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1. [Amps] Input SWR revisited (score: 1): Author: "Gary Schafer" <garyschafer@largeriver.net>; Date: Mon, 12 Jan 2015 21:05:53 -0600; This afternoon I warmed up the HP vector network analyzer and tried a few things. First I calibrated analyzer port to 50 ohms. Then I put a 75 ohm load on it and it read 1.5:1 SWR as would be expecte; /archives//html/Amps/2015-01/msg00063.html (8,295 bytes)
2. Re: [Amps] Input SWR revisited (score: 1): Author: "Gary Schafer" <garyschafer@largeriver.net>; Date: Mon, 12 Jan 2015 21:25:34 -0600; I forgot to include that with just a 4 foot cable on the output of the tuner between tuner and 75 ohm load the SWR was 1.8:1. With the 10 foot cable SWR was 1.46:1. With the 10 foot and 4 foot cable; /archives//html/Amps/2015-01/msg00065.html (9,868 bytes)
3. Re: [Amps] Input SWR revisited (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Tue, 13 Jan 2015 08:47:05 -0500; "I forgot to include that with just a 4 foot cable on the output of the tuner between tuner and 75 ohm load the SWR was 1.8:1. With the 10 foot cable SWR was 1.46:1. With the 10 foot and 4 foot cable; /archives//html/Amps/2015-01/msg00076.html (7,478 bytes)
4. Re: [Amps] Input SWR revisited (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Tue, 13 Jan 2015 10:20:51 -0500; Roger, that's right - I forgot that the VNA was being used and not a directional line coupler. The results are not surprising. However, it would be interesting to observe SWR at the VNA with random c; /archives//html/Amps/2015-01/msg00083.html (8,636 bytes)
5. Re: [Amps] Input SWR revisited (score: 1): Author: "Gary Schafer" <garyschafer@largeriver.net>; Date: Tue, 13 Jan 2015 12:42:16 -0600; Hi Paul, The VNA was calibrated at the VNA directional coupler port for 50 ohms without any cable attached. All cables used were 50 ohm. When using the 75 ohm load with no tuner the SWR always read 1; /archives//html/Amps/2015-01/msg00093.html (10,922 bytes)
6. Re: [Amps] Input SWR revisited (score: 1): Author: Roger D Johnson <n1rj@roadrunner.com>; Date: Tue, 13 Jan 2015 14:27:16 -0500; The VNA does not measure the VSWR on the line. It measures VSWR at the input to the VNA unless you do a cal at the load end of the line to remove it's effect. 73, Roger On 1/13/2015 8:47 AM, Paul Chr; /archives//html/Amps/2015-01/msg00094.html (8,493 bytes)
7. Re: [Amps] Input SWR revisited (score: 1): Author: donroden@hiwaay.net; Date: Tue, 13 Jan 2015 14:01:04 -0600; Clear as Mud ......... What does it all mean ??? Don W4DNR _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps; /archives//html/Amps/2015-01/msg00095.html (7,767 bytes)
8. Re: [Amps] Input SWR revisited (score: 1): Author: "Gary Schafer" <garyschafer@largeriver.net>; Date: Wed, 14 Jan 2015 13:57:07 -0600; It means that-- if you are looking at the SWR at your radio and there is a tuner after the SWR bridge, any changes in cable length after the tuner will show a change in SWR at the radio if you do not; /archives//html/Amps/2015-01/msg00107.html (9,694 bytes)
9. Re: [Amps] Input SWR revisited (score: 1): Author: donroden@hiwaay.net; Date: Wed, 14 Jan 2015 14:10:12 -0600; Explain the case where a 100 ohm load ( 2:1 ) can be a 1:1 swr at the transmitter with a length of 75 ohm cable. I've changed the cable length and improved the SWR. Don W4DNR It means that-- if you a; /archives//html/Amps/2015-01/msg00108.html (10,085 bytes)
10. Re: [Amps] Input SWR revisited (score: 1): Author: Gerald Williamson via Amps <amps@contesting.com>; Date: Wed, 14 Jan 2015 15:33:14 -0500; Good question Don. You have to keep in mind that the 100 ohm load will make for a 1.333 swr in the 75 ohm coax. At a length of one quarter wavelength the 100 ohm load impedance is transformed to 56 o; /archives//html/Amps/2015-01/msg00109.html (10,508 bytes)
