Well, I should point out that I'm not using a regular TNC. I'm using
this: http://www.ringolake.com/pic_proj/zcd/zcdmodem.html

It has worked very well with my little mighty Yaesu VX-2R, just not
with the Icom IC-2N.

Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

Mike


(Dave Platt) wrote in message ...
Thanks for the good advice from both you and Dave Platt. I'll try
lowering the volume and see if that has any effect.

I'm going to bet that this will probably help matters a lot.

I took a look inside the radio and it's all discrete components. The
audio even sounds pretty good (to my ears). And I can transmit
packets from my Yaesu VX-2R to the Icoms from within my apartment with
good decoding.

If you can gain short-term access to an oscilloscope, it'd be
beneficial to simply watch the waveform coming out of the audio-out
jack. Tune to a busy packet frequency (144.390 will usually get you
boatloads of APRS packets), slowly turn up the volume control, and
find the point at which the audio waveform stops increasing in
amplitude and begins exhibiting a flattening-off of the tops and
bottoms. At this point, your signal is clipping - you definitely want
the volume control turned down below this point. Further reductions
may be beneficial if you're accidentally overdriving the TNC's audio
input circuitry.

Can I build a simple filter that removes everything except 1200/2200Hz
tones?

It's possible, but it's not necessarily trivial. It can be done
fairly easily with active electronics (i.e. one op amp and a dozen or
so passive parts). Take a look at www.tnc-x.com and pull up the
schematic - the receive-audio filter is implemented by U4 and the
parts around it.

It can also be done with a strictly passive circuit, requiring no
power, but that's a bit more involved, and will probably require some
fairly large audio inductors.

What you'll want, in either case, is a bandpass filter which passes
roughly 1000 - 2500 Hz, and rolls off both the low and high
frequencies on either side of that passband.

A well-designed TNC should already have this sort of bandpass
filtering built into its input circuit, I think - adding an outboard
filter between radio and TNC ought not to be necessary.

Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

Mike-

That gets back to the +5KHz question. Have you ever had the frequency of the
IC-2N adjusted?

If it is like the IC-2A, there is one master crystal oscillator that sets the
receive frequency, and three oscillators that set transmit minus, transmit
simplex and transmit plus offsets from the receive oscillator.

If the receive oscillator was off frequency, and you had adjusted a transmit
offset oscillator to bring it back on frequency, then the receive frequency
would still be off. Try setting the receive frequency 5 KHz higher and lower
using the thumbwheel switches, and see if either makes an improvement. That
would tell you the radio needs alignment.

73, Fred, K4DII

Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

Mike-

That gets back to the +5KHz question. Have you ever had the frequency of the
IC-2N adjusted?

If it is like the IC-2A, there is one master crystal oscillator that sets the
receive frequency, and three oscillators that set transmit minus, transmit
simplex and transmit plus offsets from the receive oscillator.

If the receive oscillator was off frequency, and you had adjusted a transmit
offset oscillator to bring it back on frequency, then the receive frequency
would still be off. Try setting the receive frequency 5 KHz higher and lower
using the thumbwheel switches, and see if either makes an improvement. That
would tell you the radio needs alignment.

73, Fred, K4DII

In article ,
Radioactive Man wrote:

Well, I should point out that I'm not using a regular TNC. I'm using
this: http://www.ringolake.com/pic_proj/zcd/zcdmodem.html

It has worked very well with my little mighty Yaesu VX-2R, just not
with the Icom IC-2N.

Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

This mdemless TNC design looks to me as if it might be rather
vulnerable to the presence of high-frequency noise in the audio
signal. It's not using conventional bandpass detection, but is using
a simplified zero-crossing detector. High-frequency audio noise could
cause spurious zero crossings, which the firmware in the onboard PIC
might not be filtering out adequately. The IC-2N may have a "hotter"
receiver section which could be passing through more noise from weaker
packet stations.

First thing I might try would be adding a low-pass RC filter - one or
two stages - with a cutoff frequency of 2500 or 3000 Hz. Adding a
series capacitor to act as a high-pass filter at 800 - 1000 Hz might
also help.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
Radioactive Man wrote:

Well, I should point out that I'm not using a regular TNC. I'm using
this: http://www.ringolake.com/pic_proj/zcd/zcdmodem.html

It has worked very well with my little mighty Yaesu VX-2R, just not
with the Icom IC-2N.

Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

This mdemless TNC design looks to me as if it might be rather
vulnerable to the presence of high-frequency noise in the audio
signal. It's not using conventional bandpass detection, but is using
a simplified zero-crossing detector. High-frequency audio noise could
cause spurious zero crossings, which the firmware in the onboard PIC
might not be filtering out adequately. The IC-2N may have a "hotter"
receiver section which could be passing through more noise from weaker
packet stations.

First thing I might try would be adding a low-pass RC filter - one or
two stages - with a cutoff frequency of 2500 or 3000 Hz. Adding a
series capacitor to act as a high-pass filter at 800 - 1000 Hz might
also help.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

I found a picture of the IC-2AT at RigPix and, yes, my IC-2N looks a
lot like that except mine has no keyboard. And mine looks exactly
like the IC-2E, except instead of the 5k/0k switch mine says
Dial/Main.

Mike


(Fred McKenzie) wrote in message ...
I recently got two older Icom IC-2N HTs (2 meter) for use in decoding
APRS packet radio. Nice radios, but I get less than 10% of packets
decoded with either radio.

Mike-

I agree with Dave's assessment of your problem. My first thought was to turn
down the audio level and see if that improved things. Otherwise, check to be
sure your +5 KHz switch is off (or on if appropriate).

Back around 1990, I had an IC-3AT and an IC-2AT connected in an experimental
dual TheNet node, connecting between a 220 backbone network and local access on
Two Meters. I never had a problem like yours.

I'm not familiar with the IC-2N. Could it be a variant of the IC-2A? If not,
then it is possible that model had a differently wired earphone jack, with a DC
voltage on the shield terminal rather than ground. In that case, there could
be a short circuit when connected to a TNC that had its ground also connected
to the co-ax shield on an external antenna. I know this could be the case with
some Radio Shack handheld radios, but have never encountered it with Icom.

73, Fred, K4DII

I found a picture of the IC-2AT at RigPix and, yes, my IC-2N looks a
lot like that except mine has no keyboard. And mine looks exactly
like the IC-2E, except instead of the 5k/0k switch mine says
Dial/Main.

Mike


(Fred McKenzie) wrote in message ...
I recently got two older Icom IC-2N HTs (2 meter) for use in decoding
APRS packet radio. Nice radios, but I get less than 10% of packets
decoded with either radio.

Mike-

I agree with Dave's assessment of your problem. My first thought was to turn
down the audio level and see if that improved things. Otherwise, check to be
sure your +5 KHz switch is off (or on if appropriate).

Back around 1990, I had an IC-3AT and an IC-2AT connected in an experimental
dual TheNet node, connecting between a 220 backbone network and local access on
Two Meters. I never had a problem like yours.

I'm not familiar with the IC-2N. Could it be a variant of the IC-2A? If not,
then it is possible that model had a differently wired earphone jack, with a DC
voltage on the shield terminal rather than ground. In that case, there could
be a short circuit when connected to a TNC that had its ground also connected
to the co-ax shield on an external antenna. I know this could be the case with
some Radio Shack handheld radios, but have never encountered it with Icom.

73, Fred, K4DII

The IC-2N has only 10kHz steps.

Mike

(Fred McKenzie) wrote in message ...
Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

Mike-

That gets back to the +5KHz question. Have you ever had the frequency of the
IC-2N adjusted?

If it is like the IC-2A, there is one master crystal oscillator that sets the
receive frequency, and three oscillators that set transmit minus, transmit
simplex and transmit plus offsets from the receive oscillator.

If the receive oscillator was off frequency, and you had adjusted a transmit
offset oscillator to bring it back on frequency, then the receive frequency
would still be off. Try setting the receive frequency 5 KHz higher and lower
using the thumbwheel switches, and see if either makes an improvement. That
would tell you the radio needs alignment.

73, Fred, K4DII

The IC-2N has only 10kHz steps.

Mike

(Fred McKenzie) wrote in message ...
Did try the volume this evening...I was only able to decode packets
with the volume at least 3/4ths. And even then it wasn't packets from
the local repeater, but from my Yaesu in the other room.

Mike-

That gets back to the +5KHz question. Have you ever had the frequency of the
IC-2N adjusted?

If it is like the IC-2A, there is one master crystal oscillator that sets the
receive frequency, and three oscillators that set transmit minus, transmit
simplex and transmit plus offsets from the receive oscillator.

If the receive oscillator was off frequency, and you had adjusted a transmit
offset oscillator to bring it back on frequency, then the receive frequency
would still be off. Try setting the receive frequency 5 KHz higher and lower
using the thumbwheel switches, and see if either makes an improvement. That
would tell you the radio needs alignment.

73, Fred, K4DII