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#12
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Cecil Moore wrote in message ...
Reg Edwards wrote: How much, if any, is digital filtering better than the old-fashioned Xtl filter. What makes DSP filtering better than Xtal filters is that it is programmable, not hardwired. The parameters of a DSP filter are continuously variable although not usually implemented that way in most amateur radio receivers. Given the processing power necessary for a filter, one can theoretically have any of a near-infinite number of filter configurations. Reg, you could probably program a DSP audio filter that runs on a PC and outputs audio through the sound card like the ClearSpeech speaker systems. PSK-31 software packages for the PC certainly contain a number of DSP filters and other DSP algorithms. I' ve got 2-3 of those programs. Probably more than that out there...SBFFT is a DOS DSP program that works real well for a CW or bandpass/bandstop filter. You can notch, etc , up to six signals at once, within the stock passband width you select. It's real good for notching heterodynes, etc...You can cut just a tiny sliver, taking out the signal, but leave all the rest. I use that for MW sometimes. I have another DSP program for windows that the guy that wrote MMSSTV did...It has NR modes, which SBFFT doesn't. Chromasound is pretty good, but payware...If I use a radio which has DSP in it, such as my mk2g, I have dual DSP if I want it. Even dual auto-notch, etc. But the software on the puter is much more powerful overall than the simple DSP in the 706. All the 706 has is auto notch and NR. Neither of which I use much at all. Only bandpass filtering is really useful to me, and most radios don't have it. BTW, all those programs have the various spectrum graphs, waterfalls, etc... You can see what to notch, and what freq , etc..Kinda like PSK... One thing though...DSP is nice and all, and the filters are brick wall steep, but you can still have blowby problems with near strong signals, etc...DSP is not near as "bulletproof" as a real hardware filter. I use both. Get the best of both worlds...As an example...My 830 is pretty good as it is. Variable bandwidth, CW filters, etc...Add the puter DSP, and it's killer. But in reality, the 830 is good enough as it is...I have DSP but I don't use it all that much. It's not that practical to use. For example, my 706 doesn't have a CW filter yet, and the DSP would be real handy. But the sidetone delay on *sending* makes it nearly useless. Doesn't do any good to have a 200 cycle filter if I get tripped up sending due to the delay...:/ I'd have to rig up a separate real time sidetone. And that then means I would prefer to mute the puter audio when sending...All that mess is too much hassle...I just get on my old 830 with it's rock solid old fashioned filters, and be done with it...And the receiver is usually cleaner to boot, as no artifacts or blowby..MK |
#13
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Simon Smith wrote:
I am soon to take the Foundation licence test and I'm considering either an Icom TS50 or the Icom IC - 703. I dony know enough yet to come to a decision - What in the opinion of the newsgroup would be a wise choice for a complete Novice ? I realise the learning will continue AFTER I get the pass certificate - but I dont want to make an expensive mistake before I even get started.... Any help would be most welcome.... John I'd go with the 706MkIIG... the 703 is a QRP rig with a max output of 10 watts. The TS50 is older tech, but still a decent rig. I run a 706MkIIG in my semi, and have had no problems with the rig at all.. Antennas and tuners are a different story, though... 73 de AI8W, Chris |
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