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KL7AJ
11-13-2008, 06:23 PM
Independent Sideband has great possibliities for amateur radio. Back in the 1970s there was some flirtation with the technique (see May, 1977 QST) but it never really caught on. The main application was with SSTV...you could send your photos on upper sideband and audio on lower sideband. It was actually quite a lot of work to set this up...but with new DSP techniques it should be a snap.

But I see something even cooler about ISB. With a very well aligned system, you could run FULL DUPLEX SSB on HF. (Maritime radio has used full duplex H.F. for years, but with widely separated channels. With a good ISB system, ou could talk and listen at the same time on the same "carrier" frequency...one direction on usb and the other on lsb. With a high isolation hybrid or circulator, you could even use the same antenna. I think this is something worth experimenting with.

Eric

K4KYV
11-13-2008, 06:29 PM
Armed Forces Radio and VOA used to run feeder links to their overseas stations using HF ISB. They could be heard on odd frequencies outside the regular shortwave broadcast bands. You could hear one program on USB and another on LSB. This was before the days of long distance transmission by satellite.

KL7AJ
11-13-2008, 06:39 PM
Armed Forces Radio and VOA used to run feeder links to their overseas stations using HF ISB. They could be heard on odd frequencies outside the regular shortwave broadcast bands. You could hear one program on USB and another on LSB. This was before the days of long distance transmission by satellite.

MOTHER is the necessity of invention. :)

eric

KE4YGS
11-13-2008, 06:49 PM
Maybe it isn't necessary but I can envision the need for a timing chain somewhere for both sets to lock onto for really accurate signal processing. Maybe transmitted by the TX terminal and the Rx terminal locks its PLL, ref osc or its LO to it and vice versa so there is no freq disparity. Maybe I'm a victim of the modern age. I seem to remember some Navy testing circa. 1968-9 where they tried USB for voice and LSB for TTY. I think the intent was the same as a primitive orderwire on Satellite Links. Raven Electronics was working with the Navy on it. Was a dismal failure as I remember. I can think of several ways to make it work but they all involve dollars in fairly significant quantity compared to the cost of the radio. Voice of course, as in full duplex voice would be much less touchy.

Scotty

KL7AJ
11-13-2008, 06:54 PM
Maybe it isn't necessary but I can envision the need for a timing chain somewhere for both sets to lock onto for really accurate signal processing. Maybe transmitted by the TX terminal and the Rx terminal locks its PLL, ref osc or its LO to it and vice versa so there is no freq disparity. Maybe I'm a victim of the modern age.

Scotty


In an ISB transmitter, you use the same generator...they WILL be locked.

eric

K7JEM
11-13-2008, 07:53 PM
But I see something even cooler about ISB. With a very well aligned system, you could run FULL DUPLEX SSB on HF. (Maritime radio has used full duplex H.F. for years, but with widely separated channels. With a good ISB system, ou could talk and listen at the same time on the same "carrier" frequency...one direction on usb and the other on lsb. With a high isolation hybrid or circulator, you could even use the same antenna. I think this is something worth experimenting with.

Eric

I don't think that would work. You still have a strong transmitted signal very near the RX signal. This would cause extreme overload to the RX side. A hybrid or circulator just isn't going to be enough. Even opposite sideband suppression would have to be immense, generally it is only about 50dB. Even 100dB wouldn't be enough.

Joe

K8ERV
11-13-2008, 08:39 PM
I was associated with a 10kw Collins xmitter on Eniwetok. The two sidebands carried separate (multiplexed) RTTY channels. Why not?

TOM K8ERV Montrose Colo

KB2VXA
11-13-2008, 09:46 PM
Hmmm, sounds like the Kahn mono compatible AM stereo system. I know where there's an exciter siting in a rack just waiting to be re tuned for 160M and fed into a 1KW transmitter already there but alas, that'll never happen.

N2RJ
11-13-2008, 09:48 PM
I don't think that would work. You still have a strong transmitted signal very near the RX signal. This would cause extreme overload to the RX side. A hybrid or circulator just isn't going to be enough. Even opposite sideband suppression would have to be immense, generally it is only about 50dB. Even 100dB wouldn't be enough.

Joe

I think it could be done with modern digital signal processing.

