Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
Great wisdom this list brings. Yoda 73 Arie PA3A __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
T0-220 style power film resistors are fairly cheap and can easily be mounted on heat-sinking surfaces. David G3UNA Hm, I wonder if the KPA500 has or can have provision for this. That amp can be driven to full output by 30 watts or so, IIRC. With the K3 (or K2), power control could be done automatically by having the amp tell the radio that it's active over the serial interface, but it's clear the KPA500 has much provision for being used with radios other than the K3. 73, doug Tom W8JI wrote: The correct approach would be an attenuator pad so the radio could run at near full power and not have a chance of overdriving the amp, ... I don't understand why more people don't do that. For example, a 3 dB attenuator between the transceiver and amplifier ensures that a 100W exciter won't overdrive an amplifier that requires 50W of drive. The 3 dB loss on receive is hardly ever an issue but if you're worried about it, just put the attenuator inside the amplifier, after the T/R relay. Seems like a simple, foolproof solution. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
The KPA500 has in internal 3 dB attenuator in the drive path that will be switched in automatically by the amp in cases of overdrive. 73, Eric WA6HHQ === On 4/21/2010 10:44 AM, Doug Faunt N6TQS +1-510-655-8604 wrote: Hm, I wonder if the KPA500 has or can have provision for this. That amp can be driven to full output by 30 watts or so, IIRC. With the K3 (or K2), power control could be done automatically by having the amp tell the radio that it's active over the serial interface, but it's clear the KPA500 has much provision for being used with radios other than the K3. 73, doug From: Alan Bloomn...@cds1.net Date: Wed, 21 Apr 2010 10:32:18 -0700 On Wed, 2010-04-21 at 12:23 -0400, Tom W8JI wrote: The correct approach would be an attenuator pad so the radio could run at near full power and not have a chance of overdriving the amp, ... I don't understand why more people don't do that. For example, a 3 dB attenuator between the transceiver and amplifier ensures that a 100W exciter won't overdrive an amplifier that requires 50W of drive. The 3 dB loss on receive is hardly ever an issue but if you're worried about it, just put the attenuator inside the amplifier, after the T/R relay. Seems like a simple, foolproof solution. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
Probably the biggest issue is getting rid of the 70 watts of added heat. If there's someplace in the exiting airstream to put these resistors 73, doug From: David Cutter d.cut...@ntlworld.com Date: Wed, 21 Apr 2010 18:54:21 +0100 T0-220 style power film resistors are fairly cheap and can easily be mounted on heat-sinking surfaces. David G3UNA Hm, I wonder if the KPA500 has or can have provision for this. That amp can be driven to full output by 30 watts or so, IIRC. With the K3 (or K2), power control could be done automatically by having the amp tell the radio that it's active over the serial interface, but it's clear the KPA500 has much provision for being used with radios other than the K3. 73, doug Tom W8JI wrote: The correct approach would be an attenuator pad so the radio could run at near full power and not have a chance of overdriving the amp, ... I don't understand why more people don't do that. For example, a 3 dB attenuator between the transceiver and amplifier ensures that a 100W exciter won't overdrive an amplifier that requires 50W of drive. The 3 dB loss on receive is hardly ever an issue but if you're worried about it, just put the attenuator inside the amplifier, after the T/R relay. Seems like a simple, foolproof solution. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
When the K3 came out there was a big deal about the default ALC polarity that resulted in a mod. Will the default connections of the KPA500 work with an un-moded radio or will we need the mod? David Wilburn NM4M Sent from my Verizon Wireless BlackBerry -Original Message- From: Doug Faunt N6TQS +1-510-655-8604 fa...@panix.com Date: Wed, 21 Apr 2010 14:00:02 To: d.cut...@ntlworld.com Cc: elecraft@mailman.qth.net Subject: Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA Probably the biggest issue is getting rid of the 70 watts of added heat. If there's someplace in the exiting airstream to put these resistors 73, doug From: David Cutter d.cut...@ntlworld.com Date: Wed, 21 Apr 2010 18:54:21 +0100 T0-220 style power film resistors are fairly cheap and can easily be mounted on heat-sinking surfaces. David G3UNA Hm, I wonder if the KPA500 has or can have provision for this. That amp can be driven to full output by 30 watts or so, IIRC. With the K3 (or K2), power control could be done automatically by having the amp tell the radio that it's active over the serial interface, but it's clear the KPA500 has much provision for being used with radios other than the K3. 73, doug Tom W8JI wrote: The correct approach would be an attenuator pad so the radio could run at near full power and not have a chance of overdriving the amp, ... I don't understand why more people don't do that. For example, a 3 dB attenuator between the transceiver and amplifier ensures that a 100W exciter won't overdrive an amplifier that requires 50W of drive. The 3 dB loss on receive is hardly ever an issue but if you're worried about it, just put the attenuator inside the amplifier, after the T/R relay. Seems like a simple, foolproof solution. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
