K3 Dual Receive Surprise
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> Pretty sure it's The Weird Stuff Out There.
I have a page dedicated to all kinds of weird stuff in terms of propagation, see http://www.qslnet.de/member/la3za/prop/ The page has a collection of audio samples from unusual HF propagation phenomena, from round-the-world propagation (delay 138 ms) to moonbounced signals (delay 2.39 sec), and to ducted transmission (delay ~140-300 ms). On 160 m and 80 m, one kind of weird delayed propagation is the ducted one, where signals travel along magnetic field lines into space and back, but it is very rare. I wrote a small article about that which will appear in the March 2009 QST Technical Column. -- Sverre F/LA3ZA _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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> On 160 m and 80 m, one kind of weird delayed propagation is the ducted > one, where signals travel along magnetic field lines into space and > back, but it is very rare. And on second thought, since Matt was hearing static crashes with delay between his two receivers - one imaginative explanation could be that they are statics originating as lightning from the Southern hemisphere travelling both in the ionosphere (direct) and on a magnetic field line (delayed). Each of his two antennas could have mainly picked up just one of them. Such static crashes are responsible for whistlers at much lower frequencies (kHz - audible frequencies). The delay difference would be half of the range I indicated for magnetic field line propagation, i.e. 70 ms and up, depending on the location. Well, I don't know how credible or frequent this could be, but I think there is a remote possibility for such phenomena. -- Sverre F/LA3ZA _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I recall .... from a LONG time ago ... when I was a R/O on
a USC&GS vessel that the LORAN A (~2 mHz) receiver's display routinely showed several different "times / delays" on the arrival times of a signal from a far-off transmitter in the chain. This was especially apparent during the transition period between day and night. LORAN A depended on timing of different signal arrival times from the different transmitters in the chain, but the "propagation-caused" delays took a skilled operator to pick the correct one to use. 73! Ken Kopp - K0PP [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Sverre Holm-3
Fellow Elecrafters:
Is it possible to measure the input impedance of a linear amplifier by using an antenna analyzer (such as the Pal Star) at the input of the amplifier in place of the rig? Would the amplifier input impedance be the same for the very small signal that the analyzer generates as it would be for the 80-100 Watt drive from the rig? Is there any risk of damaging the analyzer (i.e., should I put a blocking capacitor between the analyzer and the rig?) by attempting the measurement? Thanks, Steve Kercel AA4AK _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I would say no to all three questions. The input impedance to the amp will not be the same when it is not powered and driven. The SWR indication on the driver will give you some idea of the input impedance. It should not hurt the antenna analyzer if the amplifier is not powered, but I don't think it will tell you anything useful. With power on the amp, it might.
Willis 'Cookie' Cooke K5EWJ --- On Mon, 1/26/09, Stephen W. Kercel <[hidden email]> wrote: > From: Stephen W. Kercel <[hidden email]> > Subject: [Elecraft] Amplifier Input Impedance > To: > Cc: [hidden email] > Date: Monday, January 26, 2009, 9:17 PM > Fellow Elecrafters: > > Is it possible to measure the input impedance of a linear > amplifier by > using an antenna analyzer (such as the Pal Star) at the > input of the > amplifier in place of the rig? > > Would the amplifier input impedance be the same for the > very small > signal that the analyzer generates as it would be for the > 80-100 Watt > drive from the rig? > > Is there any risk of damaging the analyzer (i.e., should I > put a > blocking capacitor between the analyzer and the rig?) by > attempting the > measurement? > > Thanks, > > Steve Kercel > AA4AK > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I would say something slightly different. Firstly I am assuming the PA is on.
