[OZAPRS] FT-290R + Signalink USB

Fri Feb 10 12:20:38 EST 2012

All,

This link has been posted previously - 
http://www.febo.com/packet/layer-one/transmit.html - but it's worth 
posting again as the article describes, in simple language and with 
oscillograms, packet tone levels, pre/deemphasis and everything else you 
need to know to properly set up a 1k2 packet station (VHF APRS is 1k2 
packet). It is invaluable reading, especially for newcomers but also for 
old hands.

Ray, vk2tv

On 10/02/12 10:57, Nick (VK3TY) wrote:
> Ray/Et-al,
>
> "Nail on the head" stuff.  Pre/de-emphasis - the bane of all communications
> equipment when you want to do something just a "little" different to what he
> manufacturer deems "ideal".
>
> You could be any closer to the mark Ray.  Without a CRO trying to do it by
> ear just does not cut the mustard.  At audio levels, just about any CRO will
> be a major asset.
>
> The Visual Analyser 2011 I have not tried - only because I already have two
> Digital Storage Oscilloscopes.
>
> The problem for many is that they do NOT have an oscilloscope, and to buy
> one JUST to do ONE setup is crazy.  Hence personal networking - finding
> someone in the local area (who is willing) that can help out with once-off
> needs.
>
> How does this help Jill.  Don't know - I just hope that what we have
> discussed does help.
>
> Nick - VK3TY
>
> -----Original Message-----
> From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
> Behalf Of Ray Wells
> Sent: Friday, 10 February 2012 9:17 AM
> To: ozaprs at aprs.net.au
> Subject: Re: [OZAPRS] FT-290R + Signalink USB
>
> Nick/All,
>
> Let's not forget that the frequencies are 1000Hz apart for 1k2 packet
> (1200/2200Hz) and frequency response at those two frequencies may be all
> important for successful decoding of packets.
>
> Assuming the correct (6dB/octave) pre-emphasis at the tx, the rx
> discriminator output will show high tone close to twice the level of the
> low tone and, for post de-emphasis, the two tone levels will be close to
> the same. Those situations are normal. Things can get a bit off the
> rails, however, if speaker audio is taken for the TNC/modem.
>
> By way of an example, the very first radio I used for packet, about
> 1985, was a Multi-750 (FM/SSB/CW). The "speaker" audio had been tailored
> so severely (presumably to make the audio sound half decent on SSB) that
> the level at 2200Hz was way short of what was required for the TNC.
> Enough that I could decode about one packet in one hundred. As a
> stop-gap measure I made an external RC filter to provide locally
> pre-emphasised audio for the TNC (TNC220). Later, I took post
> de-emphasis audio from inside the radio, via an emitter follower.
>
> Modern modems and perhaps software modems are probably more tolerant of
> incorrect audio levels than TNC's based on the Exar 2206/2211 pair where
> the decoder chip would fail to decode if the high tone was even 1-2dB
> lower in level than the low tone. The TNC2 and variants (MFJ1270, e.g.)
> all used the Exar pair.
>
> Whenever I have decode issues, the first thing I check is the relative
> tone levels with a CRO. There are plenty of software oscilloscopes
> available these days so almost everyone can have access to a CRO. I
> recommend you look at this piece of Freeware - Visual Analyser 2011. To
> quote WA8LMF, "This *FREEWARE*  program, written by an Italian
> electrical engineering PhD candidate at the University of Rome, emulates
> a whole stack of HP audio test instruments in a single 5 MB exe file."
>
> It is an impressive array of audio test equipment.
>
> Ray, vk2tv
>
> On 10/02/12 08:14, Nick (VK3TY) wrote:
>> Hi there,
>>
>> I used to used my FT290R Mk I on Packet back in the early days.  The
>> interface cable went directly to the multi-pin plug without having to
> insert
>> or bypass anything. I'll be back on air with AX.25 signals shortly - using
>> my Yaesu FT-290R and original interface a cable.
>>
>> The issue of frequency response is somewhat a mute point when only two
>> (mark/space) tones are used.
>>
>> The IRLP link I provide does have an issue using a direct link to the
>> microphone and audio output.  The radio circuits have de-emphasis and
>> pre-emphasis can have a significant effect on the full voice frequency
>> range.  That is why with IRLP, audio is take off post the discriminator
> and
>> mic. audio is fed in at another point leaving the normal microphone and
>> speaker points alone.
>>
>> Nick - VK3TY
>>
>> -----Original Message-----
>> From: ozaprs-bounces at aprs.net.au [mailto:ozaprs-bounces at aprs.net.au] On
>> Behalf Of Peter Dodd
>> Sent: Thursday, 9 February 2012 10:37 PM
>> To: Australian APRS Users
>> Subject: Re: [OZAPRS] FT-290R + Signalink USB
>>
>> Hi,
>> I have a FT-290R but have not used it with Signal link (because I don't
> have
>> one).
>>
>> I recall seeing that a capacitor possibly need removing from the mic cct.
> to
>> use the radio for packet (something about frequency response).
>>
>> Not sure if I can find article.
>>
>> Regards
>>
>> Peter
>> VK7KPC
>> ----- Original Message -----
>> From: "Liz"<edodd at billiau.net>
>> To:<OZAPRS at aprs.net.au>
>> Sent: Thursday, February 09, 2012 10:07 PM
>> Subject: [OZAPRS] FT-290R + Signalink USB
>>
>>
>>> Has anyone got this combination of an FT-290R and a Signalink USB
>>> operational?
>>> I don't think reinventing the wheel is worthwhile, so I thought I'd ask.
>>>
>>> I also realise that the radio is old, and no one may have one in use.
>>>
>>> Liz
>>> _______________________________________________
>>> OZAPRS mailing list
>>> OZAPRS at aprs.net.au
>>> http://lists.aprs.net.au/mailman/listinfo/ozaprs
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