KL7AJ
11-13-2008, 10:01 PM
Hmmm, sounds like the Kahn mono compatible AM stereo system. I know where there's an exciter siting in a rack just waiting to be re tuned for 160M and fed into a 1KW transmitter already there but alas, that'll never happen.

Funny you should mention that. I talked to Leonard Kahn once, about 20 years ago. He was a cranky eccentric back then, and I guess he's still going strong. He made some fine equipment though. We had a Symmetra-Peak on our FM station for ages....it did exactly what it was supposed to.

eric

W5HTW
11-14-2008, 12:17 AM
Want to experiment with it? Easy! Put two identical SSB transceivers side by side. Separate antennas. 100 watts output. Same carrier frequency, say 7250.000 khz. Put one on USB and one on LSB. You now have ISB.

Ok, transmit on the USB rig. How much can you hear on the LSB rig at the same time?

I spent a lot of time with ISB with the government. MUX, (AFSK multiplex) Not much use for it in amateur radio, though your suggestion of voice on one sideband and sstv on the other might be workable. Possibly a problem with bandwidth restrictions.

Ed

K7KBN
11-14-2008, 03:56 AM
We used to come up with KMI in Oakland CA from my ship (USN) when we were at anchor in places like Hong Kong. We used ISB with a WRT-2 transmitter/R-390 receiver and full duplex. The antennas were maybe 700 feet apart, if that. At 1KW from the WRT-2, there was not even a hint of cross-sideband interference. Talked home quite a few times.

KI4NGN
11-14-2008, 10:45 AM
I agree with some here that it wouldn't work.

It's one thing to discuss transmitting one piece of information in one sideband and another piece of information in the other sideband simultaneously, but it's altogether very different to discuss transmitting on one sideband while simultaneously receiving on the other.

No digital processing is going to solve the problem of having the extremely strong transmit signal as little as 600Hz away from the receive side. That signal could be millions of times stronger than any signal coming in the receive side, and it would have to be filtered out at the beginning of the front end or else the receiver would be worthless. There would also have to be a huge degree of RF isolation between the transmitter and receiver within the rig itself.

The last poster discussed doing it with transmit and receive antennas 700 feet apart. If it was done, then I suppose that distance reduced by magnitudes the level of the transmitted signal on the receiver, but how many hams can have antennas 700 feet apart?


Mike

AB0WR
11-14-2008, 12:39 PM
We used to come up with KMI in Oakland CA from my ship (USN) when we were at anchor in places like Hong Kong. We used ISB with a WRT-2 transmitter/R-390 receiver and full duplex. The antennas were maybe 700 feet apart, if that. At 1KW from the WRT-2, there was not even a hint of cross-sideband interference. Talked home quite a few times.

Are you *sure* you were operating full duplex with both transmitters on the same frequency, one in USB and one in LSB?

I've done full duplex with separate xmtr/rcvr setups but not on the same frequency.

Think about 2m FM repeaters and the efforts required to allow full duplex operation and then try to duplicate it on HF. Very, very difficult -- even for DSP.

tim ab0wr

W5HTW
11-14-2008, 04:18 PM
Not only will you have a transmitter signal extremely close in frequency to the receive signal, it will be extremely close in proximity as well, like a couple of inches. Inside the same box on the table! Imagine Field Day with an HF transceiver on say 14,210 and another, on the same table, on 14212. Even on widely separated antennas, it would be amazing if either station could hear much of anything.

I really don't want to discouorage experimentation. I have worked extensively with ISB operations.

I would imagine the R390A and the WRT-2 were on widely separated frequencies, receiving on one, transmitting on a very different one. That is indeed full duplex.

Exactly what overseas telco's did back in the late 50s and through the 1960s. , using full duplex SSB. Here's how. They put up one transmitter with two (or more, but usually two) sidebands being transmitted to the same geographic
area. For example, from a transmitter in Calif, to a receiver site in
Hawaii. That would mean two one-sided, signals TO Hawaii. To get the
other side of the conversations, a similar transmitter in Hawaii would
be beamed to Calif, only at a greatly removed frequency. For example,
the one from Calif to Hawaii might be on 5500 khz and the one from Hawaii to Calif on 5850 khz. Or further apart. You can, of course, do
the same with SSB. Or AM. Transmit TO the distant point on one
frequency and FROM the distant point on a greatly removed frequency.
Exactly what we do with repeaters!

ISB can be used, as you say, to transmit video on one sideband and audio
on another. From the same transmitter.