Dear OMs, I can not understand why one would want to run the K3 at 100 W rather than 20/30/50 Watts. Why drive the K3 harder when driving it more lightly should improve reliability and possibly improve linearity. The waste of energy is also undesirable; the fifty watts out that is discarded probably costs 100 Watts of energy. The idea of adding an attenuator for 50 Watts of energy sounds mad to me and environmentally unfriendly as well. 73 Doug EI2CN __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
You will need the mod. This change was included on All K3s shipped on Dec 10, 2008 and later. (Rev B KIO3 Digital board) See: http://www.elecraft.com/K3/k3_app_notes.htm and scroll down to: K3 Negative ALC and Ext Band Data Pull-up Mods, Rev B: REMIOUPGD 73, Eric WA6HHQ (Approx s/n 2362+) On 4/21/2010 12:24 PM, dave.wilb...@gmail.com wrote: When the K3 came out there was a big deal about the default ALC polarity that resulted in a mod. Will the default connections of the KPA500 work with an un-moded radio or will we need the mod? David Wilburn NM4M Sent from my Verizon Wireless BlackBerry __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
I agree with Doug but from another prospective. Look at the energy budget for portable work. Less total consumed power is good. Mel, K6KBE --- On Wed, 4/21/10, Doug Turnbull turnb...@net1.ie wrote: From: Doug Turnbull turnb...@net1.ie Subject: Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA To: 'Doug Faunt N6TQS +1-510-655-8604' fa...@panix.com, d.cut...@ntlworld.com Cc: elecraft@mailman.qth.net Date: Wednesday, April 21, 2010, 2:08 PM Dear OMs, I can not understand why one would want to run the K3 at 100 W rather than 20/30/50 Watts. Why drive the K3 harder when driving it more lightly should improve reliability and possibly improve linearity. The waste of energy is also undesirable; the fifty watts out that is discarded probably costs 100 Watts of energy. The idea of adding an attenuator for 50 Watts of energy sounds mad to me and environmentally unfriendly as well. 73 Doug EI2CN __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
think of it as insurance to protect against a short circuit between the headphones Lew K6LMP On Apr 21, 2010, at 2:31 PM, Mel Farrer wrote: I agree with Doug but from another prospective. [I assume you meant perspective] Look at the energy budget for portable work. Less total consumed power is good. Mel, K6KBE --- On Wed, 4/21/10, Doug Turnbull turnb...@net1.ie wrote: From: Doug Turnbull turnb...@net1.ie Subject: Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA To: 'Doug Faunt N6TQS +1-510-655-8604' fa...@panix.com, d.cut...@ntlworld.com Cc: elecraft@mailman.qth.net Date: Wednesday, April 21, 2010, 2:08 PM Dear OMs, I can not understand why one would want to run the K3 at 100 W rather than 20/30/50 Watts. Why drive the K3 harder when driving it more lightly should improve reliability and possibly improve linearity. The waste of energy is also undesirable; the fifty watts out that is discarded probably costs 100 Watts of energy. The idea of adding an attenuator for 50 Watts of energy sounds mad to me and environmentally unfriendly as well. 73 Doug EI2CN __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
I can not understand why one would want to run the K3 at 100 W rather than 20/30/50 Watts. Why drive the K3 harder when driving it more lightly should improve reliability and possibly improve linearity. The waste of energy is also undesirable; the fifty watts out that is discarded probably costs 100 Watts of energy. The idea of adding an attenuator for 50 Watts of energy sounds mad to me and environmentally unfriendly as well. Doug, The primary reason is safety, and the secondary reason is a cleaner signal. While the K3 does not have overshoot, many rigs do. This compounds the drive problem, and it compounds the overshoot problem. For example my IC706 overshoots to about 140 watts whether the output power is set at 50 watts or at 100 watts. If I have an amp that drives at 40 watts and the radio overshoots to 140, that is disaster. If I have an amp that drives at 80 watts and the rig overshoots to 140, it might not blow up and the broadband pulse generated by leading edge overdrive will be a whole lot less level and even less duration. The 3 dB attenuator is a **very** good idea, because nothing can fix or reduce these problems except a pad. External ALC won't work. 73 Tom __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
On Wed, Apr 21, 2010 at 3:14 PM, Eric Swartz - WA6HHQ, Elecraft e...@elecraft.com wrote: You will need the mod. Ah. Will the ALC connection be prescribed as mandatory for the K3/KPA500 system? Bob NW8L __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
I can not understand why one would want to run the K3 at 100 W rather than 20/30/50 Watts. Why drive the K3 harder when driving it more lightly should improve reliability and possibly improve linearity. The waste of energy is also undesirable; the fifty watts out that is discarded probably costs 100 Watts of energy. For the same concerns, I think an auto-switched pad engaged during an input fault is a good idea. In the case of the SPE amp, I would not like to have 30-watts dissipating as heat in the front end of the amp. The 3dB pad does improve return loss into the amp input by the same amount. But, the effective gain factor of the amp is then reduced by 3dB. The pad may assist with improving linearity from the driving transceiver, but improving linearity can be accomplished with better efficiency if the transceiver has an internal ATU with an auto-tune function that can be programmed to limit the transceiver's power during the tune function. Paul, W9AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
