RADEV1 Frequency delta

[Torbjörn Toreson]

While experimenting between two radios set at the same frequency (USB) I found that the sync was intermittent, changing between red and green. Finally I found that the reason was that one radio was off in frequency by about 60 Hz. When I altered the dial frequency to compensate for the difference the sync/Modem was steady green.

The Vara HF modem has an "auto tune" to compensate for frequency differences up to 100 Hz. So I have two questions:

1. Does FreeDV RADEV1 have an "auto tune" capability?

2. What is the maximum frequency deviation between two radios to permit a stable sync?

I also found that the pane 'Frequency delta' does not work with RADEV1, but it works with e.g. mode 1600.

73/Torbjörn/SM6AYM

[Brian Morrison]

On Sat, 5 Jul 2025 14:27:38 -0700 (PDT)
Torbjörn Toreson <torbjorn...@gmail.com> wrote:

> While experimenting between two radios set at the same frequency
> (USB) I found that the sync was intermittent, changing between red
> and green. Finally I found that the reason was that one radio was off
> in frequency by about 60 Hz. When I altered the dial frequency to
> compensate for the difference the sync/Modem was steady green.
>
> The Vara HF modem has an "auto tune" to compensate for frequency
> differences up to 100 Hz. So I have two questions:
>
> 1. Does FreeDV RADEV1 have an "auto tune" capability?

It does, but the frequency offset it can deal with is about 50Hz or so,
this aspect of the mode is not fully optimised and is unlikely to be
until RADEV2 appears in the future.

> 2. What is the maximum frequency deviation between two radios to
> permit a stable sync?

You can experiment with this on the spectrum plot by double clicking to
move the red centre frequency bar for the modem up or down, middle click
re-centres it.

>
> I also found that the pane 'Frequency delta' does not work with
> RADEV1, but it works with e.g. mode 1600.

No, the reason for this is that the internal operation of the RADE
modem and codec does not provide the necessary outputs to determine
these values. Machine Learning can be something of a 'black box' and
the internal parts are difficult to interact with.

You might like to read the technical blogs that David Rowe writes on
the https://freedv.org site as well as the information about the
Radio Autoencoder there, it may be able to answer some of your
questions. Comments are available on these posts, so you can ask there
too.

RADEV1 has been released now as it is a significant improvement on the
previous FreeDV modes but some aspects are as yet not fully developed
hence the need for a RADEV2 mode.

--

Brian G8SEZ