[OZAPRS] Help with THD7

[Robert Bruninga]

> > I have noticed that my THD7 no longer decodes as many 
> > broadcasts, stations and messages as it used to. 
> > I seem only to have them decoded when I have
> > line-of-sight with the digi and I get a full strength 
> > signal.

The TH-D7 uses a flat audio response and many digi's use
pre-emphasized audio.  And most digi's are not even properly
tweeaked to transmit good audio in the first place.  A lot of
them are just plugged into a TNC and let-er-rip.  So it doesn't
take much of a skew in audio tones due to the digi's modulation
levels or biases, or audio rolloff to make even tstrong packets
undecodable.

On the other hand, the D7 will properly decode a very weak
packet signal transmitted by any other radio with flat audio
response.  Typically, a D7 will decode packets all the way down
to three LCD bars on the signal display.  While at the same
time, not decoding anything from a full-scale packet from a
sloppy digi.  SO before sending the radio back, I would find a
friend with another D7 and send some packets bac and forth
DIRECT simplex on a non-aprs chanel using Extremely Low power.
Then see how well it decodes.

> > I really noticed it when yesterday evening PCSAT went 
> > almost overhead (86 degrees) and I could barely hear 
> > packets while monitoring, yet my positions were
> > uploaded without problems.

That is interesting.  It actually makes two conflicting points.
On the one hand, you say the D7 hears the digi full-strength and
get no decodes (implying a decoding problem) and this PCSAT
comment appears to sugggest an RF weakness problem?  But the
PCSAT downlink is relatively FLAT audio, and so I do expect it
to often decode on a D7 with a weak signal.

Another thing to consider is that if you have both the A and B
side receivers BOTH tuned to the same frequency then the AUDIO
out the speaker is distorted and significanly reduced in level.
This is because the audio from the two recievers is mixed
together at the audio amp and I have noticed the signals must be
180 out of phase, because they appear to cancel making the audio
ver weak.  Also check your audio BALance control to make sure
you have not suppressed the A side volume?

Ayway, just some ideas to consider before shipping it anywhere.

Bob, WB4APR

> so I think the
> > APRS receive side may need alignment?
> > 
> > Does anyone know how to align/tune the APRS receive side of 
> the THD7 or
> > can anyone recommend a service agent who could do it for me?
> > 
> > Thanks in advance
> > Ian
> > vk2him
> > AWA Limited
> > 
> > 
>
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