It might help to measure the input, especially if it is a valve amplifier. If it is solid state the input match is more likely to be RF power dependent, but if the match is really bad at low power it is not likely to get better at high power and such an amplifier would not be linear. A better way would be to measure at the power you intend to use but that requires a directional coupler. It is not ideal but an SWR meter connected with a very short lead would probably do. If the amplifier oscillates then there is a very high chance of damaging the analyzer, but if that were the case, then at least it did not destroy the rig. Make sure the amplifier output has a wideband matched load - definitely NOT an antenna. I don't think a blocking capacitor would be any use unless there is DC on the amplifier input line. If there is, there is probably a problem. Note: You can use an antenna analyser to initially measure matching circuits of a high power valve amplifier, but only when it is off. You need to load the anode with an appropriate impedance equal to the operational anode output load and tune and load for a good match at the output. It will not be spot on but it should be a good starting point. It is very hard to optimise the tank circuit in a valve PA any other way because of the high voltages both DC and RF. It does not tend to work so well with transistors as the impedances are so low and often dominated by the device capacitance. Mike
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Re: Amplifier Input Impedance
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Thanks to all who have replied.
The amplifier that I have in mind is an old Dentron GLA-1000B that I am restoring. It is a grounded grid sweep tube amplifier and uses fixed pi networks (a different network for each band, selected by the band switch) at the input. It is supposed to have a better than 2:1 SWR at input. Back in the day, I used to run it with a Kenwood T-599D transmitter whose output tank circuit was a wide range pi network, and there never was a problem coupling the transmitter energy into the amplifier. However, my K2 is much touchier about the range of loads it will tolerate. As the amp is not yet restored, I have not yet tried running it with the K2. Thus, maybe I'll have a problem and maybe I won't. I did notice that at least one poster to the list has had a problem the SWR seen by a K2 looking into a cheap tube type amplifier. Thus, I'm thinking what I might do if I run into the problem. If I do have an SWR problem, I see three possible solutions: 1) (If even possible) Change the values of the mica capacitors in the amplifier input circuits to obtain a better match in the relatively narrow CW segments in which I operate. 2) Insert an attenuator between the K2 and the amp. A 2 dB attenuator would knock down a 2:1 SWR to 1.53:1. The down side is that I'd probably need to construct the attenuator from thin film resistors. The other down side is that I'd be contributing about 35 Watts to the Heat Death of the Universe. The 63 watts (or so) coming out of the generator is adequate drive for the amp to give me 400 Watts out. The up side is that there is no tuning. 3) Insert a tuner (which do have on hand) between the K2 and the amp. This is the cheapest solution, but it makes band changing take many steps. Regarding AD6XY's precautions: 1) This is a valve amplifier and not solid state. 2) I've never had a problem with amplifier oscillation in the past. It is a grounded grid configuration and relatively low gain. It is not impossible that it will oscillate, but it is less vulnerable than other designs. 3) I have a very high quality KW dummy load for sush purposes as adjusting amplifiers. Thanks agasin & 73, Steve AA4AK AD6XY wrote: > I would say something slightly different. Firstly I am assuming the PA is on. > > It might help to measure the input, especially if it is a valve amplifier. > If it is solid state the input match is more likely to be RF power > dependent, but if the match is really bad at low power it is not likely to > get better at high power and such an amplifier would not be linear. A better > way would be to measure at the power you intend to use but that requires a > directional coupler. It is not ideal but an SWR meter connected with a very > short lead would probably do. > > If the amplifier oscillates then there is a very high chance of damaging the > analyzer, but if that were the case, then at least it did not destroy the > rig. Make sure the amplifier output has a wideband matched load - definitely > NOT an antenna. > > I don't think a blocking capacitor would be any use unless there is DC on > the amplifier input line. If there is, there is probably a problem. > > > Note: You can use an antenna analyser to initially measure matching circuits > of a high power