[App_rpt-users] AllStar Node / repeater radios

David McGough kb4fxc at inttek.net
Thu Sep 24 10:34:05 EDT 2015


Hi Skyler,

Yes, I agree with you that the 888 has amazing audio for being a $12
radio!

While I haven't personally tested the 888 for the various parameters
needed to make a high-speed MODEM work (such as needed for D-STAR or 
9600baud packet radio), I don't expect the 888 would ever be suitable.

High speed MODEMs require a very clean and consistent audio pass band,
hence why discriminator audio and direct modulation are used. Without
getting deeply into the details, what I mean by this is that audio
processing and various filtering (e.g.: high-pass to eliminate PL tones
and low-pass for de-emphasis, etc.) causes frequency-specific audio phase
shifts and changes in group delay. None of this particularly matters to
the human ear. But, to a high speed MODEM, these minute changes are deal
breakers--the MODEM won't be able to decode. Years ago (in the packet
radio era) there were some good articles with photos describing all this
in detail. I'll try to find more info if you're interested?

73, David KB4FXC







On Thu, 24 Sep 2015, Skyler F wrote:

> Well my personal experience with a baofeng node is really good audio
> reports, and sometimes better than my motorola SM-50 discriminator audio. I
> just use the internal tone decoder in those baofeng radios for COR.
> 
> Would they not be suitable for DSTAR though?
> 
> On Thu, Sep 24, 2015 at 8:05 AM, Skyler F <electricity440 at gmail.com> wrote:
> 
> > Well my personal experience with a baofeng node is really good audio
> > reports, and sometimes better than my motorola SM-50 discriminator audio. I
> > just use the internal tone decoder in those baofeng radios for COR.
> >
> > Would they not be suitable for DSTAR though?
> >
> > On Thu, Sep 24, 2015 at 7:41 AM, Steve Zingman <szingman at msgstor.com>
> > wrote:
> >
> >>
> >>
> >> On 9/24/2015 9:30 AM, Skyler Fennell wrote:
> >>
> >>> Can I have an explanation of why discriminator is needed for anything
> >>> but actual digital modulation like 9600 baud?
> >>>
> >>> To prevent PL tones?
> >>> Nope, when plugging in good headsets I can hear the CTCSS tone from the
> >>> repeater and even on the baofeng.
> >>>
> >>> Lack of high frequency noise?
> >>> Put a high pass filter
> >>>
> >>> Someone please explain why discrim is needed. Good audio is good audio
> >>> and can't it be manipulated to fit the needs of the application?
> >>>
> >>> Maybe I don't want other filters inline, I want total control of the
> >> receive audio. de-emphases CTCSS filtering etc.
> >>
> >> If worried about audio levels, put an AlC which automatically feeds the
> >>> system (weather Allstar or free star) with the perfect level independent of
> >>> the level of the user.
> >>>
> >>> Please note I'm only talking analog.
> >>>
> >>> 73
> >>> Skyler KD0WHB
> >>>
> >>> On Sep 24, 2015, at 7:15 AM, Steve Zingman <szingman at msgstor.com> wrote:
> >>>>
> >>>> Being a DSP based radio, the BF888 is a cheap low power analog only RF
> >>>> package. Given the lack of discriminator and modulator access it is limited.
> >>>>
> >>>> For a receiver the Maxtrac  / Radius / GM300 work well. For a
> >>>> transmitter not so much. Heat output and with the Maxtrac, problems with
> >>>> power and deviation control out of band can cause problems without custom
> >>>> firmware or hardware hacks.
> >>>>
> >>>> My absolute favorite RF gear for Analog / Digital repeaters is Tait.
> >>>> The T800 series is a purpose built programmable Exciter / Receiver package.
> >>>> With access to all the signals anyone would want. I started using them for
> >>>> 927 MHz repeaters and have had great performance on UHF and VHF. Mix and
> >>>> match at will. Pair a VHF receiver with a UHF or 900 MHz transmitter for a
> >>>> nice RF linked receiver site. For link radios simplex nodes and "Hot Spots"
> >>>> I've come to favor the Tait T2000 mobiles. They are easy to program, well
> >>>> documented, lots of IO and run cool in transmit.
> >>>>
> >>>> The above is not to say there are not a LOT of great repeater / node
> >>>> packages out there. The GE MASTR II comes to mind. I have to mention the
> >>>> Micor to keep the flack down. ;) I've built repeaters using everything from
> >>>> a Motorola 30D to current equipment.
> >>>>
> >>>> Your mileage may vary.
> >>>>
> >>>> 73, Steve N4IRS
> >>>>
> >>>> --
> >>>>          ,,,
> >>>>         (o o)
> >>>> -----ooO-(_)-Ooo------
> >>>> --- N4IRS was Here ---
> >>>>
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> >>>
> >>
> >
> >
> > --
> > Skyler Fennell
> > amsatnet.info
> > KDØWHB
> > electricity440 at gmail.com
> >
> 
> 
> 
> 




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