In commercial use, ISB uses a pilot carrier. But whether it has such a
carrier or not, there IS one present, just suppressed, and at a couple of inches away inside that transceiver box, it is going to be a very strong signal. That is the center frequency. Even at a few milliwats of suppressed carrier (55 db down) the adjacent opposite sideband is not usable for reception.

I worked with four channel MUX in ISB operations. The exciter had two audio
inputs, one for each sideband, upper and lower. But each sideband's
audio input is fed by extremely sharp filters, that will put two audio
signals into that input. Example. The carrier frequency might be
5500.000. On USB two different audio signals are applied. The first
ranges from 400 to 570 Hertz, for 170 hertz shift, and the second from
700 to 770 Hertz, for 170 Hertz shift. Each is independent information,
so is in effect, two intelligent signals. We duplicate that on the
lower sideband. That allows for AFSK signals on the same transmitter,
to be received by four different stations at the distant end, perhaps in
Bolivia, Argentia, Brazil and Columbia, for example. Each station tunes
to his desired signal.

The carrier is transmitted, but 20 db below PEP power output in the
sidebands. The carrier is used as a phase lock signal, for distant
receivers to lock on. Then they use a "sideband slicer" which allows them to select which of the four AFSK signals they will receive. This is only useful when you have two or more stations in the same general direction from the transmitter.

It is very old technology, and probably led to the invention of PSK31.
This was AFSK mutliplex (MUX) operations in the mid 1960s, and it
followed the earlier FSK 850 Hertz RTTY. It was, actually, sound card
operation before sound cards were invented!

Now, as to voice operation, that, too, is possible, but only two
channel in analog operation, due to the bandwidth required for intelligible voice. Theoretically, 300 to 3000 hertz below and 300 to 3000 hertz above the carrier. Those same dual channel exciters (TMC SB1E models) could do
voice just as easily and often did. Reception at the distant end was
simply a matter of selection USB or LSB. In these operations, no pilot
carrier was necessary, but was usually used to provide long term stability.
Again, it was 20 db below PEP ouput.

The application in amateur radio would be pretty limited, about what
you say, SSTV on one sideband, voice on the other. Or some sort of data
on the other. In that case, it is at the receiving end where the difficulty lies. The fellow there must be using either two separate receivers, or a DSB receiver with two channel outputs. This makes it very difficult to apply to amateur radio.


In another application, some microwave links used the same technique,
but with up to 48 total channels, 24 of them narrow shift below the
carrier freq and 24 of them narrow shift above the carrier freq. In
some of these systems, the total shift was only 85 hertz (cycles back
then!!) between Mark and Space. Most of our HF stuff was 170 Hertz, but
we could run two ISB channels at 850 hertz, one upper and one lower.
And we did a little of that.

Later, more sidebands were created with the use of digitized voice.
Certain crypto equipment could run as many as 16 channels, one of them
digital voice, into a single SSB exciter. And, if needed, a second
crypto unit could do the same on the opposite sideband! That meant two
secure voice conversations, totally unrelated to each other, and 32
channels of data, all independent, at the same time. On HF. Neat.

Ed

K7FE
11-14-2008, 04:55 PM
I was associated with a 10kw Collins xmitter on Eniwetok. The two sidebands carried separate (multiplexed) RTTY channels. Why not?

TOM K8ERV Montrose Colo

Tom, My father helped blow that place up.

http://www.aracnet.com/~pdxavets/ivy.htm



I foresee bandwidth complaints, but hey, look at HI FI SSB.

73,
Terry, K7FE

KL7AJ
11-14-2008, 05:09 PM
Tom, My father helped blow that place up.

http://www.aracnet.com/~pdxavets/ivy.htm



I foresee bandwidth complaints, but hey, look at HI FI SSB.

73,
Terry, K7FE


ISB is authorized for amateur use by the FCC. This was brought up in the may 77 QST article.

eric

AF6LJ
11-14-2008, 05:40 PM
Hmmm, sounds like the Kahn mono compatible AM stereo system. I know where there's an exciter siting in a rack just waiting to be re tuned for 160M and fed into a 1KW transmitter already there but alas, that'll never happen.
That would be totally Kool.

WA4ILH
11-14-2008, 08:22 PM
Are you *sure* you were operating full duplex with both transmitters on the same frequency, one in USB and one in LSB?

