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On 7/9/2023 11:19 AM, Kevin Custer wrote:

Or better yet - programs could be customized to align PTT timing with the capabilities of the radio - taking the sound cards PTT method out of the equation.

This has been done since the beginning of packet in the very early 1980s.? It's called a setting called TXD (TX Delay) and determines a delay between PTT and the beginning of the data tones. Usually specified in milliseconds, it is user adjustable to correct for the "slow-on-the-draw" issues of individual radios.

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The way this is written seems to generalize that all Class-D audio power amplification results in distortion.? While some Class-D audio amps are terrible - (and the ones in these portable radios certainly are) - not all Class-D audio amplification is flawed where distortions are concerned.? Plus - we're not really dealing with "complex data waveforms" here - it's just audio.

It's not "just audio".? If the class-D amp doesn't switch cleanly or isn't switched at a high-enough frequency, it can/will produce a lot of IMD (Inter -Moduation Distortion.

This doesn't affect modes like AX.25 packet or SSTV that use a single audio tone at a time very much --- but is disastrous to modes with complex waveforms that use multiple SIMULTANEOUS audio tones like VARA, MT-2000, etc.,?

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Or better yet - programs could be customized to align PTT timing with the capabilities of the radio - taking the sound cards PTT method out of the equation.

This has been done since the beginning of packet in the very early 1980s.? It's called a setting called TXD (TX Delay) and determines a delay between PTT and the beginning of the data tones. Usually specified in milliseconds, it is user adjustable to correct for the "slow-on-the-draw" issues of individual radios.

Hi Pedro,
I think you will need to use virtual audio cable connections between the ZS-1 software and the Vara software.?

Mike KV4TT?

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The way this is written seems to generalize that all Class-D audio power amplification results in distortion.? While some Class-D audio amps are terrible - (and the ones in these portable radios certainly are) - not all Class-D audio amplification is flawed where distortions are concerned.? Plus - we're not really dealing with "complex data waveforms" here - it's just audio.

It's not "just audio".? If the class-D amp doesn't switch cleanly or isn't switched at a high-enough frequency, it can/will produce a lot of IMD (Inter -Moduation Distortion.

This doesn't affect modes like AX.25 packet or SSTV that use a single audio tone at a time very much --- but is disastrous to modes with complex waveforms that use multiple SIMULTANEOUS audio tones like VARA, MT-2000, etc., ?

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I actually disagree. I have many HTs such as a th-d72, th-d74, th-f6a, and a ic Id-52a. All of which work just fine with either a digirig or a mobilinkd tnc3/4. All work with either the stock antenna, after market antenna or externally connected antennas ?

The Kenwood TH-D72 and D74 are the rare exceptions among hand helds in that they are actually purpose-built for data.? The RX-to-TX and TX-to-RX turnaround times are optimized for data to support the built-in TNCs.? I don't know about the others you mention.

You must have a remarkably clean unobstructed path to the digipeater or other station if the on-set antennas actually work for destinations more than a few miles away.? Or you have the western scenario of digipeaters on mountains THOUSANDS of feet above the users, yielding a true line-of-sight low-loss path over long distances. ? Or the digi is sited on a TV broadcast tower HUNDREDS of feet above ground level.?

Normally, any kind of? on-the-set? antennas are going provide NEGATIVE gain, due to the radio chassis being too small to provide a decent ground plane/counterpoise to the whip.? (On two meters, the radio chassis would have to be 19" tall to be a decent ground to the whip.)? The "rubber duck" or other whip may be tuned to match the 50-ohm output of the transmitter -- but the radiation pattern is mostly skewed up in the air? instead of straight out at the horizon.?? The only exception would be end-fed half-wave antenna designs which are 38" tall on 2M.?

FURTHER.....

Traditional 1200-baud packet/APRS uses audio frequency-shift keying of a single sine-wave audio tone. Simple AFSK can tolerate a lot of audio distortion and uneven frequency response in the TX and RX audio systems, and still work. ?

ON THE OTHER HAND...

