[digitalradio] RFSM-8000 v.0536
New releases RFSM-8000 v.0536 on http://rfsm2400.radioscanner.ru
[digitalradio] RFSM-8000 v.0536
New releases RFSM-8000 on http://rfsm2400.radioscanner.ru
[digitalradio] Re: RFSM 8000
Hello Rick. Let's turn our attention to the "astonishing" robustness of Pactor-2/3. Surprisingly low signal to noise ratio can be reached due to using low-speed rate of the low band signal ONLY. How does it work? First of all low signal to noise ratio declared by the producer are not measured in the small band, used by Pactor signal, but in the whole band of the standard telephone channel (0,3-3,4 kHz). So the noise is assigned evenly to the whole band. Then the process of treatment is as follows: as the "useful" signal is concentrated in a certain definitely appointed frequency area the preliminary digital filtration is used. As a result the noise that does not get to the "useful" signals would be filtered consequently the signal to noise ratio will be much better in fact. So the question arises "it still works" where is dirty trick? In fact it works if the noise is assigned evenly. But it would fail because of any interference in "useful" Pactor signal, even if the signal to noise ratio in the whole band is more than 30 dB. Furthermore if considerable staggering of transceiver or Doppler shift occurs the system will work badly or even stop working as the part of "useful" Pactor signal will be cut by the filters. The experience shows that the situations of that kind are widespread. Ok I believe that the further development of this technology can be in using much more low band signals like CW. Especially if transmit symbols at a rather low speed. The duration of sending will be high and signal to noise ratio (for the WHOLE band) will be really impressive... don't you think that it is rather amazing and this way carries to the point of absurdity... If use the decision like this using low band signal, one should provide a frequency hopping in band 0,32.7 êÃö. In that case it will work in lager number of occasions, but still not in every one. The technologies like this are going out of use in professional radio-communication. As for serial tone modems with adaptive algorithms they are of far-reaching importance. In particular using the antenna diversity method allows improving the signal to noise ratio and filter out the noise from other directions. Speaking about changing the modulation in MIL-STD modems it should be remarked that in supplement to the standard the 39-tone OFDM modem is really described. But I'm afraid that standard software (like STANAG-5066) will fail to switch rapidly from one rate to another due to rather simple reason. To choose the optimal rate one should always estimate the channel characteristics. Only this information can help to make a good choice. Such modems do not estimate this and however can not give them to the application software. In RFSM uninterrupted estimation of channel state takes place and this very estimation allows choosing the optimal speed of data transmission. So if the state improves RFSM will choose the maximum speed that is possible. For example in Pactor-2/3 increasing/decreasing the speed carries stepwise. Like the method "now I feel better so I can transmit faster" or vise versa "I feel bad so I should decrease the speed at one level" :) About using MIL-STD 188-110A/B technology. The modems used in MIL- STD are "dumb", and can provide just non-guaranteed simple txt-files transmission. In that case even the speed of transmission must be chosen by the user. The software that realizes data link protocol and different user's services provided additionally. The RFSM has not only a "dumb" modem, but also data link protocol optimized for this standard, and different users services. Dmitry.
[digitalradio] Re: RFSM 8000
Hello, Chuck. About your question. You may go to our web-page: http://rfsm2400.radioscanner.ru There is links to e-shop "plimus.com" 73, Dmitry.
[digitalradio] Re: RFSM 8000
Hello Rick. As regards the speed that is slower 600 in MIL-STD 188-110A/B. There are 300, 150, 75. In my opinion speed reduction has been made nonoptimal, using "dumb" repetition of data in 300 and 150 is not needed. The theory of coding says that repetition is the worst way to improve noise immunity. Speed 75 based on the method of "spectrum spread" by orthogonal consecution by Walsh. It's rater good but this speed uses repetition as well. We consider that the speed 300, 150, 75 allows reaching better characteristics of noise immunity that the standard MIL-STD 188- 110A/B allows. Frankly speaking the standard MIL-STD 188-110A/B has been used our product to be noticed by customers. But true to say it contains nonoptimal solutions. Turning to the point of RFSM we should admit that we have mistaken making the minimal speed - 600. I hope we improve it in the near future. Dmitry.