I've done full duplex with separate xmtr/rcvr setups but not on the same frequency.

Think about 2m FM repeaters and the efforts required to allow full duplex operation and then try to duplicate it on HF. Very, very difficult -- even for DSP.

tim ab0wr

Full duplex?, yes. same frequency?, hardly. for example, just below the 20 meter band, KMI transmitted to ships on channel 1229 or 13,161 Khz and listened on 12,314 Khz. (a "split" of nearly 850 Khz) On the 8 Mhz band, KMI transmitted to ships on channel 804 or 8,728 Khz and listened on 8,204 Khz. They also operated in the 2,4,6,16,22 and possibly the 26 Mhz band.
Tom WA4ILH

BTW, The R-390A was one fine receiver. Sure was a lot better than it's "replacement" the R1051.

AI3V
11-14-2008, 10:33 PM
Naval Communication Station, Diego Garcia,BIOT (British Indian Ocean Territory) checking in! (1980-1981)

Back on VQ9 the transmitters and receivers were seperated by about ten miles, So there was not much crosstalk between them. That seperation was nothing on a HF path, compare that to a uhf repeater, where 10 miles would be terrible from a systems point.

I was in for the R1051, we had a couple 390's for messing around, but didn't use them for NAVY traffic, the 1051 had the advantage of being synthesised, so the radiomen could just dial in the frequency to the 1 khz and go (5 knobs!) , and that revolving band turret in the front end was fun to watch go round!

Note the ISB position all the way CW on the mode switch on the attached thumbnail.
Also note the two meters,And two headphone jacks, one for lsb, one for usb, or both for isb.

Here is a website to restore your 1051
http://images.google.com/imgres?imgurl=http://www.schmitzhouse.com/images/R1051.JPG&imgrefurl=http://www.schmitzhouse.com/Johns_Electronics_28.htm&usg=__RCMX6QAcMvzS82Zj9cm2Sm6x77E=&h=554&w=1068&sz=138&hl=en&start=14&tbnid=Bmvb74izNeJh1M:&tbnh=78&tbnw=150&prev=/images%3Fq%3Dan%2Burr%2B1051%26gbv%3D2%26hl%3Den

Now That's a bandswitch!:eek:

Rege

K7KBN
11-15-2008, 06:00 AM
Are you *sure* you were operating full duplex with both transmitters on the same frequency, one in USB and one in LSB?

I've done full duplex with separate xmtr/rcvr setups but not on the same frequency.

Think about 2m FM repeaters and the efforts required to allow full duplex operation and then try to duplicate it on HF. Very, very difficult -- even for DSP.

tim ab0wr

Tim - we were only using one transmitter, and KMI was only using one transmitter. We'd generally use USB from the ship, and KMI would use LSB. Same frequency, and while we were talking, we could hear the folks on the stateside end of the call without releasing the PTT on the handset.

FM repeaters of course use both sides of the center frequency because they're FM. The sideband filtering in the R-390A/URR is the stuff of which legends are made, because they were, and are, some of the best. The sideband filtering in the WRT-2 transmitter, likewise, was nothing short of superb.

And speaking of radio station KMI: http://bobgowa.net/Dixon__California_HF_statio.php ...

W3JN
11-15-2008, 03:48 PM
^^ But you don't state that the center (carrier) freqs were the same. There isn't a receiver made (before, now, or probably ever) that could pull that off.

Every once in a while I see old TMC SSB/ISB exciters at hamfests. Nobody wants 'em because the need an external VFO and power supply. What is really cool about them is they have a 6146 in the final - running about 1 watt output in Class A. Talk about low distortion!


FM repeaters of course use both sides of the center frequency because they're FM.

Huh :confused:

W5HTW
11-15-2008, 04:08 PM
I know of no receiver ever made that would do full duplex on the same carrier frequency as the transmitter, regardless of filtering. Even with substantial antenna separation it won't work unless the transmitter antenna is far enough away there is neither sky wave nor ground wave at the receiver. But .... read on!!

Most transmitter sites are separated from receiver sites by at least a mile, and often up to five miles on HF. Beyond that distance, propagataion may affect the T-site one way and the R-site another. Typical separations are about a mile. But at a mile, the transmitted signal will very nearly overload even an R390A, on any frequency below about 18 mhz.

