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## Re: [Amps] PARALLEL CAPS IN OUTPUT

 To: , , Re: [Amps] PARALLEL CAPS IN OUTPUT "Carl" Sat, 7 Dec 2013 10:36:29 -0500 mailto:amps@contesting.com>
 ``` ```----- Original Message ----- From: ```To: ; Sent: Saturday, December 07, 2013 9:30 AM Subject: Re: [Amps] PARALLEL CAPS IN OUTPUT ``````Hey guys,. this is the kind of thing that can easily be modeled and derive some factual data. If a 50R load is connected to the amplifier output then through a strap, ```wire or coax of a given length, say six inches long what happens to the 50R ```is dependent on the characteristic impedance of the 6 inch piece. Transmission line software will show what happens. At 28MHz, 6 inches og ```RG213 would be about 8 degrees long. Also, the 50R load would still be 50R at ```the end of the line. Changing from RG213 to a wire or strap would lower the velocity factor ```which will shorten the line length to about 5 degrees and the impedance would ```increase to a number determined by the spacing of the wire or strap to the ```underlying ground plane (chassis). A highish impedance could be on the order ```of 250 ohms for a wire that is .125" in diameter. Smaller diameter would ```have higher Z and larger diameter = lower Z. Closer spacing to ground plane ```= lower Z. Anyway, taking the 250 ohm value, the 50R would be rotated to about 61R ```shunted with about +125 ohms X. To restore proper matching in this case would ```require a reduction in the load C to match 61R and cancel the +125 X. ```Use of a wider strap would lower the impedance and require a smaller change ```in the load C to restore the match. Obviously a shorter length would reduce the correction needed. If the amplifier doesn't follow this kind of prediction then there is some nuisance reactance present and not accounted for. At a lower frequency such as 3.8MHz, the line length becomes so short that a very small rotation of the R and X happens and the effect is basically negligible. This can also be plotted on a Smith Chart for a better visualization of what is happening. 73, Gerald K5GW `````` I agree in part Gerald but that is not what happens in the real world. ```A relay is used which has its own imedance bump which far exceeds a 6" strap at 28MHz. ``` Edit: I see you corrected the VF while I was typing this. ```But the argument has been about the term "coax" and I maintain that it is inmaterial what sort of shielded wire is used. The lower the C and ability to handle the current with minimal heating the better.....period. ``` ```My 2M 3CX1000A7 stripline amp does not even use a variable Load cap which are generally troublesome at homebrew QRO. I tap right off the line at the sweet spot that gives me a solid ~65% efficiency with the external DowKey transfer relay in place. Many so called "experts" said it couldnt be done but it has been chugging along about 30 years now. ``` Carl `````` In a message dated 12/7/2013 7:22:22 A.M. Central Standard Time, jim.thom@telus.net writes: From: "Carl" ``````To: "Jim Thomson" , Subject: Re: [Amps] PARALLEL CAPS IN OUTPUT `````` With all your bluster you still dont get it. All you are using is a short ```piece of shielded cable, impedance has no bearing since it is too short to ```present a meaningful reactance. Your load cap change is due to the added C to ground of that shielded cable. Having it is beneficial if the cable is long or passes near other circuitry such as the input. Lift the RG-8 shield on a SB-220 and see what happens. A high percentage of the ones I get thru here have cold solder joints which will do wonders for stability. Carl ### heres one way to test my theory. Toss the load cap..and replace it with a 50 ohm resistor.... then wire from top of resistor with strap, wire etc, over to a coax connector......then on to the MFJ-259B. Now see if the MFJ says 1:1 swr. Jim VE7RF _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1432 / Virus Database: 3658/6399 - Release Date: 12/07/13 `````` _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
 Current Thread Re: [Amps] PARALLEL CAPS IN OUTPUT, (continued) Re: [Amps] PARALLEL CAPS IN OUTPUT, Bill Turner Re: [Amps] PARALLEL CAPS IN OUTPUT, Jim W7RY Re: [Amps] PARALLEL CAPS IN OUTPUT, peter chadwick Re: [Amps] PARALLEL CAPS IN OUTPUT, Carl Re: [Amps] PARALLEL CAPS IN OUTPUT, Larry Benko Re: [Amps] PARALLEL CAPS IN OUTPUT, Jim Thomson Re: [Amps] PARALLEL CAPS IN OUTPUT, Manfred Mornhinweg Re: [Amps] PARALLEL CAPS IN OUTPUT, TexasRF Re: [Amps] PARALLEL CAPS IN OUTPUT, TexasRF Re: [Amps] PARALLEL CAPS IN OUTPUT, Carl <= Re: [Amps] PARALLEL CAPS IN OUTPUT, TexasRF Re: [Amps] PARALLEL CAPS IN OUTPUT, donroden