30-watts dissipating as heat in the front end of the amp. The 3dB pad does improve return loss into the amp input by the same amount. But, the effective gain factor of the amp is then reduced by 3dB. A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (5.5dB RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1 SWR). A 3 dB 50 ohm pad with an open circuited output looks like 150 ohms. You can make a 3:1 SWR test fixture by opening and shorting the output. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
Yes, that's right, 3 dB per trip to and from the load. Not 3 dB in total as I indicated. Paul, W9AC - Original Message - From: Tom W8JI w...@w8ji.com To: Paul Christensen w...@arrl.net; elecraft@mailman.qth.net Sent: Wednesday, April 21, 2010 7:05 PM Subject: Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA 30-watts dissipating as heat in the front end of the amp. The 3dB pad does improve return loss into the amp input by the same amount. But, the effective gain factor of the amp is then reduced by 3dB. A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (5.5dB RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1 SWR). A 3 dB 50 ohm pad with an open circuited output looks like 150 ohms. You can make a 3:1 SWR test fixture by opening and shorting the output. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (5.5dB RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1 SWR). Tom, The 6 dB R/L from the 3 dB pad is definitely correct but you lost me on the 2:1 SWR and corresponding R/L figure above. I calculate a 2:1 VSWR as a 9.3 dB R/L and a 1.4:1 SWR at 15.56 dB R/L. What am I not taking into consideration? Paul, W9AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
The actual return loss improvement is twice the attenuation, but I know Paul knows that. --- On Wed, 4/21/10, Paul Christensen w...@arrl.net wrote: For the same concerns, I think an auto-switched pad engaged during an input fault is a good idea. In the case of the SPE amp, I would not like to have 30-watts dissipating as heat in the front end of the amp. The 3dB pad does improve return loss into the amp input by the same amount. But, the effective gain factor of the amp is then reduced by 3dB. The pad may assist with improving linearity from the driving transceiver, but improving linearity can be accomplished with better efficiency if the transceiver has an internal ATU with an auto-tune function that can be programmed to limit the transceiver's power during the tune function. Paul, W9AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
This thread started off with a K3 owner driving an Expert 1K-FA with the power control set to 100 watts. That K3 owner can just set the power knob to 30 watts and move on. Based upon the performance of the current firmware in a K3, can't any K3 owner driving any amp can just set the power control to the proper drive, and forget the ALC? ALC doesn't fix leading spikes anyway, so what's it good for? All my amps have ALC circuits but I haven't hooked them up in years. 73, Guy. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
- Original Message - From: Paul Christensen w...@arrl.net To: elecraft@mailman.qth.net Sent: Wednesday, April 21, 2010 7:43 PM Subject: Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (5.5dB RL) and we add a 3 dB pad, return loss is 9.5 dB (1.4:1 SWR). My bad dyslexia Paul. A 3dB pad gives 6 dB return loss. For example if load SWR is 2:1 (9.5dB RL) and we add a 3 dB pad, return loss is 15.5 dB (1.4:1 SWR). That should make more sense! __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
set the power control to the proper drive, and forget the ALC? ALC doesn't fix leading spikes anyway, so what's it good for? Arguably, ALC helps to function as a time-averaging RF level control that can protect against ongoing over-drive but not necessarily peak power busts. What I don't like about traditional ALC are the unknown side-effects (e.g., non-linearity) that can occur as a result of level-setting and timing differences between the transmitter and amp. Dynamic monitoring for amp SSB non-linearity can be accomplished with reasonably good accuracy using a scope in trapezoid mode. However, once transceivers began introducing delay as result of DSP, it's become nearly impossible to use the trapezoid method to look at system linearity of both the transceiver and amp, and the corresponding ALC effect. Other methods for measurement are probably beyond the cost and effort at most stations. Since the input Z of most solid-state amps is well-controlled at 50-ohms, that the input Z should not appreciably change as output Z changes, then can't we simply use a feed-forward ALC system instead of feedback ALC? A fast RF voltage peak detector can be bridged across the amp's input Z. When the RF voltage exceeds ~ 70.7Vpk, correction bias is applied to the solid-state PA. Simultaneously, a 3dB pad could then be inserted at the amp input until average input power drops below 50W. With the exception of the pad, the SPE amp works like this -- only it has a fault summing network that looks at half a dozen other parameters, all of which instantly apply MOSFET bias through the summing network to cut-off RF, and place the amp in bypass when any one of the non-ALC faults occur. Paul, W9AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
