckenna]

Re Idea: I don't imagine it will be easy, or we would be using it now.
As for choppy!, strereo isn't choppy, so using this speed also won't be. Instead of RIGHT/SWITCH/LEFT etc, it would be TX/SWITCH/RX etc.
C.

Stereo broadcasts use separate subcarriers to transmit multiple audio paths at the same time. It's still just one RF signal with 2 or more audio paths on it.
That's not going to work for what you want, not in analog.

TX/SWITCH/RX etc.
So, doing that at 20KHz may be possible with the right stuff, but you create an issue where when the radio is transmitting, it won't hear the other incoming signal. Chopping up audio at 20KHz in an analog radio is going to impact it. The way it works on DMR single frequency repeat is to receive the DMR packet that has compressed the audio and retransmit it on the other slot. Since the DMR radios are only looking at one slot at a time this works. It's designed to take an analog audio signal and compress it down into a digital packet that can be transmitted faster than the compression ratio. That's what TDMA is. We do it at work with PRI phone trunks. We take 23 voice paths and slice it up so fast that it won't impact the audio, and then transmit that to the carrier. When it gets to the far end, the digital packet is unpacked and converted back into an analog signal. Works well and sounds just like a standard analog phone call.

Cross band repeat, either automatic, or controlled by the radio operator would do this. You could take the received audio send some to your speaker for you to hear and some to a radio on a different band to be retransmitted to the guy out of range of the net control. Essentially it's a repeater, but using VHF on one side and UHF on the other, there can be enough frequency separation that duplexers are not required. many modern ham dual band radios will do this. If you want to build your own system, it's totally do-able. You can get small mobile repeater boxes that you can interface to your radio. No switching necessary.

 

[FKimble]

Another thing, when the ant is in RX position, your TX is now pushing RF into a ground connection. Also you will not be doing a 50/50 split between RX and TX. There must be a safety margin, so maybe TX 40 on, 10 off, RX 40 on, 10 off. The deaf guys may be able to hear but I can't see it sounding good.

Frank

 

[popnokick]

DMR performs Tx-Rx switching between Time Slot (TS) 1 and TS2 every 30ms. This is part of the native DMR protocol and every compliant radio does it. So as mmckenna points out, very capable of high speed switching.

 

[k7ng]

How about a mesh network?

 

[Camerart]

Another thing, when the ant is in RX position, your TX is now pushing RF into a ground connection. Also you will not be doing a 50/50 split between RX and TX. There must be a safety margin, so maybe TX 40 on, 10 off, RX 40 on, 10 off. The deaf guys may be able to hear but I can't see it sounding good.

Frank

Hi F, Ok on the not 50/50.

I doubt the TX would be to ground, but more like a dummy load type 'thing'

If it doesn't sound good, then this won't work for many of my 1/2 deaf net friend.
C

 

[Camerart]

DMR performs Tx-Rx switching between Time Slot (TS) 1 and TS2 every 30ms. This is part of the native DMR protocol and every compliant radio does it. So as mmckenna points out, very capable of high speed switching.

Hi P,
This only will work if all of us can keep the same radios, so if DMR needs either a DMR radio, or a repeater, then then it won't suit.
C

 

[Camerart]

How about a mesh network?

Hi K,
I'm not sure what a mesh network is but as it sounds like my comment of like the internet, but no comuter, then perhaps this is what it could be called.
C

 

[tweiss3]

Is this FM simplex, or is this net going on over a repeater? Also, is it the same net control every time, or does it have a rotation?

Sounds like you really need to get either a second repeater, or have net control get their antenna up much higher.

 

[Camerart]

Is this FM simplex, or is this net going on over a repeater? Also, is it the same net control every time, or does it have a rotation?

Sounds like you really need to get either a second repeater, or have net control get their antenna up much higher.

Hi T,
It is simplex. No repeaters.

This doesn't need a net contoller, only more than two operators, each with two radios and one antenna, where two of them can't hear each other.

All the radios will be the same.
C.

 

[tweiss3]

Simplex, yes I remember that was an interesting exercise when we tried that once. There is a lot of relaying.

As for net controller, I was referring to the person running the net, not a piece of equipment. Is it always the same person/location, or does it change from week to week?

What are the radios? Is this UHF or VHF?

I like your thinking, but I have a feeling that you are going to hit de-sensitization in one or both of the radios, or get a picket fence effect that will drive some nuts.

I think we can help come up with a solution, but we do need more information. DMR Single Frequency Repeater is a viable option if you are willing to go digital, but cross band repeat would also work well for analog, and would reduce some of the side effects that might plague those that can already hear your net control operator.

 

[ramal121]

Simplex analog? No. There is no easy way to do this. If you are switching TX and RX, when transmit is up there will be no receive to pass audio to. When receive is live the transmitter is switched to a dummy load. How is that going to work? Even if you hook up two radios to two antennas the instant it is triggered it will go into RF feedback on simplex and you're hosed.

Using DMR or some type of digital scheme you can employ what's called store and forward. Kind of like a packet digipeater. But that requires digital all the way through.

The only easy way to do this is a cross band repeat set up somewhere in the middle and divide locations by band. I would think most hams would buy at least a dual bander and have the capability already.

 

[Camerart]

Simplex, yes I remember that was an interesting exercise when we tried that once. There is a lot of relaying.

As for net controller, I was referring to the person running the net, not a piece of equipment. Is it always the same person/location, or does it change from week to week?

What are the radios? Is this UHF or VHF?

I like your thinking, but I have a feeling that you are going to hit de-sensitization in one or both of the radios, or get a picket fence effect that will drive some nuts.

I think we can help come up with a solution, but we do need more information. DMR Single Frequency Repeater is a viable option if you are willing to go digital, but cross band repeat would also work well for analog, and would reduce some of the side effects that might plague those that can already hear your net control operator.

Hi T,
No net controller person. This morning it was three of us chatting, passing it on as we finished.

At the moment FM.

I don't know what 'picket fence affect is. If I guess d-d-d-d-d-d-d, then it is switcing too slowly, I'm talking about above hearing frequency.

No DMR repeatewr or a change to our radios, one of us is 100, so I don't see him buying another radio
C

 

[Camerart]

Simplex analog? No. There is no easy way to do this. If you are switching TX and RX, when transmit is up there will be no receive to pass audio to. When receive is live the transmitter is switched to a dummy load. How is that going to work? Even if you hook up two radios to two antennas the instant it is triggered it will go into RF feedback on simplex and you're hosed.

Using DMR or some type of digital scheme you can employ what's called store and forward. Kind of like a packet digipeater. But that requires digital all the way through.

The only easy way to do this is a cross band repeat set up somewhere in the middle and divide locations by band. I would think most hams would buy at least a dual bander and have the capability already.

Hi R,
No DMR, no cross band!

C.

 

[Camerart]

Hi all,
I've just had a thought !

When transmitting, then on the switcher will be only switched to transmision, on this radio.

When receiving, in order to relay, it will need to capture, a 50% section of the received voice, then transmit it in 50% time, then back to receive.

Less than 50% of the voice relayed isn't perhaps good enough.
C.