FM Audio very weak and looks like Amplitude Modulation, 7000DLE

[KA9UVY]

With 10 meters working well here I have taken an interest in 10 FM.
When trying to access a few repeaters I have noticed that my audio level is very weak, in fact I seem to still be in AM mode with a change in Amplitude when speaking.
I have tried the Pre-emphasis before and after limiting and also disengaging the Leveler. Turning off the leveler helped a great deal with the change in Amplitude when modulating but I clearly have a center carrier spike and waveform of AM.
The Audio remains quite distant when received on another RX nearby.

If anyone here is using their ANAN 7000dle on FM with Thetis with success please drop me a line and point me into the right direction.
Can this radio do FM 5Khz Dev or not ?

[K1LSB]

FM does look very much like AM, in the sense that there's a carrier and two sidebands.

Mark

[w-u-2-o]

When trying to access a few repeaters I have noticed that my audio level is very weak, in fact I seem to still be in AM mode with a change in Amplitude when speaking.

You are definitely not in AM mode. If you are not used to watching FM signal spectra you might be fooled. When operating with FM, you may have to change the scaling on your TX spectrum display to see further down in signal level. Put the carrier spike near the top of the grid and make sure you've got at least 70 dB visible below that point.

I have tried the Pre-emphasis before and after limiting and also disengaging the Leveler.

Pre-emphasis will cause little to no difference in terms of quieting on the repeater.

Turning off the leveler helped a great deal with the change in Amplitude when modulating

Turning off the leveler is exactly the wrong thing to do, regardless of what you are seeing on your transmit spectra. If you want greater average loudness you need to compress your audio dynamic range, which is exactly what the leveler and CFC do.

Other than adjusting the transmit passband, I use the exact same audio settings for SSB as I do for FM ("loud" ).

Don't forget that your FM passband settings for RX and TX are found in Settings > DSP > FM. These settings will be saved in the transmit profile.

The default settings for maximum audio frequency are 3KHz. This provides the "traditional" modulation index of 1.63 with 5 KHz deviation and 0.83 with 2.5 KHz deviation. However you are certainly welcome to play with that.

but I clearly have a center carrier spike and waveform of AM.

That is what an FM spectrum looks like.

The Audio remains quite distant when received on another RX nearby.

This seems more like an audio chain setup problem than anything else. Is your mic level coming close to 0 dB? If not, add more mic gain. Same for the leveler and CFC and post-EQ output levels. ALC Group levels should hit +1 to +2 dB reliably and often, but not exceed that level.

If anyone here is using their ANAN 7000dle on FM with Thetis with success please drop me a line and point me into the right direction.

It has nothing to do with the hardware. I.e. that you are using a 7000 is not important. All Thetis-compatible hardware, from the original Hermes to the G2 to the HL2, is essentially equivalent. They question to ask is whether or not Thetis is set up correctly. All demodulation and demodulation is done in Thetis, other than the direct frequency conversion and amplification nothing relevant is being done in the hardware.

Can this radio do FM 5Khz Dev or not ?

Can Thetis do FM 5 KHz deviation? Of course it can, and does. Simply select the deviation setting you would like to operate with using the controls on the main console screen (right below the mic gain slider).

I've dabbled in FM on our radios and found it to work quite well, making more than a few DX contacts. Indeed, since Warren added the receive limiter function it has worked better than ever

[KA9UVY]

Well, Maybe I should have chosen my words more carefully, Instead of LOOKS like let's say BEHAVES like.
My PEP power output increases by at least 50% when speaking on FM. When on AM I get more of an increase and nearly the perfect 4:1 ratio of a fully modulated AM carrier.
I do not have a lot of experience observing the FM waveform but when comparing mine to the others I'm watching, I can see that my sidebands are not well rounded, (some frequencies seem to me standing out and increasing, like AM) and my carrier spike doesn't pull down with modulation.
Besides that my local air check yesterday confirms I sound like Do Do, (weak audio).
I'll try to get my audio level to stay more consistent, and possibly experiment with a different audio driver on my FM profile.
Thanks for any constructive input.

[K1LSB]

Scott,

This thread has also got me trying to effect a good FM signal out of Thetis, and I'm having some of the same issues Robert is describing (mainly less than full TUN power during FM TX).

However, another thing that concerns me is that PureSignal doesn't seem to be working on FM (at least not for me).

Is that per design intent?

Mark

[dj1yr]

I have the same issue with performance. The performance increases by approx. 60-70% during modulation.
This is the case with FM, which I am familiar with, but not with any other device. Even the measuring transmitters do not do this.

The volume can be significantly improved by activating the limiter under DSP-> FM and adjusting the gain accordingly.

[w-u-2-o]

Again, there is nothing intrinsically wrong with FM functionality in Thetis, or in the hardware/firmware.

I proved this to myself by injecting a single audio tone at the mic input. (Note: both TUN and Two-tone bypass all modulation stages, so there is no difference in their operation regardless of operating mode, and thus they cannot be used for this test.)

Single-tone FM will result in an output RF spectrum that is relatively easy to recognize. Here is a good reference: https://dsp.stackexchange.com/questions ... -fm-signal

When injecting a single tone through the mic input the typical single-tone FM spectrum can be seen on the DUP display. If you really want to sharpen a pencil, go through the math to ensure the spectrum is correct with respect to sideband locations and amplitudes. By doing this test it's easy to prove that the FM modulation process is working correctly. Obviously this is essentially impossible to do with the complex and time-varying nature of human speech.

Going back to the issue of poor transmit audio quality, again I can only recommend that the audio processing configuration be looked at with a fine-toothed comb, and that some compression be applied using the leveler and CFC.

The only other adjustments are, again, located in Setup > DSP > FM, and they are limited to AF bandwidth (default 300-3000 Hz), and (non-defeatable) pre-emphasis location. The normal and default setting for pre-emphasis is after the FM limiter. This is a frequency limiter to prevent over-modulation, not an amplitude limiter, and has nothing to do with the FM receive limiter. However, it has been reported that by moving the pre-emphasis to before the FM (frequency) limiter it will have the effect of additional compression on the audio and thus make it sound "louder".

PureSignal does operate in FM mode. However, because FM produces a constant power output, it does not work very well in automatic mode, and provides very little in the way of improving the transmitted signal quality. If you desire perfection (who doesn't? ), Single Cal can be used to "lock in" a PureSignal correction prior to operating FM.

The volume can be significantly improved by activating the limiter under DSP-> FM and adjusting the gain accordingly.

That is a receiver setting and not a transmitter setting. It will certainly improve the quality of FM reception. The FM receive limiter was added back in the early part of 2023. See this topic for more information: viewtopic.php?p=23188