Best Input For Data Interface…

[BMDaug]

So I’m using a soundcard interface for APRS and WinLink over VARA FM with one of my XG100Ms. I have the sound card interface (DRA-30) connected to the 40 pin accessory port using a custom cable. Right now, I’m using the ‘fdisc’ filtered discriminator output pin to get audio out of the radio, which I think is the best option as far as output audio bandwidth, but I’m just using the ‘ext mic’ pin to send sound into the radio. I think I’m limiting the bandwidth by doing so. Would it be better to use the ‘ext tone encode’ input? Would this bypass some of the filtering and yield a higher data transfer speed? I use one of the aux inputs as ptt, well actually ‘alt ptt’, which allows me to specify an alt ptt channel per frequency set/system so I can use a designated channel for data without constantly sitting on that channel… the radio will always TX data on the specified data channel, which defaults to APRS, but may be FPP’d when using other modes.

APRS works great, but like I said, I think I’m limiting throughput by using a mic input, I’m just not sure what the best (read least filtered and widest bandwidth) input actually is…

Is an external tone encode input generally considered unfiltered or at least less filtered than a mic input?

Thanks for reading!

-Brian

 

[AK9R]

Maybe.

APRS at 1200 baud is AFSK using two tones, 1200 and 2200 Hz.

I don't know what VARA FM uses, but I doubt that any of the tones are higher than 3000 Hz.

The issue may be that the audio going in through the microphone input is pre-emphasized in that the high frequencies are increased in amplitude (the receiving radio de-emphasizes the audio so things sound natural). Discriminator audio is often not de-emphasized, but maybe the "filtered discriminator" output is. However, I think I'd contact Kevin Custer at Masters Communications, the people who built your DRA-30, to see what they say about it.

There's an extensive discussion about pre-emphasis, de-emphasis on the Repeater Builder website.

 

[BMDaug]

Maybe.

APRS at 1200 baud is AFSK using two tones, 1200 and 2200 Hz.

I don't know what VARA FM uses, but I doubt that any of the tones are higher than 3000 Hz.

The issue may be that the audio going in through the microphone input is pre-emphasized in that the high frequencies are increased in amplitude (the receiving radio de-emphasizes the audio so things sound natural). Discriminator audio is often not de-emphasized, but maybe the "filtered discriminator" output is. However, I think I'd contact Kevin Custer at Masters Communications, the people who built your DRA-30, to see what they say about it.

There's an extensive discussion about pre-emphasis, de-emphasis on the Repeater Builder website.

Thanks! Kevin is a great guy. I’ll definitely reach out to him. I’m really just asking generally about external tone encode inputs. I know they are used when building ham repeaters where you want to auto-identify without a code, but still want subscriber radios to use coded squelch. So it would seem that the input would be less filtered as you are needing fairly broadband signals when using codes, when compared to a mic input which is optimized for voice.

Thanks for the help!

-B