Since the input Z of most solid-state amps is well-controlled at 50-ohms, that the input Z should not appreciably change as output Z changes, then can't we simply use a feed-forward ALC system instead of feedback ALC? A fast RF voltage peak detector can be bridged across the amp's input Z. When the RF voltage exceeds ~ 70.7Vpk, correction bias is applied to the solid-state PA. Simultaneously, a 3dB pad could then be inserted at the amp input until average input power drops below 50W. We can protect the amp if we can change bias or switch a pad a lot faster than the rise time of the envelope, but that does not help the bandwidth. It could actually make the bandwidth problem worse, and is unlikely to make it better. The ideal solution would be to have a system that remembers the ALC required, and starts the transmitter with just a bit less than the expected voltage and makes slow or small adjustments or corrections from there. Better yet, why are most radios made the way they are? Put the SSB ALC entirely in the audio system. For example we could split-frequency process the audio with far more effective results and less intermodulation or harmonic distortion than any type of RF clipping or compression. The VOMAX did that, although not nearly as well as we could do with a DSP system, in the 70's or 80's. We should be doing all the gain control and processing at audio. Trying to fix transmitter issues at the amplifier by wrapping the amp back into the transmitter controls just doesn't seem logical. RF clipping or limiting, unless it is gain reduction with a PIN diode attenuator, doesn't make much sense to me. 73 Tom __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
I get that in general given all the various TRX out there. But for the K3, the digital functions in firmware do a far better job of signal management before the signal is ever analog, much less RF, which can include pre-compensating for issues in the analog circuits. Much of the talk seems to assume that level control can only take place in analog circuits with their limited portfolio of tricks. The digital effects all of those, and others not possible in analog, accomplishing it all before DAC. While over time some number of K3 TX level issues have been reported and fixed by Elecraft, none of those have been solved by analog circuit changes, all done in firmware. It seems that the STRATEGY of using a feedback voltage from the amplifier is obsolete. The Expert amp has a very quick protection circuit that kicks in before damage can occur. If the protection function of AGC feedback voltage is handled well by the amplifier using other means, there is nothing to be done by AGC using a TRX like a K3. 73, Guy On Wed, Apr 21, 2010 at 8:54 PM, Paul Christensen w...@arrl.net wrote: set the power control to the proper drive, and forget the ALC? ALC doesn't fix leading spikes anyway, so what's it good for? Arguably, ALC helps to function as a time-averaging RF level control that can protect against ongoing over-drive but not necessarily peak power busts. What I don't like about traditional ALC are the unknown side-effects (e.g., non-linearity) that can occur as a result of level-setting and timing differences between the transmitter and amp. Dynamic monitoring for amp SSB non-linearity can be accomplished with reasonably good accuracy using a scope in trapezoid mode. However, once transceivers began introducing delay as result of DSP, it's become nearly impossible to use the trapezoid method to look at system linearity of both the transceiver and amp, and the corresponding ALC effect. Other methods for measurement are probably beyond the cost and effort at most stations. Since the input Z of most solid-state amps is well-controlled at 50-ohms, that the input Z should not appreciably change as output Z changes, then can't we simply use a feed-forward ALC system instead of feedback ALC? A fast RF voltage peak detector can be bridged across the amp's input Z. When the RF voltage exceeds ~ 70.7Vpk, correction bias is applied to the solid-state PA. Simultaneously, a 3dB pad could then be inserted at the amp input until average input power drops below 50W. With the exception of the pad, the SPE amp works like this -- only it has a fault summing network that looks at half a dozen other parameters, all of which instantly apply MOSFET bias through the summing network to cut-off RF, and place the amp in bypass when any one of the non-ALC faults occur. Paul, W9AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA
Couldn't agree more. Especially the split-band processing part :-) http://k6mhe.com/n7ws/S_PROC.pdf BTW, arguably one of the best sounding SSB rigs around, the TS870 does use split-band speech clipping done in DSP. I bought mine new in 1998 and it's a late S/N. Wes N7WS --- On Wed, 4/21/10, Tom W8JI w...@w8ji.com wrote: Better yet, why are most radios made the way they are? Put the SSB ALC entirely in the audio system. For example we could split-frequency process the audio with far more effective results and less intermodulation or harmonic distortion than any type of RF clipping or compression. The VOMAX did that, although not nearly as well as we could do with a DSP system, in the 70's or 80's. We should be doing all the gain control and processing at audio. Trying to fix transmitter issues at the amplifier by wrapping the amp back into the transmitter controls just doesn't seem logical. RF clipping or limiting, unless it is gain reduction with a PIN diode attenuator, doesn't make much sense to me. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