valve amplifier, but only when it is off. You need to load > the anode with an appropriate impedance equal to the operational anode > output load and tune and load for a good match at the output. It will not be > spot on but it should be a good starting point. It is very hard to optimise > the tank circuit in a valve PA any other way because of the high voltages > both DC and RF. It does not tend to work so well with transistors as the > impedances are so low and often dominated by the device capacitance. > > Mike > > > > WILLIS COOKE wrote: > >> I would say no to all three questions. The input impedance to the amp >> will not be the same when it is not powered and driven. The SWR >> indication on the driver will give you some idea of the input impedance. >> It should not hurt the antenna analyzer if the amplifier is not powered, >> but I don't think it will tell you anything useful. With power on the >> amp, it might. >> >> Willis 'Cookie' Cooke >> K5EWJ >> >> >> > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Steve,
The KPA100 will tolerate a 2:1 SWR with no problem. That is not uncommon with solid state amps. If you do have a HI SWR problem with the input circuit, it would likely indicate a defective component in the input circuit (most likely a capacitor). My GLA1000 is not up and running either so I can't give you any 'tried and true' data. 73, Don W3FPR Stephen W. Kercel wrote: > Thanks to all who have replied. > > The amplifier that I have in mind is an old Dentron GLA-1000B that I am > restoring. It is a grounded grid sweep tube amplifier and uses fixed pi > networks (a different network for each band, selected by the band > switch) at the input. It is supposed to have a better than 2:1 SWR at > input. Back in the day, I used to run it with a Kenwood T-599D > transmitter whose output tank circuit was a wide range pi network, and > there never was a problem coupling the transmitter energy into the > amplifier. > > However, my K2 is much touchier about the range of loads it will tolerate. > > As the amp is not yet restored, I have not yet tried running it with the > K2. Thus, maybe I'll have a problem and maybe I won't. I did notice that > at least one poster to the list has had a problem the SWR seen by a K2 > looking into a cheap tube type amplifier. Thus, I'm thinking what I > might do if I run into the problem. > > If I do have an SWR problem, I see three possible solutions: > > 1) (If even possible) Change the values of the mica capacitors in the > amplifier input circuits to obtain a better match in the relatively > narrow CW segments in which I operate. > > 2) Insert an attenuator between the K2 and the amp. A 2 dB attenuator > would knock down a 2:1 SWR to 1.53:1. The down side is that I'd probably > need to construct the attenuator from thin film resistors. The other > down side is that I'd be contributing about 35 Watts to the Heat Death > of the Universe. The 63 watts (or so) coming out of the generator is > adequate drive for the amp to give me 400 Watts out. The up side is that > there is no tuning. > > 3) Insert a tuner (which do have on hand) between the K2 and the amp. > This is the cheapest solution, but it makes band changing take many steps. > > Regarding AD6XY's precautions: > > 1) This is a valve amplifier and not solid state. > > 2) I've never had a problem with amplifier oscillation in the past. It > is a grounded grid configuration and relatively low gain. It is not > impossible that it will oscillate, but it is less vulnerable than other > designs. > > 3) I have a very high quality KW dummy load for sush purposes as > adjusting amplifiers. > > Thanks agasin & 73, > > Steve > AA4AK > > > > > AD6XY wrote: > >> I would say something slightly different. Firstly I am assuming the PA is on. >> >> It might help to measure the input, especially if it is a valve amplifier. >> If it is solid state the input match is more likely to be RF power >> dependent, but if the match is really bad at low power it is not likely to >> get better at high power and such an amplifier would not be linear. A better >> way would be to measure at the power you intend to use but that requires a >> directional coupler. It is not ideal but an SWR meter connected with a very >> short lead would probably do. >> >> If the amplifier oscillates then there is a very high chance of damaging the >> analyzer, but if that were the case, then at least it did not destroy the >> rig. Make sure the amplifier output has a wideband matched load - definitely >> NOT an antenna. >> >> I don't think a blocking capacitor would be any use unless there is DC on >> the amplifier input line. If there is, there is probably a problem. >> >> >> Note: You can use an antenna analyser to initially measure matching circuits >> of a high power valve amplifier, but only when it is