Just FYI, I recently received a communication between a member and the ARRL Lab staff. The Member even commented that the ARRL is Great! The message is below. ‘73 de Jim N2ZZ Director – Roanoke Division Representing ARRL members in North Carolina, South Carolina, Virginia and West Virginia ARRL – the national association for Amateur Radio Facebook Page: ARRL Roanoke Division Website: www.arrl-roanoke.org<http://www.arrl-roanoke.org/> [Text, logo Description automatically generated] -----Original Message----- From: Bill Overstreet <billdox@cox.net<mailto:billdox@cox.net>> Sent: Thursday, April 18, 2024 10:21 PM To: McAuliffe, John, KD2ZWN <jmcauliffe@arrl.org<mailto:jmcauliffe@arrl.org>> Subject: Re: SWR question John, Thanks again for the rapid response. Much appreciated. One thing to note is that the transmission line calculator TLW confirms that Vmax=sqrt(P*Zo*SWR). So all the articles in QST are correct. I see now that because P=Pf-Pr that at high SWR both Pf and Pr can attain high values with resultant high voltages. You have been very helpful. ARRL is great! 73, Bill, K4AJ On 4/18/24 10:24, McAuliffe, John, KD2ZWN wrote:
Hello Bill,
I looked at the books you have and you're right, the formula is missing from those editions. It looks like it was pulled from the antenna book's chapter on transmission lines since there isn't any derivation in the book. Reading the antenna book. While I cant give you a copy of the pages, I did find this page that does the same derivation and explanation https://www.radioworld.com/news-and-business/the-abcs-of-swr-vswr-reflected-.... Hope this helps you understand the concept.
John
-----Original Message----- From: Bill Overstreet <billdox@cox.net<mailto:billdox@cox.net>> Sent: Wednesday, April 17, 2024 10:53 PM To: McAuliffe, John, KD2ZWN <jmcauliffe@arrl.org<mailto:jmcauliffe@arrl.org>> Subject: Re: SWR question
John,
Thanks for the quick reply. That is great service!
I have a 2012 and a 2020 Handbook, and unfortunately neither have the section 20.1.5 that you reference. I assume the formula Vmax=sqrt(P*Zo*SWR) is derived there. Is there any way I can get a copy of that section of the Handbook?
I agree with you that the confusion comes from the definition of "P" which would be the power delivered to the load. With a high SWR then both Pf and Pr could attain large values giving rise to a large Vmax, supposedly proportional to sqrt(SWR).
I am still working through the issue. So I might get back with you for follow-up questions. Again, being able to see 20.1.5 might be helpful.
73, Bill Overstreet, K4AJ
On 4/17/24 11:49, McAuliffe, John, KD2ZWN wrote:
Hello Bill,
VSWR is a function of the ratio of the forward power to the reflected power and can be represented by the formula VSWR=(1+sqrt(Pr/Pf))/(1-sqrt(Pr/Pf)). In the article you are looking at it misstates power as voltage. In the ARRL Handbook Chapter 20.1.5 the formula is Vmax=sqrt(P*Zo*VSWR) where P is the net power in the line (Forward power minus reflected power) and Zo is the impedance of the line. When the SWR is infinite the net power in the line reduces to 0 because the forward and reflected power are equal and therefore the maximum voltage is 0. I used V instead of E to represent voltage just to make things easier to understand. I hope this answers your question, feel free to call or email if you have any other questions.
Best Regards,
John
John Jobin McAuliffe KD2ZWN Digital RF Engineer ARRL, The National Association for Amateur Radio 225 Main Street, Newington, CT 0611 jmcauliffe@arrl.org<mailto:jmcauliffe@arrl.org> Tel. 860 594 0279 Ext 294
From: arrl-odv <arrl-odv-bounces@reflector.arrl.org> On Behalf Of Michael Ritz Sent: Wednesday, April 24, 2024 6:15 PM To: arrl-odv@reflector.arrl.org Subject: [arrl-odv:35761] Re: ARRL technical assistance "....Dick made NO EFFORT to reach out to me or to Ed Hare’s successor to ask about emails forwarded to directors re: TIS support." David; I am now out of that loop and may be out of touch with reality here, but it seems that Lab staff stopped copying the appropriate Director about tech support they provided to members when Zack left. At least I stopped seeing any e-mails, but maybe there just weren't any from my members at the time. I always enjoyed seeing the interactions between my members and Zack, and often provided some additional technical support or context beyond the answers that Zack gave when required. Is there any plan to re-start the notification practice, if indeed it was terminated? It seems that it would help Directors, especially new ones, to know and better understand the needs of their constituents. 73; Mike W7VO On 04/24/2024 11:26 AM PDT Minster, David NA2AA (CEO) <dminster@arrl.org<mailto:dminster@arrl.org>> wrote: Phil Thanks for asking. Dick’s slide is ABSOLUTELY NOT correct. In fact, his entire presentation is fraught with errors, omissions, lies, slander, and disparagement. The lab has never stopped proving TIS support to members. Ed Hare, who is fully retired, still works in the lab every week as a volunteer and can support the team with additional support. Dick made NO EFFORT to reach out to me or to Ed Hare’s successor to ask about emails forwarded to directors re: TIS support. Dick’s presentation was meant to, among other things, DISPARAGE me and members of my staff in the lab and editorial. If you have any questions, please let me know and I’ll get them answered for you. Thanks David From: Phil Temples <phil@temples.com<mailto:phil@temples.com>> Sent: Wednesday, April 24, 2024 1:36 PM To: Minster, David NA2AA (CEO) <dminster@arrl.org<mailto:dminster@arrl.org>> Subject: ARRL technical assistance David, Dick Norton presented a slide at Visalia claiming that Hq. no longer offers technical assistance from the Lab in the aftermath of Zach Lau's retirement. Is that correct? I'm presenting at a hamfest about ARRL this coming Sunday, and don't want to convey inaccurate information. Phil, K9HI -- Phil Temples <phil@temples.com<mailto:phil@temples.com>> _______________________________________________ arrl-odv mailing list arrl-odv@reflector.arrl.org<mailto:arrl-odv@reflector.arrl.org> https://reflector.arrl.org/mailman/listinfo/arrl-odv
