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. Compared to 100% of packets using my Yaesu
VX-2R. I know the problem is not the decoder, but the radio audio,
and wondered if there is anything I can do to improve the Icoms.

(And, no, I do not have an oscilloscope.)

Mike

In article ,
Radioactive Man wrote:

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. Compared to 100% of packets using my Yaesu
VX-2R. I know the problem is not the decoder, but the radio audio,
and wondered if there is anything I can do to improve the Icoms.

The first and simplest things I'd suggest a

- Make sure that you've turned the HT's power-saving receiver mode
off! A lot of HTs save battery power by spending most of their
time with the receiver "asleep", turning the receiver on several
times per second, and checking for the presence of carrier. This
will play merry hob with packet reception, as you'll almost always
lose most of the packet-synchronization preamble.

- Turn the HT's volume level down fairly low. You want to make sure
that the analog signal coming out of the HT isn't clipping
(overdriving the HT's audio output circuitry) and isn't overdriving
the TNC's input circuit. It's usually a good deal easier for a TNC
(hard or soft) to track a low-level audio signal, than it is for it
to track an overdriven high-amplitude signal full of distortion and
intermodulation.

If neither of these helps, then I'd suspect that there's some nasty
noise or distortion, or excessive receive equalization occurring in
the HT's audio circuitry, and that some substantial circuit mods might
be required. These would probably require a schematic, 'scope, and
some audio analysis tools such as an audio spectrum analyzer to figure
out properly.

--
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:

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. Compared to 100% of packets using my Yaesu
VX-2R. I know the problem is not the decoder, but the radio audio,
and wondered if there is anything I can do to improve the Icoms.

The first and simplest things I'd suggest a

- Make sure that you've turned the HT's power-saving receiver mode
off! A lot of HTs save battery power by spending most of their
time with the receiver "asleep", turning the receiver on several
times per second, and checking for the presence of carrier. This
will play merry hob with packet reception, as you'll almost always
lose most of the packet-synchronization preamble.

- Turn the HT's volume level down fairly low. You want to make sure
that the analog signal coming out of the HT isn't clipping
(overdriving the HT's audio output circuitry) and isn't overdriving
the TNC's input circuit. It's usually a good deal easier for a TNC
(hard or soft) to track a low-level audio signal, than it is for it
to track an overdriven high-amplitude signal full of distortion and
intermodulation.

If neither of these helps, then I'd suspect that there's some nasty
noise or distortion, or excessive receive equalization occurring in
the HT's audio circuitry, and that some substantial circuit mods might
be required. These would probably require a schematic, 'scope, and
some audio analysis tools such as an audio spectrum analyzer to figure
out properly.

--
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 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 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

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

There's no power save mode or any +5 KHz switch; the radio is very
simple with just a squelch, volume, and transmitting Hi/Lo switch.
And the thumbdials for the frequency. I experimented with the Hi/Lo
switch just to rule that out too.

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.

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

Mike

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

There's no power save mode or any +5 KHz switch; the radio is very
simple with just a squelch, volume, and transmitting Hi/Lo switch.
And the thumbdials for the frequency. I experimented with the Hi/Lo
switch just to rule that out too.

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.

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

Mike

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.

--
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!

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.

--
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!

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.