11. Re: [Amps] Input SWR revisited (score: 1): Author: "Gary Schafer" <garyschafer@largeriver.net>; Date: Wed, 14 Jan 2015 14:33:53 -0600; Yes Don, with a 1/4 wavelength of 75 ohm cable you will get an impedance transformation from 100 ohms to 50 ohms. If the cable is other than a quarter wavelength or multiple of you will have a differ; /archives//html/Amps/2015-01/msg00110.html (11,855 bytes)
12. Re: [Amps] Input SWR revisited (score: 1): Author: Paul Christensen <w9ac@arrl.net>; Date: Wed, 14 Jan 2015 15:39:42 -0500; transmitter with a length of 75 ohm cable. I've changed the cable length and improved the SWR. Don W4DNR² See "My Feed Line Tunes My Antenna!² by By Goodman, W1DX In your example, let¹s assume the a; /archives//html/Amps/2015-01/msg00111.html (9,078 bytes)
13. Re: [Amps] Input SWR revisited (score: 1): Author: Roger D Johnson <n1rj@roadrunner.com>; Date: Wed, 14 Jan 2015 16:18:00 -0500; I think we're getting a couple of things confused here. The SWR on a transmission line and the impedance along the line. In Don's example, we have a 100 Ohm load fed thru a piece of 75 Ohm line. The; /archives//html/Amps/2015-01/msg00112.html (12,239 bytes)
14. Re: [Amps] Input SWR revisited (score: 1): Author: donroden@hiwaay.net; Date: Wed, 14 Jan 2015 16:08:15 -0600; Yes, and if I add another 1/4 wave of 75 ohm cable to the length, the transmitter is now looking into a 2:1 ( 100 ohm ) Load and will start folding back. So saying : the SWR will always remain the sa; /archives//html/Amps/2015-01/msg00113.html (11,934 bytes)
15. Re: [Amps] Input SWR revisited (score: 1): Author: donroden@hiwaay.net; Date: Wed, 14 Jan 2015 16:12:37 -0600; But, the swr inside the 75 ohm coax is still 1.333 at all points along the cable. No, not at either end. Why does the swr "inside" the coax even matter when we are discussing load and source impedanc; /archives//html/Amps/2015-01/msg00114.html (8,503 bytes)
16. Re: [Amps] Input SWR revisited (score: 1): Author: "Robert Carroll" <w2wg@comcast.net>; Date: Wed, 14 Jan 2015 17:36:55 -0500; I suggest a look at this non-mathematical paper--assuming this list supports links. Forward and Reflected Power <http://www.advanced-energy.com/upload/File/White_Paper s/SL-WHITE7-270-01.pdf> You can; /archives//html/Amps/2015-01/msg00115.html (10,278 bytes)
17. Re: [Amps] Input SWR revisited (score: 1): Author: donroden@hiwaay.net; Date: Wed, 14 Jan 2015 16:49:30 -0600; In practice, few of us run amplifier input cables in the multi-quarter wave length category, so spiraling around the Smith is not an option. Just Saying ....... Don W4DNR I suggest a look at this non; /archives//html/Amps/2015-01/msg00116.html (10,969 bytes)
18. Re: [Amps] Input SWR revisited (score: 1): Author: Gerald Williamson via Amps <amps@contesting.com>; Date: Wed, 14 Jan 2015 17:59:39 -0500; Don, the swr at the 100 ohm end of the 75 ohm coax is 100/75=1.333. In the case the 75 ohm coax is 1/4 wavelength long the impedance at the other end is 75/1.333 or 56.26 ohms. The swr at the 56.26 o; /archives//html/Amps/2015-01/msg00117.html (9,489 bytes)
19. Re: [Amps] Input SWR revisited (score: 1): Author: "Gary Schafer" <garyschafer@largeriver.net>; Date: Wed, 14 Jan 2015 17:06:46 -0600; Don, You are confusing what I said by throwing in the 75 ohm line. Look again what I wrote and remember that I said it was with all 50 ohm line. 73 Gary K4FMX ________________________________________; /archives//html/Amps/2015-01/msg00118.html (13,859 bytes)
20. Re: [Amps] Input SWR revisited (score: 1): Author: donroden@hiwaay.net; Date: Wed, 14 Jan 2015 17:20:13 -0600; Gerald, I am not ignorant of transmission line theory. I maintained high power UHF klystrons for many years, and fed kilowatts out of a 50 ohm transmitter into 70 ohm 6 inch lines. Just don't make a; /archives//html/Amps/2015-01/msg00119.html (10,093 bytes)

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