[digitalradio] Re: RFSM 8000
1. A few words about OFDM and serial tone modem. Let's find out how the fight between ISI and Doppler shift takes place in these systems. OFDM uses the great number of low speed channels so the symbol duration increases. While the duration of ISI is much smaller than symbol duration everything goes well. Consequently there is an aim to increase the number of channels ad infinitum BUT at the same time natural limitation takes place. It's just a Doppler shift effect. Hence there is always a compromise between ISI and Doppler shift. Moreover we should take into consideration a big peak factor which results in non-effective usage of power of transceiver. There are methods directed at improvement of peak-factor, but the most part of them makes the system characteristics worse. In case of serial tone modulation the fight ISI with Doppler is provided with adaptive algorithms. The more effective and faster they are the larger number of Doppler and ISI the modem can manage. As for RFSM it should be mentioned that now it includes rather efficient adaptive algorithms that work properly at a speed of 600(500) up to 4800(4000) bps (wide/narrow mode). To work at a speed 6400(5333) - 8000() much more compound algorithms are needed. In particular using turbo-equalization will improve noise proof feature at all rates. Therefore OFDM and serial tone modem can be more efficient in dependence on channel statement. In my opinion serial tone modem with effective adaptive algorithms is the most effective. We'd like to mention that under certain circumstances either serial tone or OFDM modem can fail to provide connection, for example, when the Doppler shift is extremely high (polar communications). In that case one should use the methods of "spectrum spread" that extending the symbol in time and frequency. Unfortunately the speed would not be high in this case. So the best way out is to measure the channel characteristics and choose the speed of transmission and modulation method according to them. The full adaptation of the all characteristics is required. 2. About our users. The project RFSM-2400/8000 was initially aimed at organizations (not for HAMs)! (First version had no 0,3-2,7 band, which is adapted for HAMs). Its prime value is that high-performance algorithm is used in it. Consequently only technical specialists of organizations where data (files, mail etc.) transmission through HF is needed can estimate the program at its true worth. They need the following: high speed of connection and data transmission. They are the FIRS GROUP OF OUR USERS. For example there are organizations (our users at the moment) who even haven't looked upon HAM -modems (little speed, instability, absence of files transmission in spite of excellent chat-exchange). If you are interested in RFSM as in a program for chat- exchange (or even for file transmitting but you do not need a high speed) and runner is not important for you:. You are the SECOND GROUP OF OUR USERS. $60 may be a pretty penny for this product for you. There is also not numerous GROUP OF USERS - THE THIRD ONE The representatives of this group are specialists in HF- radiocommunications and radioamateurs at the same time who is interested in algorithms of a high efficiency - the runner of the program. May be $60 is rather expensive for them but they can trial versions for free. They communicate with us suggesting interesting and moreover useful ideas. We really appreciate their advices and suggestions. Due to the THIRD GROUP the first version of RFSM has transformed in the product adopted for HAM. 3 . There are several remarks on the open source codes. a) RFSM-2400 (and all the more RFSM-8000) is not just a "dumb" modem though such a rate is also possible (it was used in PSKMail). Our product is an accomplished system of communication thatprovides different types of services including receiving/transmitting e-mail on Internet. b) Speaking about OFDM it should be pointed out that we have got experience in such a kind of modulation and can remark that to construct this modem is incommensurably easier than Serial Tone Modem. But the modem of this kind doesn't compare with RFSM characteristics. If we were not be able to realize Mil-STD correctly and use OFDM in RFSM, we would not be sorry to distribute source codes. c) Philosophy. Professional free software is possible because qualified developer has been grown up by certain company. The buyers have already paid for software and progressive developer as well. Then at the same time free software appears (like RFSM-2400) - like an ad, to create an image or ease consumers' tasks. The fact that softw
[digitalradio] Re: RFSM 8000 Different pricing structure
My comments about changing price. RFSM is our first project in HAM's market, and we just was not know, what prices will be acceptable for HAMs. And, we try find "right" price. We think, that now prices is OK. About release number (0.xxx). There is many unreleased features in our "wish"-list, which we want (and will) to release in RFSM-8000. And, version 1.0 (in our opinion) must be more featured and powerful. So, current version can not be marked as "1.0". Dmitry.
[digitalradio] Re: RFSM 8000
Hi, All. About bit-rates and Baud-rates (in RFSM-8000). RFSM-8000 uses vary bit-rates: 1) 600, 1200, 2400, 3200, 4800, 6400, 8000 - in "wide" (standard) mode; 2) 500, 1000, 2000, 2666, 4000, 5333, - in "narrow" (non-standard) mode. But, Baud-rate is not changing: 1) for standard mode - 2400 Baud (symbols per seconds) - for any bitrates; 2) for non-standard mode - 2000 Baud (symbols per second) - for any bitrates also. Dmitry.
[digitalradio] Re: Report on RFSM2400 vs. OFDM
Hi Les, Rick and all. About prices of RFSM-8000. I'm sorry, but Les was wrote incorrect information. In January, we offer special low prices. Price of FULL Featured (with Mail-Server) version is 60 USD (only for HAMs). Mail-Client version is unavailable. And, we think, this action (special low prices for HAMs) will be continued - in February and more. Please, see our web-page for last correct information: http://rfsm2400.radioscanner.ru 73, Dmitry (RFSM-IDE Group).
[digitalradio] Re: rfsm-2400
Hello Simon. >I took a look at http://rfsm2400.radioscanner.ru and was shocked by >the price. I About "shocked" price. 1. RFSM-2400 is FREEWARE. 2. RFSM-8000 for Hams cost 60 USD. Let's compare similar hardware and software products: - Pactor-3 cost about 1000 USD; - SkySweep Messenger Client Plus - 790 EUR (http://www.skysweep.com/binaries/doc/SkySweepMessenger.pdf); II About open source. Why have you decided, what you can get source codes free, when they are the result of several years of work of group of people? People suggested to buy them for the rather high sums :). Dmitry.
[digitalradio] Re: RFSM2400 vs. PC-ALE
About CAT PTT. Support for most of ICom-transceivers is alredy built-in to RFSM-8000. User can define ANY commands for CAT PTT. Dmitry.
