On Sep 12, 2024, at 18:19, K3EUI Barry <k3euibarry@...> wrote:

?

Recently a question was raised about the optimum TX audio for digital modes on 2m FM.

Great question.

The old guideline was to listen to your audio with a second FM radio (HT will work fine)?

?? "the sound from any of the sound card digi modes should be about the same loudness of a human voice with a microphone"

That is a pretty rough guideline, and not a very accurate nor precise guideline.

First, some modes sound louder than others: the Olivia, THOR, MFSK modes are simple single-pitch sine waves but always played one tone at a time

at a specific duration of each tone (the baud is tone per second).? Usually the pitch is 500 Hz to 2500 Hz for the multiple tones.

So the tone duration (seconds) is simply? 1/baud.

Longer duration tones are lower baud values and are easy on the ears; THOR, Olivia, MFSK

Thus? each THOR 11 tone is twice as long as a THOR22 tone, as well as a smaller bandwidth for the mode.

The psk type modes (PSK31, PSK63, 8PSK and VARA)? are changes in both phase and amplitude, so the "loudness" of phase-shift modes can be deceiving based on human ears.

Humans hearing is more sensitive to sounds from 2000 - 3000 Hz, than sounds at 500 Hz, so higher pitch sounds of any mode will appear louder than lower pitch sounds.

The optimum TX audio is based on the? deviation on an FM transmitter.

Can we measure the deviation? (directly, or indirectly) and not the loudness based on human hearing and speaker quality.

Yes.

If you have access to an SDR that can look at the RF spectrum (I will pick 2m FM) then adjust the amplitude of the TX audio until you get the following picture on your SDR app.?

I am using an RSP (hardware) and usb cable and RSP Spectrum Analyzer (software) with Windows 10.

For this test I? set the vfo on the radio (Icom 2820) to 145.690 MHz on an Icom dual-band FM rig.

My sound "card" is a Masters Communications DRA SR? feeding TX audio into the radio's? 6 pin MINI DIN data jack.

I set the Fldigi TUNE with the cursor to? 1500 Hz? in the waterfall.

Be sure to turn OFF any TxID signal sounds, and turn off any PL tones - these will mess up the image.

Don't try this on a analog voice repeater (that needs PL tones).

Look at the RF Spectrum of the? 1500 Hz TUNE ? - note the carrier (@145.690 MHz) and the multiple sidebands.

We get this picture (multiple sidebands) on FM, but not on AM or SSB.

Louder TX audio results in more sidebands (and a drop in the carrier amplitude).

However, on FM, you get the same POWER? (watts to antenna) independent of the TX audio level.

When the amplitude of the ? pair of 1st sidebands?? matches the amplitude (height) of the original carrier --- STOP.

Mark the TX audio levels (sound card TX setting, FLDIGI TX attenuator, Windows Speaker output).

The deviation is the product of the ? "modulation index"?? and the audio pitch in kHz.

So at this level of TX audio, the modulation index is about? 1.5? and the audio pitch is? 1.5 kHz? (1500 Hz) so

the?? deviation is about? 2.25 kHz.??

That is about ideal.? You won't over modulate and distort the sound card digi modes.

Questions?? contact me at

k3euibarry@...

<ZESkFF8u8YQykQ5D.jpg>

<TUNE at 1500 Hz on 2m FM simplex yield 2.2 kHz deviation.jpg>

Bob,

thanks?for the ti ps!

I will poke some more.

On Wed, Aug 21, 2024 at 3:05?PM Bob Cameron via <bob3bob3=[email protected]> wrote:

Hi Don

I vaguely also remember that squelch action interrupted good decoding, so squelch disabled as one would for Olivia. Most of my tests though were with Thor Micro. FEC can also be enabled/disabled with Domino modes manually so ensure all stations have the same settings. I saw "first block loss" with flamp transfers and Thor 22 as well, which is where my squelch action concerns comes from. For a while there I would manually edit the block list with an additional first. Possibly try a longer idle before sending data for experimenting?

I also have a way out untested theory that sound card resampling/CPU/maths issues may degrade low s/n signals. I'll test that some day!

And on that note I did some VK<>UK tests some years ago using Olivia 16/250 and 32/250 "non standard" modes that yielded a worthwhile improvement over (say) 8/250 for flaky paths. It was "so good" that the UK end requested an RsID be allocated. Very slow of course. Fldigi's s/n and f/o display polling time does mess up and periodically vanish on the super slow Olivia modes though.