off. You need to load >> the anode with an appropriate impedance equal to the operational anode >> output load and tune and load for a good match at the output. It will not be >> spot on but it should be a good starting point. It is very hard to optimise >> the tank circuit in a valve PA any other way because of the high voltages >> both DC and RF. It does not tend to work so well with transistors as the >> impedances are so low and often dominated by the device capacitance. >> >> Mike >> >> >> >> WILLIS COOKE wrote: >> >> >>> I would say no to all three questions. The input impedance to the amp >>> will not be the same when it is not powered and driven. The SWR >>> indication on the driver will give you some idea of the input impedance. >>> It should not hurt the antenna analyzer if the amplifier is not powered, >>> but I don't think it will tell you anything useful. With power on the >>> amp, it might. >>> >>> Willis 'Cookie' Cooke >>> K5EWJ >>> >>> >>> >>> >> >> > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - http://www.avg.com > Version: 8.0.176 / Virus Database: 270.10.14/1918 - Release Date: 1/27/2009 7:26 AM > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Stephen W. Kercel
Steve,
It sounds like you have a good handle on all of the issues. I have the same problem with my old Swan 1200X sweep tube amp that I have used with my K2 and with my current K3. This amp has no input matching networks at all! I also have an old SB200 Heathkit amp that does have input L-network matching networks. I found that the SB200 worked fine with the K2 at reasonable (around 1.5 to 1) SWR although I only used it on 80 and 40 meters. I'm sure that I could have easily tweaked the input networks on the SB200 for improved SWR if I had needed to do so but I so seldom used it that I never felt it was necessary. With my Swan, though, the solid state radios would not drive the amp at all. I used an antenna tuner in between the K2 and the amp for a while but eventually modified the Swan to add small input matching networks built up from small ferrite toroids and mica capacitors switched by a rotary switch on the front panel of the amp. It was a fairly simple matter to find the correct values by cut and try. With your amp, which already has switched input networks, it should be a fairly simple matter to tweak the existing networks to get a very low SWR. I don't think you will have a big problem getting it to work the way you like. Don K7FJ > Thanks to all who have replied. > > The amplifier that I have in mind is an old Dentron GLA-1000B that I am > restoring. It is a grounded grid sweep tube amplifier and uses fixed pi > networks (a different network for each band, selected by the band > switch) at the input. It is supposed to have a better than 2:1 SWR at > input. Back in the day, I used to run it with a Kenwood T-599D > transmitter whose output tank circuit was a wide range pi network, and > there never was a problem coupling the transmitter energy into the > amplifier. > > However, my K2 is much touchier about the range of loads it will tolerate. > > As the amp is not yet restored, I have not yet tried running it with the > K2. Thus, maybe I'll have a problem and maybe I won't. I did notice that > at least one poster to the list has had a problem the SWR seen by a K2 > looking into a cheap tube type amplifier. Thus, I'm thinking what I > might do if I run into the problem. > > If I do have an SWR problem, I see three possible solutions: > > 1) (If even possible) Change the values of the mica capacitors in the > amplifier input circuits to obtain a better match in the relatively > narrow CW segments in which I operate. > > 2) Insert an attenuator between the K2 and the amp. A 2 dB attenuator > would knock down a 2:1 SWR to 1.53:1. The down side is that I'd probably > need to construct the attenuator from thin film resistors. The other > down side is that I'd be contributing about 35 Watts to the Heat Death > of the Universe. The 63 watts (or so) coming out of the generator is > adequate drive for the amp to give me 400 Watts out. The up side is that > there is no tuning. > > 3) Insert a tuner (which do have on hand) between the K2 and the amp. > This is the cheapest solution, but it makes band changing take many steps. > > Regarding AD6XY's precautions: > > 1) This is a valve amplifier and not solid state. > > 2) I've never had a problem with amplifier oscillation in the past. It > is a grounded grid configuration and relatively low gain. It is not > impossible that it will oscillate, but it is less vulnerable than other > designs. > > 3) I have a very high quality KW dummy load for sush purposes as > adjusting amplifiers. > > Thanks agasin & 73, > > Steve > AA4AK _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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