Re: [digitalradio] QEX Article on HF Digital Propagation
Is there a way of getting the article for the group. It is very important. Thanks Omar YK1AO (now operating under 6C60O commemorating 60 years amateur radio in YK-land) - Original Message - From: Rud Merriam To: digitalradio@yahoogroups.com Sent: Thursday, October 25, 2007 8:10 PM Subject: [digitalradio] QEX Article on HF Digital Propagation There is a great article in the QEX I just received (Nov/Dec 2007). The author is Daniel Crausaz HB9TPL in Switzerland. He reports on modeling and testing PSK, RTTY, Olivia, MFSK, DominoEx and Feld-Hell under various propagation conditions. I need to digest his work with respect to the OFDM proposal since the results indicate PSK may not be an optimal choice. Olivia works better under all the conditions tested. MFSK seems to be second. At first glance I would say this is because the transmission rate is so slow for Olivia at 2.5 character per second. I would find that painfully slow for even a chat mode. Interestingly, RTTY performs about the same under all the conditions tested. PSK either works well or just fails. It has problems in flutter conditions which seem to me be the conditions prevalent a lot of the time. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net
RE: [digitalradio] QEX Article on HF Digital Propagation
There is a great article in the QEX I just received (Nov/Dec 2007). Darn! I KNEW that as soon as I didn't renew my subscription, they'd publish an article that I'd want to read. I don't s'pose somebody wants to violate the copyright by scanning the article in and post it somewhere, huh?? Oh, never mind... forget that I asked that. de Peter K1PGV
RE: [digitalradio] QEX Article on HF Digital Propagation
You might try emailing the author for a copy. I checked the QEX web page because they always feature an article. Unfortunately it was another article for this issue. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net -Original Message- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Peter G. Viscarola Sent: Thursday, October 25, 2007 4:06 PM To: digitalradio@yahoogroups.com Subject: RE: [digitalradio] QEX Article on HF Digital Propagation There is a great article in the QEX I just received (Nov/Dec 2007). Darn! I KNEW that as soon as I didn't renew my subscription, they'd publish an article that I'd want to read. I don't s'pose somebody wants to violate the copyright by scanning the article in and post it somewhere, huh?? Oh, never mind... forget that I asked that. de Peter K1PGV Announce your digital presence via our Interactive Sked Page at http://www.obriensweb.com/drsked/drsked.php Yahoo! Groups Links
Re: [digitalradio] QEX Article on HF Digital Propagation
Dan, HB9TPL, has put a summary of this data on his web page http://www.hb9tpl.ch/5009.html and while you are at it, take a look at his QTH! Perhaps the most spectacular station location I have seen. (even if he does have to do some hiking in during the winter time. Wes, WZ7I On 10/25/07, Rud Merriam [EMAIL PROTECTED] wrote: You might try emailing the author for a copy. I checked the QEX web page because they always feature an article. Unfortunately it was another article for this issue.
Re: [digitalradio] QEX Article on HF Digital Propagation
The best mode to use depends on how much data you want to transmit in a given bandwidth. Moving lots of data in a small bandwidth requires sending one or more bits per subcarrier. Otherwise, you can spread one bit out over multiple subcarriers. For any given user data rate, increasing the bandwidth decreases the required signal to noise ratio. MFSK uses multiple subcarriers but activates only one at a time, encoding 3 bits onto 8 subcarriers, 4 bits onto 16 subcarriers, etc. This is just N-ary RTTY. Multiple subcarriers can be used simultaneously with error-correcting codes like the Walsh function (a Hadamard matrix) which maps 8-bits into 128 subcarriers, 7 bits into 64 subcarriers, 6 bits into 64 subcarriers, etc. This is actually OFDM, but with rate 1/16, 7/64 or 3/32 error-correcting codes. With low SNRs, the hard part is achieving time and frequency synchronization. It seems to me that the ideal HF modem would use OFDM that occupyies a constant bandwidth using a subcarrier spacing that suits the Doppler spread and multipath spread for the current path and changes the code rate to suit the available SNR. 73, John KD6OZH - Original Message - From: Rud Merriam To: digitalradio@yahoogroups.com Sent: Thursday, October 25, 2007 18:10 UTC Subject: [digitalradio] QEX Article on HF Digital Propagation There is a great article in the QEX I just received (Nov/Dec 2007). The author is Daniel Crausaz HB9TPL in Switzerland. He reports on modeling and testing PSK, RTTY, Olivia, MFSK, DominoEx and Feld-Hell under various propagation conditions. I need to digest his work with respect to the OFDM proposal since the results indicate PSK may not be an optimal choice. Olivia works better under all the conditions tested. MFSK seems to be second. At first glance I would say this is because the transmission rate is so slow for Olivia at 2.5 character per second. I would find that painfully slow for even a chat mode. Interestingly, RTTY performs about the same under all the conditions tested. PSK either works well or just fails. It has problems in flutter conditions which seem to me be the conditions prevalent a lot of the time. Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net
Re: [digitalradio] QEX Article on HF Digital Propagation
One thing that would be helpful is that comparisons with Olivia would also indicate which mode they were using. Based on some of his other comments, he felt that you should not have to use more than 500 Hz on 80 meters, so this may have been 500/16. I always try and keep in mind, with mode comparison charts, is that it is for only one set of parameters with specified doppler/multipath, etc. If there was significant polar flutter, the PSK would not operate at all and Domino EX might be a good performer. 73, Rick, KV9U Rud Merriam wrote: There is a great article in the QEX I just received (Nov/Dec 2007). The author is Daniel Crausaz HB9TPL in Switzerland. He reports on modeling and testing PSK, RTTY, Olivia, MFSK, DominoEx and Feld-Hell under various propagation conditions. I need to digest his work with respect to the OFDM proposal since the results indicate PSK may not be an optimal choice. Olivia works better under all the conditions tested. MFSK seems to be second. At first glance I would say this is because the transmission rate is so slow for Olivia at 2.5 character per second. I would find that painfully slow for even a chat mode. Interestingly, RTTY performs about the same under all the conditions tested. PSK either works well or just fails. It has problems in flutter conditions which seem to me be the conditions prevalent a lot of the time. *Rud Merriam K5RUD* ARES AEC Montgomery County, TX /_http://TheHamNetwork.net_/ __._,_.__