Vague thoughts sorry, but thought worth a mention.

Cheers Bob VK2YQA

On 22/8/24 03:58, Don Rolph wrote:

We were exploring Domino EX micro to break through poor propagation?conditions.

Small scale testing?demonstrated?that it functioned, but when we tested at scale with multiple stations we got inconsistent results.

In many cases I could clearly see the signal in the waterfall?but the signal would not decode.? Other times?I could barely see the signal but decoded nicely.

We did address centering issues since this is a very narrow bandwidth signal?but that seemed to provide minimal?impact on the issue.? We also worked to ensure that we did not use software SQL.

It is almost as if when the initial part of the signal was not decoded that the rest of the signal ?could not be decoded either.

Can anyone help provide insight here?? What?are the issues required for successful use of Domino EX micro?

Thanks!

--

73,

AB1PH

Don Rolph

We were exploring Domino EX micro to break through poor propagation?conditions.

Small scale testing?demonstrated?that it functioned, but when we tested at scale with multiple stations we got inconsistent results.

In many cases I could clearly see the signal in the waterfall?but the signal would not decode.? Other times?I could barely see the signal but decoded nicely.

We did address centering issues since this is a very narrow bandwidth signal?but that seemed to provide minimal?impact on the issue.? We also worked to ensure that we did not use software SQL.

It is almost as if when the initial part of the signal was not decoded that the rest of the signal ?could not be decoded either.

Can anyone help provide insight here?? What?are the issues required for successful use of Domino EX micro?

Thanks!

Not going to mention names, so people can avoid this inadequate radio?

Andrew, KA2DDO

________________________________________
From: [email protected] <[email protected]> on behalf of Dave <w1hkj@...>
Sent: Monday, August 5, 2024 9:30 AM
To: [email protected]
Subject: Re: [nbems] FSQ in FLDIGI: center frequency questions

There is one manufacturer of kit radios that is advertized for use with the FT modes.  It is a simple double sideband transceiver.  Even if not overdriven with hot audio it produces both an upper and lower sideband FT signal on the air.  NOT FRIENDLY.  And worse if the audio is overdriven.

David

On 8/4/24 15:01, Bob Cameron wrote:

Great post Dave. I see this QRM on 20m clobbering what is primarily the Olivia operating area quite often.

Maybe even IMD in the TX mixer combined with the obvious other sideband suppression of the more recent "direct conversion" style TX's. TX Sideband suppression in even a "full" rig is somewhere better than 55dB so a strong (main) RX of >S9 will be quite visible AFx2 away on a wfall, especially if a tone pattern. I am also quite embarrassed to say that my Icom TX spec at 1200Hz is only 40dB suppression!

Quite easy to figure out the station ID. Decode the FT8 on 20m using LSB. The double/triple mixing ones will need recording and playing with the sample rate by multiples maybe using Audacity, before playing back through WSJT-x etc. Usually though I just slot in between them..

Cheers Bob VK2YQA

On 4/8/24 18:32, Dave_G0WBX via groups.io wrote:
Hi.

One thing to be aware of, if you run a mode with an audio component less than half the highest audio frequency your radio will pass on transmit, is that any audio distortion products will be radiated at RF too.

Often, it is not a faulty computer/sound-card, but the radio's audio input (mic) stages being over-driven into distortion..

Great post Dave. I see this QRM on 20m clobbering what is primarily the Olivia operating area quite often.

Maybe even IMD in the TX mixer combined with the obvious other sideband suppression of the more recent "direct conversion" style TX's. TX Sideband suppression in even a "full" rig is somewhere better than 55dB so a strong (main) RX of >S9 will be quite visible AFx2 away on a wfall, especially if a tone pattern. I am also quite embarrassed to say that my Icom TX spec at 1200Hz is only 40dB suppression!

Quite easy to figure out the station ID. Decode the FT8 on 20m using LSB. The double/triple mixing ones will need recording and playing with the sample rate by multiples maybe using Audacity, before playing back through WSJT-x etc. Usually though I just slot in between them..

Cheers Bob VK2YQA

On 4/8/24 18:32, Dave_G0WBX via groups.io wrote:

Hi.

One thing to be aware of, if you run a mode with an audio component less than half the highest audio frequency your radio will pass on transmit, is that any audio distortion products will be radiated at RF too.

Often, it is not a faulty computer/sound-card, but the radio's audio input (mic) stages being over-driven into distortion..