Receive Diversity Tool

[Emmanuel SV1BTL]

A Receive Diversity tool is testing now. You can work with it in  http://phantomsdr.no-ip.org:8900

The goal is to pair the receiver with a second one somewhere else and listen to whichever site currently has the better signal, so a fade at one is covered by the other. The second receiver can be another PhantomSDR-Plus, a KiwiSDR, an UberSDR or a WebSDR — the first three need nothing at all beyond the listener's browser, and only a WebSDR needs a small relay on your own server. Alignment takes about twenty seconds.

What it does, and what it does not

Diversity here means **selection**: at any moment you are listening to one site or the other, with a short crossfade when it switches. It is not a phased array and it does not add the two signals together.

That is a deliberate choice, and the reason is physics rather than software. Two receivers hundreds of kilometres apart hear the same transmission over different ionospheric paths. The two audio waveforms arrive with unrelated phase and slightly different Doppler, so adding them sounds hollow and comb-filtered — the classic "phasey" artefact. True coherent combining needs two receivers on a **common clock**, sample-aligned; two independent receivers connected over the internet can never provide that.

So what you gain is continuity, not raw signal strength:

- On a stable path where one receiver is simply better, you will hear that receiver and gain nothing. This is normal.
- On a fluttery path with deep QSB, fades at two distant sites are largely uncorrelated. Site A drops out for three seconds, site B does not, and the audio carries on. Expect "I stopped losing words", not "S3 became S7".
- The second win is often local noise and QRM. Two sites have different neighbours, different power lines and different broadcast splatter. On a noisy band this can matter more than the fading.

There is a cost: you listen one to three seconds behind real time, because the earlier stream has to be delayed to match the later one. That is irrelevant for listening and decoding, and unhelpful if you are trying to work a station.

After the tests, the tool will be released in the next version.

[F1NSK]

Very good Idea Emmanuel !

I've tried on your phantom.

Synchro issues

73's

[F1NSK]

Hello Emmanuel

After a new test, The tool work.

The synchro come after one or two minuts.

73's

[Emmanuel SV1BTL]

Synchro issues

Hi Eric,
There are not issues when the two receivers start with a 'heard' signal, so to be synchronized. Then and after synchronization, you can move everywhere on the band(s).
Try for example 14074 KHz USB (FT8) where almost all SDR's are detecting a signal. Synchonization after around 20-30 sec. and then QSY freely.

[F1NSK]

When in the PR ?

[Emmanuel SV1BTL]

Well, now we test it (me, Darko, and George).
I hope until the end of the week it will be ready.
I am also working on audio of the mobile GUI, trying to fix some audio bitrate issues.