VARA uses multiple QAM (quadrature amplitude modulation) audio subcarrier tones SIMULTANEOUSLY. This kind of very-complex wave form is FAR FAR less tolerant of audio distortion, uneven frequency response and over-driven transmit audio limiters in the radio, than the simple single-tone sine-wave modes like AX.25 packet or SSTV.
??? Audio Inter-modulation distortion (a.k.a. "IMD") in the TX and/or RX audio stages takes the original multiple tones and adds/subtracts them to/from each other, creating numerous additional audio frequencies in the pass-band. All this additional "trash" in the audio pass-band then makes decoding the original tones much more difficult.? Note that this kind of IMD can happen either in the transmit audio chain, or in the receive audio chain if levels are set too high.
??? Transmit audio level setting is very critical on modes like VARA -- You MUST keep the TX audio level low enough that no clipping or IMD happens in the TX mic amp and modulator chain. ??
??? (This is the reason for the complex "auto-tune" trial-and-error level-setting feature in VARA. If you have a communications monitor with a modulation scope, you don't need the auto-tune process -- you can instantly see if the audio wave forms of the transmitted VARA signal have clipped flat tops instead of a mass of smooth rounded over-lapping sine waves)

On receive, it uses a class-D (switching mode) audio power amp to drive the speaker or headphone jack. This amp is very efficient extending the battery life, but has horrendous levels of distortion.? This makes voice sound crappy but still intelligible. It absolutely mangles complex data waveforms.

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Thanks for your email. My end plan is to be able to do VARA? FM mobile with a hand held radio and if I have to, use a portable antenna.? Can you recommend a hand held that will work with a digirg VARA?

Paulbuchanan51@... KO4QWS?

It is utterly unrealistic to use an under-powered handheld as a mobile for data, especially if you don't use a decent external gain antenna.?? Unlike voice, data requires a fully-quieted noise-free signal at the receiving end to work reliably. The kind of signal with occasional pops, snaps and drop-outs that is usable on voice simply WON'T WORK for data.? You MUST have a? "Full smash" hard-quieted signal free of fading or multipath for data applications. It must have enough excess signal that you don't hear "mobile flutter".?

Roughly speaking, you will need two to three times the transmit radiated power? (TX power times antenna gain) for reliable data compared to usable voice over the same path.? If you don't have that kind of solid path, you will flood the radio channel with endless failed transmissions, NAKs and retries. The actual net transmission rate will be a small fraction of the claimed rate for the mode. ?

On Sat, Jul 8, 2023, 9:23 PM Rich Holtman, KD9ANU <rich.holtman@...> wrote:

Paul,

As much as I like my Baofengs for voice work, from everything that I have learned over the past 5 years regarding doing Packet (and VARA), you should expect to be disappointed trying to do VARA or Packet with Chinese HT's.? I don't remember all of the technical reasons, but these include not being fast enough to switch from transmit to receive and vice-versa, therefore data is lost, and the connection fails.? I live 9 miles from our local RMS Gateway (Packet) here in Central Illinois, it is pretty much line of sight except for a few trees, and I have made it work, but not consistently.? Need at least an antenna in the window, or better yet an outside antenna.? So I do 99.9% of my Packet work using a Kenwood TM-71, with an antenna whose base is at 25 feet.

Best of luck,

Rich, KD9ANU

_._,_._,_

---

The Baofeng is a low-end? low-performance? trash radio.?? It is the ONLY radio to ever fail the ARRL's tests for compliance with the FCC's spurious emission standards.??

The problems using it for data are numerous.

It is plagued with a low-performance wobbly unstable frequency synthesizer that takes hundreds of milliseconds to shift from receive to settling on the transmit frequency, when you key up. This can cause part of the header in data modes to be lost before the TX signal is actually on-the-air and on-frequency.
??? Further, there is no TX inhibit that prevents the transmitter from producing output BEFORE the RF carrier is settled on the desired frequency.? Keying up a Baofeng actually causes a full-power carrier to "swish" across several adjacent channels before settling on your channel!? You can see this effect clearly on a high-resolution spectrum analyzer.
??? Even after it gets on frequency, it's carrier has a constant low-frequency jittering or wobbling, not noticeable on voice, that degrades data significantly.?

On receive, it uses a class-D (switching mode) audio power amp to drive the speaker or headphone jack. This amp is very efficient extending the battery life, but has horrendous levels of distortion.? This makes voice sound crappy but still intelligible. It absolutely mangles complex data waveforms. ?

Further (like all handhelds) it lacks the unfiltered flat-frequency-response receiver discriminator output present on full-size mobiles with the 6-pin mini-DIN "data" port. This wide-band receive output is essential for the higher-speeds of VARA-FM.?? (This is a reason nearly all hand helds are a terrible choice for data applications.)

On transmit, you are forced to send the TX data into the mic jack rather than into a dedicated data port.? The transmit speech chain also has a rather high level of distortion that damages data before it even leaves your antenna.? (This problem, common to all hand helds,? is just another reason why hand-helds are a terrible choice for data operations.)

I have a Zeus ZS-1 that unlike Icom 7300 and others only has 1 USB connection that shows up as a com port.

In vara modem setup I can only select the analog audio card of the PC that is not doing anything with the ZS-1.

Any tips how to get the audio routed to Vara modem????

Pedro.wyns@...? ON7WP