--- jgorman01 <[EMAIL PROTECTED]> wrote: > --- In [email protected], Jose Amador > <[EMAIL PROTECTED]> wrote: > > --- jgorman01 <[EMAIL PROTECTED]> wrote: > > > > > I've been reading all the posts over the last > > > several weeks about > > > single tone/multi-tone, baud/bps, narrow/wide, > etc. > > > digital > > > modes/modems. The one thing I see missing is > any > > > discussion of the > > > actual RADIO's being used in these systems.
Well, maybe because some on the group are feeling that what is failed is the modulation format used on HF packet, which had been the "reliable mode" for amateur data comms on HF . The key problems have been inter symbol interference, using a too high transmit speed at times, and the fact that a single bit error trashes a frame. Be it ISI, collissions or whatever, it does generate much more activity on the air than really transferred data. Pactor is one solution, but a costly one for many. I have been a packet sysop (FBB/JNOS/etc..)for some 15 years, and I switched to pactor for forwarding about 8 years ago. I did see a 10:1 improvement in thruput in the switchover. So I do know that better solutions DO exist, the point is finding out an affordable better one. > Kind of > > > funny in a > > > digital RADIO forum populated by amateur RADIO > > > operators. Perhaps I > > > am just too impatient and the discussions will > > > eventually > > > end up discussing the radios being used. I believe that with the modes nowadays in use, "the channeĺ" (read, the ionosphere) imposes more restrictions than the radios we are using. Of course, the radio must be considered in the design of newer modes and communications formats. I do believe it is sort of automatic, if the guy is clever enough to develop it, will do it considering the existing regulations and the available radios. Maybe some will consider some hardware modifications . But so far, the ionosphere, and REGULATIONS are the straitjackets we face. I believe this is a team effort, and everyone will contribute with whatever he/she feels can do to help. > > At least I am assuming a COTS radio, 300 to 2700 > Hz > > audio bandwidth. That's what I have. > > > > > Some of my observations. > > > > > > Lots of discussions about specifications for > > > different modems and > > > their operation. I haven't seen any discussion > > > > about the > > > corresponding specifications of the radios they > are > > > connected to. Because most of the available radios have not been the worst offenders in the system when properly used. Packet radio was born with the extrapolation of a protocol thought for line transmission, using the AVAILABLE modems at that time, and somehow, it worked. But it was not a perfect solution. > > > Just wonder how ham radio transceiver audio > chains, > > > mixers, filters, > > > and RF chains, both transmit and receive, > compare to > > > the mil spec > > > transceivers used with mil spec modems? Maybe mil spec modems prove to be not adequate in their original form. But knowing they do exist, and what have attained is something good to know. It is not the same to figure out the wheel, as seeing it on use. Maybe if it is too wide for our trail we can chop it a bit on each side until it fits... > > > > > > Audio purists spend thousands of dollars on > > > pink/white noise > > > generators, equalizers, audio amps, speakers, > etc. > > > to insure flat > > > responses. What kind of distortions do you > think > > > are allowed in ham > > > radio audio chains. > > > > So far....10%....- 20 dB at worst case. Should be > > > better for complex modulation formats. > > That's 10% at one end. Add another 10% for the > other end. That is, > 10% distortion in the transmit audio and another 10% > in the receive > chain. Not very good! Well, on digital, nonlinear distortions add up as noise. You will get just a bit higher BER and a bit broader signal. > > > > > Are there amplitude/frequency > > > variances > > > introduced in the preamps and amps? Are there > > > phase/frequency > > > variations introduced in the mixers, amps, and > > > filters? Do these > > > have any effect on trying to cram high speed > modem > > > tones through the > > > system? I suspect that there can be as much or > more > > > effects due to > > > these variables as propagation introduces. > > > > If you stay near the center of the passband and > shy > > away from the slopes, shouldn't create serious > > problems > > I guess my point is, do you know what your passband > is in your > radio. Are the 3 db points really at 300 and 2700 > Hz? Yes, I can see the spectrum on my PC. > Are there any fluctuations at other frequencies in > the passband? None to consider with the filters I am using. There is NO RIPPLE in