KPA1500 and FT8
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Use of more power than necessary is likely to bother someone who is using
the same frequency in a different locale. There seems to be a large majority of digital modes operators that object to the use of high power. The reason seems to be that they have been taught to use a wide receiver in combination with a sound card, so as to get a panoramic view including other stations. This lets a strong nearby station control the agc, and affects reception of stations on a range of frequencies. This negates the dearly paid for capability of our Elecraft radios, which we bought in part because they can eliminate the influence of strong nearby signals. Sure, the ease and cheapness of getting on digital modes with just a soundcard and a wide receiver helps bring many into the hobby. The large majority of digital users that use such a setup do benefit if every station is equally strong, so that agc never makes a gain adjustment (or manual rf gain never needs to change). However, that goal will never be reached, as common natural causes will affect signal strength even more than the difference between a a 30W station and a 1500W station. The operator that has a separate panadapter like the P3 that is independent of the radio selectivity and agc system, or an SDR radio that knows to take agc from one station at a time, needs not have any problem with high-powered stations nearby. The many op's that look down on high power operation for certain digital modes are in effect saying: Don't make this hobby into an unfair competition by giving an advantage to those that spend on their setup beyond the cheap, wide ssb rig plus soundcard. This is opposite to what applies to traditional modes. It goes against the natural pursuit of higher performance through improvement of equipment (at a price). Maybe it is wise to let these anti-progress kids have their sandbox undisturbed. There is much to be said for allowing different sub-hobbies for different tastes and pocketbooks. But getting there would be easier accomplished if the proponents would admit their motives and stop implying that communication with certain modes doesn't get better with higher power, like happens with any other modes. 73, Erik K7TV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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I run with the AGC off, and the audio limiter set carefully...
I control gain via the RF gain control. If a strong station pops on, I use the notch, if a really decent DX station is calling me, I narrow the filters to show just that station... I can operate with a station one mile away, running 100 W on FT8 with no issues... 73s and thanks, Dave NK7Z https://www.nk7z.net On 03/04/2018 11:58 AM, Erik Basilier wrote: > Use of more power than necessary is likely to bother someone who is using > the same frequency in a different locale. > There seems to be a large majority of digital modes operators that object to > the use of high power. > The reason seems to be that they have been taught to use a wide receiver in > combination with a sound card, so as to get a panoramic view including other > stations. This lets a strong nearby station control the agc, and affects > reception of stations on a range of frequencies. This negates the dearly > paid for capability of our Elecraft radios, which we bought in part because > they can eliminate the influence of strong nearby signals. Sure, the ease > and cheapness of getting on digital modes with just a soundcard and a wide > receiver helps bring many into the hobby. The large majority of digital > users that use such a setup do benefit if every station is equally strong, > so that agc never makes a gain adjustment (or manual rf gain never needs to > change). However, that goal will never be reached, as common natural causes > will affect signal strength even more than the difference between a a 30W > station and a 1500W station. The operator that has a separate panadapter > like the P3 that is independent of the radio selectivity and agc system, or > an SDR radio that knows to take agc from one station at a time, needs not > have any problem with high-powered stations nearby. The many op's that look > down on high power operation for certain digital modes are in effect saying: > Don't make this hobby into an unfair competition by giving an advantage to > those that spend on their setup beyond the cheap, wide ssb rig plus > soundcard. This is opposite to what applies to traditional modes. It goes > against the natural pursuit of higher performance through improvement of > equipment (at a price). Maybe it is wise to let these anti-progress kids > have their sandbox undisturbed. There is much to be said for allowing > different sub-hobbies for different tastes and pocketbooks. But getting > there would be easier accomplished if the proponents would admit their > motives and stop implying that communication with certain modes doesn't get > better with higher power, like happens with any other modes. > > 73, > Erik K7TV > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by K7TV