I would think, though, with an extremely good selectable side band receiver, and a mile or two separation between transmitter and receiver, that the receiver could actually hear on the other sideband. I never tried it, I admit! A receiver such as the 51S1 might do it, or some of the Harris models. At that mile or so separation, it is opposite sideband rejection that would be the deciding factor. But you have to be far enough away your own transmitted signal doesn't overload the front end of your receiver. So, with sufficient physical separation, it would likely work.

Here's a possibily. With an amateur radio situation, using a remote base, it may could be done without much problem. With the remote transceiver located far enough away from the operating position that it did not overload a HF receiver at that position, then likely there'd be no problem. That might be worthy of expermenting with, though I'm not sure what the advantages would be, since the guy at the other end would also have to be running a remote base and an HF receiver as his operating station.

Still another way would be -- possibly, not sure of legalities - to call your buddy on the phone, if he's a few miles away, have him put you on the phone patch, and you receive at your location. Take some refining. But the object is to get the transmitter and its antenna far away from the receiver and its antenna. That done, it becomes a simple task! Then we ask "Why?" And, is it legal?

Ed

WB6BNQ
11-15-2008, 10:24 PM
Still another way would be -- possibly, not sure of legalities - to call your buddy on the phone, if he's a few miles away, have him put you on the phone patch, and you receive at your location. Take some refining. But the object is to get the transmitter and its antenna far away from the receiver and its antenna. That done, it becomes a simple task! Then we ask "Why?" And, is it legal?
#
Ed
Hi ED,

Sure it is legal, particularly if you do the transmitting at your end of the loop. That way “YOU” have control of the transmission and the responsibility as described by the FCC rules. There is NO rule defining any responsibility for the operation and control of the receiver, no matter where it is located.

Done did that back in 1970 with a remotely controlled base station using 440 MHz band for the control and audio links. At that time you had to get specific permission to operate such a station from the FCC. Mine was located on a mountain about 50 airline miles away.

The problem with too much separation is the DELAY encountered in the received audio. Even a little delay makes it hard to talk if you are listening to your own transmitted signal.

Bill....WB6BNQ

N4CD
11-16-2008, 05:48 PM
You are not likely to do this without maybe 100 miles of separateion between your transmit and receive site.

The sideband of the transmitted signal is at best 35 dB down due to IM products. Your recieve site has to be far enough away that you don't even hear your own transmit signal, otherwise you will cover up the receive signal totally.

You would need two stations, one just operating on say 14.275 LSB for transmit, and one 100 miles away listening on 14.275 USB.

The FCC might not be too happy with you doing that on a crowded band either. You are not using bandwidth efficiently if you run 'full duplex'. On 6m, no one is going to likely worry about it.....

This is no different than figuring out the requirements for a duplexer on VHF or UHF. You need to reduce the transmit signal sidebands (IM products and noise on the signal and noise floor of the amp chain) into the receiver at the receiver frequency. You need to prevent the transmit signal from overloading the front end on the transmit frequency.

That isn't going to happen at 0 KHz spacing unless you virtually have two sites that can't hear each other as your T and R sites.

Now, using both independent sidebands for sending information is easy....provided you use modulation that is compatible and operate ultra linear system if needed.

M3KXZ
11-16-2008, 06:39 PM
How about almost duplex on the same frequency and on the same sideband? Loads of voice data can be compressed into a fraction of a second of digital data, so would it be possible to send a burst - very short - of digitised voice data, then switch to receive to receive a burst of digitised voice data? Provided the transcievers at each end were synchronised in some way - i.e. the TX burst from one ended with a signal to switch the other transceiver to TX to send its burst, and that then signaled the first to switch to TX to send it's burst, and this could be done many times a second, then you would have pretty close to full duplex. If data is missed then this can be called up in subsequent burst, and the whole lot pieced together in pretty close to real time.

M3KXZ
11-16-2008, 06:45 PM
And....the time to send and receive these small bursts would be so small that they would not be noticeable during the course of a QSO. While you are talking into your mic, the setup would be sampling perhaps 10th of a second sequences and sending them as 100th second bursts, it could send the burst several times during the 1/10th second to ensure that all the data is properly received at the other end. While you are talking the set up would also be receiving 100th second data bursts of the 1/10th second of audio that's been captured at the other end, and it would be piecing these together properly (in a similar way to how P2P file sharing works) and sending them out your speaker.

