Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
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 |
#2
|
|||
|
|||
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! |
#4
|
|||
|
|||
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 |
#6
|
|||
|
|||
|
#7
|
|||
|
|||
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! |
#8
|
|||
|
|||
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 |
#9
|
|||
|
|||
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! |
#10
|
|||
|
|||
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. |
Reply |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Improve handheld audio? | Digital | |||
Improve handheld audio? | Digital | |||
Amateur Radio Newslin(tm) Report 1385 – February 27, 2004 | Dx | |||
Amateur Radio Newslin(tm) Report 1385 – February 27, 2004 | Dx | |||
Automatic RF noise cancellation and audio noise measurement | Homebrew |