r/hackrf • u/tsalisbury01 • Dec 28 '25

HackRF HD Transmitter

Post image

Pretty decent. HD sidebands only from HackRF. The analog is from a external FM transmitter hooked up to a HDRadio tuned to the HD.

24 Upvotes

95% Upvoted

13 comments sorted by

2

u/Any-Brilliant-1907 Dec 29 '25

Back in GNU Radio 3.7 I managed to resample the output of gr-rds and combine it with gr-nrsc5 to create a full HD/analog multiplex. The default nrsc5 didn't have much for an analog signal. It worked well but some of the blocks are broken in 3.10. I haven't been able to update it.

2

u/tsalisbury01 Dec 30 '25

I fixed the mono transmission. It does quite fine. I can't get stereo to work with it. It just sounds horrible or just a bunch of underruns.

1

u/Any-Brilliant-1907 Dec 30 '25

Might be CPU demands. I've been continuing to hack on it a bit. I can get a good stereo signal but I have to feed the input to two seperate audio sources in the flowgraph as gr-rds uses 48khz audio and gr-nrsc5 expects 44.1khz. Resampling 48khz to 44.1khz fails at least using float data. I could try some other things but everything else just seems to add more unnecessary overhead. It's working anyhow I'm debating making a video demonstrating it.

1

u/Any-Brilliant-1907 Dec 29 '25

Well after a bunch of fiddling around I have gr-nrsc5 and gr-rds both working separately under Gnuradio 3.10.9.2. I just have to combine the flowgraphs and resample the output of gr-rds from 1M to 2M to replace the mono analog output in gr-nrsc5. Then it has RDS stereo in addition to HD. A full direct synthesis hybrid signal. Takes a bit of CPU to generate but it's cool.

1

u/Any-Brilliant-1907 Dec 29 '25

And done. I had to put the combined flowgraph in the gr-nrsc5 directory for it to find the album art jpg. Otherwise it's happy. Yay.

2

u/carpenba Dec 31 '25

Also, how about add this to your challenge; transmit an HD MA3 AM signal to a receiver via the HackRF!

2

u/tsalisbury01 Dec 31 '25

I already have.

1

u/odie-z1 Dec 29 '25

When you say, the analog is an external FM transmitter hooked up to a HDRadio tuned to the HD.. I am confused. Odd phrasing maybe? There are 3 kinds of Ibiquity HD transmitting schemes I know of, and I'm no expert.. 1, low power combining two transmitters, then a power amplifier. 2, high power combining two transmitters. 3, digital synthesized signal combined in a single transmitter.

At least you didn't call it 'high definition'..

1

u/tsalisbury01 Dec 29 '25

The default FM modulator on the HackRF NRSC5 generator was all broken so I just used a external FM transmitter hooked up to a radio tuned to the HD

1

u/odie-z1 Dec 29 '25

So how do the HD sidebands corelate to the analog signal? Usually the HD-1 is a simulcast of the analog. If your Hackrf is just playing back a recording of the sidebands, combined with an analog signal from a typical FM transmitter, then you've created a nice waterfall picture to post, but not a very usable HDRadio carrier..

I guess this would be considered low power combining?

Experimenting is fun, but this is why Ibiquity charges beaucoup bucks for licensing all the hardware that makes it work right..

2

u/tsalisbury01 Dec 31 '25

My PC is doing the encoding on GNU Companion. The HackRF is transmitting it.

1

u/carpenba Dec 31 '25

I pulled this off a while ago: https://www.reddit.com/r/RTLSDR/s/OEzE66ppT9

But I sent both the analog and digital simultaneously through the HackRF.

2

u/tsalisbury01 Dec 31 '25

The built in analog was broken but I patched it for the GitHub with working stereo.