M3KXZ
11-16-2008, 06:47 PM
This would use a much narrower bandwidth than trying to do the same with ISB, and it would also overcome the problem of trying to receive in very close proximity to your own transmission.

W8HDU
11-16-2008, 06:57 PM
I seem to recall, (years ago), someone had written an article on a web site about this, complete with schematics, etc. From what I could remember it was an "exciter" that would do ISB, DSB, SSB, and AM.

I'm drawing a blank on where and how I found it, but from the article's content I got the impression that it had something to do with WBCQ up in Maine.

SM0AOM
11-16-2008, 07:04 PM
I design maritime and aeronautical MF/HF systems for a living, and it is considered completely impractical in "the business" to operate full-duplex ISB in opposite directions with co-located receivers and transmitters.

The demands on both transmitters and receivers cannot be fulfilled by any equipment currently on the market. For example, the first transmitter adjacent channel suppression, assuming a co-sited receiver-transmitter isolation of 50 dB (which is high), would have to be about 110 dB for a 1 kW system operating in the lower HF range. It is highly unusual to find equipment with better than 70 dB suppression.

For MF systems, the ground-wave propagation makes it very difficult to meet the protection criteria between the 2182 kHz voice and the 2187.5 kHz DSC distress channels on co-sited installations. Even with exceptionally good transmitters and receivers, antenna separations exceeding 1000 m are required to prevent receiver desensitation (Guidance can be found in ITU-R Recommendation M.1467). Common practice is to separate receiver and transmitter sites by at least 3 - 4 km to be reasonably unaffected by receiver and transmitter close-in noise and IMD products.

On HF, there is more or less the same situation, but as the horizontally polarized ground-wave falls off very rapidly (measurements indicate an isolation of the order of 100 dB between receiver and transmitter antennas at HF sites separated by 4 km, cross-polarization can increase these values) it is possible to exploit the skip-zone and the antenna patterns to acheive sufficient isolation between transmitters and receivers to permit "single-frequency duplex operation"

Experience and measurements from the Stockholm Radio Air-Ground system show that the cross-talk between transmitters and receivers at operating frequencies above the ionospheric critical frequencies is in the order of -150 dB, which can be handled by conventional echo-suppressors. The distance between receivers and transmitters is 200 km, which "happened" to be about the right distance to prevent direct propagation between receivers and transmitters.

It is to my knowledge very unusual to exploit these properties of the ionospheric radio circuit. The only other recent reference I have encountered is in the CCIR Study Group 3 documentation, to which a Japanese report was submitted in the 60's, where the "skip-zone" was used to create single-frequency point-to-point "duplex" circuits in a somewhat related manner.

The examples cited in earlier posts are most likely referring to the standard maritime radio practice of operating full-duplex with USB emissions and a 500 kHz or so "duplex spacing", augemented by a substantial geographical separation.

73/

Karl-Arne
SM0AOM

W5HTW
11-16-2008, 10:14 PM
Yep, that's how TELCO did it, and how maritime networks did it.

But we are really talking about two different things in this thread.

1. ISB. That's the very easy part. With an ISB exciter, it is no task at all to transmit different information on each of the two sidebands. That has been done for many decades. So an SSTV signal on USB and a voice signal on LSB is very possible. Just takes an ISB exciter with separate audio inputs for upper and lower sidebands.

2. Full duplex. That's where the cookie crumbs fall into the mop bucket. We have discussed transmitter-receiver separation, antenna separation, and frequency separation. But full duplex in ham radio has one requirement we have not been able to cover. That is a transmceiver that can simultaneously transmit and receive on the same carrier frequency. That means all in one box, on your one desktop, on your one antenna, at your one location. I know of no such animal!

One guy mentions transmitting a burst of data. Yes, possible. A digitized voice could be transmitted as bursts, and between bursts the radio could receive bursts from the distant station. However, that doesn't require duplex, and, in fact, it isn't. It is fast-switching simplex. That, too, has been done for decades. And at a slower speed, we do exactly that with full QSK on CW!

To get full duplex, that one box radio has to transmit and receive at the same time. Well, we do that with cross band repeaters, or in band repeaters, with transmitter output and receiver input separated by 600 khz. Again, been doing it for decades. But the radio working into the repeater is either transmitting or receiving, not both.

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