the passband. Yes, I am lucky.... > What about phase variances throughout the passband? Does it really matter NOW ? > Your answer assumes that the design of the amps are > adequate to begin with. Have you actually measured > this? Exhaustively....no, I have not. I have done the measurements required to know they are good enough. Period. > > > > > Has anyone measured the difference between a > $50,000 > > > Harris HF > > > tranceiver designed for this purpose and a $500 > Icom > > > tranceiver to > > > see if the throughput is better? > > > > Maybe the performance difference does not justify > the > > price difference...makes me remember the $500 > > hammer... > > Maybe the cost difference isn't justified, but that > wasn't my > question. Is there a substantial difference in > performance? Who has such a radio to do the comparisons? > > > Perhaps I'm just an old fogey who still enjoys > > > messing with and > > > building radios and am not competent enough in > the > > > digital modes to > > > add much to this discussion. However, I can > assure > > > you building a > > > mic preamp or a receive audio amp that has a > flat > > > amplitude response > > > over 300 Hz to 3500 Hz is no mean feat let alone > the > > > phase > > > differences that can be introduced by using > heavy > > > feedback to > > > acheive this response. I can also tell you from > > > > first hand > > > experience that building a crystal filter > without > > > amplitude/phase > > > variances is very difficult. Yes, I do know. Phasing and DSP methods can achieve better results than homebrewing crystal filters. My first serious transmitter, built by myself, was a phasing one. It had a hard to beat audio quality. I did the two tone measurements, comparing inputs and outputs, from the microphone to the antenna. > > Well, the problem in the past has been more of > > inapropiate modulation and coding formats rather > than > > radio insufficiencies, in general. > > You say this in a manner that leads me to believe > you have made > actual performance measurements of different stages > in your > transceiver so that you are sure it has no > significant effects on > the transmitted digital signal. Would you mind > sharing these? Well, I have spent much more time operating than measuring. And seen it did not only happen to me, but to others as well. Using a too sharp filter can be good for QRM elimination, but may hit the thruput. You have to choose whatever is best on the fly... > I'll mention just one item to consider. Do you run > PSK31 at full > output or do you have to reduce your output in order > to minimize the > IMD distortion. It depends on what you name as "full output". For me, power output is the PEP power you can achieve with -30 dB IMD on modes with an envelope. Of course, it will show as a much lower "RMS" output power. Some manufacturers may set the limit lower, say -40 dB, or even lower. How much does it add up to the cost? Does it really matter? > Do you think the military high > dollar rigs require > their power to be turned down to 20% of rated > output? What does > this tell you about the design of the high power RF > stages in an > amateur transceiver? I don't know. But all radios are not made equally, be them ham radios or MILSPEC radios. > > > > > I just wonder if some of this shouldn't also be > > > > discussed along with > > > the "digital" side of the conversation. A > system > > > must have all of > > > its individual components discussed and > designed. > > > The RADIO is a > > > very important part of this. Every person is entitled to see priorities in a different order. That allows, on a group, that everyone chooses the area he is most competent or likes best. > > Of course. Certainly my old HRO or a Viking > Valiant is > > insufficient for this. It is generally accepted > that > > it takes a synthesized radio to start with. > > Why does it take a synthesized radio to start with? > Even a > synthesized radio can have frequency stability > issues. Frequency > stability is only one issue in a whole slew of them. To my experience, it is one of the worst offenders in real life. I have built, modified and repaired transmitters, receivers, and many components in my ham station. I have been a licensed ham for 34 years, built some of my own equipment until I have been fortunate enough to use factory made radios, not an easy feat in my environment. Some factory made radios are good, some stink. I do know I have not seen everything. I do have some modest instrumentation and I believe that state of the art ham radios are not the limit we face nowadays. 73 de Jose, CO2JA __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! 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