Hi Scott: Apparently, the designers of the PK232s did not think a software method of changing the transmit signal shift width was important enough when they decided that demodulating the 170 Hz shift modes (e.g. RTTY) would be accommodated. Reception of 200/170 Hz shifted signal by a 170/200 Hz Mark/Space decoder might not be possible during adverse propagation conditions. The ease of swapping resistor component that determine the amount of shift spacing depends on the skill level of the individual. Speaking candidly for myself, in some cases, I have not been able to separate the case of a VCR or of a CD player from the main chassis !
Some would also argue that a diddle signal is not important, but it might very well be. Again, under adverse propagation conditions, the absence of a diddle signal could mean no printing of the received RTTY signal. When a diddle signal is included within a RTTY transmission, typing ahead of the spooling transmit text buffer is less important. There are few RTTY operators that can type with accuracy at a rate greater than 60 wpm, and I am NoT a member of that elite group. Once the spooling transmit buffer empties, the keys struck by the operator demonstrate his true typing and spelling skills. OTOH, Level of education (grammar skills) is not affected by the use of the type ahead transmit buffer. I have read an article published on the internet about adjustment/calibration of a PK232 for 170 Hz shift, by changing a couple of resistors; however, if I recall correctly, that article mentioned a built-in PK232 calibration command for setting up the center frequency/mark frequency/space frequency. But, I do like your idea of using MMTTY as a reference/detector. Recently, I have been thinking about how the WWVH standard audio signals and MMSSTV's 1200 Hz sync pulse hairline can be used for calibration purposes. I use MMTTY here, and appreciate that software a whole lot. When printing those stations using PK232 200 Hz shift, I have noted that the MMTTY demodulator Mark tone changes, even when AFC is enabled, if the station that was previously transmitting was using 170 Hz shifted tones. It seems that two stations, one using 170 Hz spacing, the other using 200 Hz spacing, can never be "displayed" as being on the same Mark frequency point. Have you, or anyone else, observed this same phenomenon ? Perhaps those that began with TNCs stayed with the 200 Hz shift width that was forced upon them; however, I have yet to come across a MMTTY or MixW user that chooses to use a transmit shift width of 200 Hz.. OTOH, choice of low tones vs high tones is yet another story. 73, de ~ Vince ~ Scott Erwin wrote: >The PK-232 and KAM TNC's are setup for 200 HZ shifts, >which is used for Packet and Pactor modes. The other >modes were added as an afterthought. When Packet came >along the Terminal units of the day could not manage >speeds faster than 110 Baud with a 170 Hz shift used >for ASCII mode. The "new" modems contained not only an >internal computer that operated the high-speed >1200-baud packet modem but it could be run at 300 baud >rates as well to allow packet operation below 28 MHz. >The filter system was optimized for 200 Hz shift and >all other modes were programmed into the onboard >computer to allow operation of Amtor, RTTY, ASCII, and >FAX modes as well. 200 Hz was not really that for off >and as many thousands of the PK-232 and KAM TNC's were >built no one really noticed as almost everyone had >simply started operating at 200 Hz shift for >everything. With the advent of the sound card used as >a modem problems started cropping up due to improper >interfacing between the sound card and the >transceiver. Operator error also comes into play as >can be seen daily on the amateur bands with not one or >two stations overdriving the microphone input but many >stations using many different modes up and down >several bands creating distorted and overly wide >signals. Another problem with the sound card is the >high noise environment of the computer case it resides >in. HAL faced this problem early on by producing their >internal TNC cards with four layer circuit boards with >both outside layers as ground shields. Cheap computer >sound cards do not have this feature. As far the >170/200 Hz problems, that can easily be overcome with >a few resistors in the input audio filter sections >that bring the 200 Hz shifts back to 170 Hz shifts and >a turn of a pot takes care of the transmit shifts. A >better way is to simply plug a high quality Terminal >Unit into the TNC at the point where the internal >modems would be connected to the internal computer. A >simple switch arrangement would allow switching >between the internal modems for Packet and Pactor or >the external Terminal Unit for all other "170 Hz" >shift modes. I personally have never had any problems >running 170 Hz shift with a HAL ST-6000 with it's >extremely narrow active filters in AM or FM mode and >another station running 200 Hz shift on transmit. The >difference in shift is not so great that it impacts >operation all that much. If this causes a problem with >a sound card the solution would be simple, simply >change the settings of the sound card program to use >200 Hz shift to match the hardware of the station your >working. MMTTY allows this and I have used this >program as a way to calibrate many TNC's after making >repairs. Simply make a null audio cable interface >between the TNC and the sound card. This allows you to >see the transmitted audio from the TNC AFSK output to >the sound card line in jack and the sound card speaker >output via a 10K and 100-ohm attenuator pad to the TNC >audio input jack. With this setup you can check the >TNC audio input and output circuits and indicators. >--- Vince <[EMAIL PROTECTED]> wrote: > > >>Is this thread: THEM vs US ? I got here late >>because McAffee SPAM >>KILLER was killing this reflector's messages ..... >> >>John: Are you saying that 40% of the tones are >>generated out of spec? >> >>I have not ever owned a TNC; however, I have managed >>to decode RTTY >>signals that are playing within the same ballpark, >>even with a Radio >>Shack Color Computer (CoCo) back in 1986, and decode >>with a PC and sound >>card, since 1994. Perhaps the problem is that 40% >>of the RTTY oprs are >>using a TNC that does not use the standard 170 Hz >>shift for RTTY; mabbe, >>if the ST-6 filters are that sharp . >> >>It is a shame that PK232s and KAMs cannot be easily >>adjusted for a 170 >>Hz shift, or can they be? Two stations that I hear >>often still use 200 >>Hz shift while on RTTY mode with their PK232s. >>Apparently, the TNCs are >>not flexible, or those two stations do not know/want >>to use the standard >>shift for the mode. The RTTY sound card software >>DSP filters are sharp, >>and they do not present any problem printing either >>TNC or sound card >>generated tones. >> >>73, de ~ Vince ~ >>WA2RSX IOTA NA-026 >> The K3UK DIGITAL MODES SPOTTING CLUSTER AT telnet://208.15.25.196/ <a href="http://dxcluster.blogspot.com";><img src="http://feeds.feedburner.com/DigitalSpotter.gif"; height="67" width="200" style="border:0" alt="Digital Spotter"/></a> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
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