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I'm new to SDR. Is it possible to transmit on more than one frequency, and if so what do I need?

more on computer type network side one for each 800, 2.4, 5, 60

How can I get more than one SDR to work together? trunking, handoff

I'm dyslexic and dysgraphic

so my write not all and all ok not it sucks

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Yes.

A direct conversion SDR (one with an ADC and DAC that covers the entire HF band, for instance) might be able to transmit not only on multiple frequencies, but with custom firmware/gateware, possibly on multiple bands at the same time. But you might have to design a very unusual custom low-pass plus notch filter to make sure the harmonics of all the bands and frequencies used are properly suppressed to stay within legal limits.

A non-custom IQ SDR transceiver (LimeSDR Mini, Hermes Lite 2, et.al.) can transmit on any number of frequencies that all fit under the bandwidth of the IQ data input, possibly an entire HF band, or CW segment thereof.

A non-custom sound card SDR transceiver can transmit on any number of frequencies that all fit under half the audio sample rate or audio bandwidth allowed.

There are lots of articles and web pages on wiring multiple RTL-SDRs together modified to share one clock for synchronous or diversity receive. The TAPR/Hermes line of SDRs often have clock out/in ports for the same for transmit as well as receive.

Or you can do non-synchronous simultaneous SDR QSOs just hooking up multiple SDRs to one console (PC, Raspberry Pi, et.al.). You need to check (spec, benchmark, etc.) to make sure the total bandwidth required (USB, network, memory, page-out to storage, FLOPS, GPU visualization, etc.) do not exceed the max stable load for the system.

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Since you are new to SDR (Software Defined Radio), I will assume that you're wondering why one can receive more than one signal but transmit only a single signal with off-the-shelf SDR units. Note that an "SDR" comprises the hardware, some companion software and the means for the software to operate on information supplied by the hardware.

An SDR receiver samples a band of frequencies and digitally demodulates those samples into a form that a human or machine can decode to recreate the original information. In general, the band of frequencies results from the mixing of band-limited signals from an antenna with a single oscillator, followed by a filter to restrict the frequency range of the resulting signals. High sample rates allow sampling of large bands of frequencies that comprise numerous signals. Faster digital processors - whether hardware, software, or a combination - may allow more than one of the signals in the sampled band of frequencies to be demodulated.

An SDR transmitter digitally modulates information onto a carrier generated by an oscillator. The modulated carrier signal will occupy a range of frequencies corresponding to the content of the source information and the way the carrier is modulated. An SDR transmitter may transmit on more than one frequency by appropriately combining multiple sources of information and modulating them onto the carrier.

A simple and practical example is the two-tone test commonly used to characterize an SSB transmitter. Two audio frequencies are fed into the transmitter, which produces an RF signal comprising two carriers separated by the difference in frequency between the two audio tones. This is entirely equivalent to simultaneously transmitting two signals. One could encode different information sources into each of the two tones. Generalizing this process with appropriate software and adequately fast hardware, one could transmit an arbitrarily large number of signals at selected frequencies.

However, as long as the transmitter is "on" for any of the information sources, the receiver on that frequency might have to be "off" to prevent destructive overload. This could seriously compromise the utility of such a system in a two-way communications application.

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Yes it is possible to transmit on multiple frequencies with an SDR, assuming it can transmit, and those frequencies are all within the bandwith of the SDR's transmit bandwidth at the same time.

Many SDR based modes do this, such as freedv (which uses multiple adjacent carriers with gaps between them) and js8call, ft8, etc., which use contiguous frequencies. Technically, these are emitting a single signal with a particular bandwidth, but practically, these are using multiple frequencies at the same time.

There's nothing to prevent the frequencies in use to be separated widely. However, you do have to realize that the transmit power will be spread over the frequencies, and legal requirements to filter spurious emissions still apply.

Yes, it is possible to get more than one SDR to work together. However, typically to make this work, the SDRs are all part of the same device and share an oscillator so they can be phase coherent. Look for SDRs that support MIMO. I know of two currently available. I've also seen projects to modify SDR receivers to share oscillators. Both the MIMO SDRs and the modification projects can be found at rtl-sdr.com

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