On 3/4/2018 11:58 AM, Erik Basilier wrote:
> The reason seems to be that they have been taught to use a wide receiver in > combination with a sound card, so as to get a panoramic view including other > stations. This lets a strong nearby station control the agc, and affects > reception of stations on a range of frequencies. There is a VERY good reason why WSJT developer, K1JT, advises users to use wide IF bandwidth, and it's NOT the panoramic display. The reason is that filters introduce phase shift in the passband, and phase shift is the enemy of good decoding. The same physics, by the way, applies to other digital modes, including RTTY. Serious RTTY contesters have learned that 500 Hz is a good setting. Our ears may hear off-frequency QRM louder than the signal we're trying to detect, but the decoder does just fine. This is true of both WSJT and other decoders I use for RTTY. Indeed, even though a strong signal may APPEAR to cover much of the display, if the strong signal is CLEAN and you have your receive audio levels to the computer set to that the strong signal doesn't overload the computer, the decoder is likely to copy signals that appear to be covered by it. If you consider AGC pumping a problem, simply turn it off. FWIW, with both FT8 and RTTY, I keep AGC on Slow, and set WSJT-X for an indicated level as high as 50 dB, using the RF Gain. With this setting, if a strong signal reduces gain in the radio, weak signals will still be strong enough at the computer to be decoded. I mostly use WSJT-X on 6M and 160M, but the few times I've gone to FT8 on HF to work a DX trip, I've more than filled the 36 slots in JTAlert. So I guess it's working. :) 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by K7TV
Jim, I totally agree about the choice of bandwidth for RTTY, i.e. wider than what one would first assume based on the frequency shift. The same surely applies to PSK and WSJT modes too, although I haven't yet tried the latter. But I don't think PSK31 with its tiny shift requires anything close to 500 Hz. Maybe 150 Hz, which is a lot smaller than 2.5 kHz. When I wrote about using a wide receiver, I was referring to SSB bandwidth for modes like PSK, which is clearly non-optimal. Personally often find it helps to turn off AGC entirely, even if the slow setting may minimize decoding problems caused by pumping AGC. And, as Dave suggests (and I implied in my previous post) I crank down the K3 bandwidth to something related to the width of the signal I want to copy. The purpose of that post of mine was not to suggest I have problems, but to point out that some users of mainly PSK criticize use of high power based on limits of their receiver's selectivity or limits of their understan
ding of how/when to use it, and this leads to myths about higher power being harmful. Again, I have no experience with FT8, but I made the assumption that the discussion of high power for FT8 is mostly a repeat of the discussion of high power for PSK. On the topic of digital myths, it seems many users of digital modes look at a strong signal, see that it is visible over certain frequency range, and judge it to be "broad" as in improperly modulated based on that, even if the signal is properly modulated but just strong. I believe the reason of such a mistake is that these modulation types (like also FM) do not have a definite cutoff in bandwidth; it just tapers off. Which is another way of showing that the filter needs to be wider than what would first be assumed. However, as filter bandwidth is increased, the returns in copyability decline rather quickly, while interference from other stations steadily increases. When I get to trying FT8, I don't expect it to be very differe nt from PSK31 when it comes to the choice of power etc, but I may want at that time to review advice given in this thread by you and others. 73, Erik K7TV -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Jim Brown Sent: Sunday, March 04, 2018 2:15 PM To: [hidden email] Subject: Re: [Elecraft] KPA1500 and FT8 On 3/4/2018 11:58 AM, Erik Basilier wrote: > The reason seems to be that they have been taught to use a wide > receiver in combination with a sound card, so as to get a panoramic > view including other stations. This lets a strong nearby station > control the agc, and affects reception of stations on a range of frequencies. There is a VERY good reason why WSJT developer, K1JT, advises users to use wide IF bandwidth, and it's NOT the panoramic display. The reason is that filters introduce phase shift in the passband, and phase shift is the enemy of good decoding. The same physics, by the way, applies to other digital modes, including RTTY. Serious RTTY contesters have learned that 500 Hz is a good setting. Our ears may hear off-frequency QRM louder than the signal we're trying to detect, but the decoder does just fine. This is true of both WSJT and other decoders I use for RTTY. Indeed, even though a strong signal may APPEAR to cover much of the display, if