> Walt K5YFW wrote: > Another consideration is what would the bandwidth be with > DSB where two 350 Hz PSK modes were sent? The bandwidth > would be 770+ Hz. >... > problem is finding an ISB receiver which you would need. > Perhaps a direct conversion receiver with a Q/I (?) detector > and DSP brickwall filter would work. >
Hi Walt, Some PSK31 software programs presently have the capability to simultaneously receive multiple PSK carriers. They could be used with an ordinary 2.8kHz bandwidth SSB receiver to decode DSB-transmitted PSK if the PSK if the audio frequency isn't higher than about 1.2kHz. Only a simple frequency offset of the receiver is needed. Some method to vote/combine the two PSK sigs would be needed, if the intent was to achieve some type of decoding gain. This is similar to "RMPSK", which I proposed several years ago, for ham development. So far, no ham digital software author has taken it on. It is still open :) RMPSK (Redundant Multiple PSK) 2 (or more) carriers of PSK separated by 200Hz to 500Hz or more, all transmitting "separately" with the same text/information. The purpose of the "RMPSK" Redundant-Multiple-PSK signal is to communicate through frequency-selective noise and fading, and carrier type RFI and QRM. It is superior to other modes we presently have, because it is backwards compatible with PSK, and one stream of the signal could be received if the other ones are missing or buried in QRM. Another big advantage of RMPSK is complete compatibility with existing amateur standard single carrier PSK reception and transmission. Regular PSK can talk to RMPSK, and RMPSK can talk to PSK. Time Synchronisation The PSK carriers may transmit information synchronised with either: (A) Simultaneous, with "zero" no time delay between carriers. (B) Fixed synchronized time delay of 0.10sec to 2.50sec. The time delay may be requested automatically by the receiving station, or set manually by the transmitting station, or adjusted for propagation conditions. It is especially useful for situations where the receiving station has interference from digital RFI noise sources (such as RFI, BPL, HomePlug, TVI, computer-I, etc). Up until now, most of the ham digital modes have been designed for best performance in a "random noise" channel. But hams also need modes that can work in a "carrier noise" channel. Many of the RFI noise sources we experience now on HF are from devices such as plasma TV sets, computers, microprocessors, and other digital semiconductor devices that put out multiple carriers and frequency-selective noise. Many amateur operators live in apartments, condos, and flats where noise levels are high and external antennas are limited. In most of these cases, the operator does not have control over these noise sources. With a frequency-redundant signal being transmitted, the receiving operator (or the receiving PSK software) can pick the best PSK signal(s) or request certain spacing of the PSK carriers from the transmitting operator. Alternatively, all of the carriers may be combined and/or voted upon by the software receiver as a type of FEC, multi-path fading reduction, or frequency-selective fading reduction. In better signal/noise conditions, all of the carriers of the system may be combined for faster throughput of digital files, or image information, as an MPSK signal. As another alternate example, the content of the carriers could be multi-media, with one carrier having keyboarding text and the other carriers having image or data. About 5 years ago, one of the commercial products I invented and developed used a similar technique (Redundant Multiple OFDM) although I did it with very large (and expensive) DSP engines on both ends of the comm link. This type of RMPSK technique is a solution for ham operators to communicate signals through BPL - PLC (Broadband over PowerLine) HF interference. ARRL probably wouldn't want us to develop such BPL- busting modes, because it might undermine their BPL lawsuit. :) But the fact is, in home-BPL is already deployed, and will continue to be in the future, and ARRL can't sue every home owner who plugs a BPL-enabled in-home modem into the wall. If you live in an apartment or near a house that has in-home BPL, you are likely to face interference. This may affect many hams in the future as these things become more common. Bonnie VR2/KQ6XA .