the strong signal is CLEAN and you have your receive audio levels to the computer set to that the strong signal doesn't overload the computer, the decoder is likely to copy signals that appear to be covered by it. If you consider AGC pumping a problem, simply turn it off. FWIW, with both FT8 and RTTY, I keep AGC on Slow, and set WSJT-X for an indicated level as high as 50 dB, using the RF Gain. With this setting, if a strong signal reduces gain in the radio, weak signals will still be strong enough at the computer to be decoded. I mostly use WSJT-X on 6M and 160M, but the few times I've gone to FT8 on HF to work a DX trip, I've more than filled the 36 slots in JTAlert. So I guess it's working. :) 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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I find FT8 more works better with strong, nearby signals and a
wide bandwidth. I have only once or twice narrowed the bandwidth from 4K Hz because of a strong signal outside the FT8 subband. Otherwise, reducing the RF gain has fixed things for me. BTW - If I'm trying to copy a very strong FT8 signal -- full red on the waterfall -- reducing RF gain frequently improves decode. 73 Bill AE6JV On 3/4/18 at 2:00 PM, [hidden email] (Erik Basilier) wrote: >When I get to trying FT8, I don't expect it to be very differe >nt from PSK31 when it comes to the choice of power etc, but I >may want at that time to review advice given in this thread by >you and others. ------------------------------------------------------------------------------------- Bill Frantz | Government is not reason, it is not eloquence, it is force; like 408-356-8506 | a fire, a troublesome servant and a fearful master. Never for a www.pwpconsult.com | moment should it be left to irresponsible action. Geo Washington ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Jim Brown-10
I believe at least some of the DSP filters in the K3 are FIR (Finite
Impulse Response) ones, which should be phase linear. The roofing filters will not be phase linear, so I would think you could get away with using a narrow DSP filter, as long as you used a relatively wide roofing filter. This will still leave the ADC, and the analogue circuitry between the roofing filter and it, open to overloads, but will protect the sound card. On 04/03/18 21:15, Jim Brown wrote: > There is a VERY good reason why WSJT developer, K1JT, advises users to > use wide IF bandwidth, and it's NOT the panoramic display. The reason is > that filters introduce phase shift in the passband, and phase shift is > the enemy of good decoding. The same physics, by ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Jim Brown-10
They recommend turning agc off and manually adjusting RF gain.
There is more to the mode than pushing a button and waiting for your honor roll DXCC to come in. W0MU On 3/4/2018 2:15 PM, Jim Brown wrote: > On 3/4/2018 11:58 AM, Erik Basilier wrote: >> The reason seems to be that they have been taught to use a wide >> receiver in >> combination with a sound card, so as to get a panoramic view >> including other >> stations. This lets a strong nearby station control the agc, and affects >> reception of stations on a range of frequencies. > > There is a VERY good reason why WSJT developer, K1JT, advises users to > use wide IF bandwidth, and it's NOT the panoramic display. The reason > is that filters introduce phase shift in the passband, and phase shift > is the enemy of good decoding. The same physics, by the way, applies > to other digital modes, including RTTY. Serious RTTY contesters have > learned that 500 Hz is a good setting. Our ears may hear off-frequency > QRM louder than the signal we're trying to detect, but the decoder > does just fine. > > This is true of both WSJT and other decoders I use for RTTY. Indeed, > even though a strong signal may APPEAR to cover much of the display, > if the strong signal is CLEAN and you have your receive audio levels > to the computer set to that the strong signal doesn't overload the > computer, the decoder is likely to copy signals that appear to be > covered by it. If you consider AGC pumping a problem, simply turn it off. > > FWIW, with both FT8 and RTTY, I keep AGC on Slow, and set WSJT-X for > an indicated level as high as 50 dB, using the RF Gain. With this > setting, if a strong signal reduces gain in the radio, weak signals > will still be strong enough at the computer to be decoded. I mostly > use WSJT-X on 6M and 160M, but the few times I've gone to FT8 on HF to > work a DX trip, I've more than filled the 36 slots in JTAlert. So I > guess it's working. :) > > 73, Jim K9YC > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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Well, then .. what good is it If it can’t make Honor Roll on its own? Too much work. …. ;-)
> There is more to the mode than pushing a button and waiting for your honor roll DXCC to come in. > Grant NQ5T K3 #2091, KX3 #8342 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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