[Elecraft] Elecraft Digest, Vol 263, Issue 17
Jack Brindle
jackbrindle at me.com
Tue Mar 24 10:52:50 EDT 2026
George, thank you for pointing this out. Not sampling the forward and reflected voltages simultaneously can indeed be a problem. It is especially so on voice, where voice peaks and dips can occur with as little as 1 microsecond separation!
The SWR calculations are generally done using averaged values, which tends to mitigate major changes, but this method is not perfect. The best way is to sample the signals simultaneously.
But, your assertion that no device does this is incorrect. The KPA500 employs sample and hold circuits in its A/D input circuitry. Both forward and reflected voltages pass through these circuits, and are triggered simultaneously. Thus the KPA500 SWR is actually properly calculated. As you also say, the proper protection of amplifier circuitry is using reflected power, not SWR. This is also the case in Elecraft’s amplifiers, where the only protective use of SWR is when it is way too high. This picks up the case where output power is low, but the antenna is severely mismatched. The overall protection system works very well in the KPA500. You should try it!
73,
Jack, W6FB
> On Mar 24, 2026, at 9:19 AM, George Danner via Elecraft <elecraft at mailman.qth.net> wrote:
>
> This was observed and discussed shortly after the release of the K3. I
> honestly don't remember when.
> My recollection:
>
> SWR is a calculation of the forward and reverse signal from the two output
> directional couplers.
> For the calculation to be accurate it must be done simultaneously.
>
> Unfortunately the sampling it is not done simultaneously!
>
> Therefore The SWR reading is only accurate when the transmitted signal is
> stable and not varying or varying so slowly as to make the calculation
> reasonably accurate.
>
> I have no direct insight as to the software used to make the calculation,
> but suspect the values of forward and reverse signals are stored in memory
> sequentially, then calculated.
>
> Any downstream equipment must take this into account or only use the
> information while the transmission is stable. It is not the fault of the
> Elecraft equipment but the lack of understanding of the limitations of the
> equipment. NO perfect equipment has been designed - YET!
>
> BTW - all transmitters that protect themselves that I have used, use the
> signal from a reverse directional coupler to protect themselves not
> calculated VSWR .
> In broadcasting we did not have nor use VSWR in our broadcast plants, we
> used 2 seperate power reading directional couplers to keep within FCC rules
> (forward) and evaluate the antenna system (reverse).
>
> 73 George AI4VZ
>
> On Mon, Mar 23, 2026 at 3:02 PM Brian Collamer via Elecraft <
> elecraft at mailman.qth.net <mailto:elecraft at mailman.qth.net>> wrote:
>
>> I think this has been an issue for some time.
>> Here is a video from 11 years ago:
>>
>>
>> https://www.youtube.com/watch?v=cwxk4E01IfM&list=FLJDlKHD7Q3VCRPJ-mx-f5Og&index=9
>>
>> Brian
>>
>> On Mon, Mar 23, 2026 at 12:03 PM <elecraft-request at mailman.qth.net> wrote:
>>
>>> Send Elecraft mailing list submissions to
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>>> When replying, please edit your Subject line so it is more specific
>>> than "Re: Contents of Elecraft digest..."
>>>
>>>
>>> Today's Topics:
>>>
>>> 1. Elecraft 80M SSB Net Announcement (Dave New, N8SBE)
>>> 2. Elecraft 20M SSB Net Results: March 22, 2026 (Brian Maynard)
>>> 3. Re: K3 high SWR at end of transmission (w2yf)
>>> 4. Elecraft CW Net Report (kevin)
>>> 5. Elecraft 80M SSB Net Report (Dave New, N8SBE)
>>> 6. Re: Elecraft Digest, Vol 263, Issue 15 (Ronald Motyl)
>>>
>>>
>>> ----------------------------------------------------------------------
>>>
>>> Message: 1
>>> Date: Sun, 22 Mar 2026 15:08:09 -0400
>>> From: "Dave New, N8SBE" <n8sbe at densbe.com>
>>> To: Elecraft Reflector <elecraft at mailman.qth.net>, Elecraft K4
>>> <Elecraft-K4 at groups.io>, Main <main at elecraft-kx.groups.io>
>>> Subject: [Elecraft] Elecraft 80M SSB Net Announcement
>>> Message-ID: <77cbfea03c80d6dac19694bc2c51ae60 at densbe.com>
>>> Content-Type: text/plain; charset=US-ASCII; format=flowed
>>>
>>> Please join us on 3803kHz plus (not minus) QRM (see the Netlogger
>>> discussion, below), 9PM ET Sunday (0100Z Monday). Note that the net
>>> stays on the same local time, when we switch back and forth to/from
>>> Daylight time, so the UTC time changes, but not the local time.
>>>
>>> Your net control for this week is N8SBE, who will be operating remote
>>> from K1AV in Rhode Island (thanks Peter!).
>>>
>>> The group that meets on 3803 kHz before us has been wrapping up
>>> operations promptly at or before 9PM ET. There is also another group
>>> that normally comes on at 10PM ET, so we need to make sure to wrap up
>>> operations by 10PM ET. If any stations wish to continue past that time,
>>> please QSY to a clear frequency.
>>>
>>> If you are a US General class licensee, please ensure that your dial is
>>> accurately calibrated and that your transmitter/amplifier combination is
>>> clean and free of splatter, since we will be operating LSB within 3 kHz
>>> of the lower band edge of the 80M US General class band.
>>>
>>> If we find 3803 kHz busy, we will move UP the band a few kHz, so we can
>>> stay in the 80M US General class band.
>>>
>>> Hope to see you this evening on the net.
>>>
>>> 73,
>>>
>>> -- Dave, N8SBE, Hamshack Hotline RIP, HamsOverIP 101018, AmateurWire
>>> 1348
>>>
>>> ------------------------------
>>>
>>> Message: 2
>>> Date: Sun, 22 Mar 2026 19:37:03 -0400
>>> From: Brian Maynard <briankmaynard at gmail.com>
>>> To: elecraft at mailman.qth.net
>>> Subject: [Elecraft] Elecraft 20M SSB Net Results: March 22, 2026
>>> Message-ID: <F26D5FF5-62F0-4144-912A-5F1D9C9C0686 at gmail.com>
>>> Content-Type: text/plain; charset=us-ascii
>>>
>>> Challenging band conditions today. Thanks to our relays: K1DIH (Brian)
>> and
>>> N6JW (John), and Dave New for logging. Please join us next Sunday at 1800
>>> UTC on 14.3035 MHz. All Welcome!
>>>
>>> CI # Callsign Operator State Rig Notes
>>> 1 N8SBE Dave MI Off the air logger
>>> 2 N6JW John CA K3 #936 relay
>>> 3 WB7SKK Mike TX K3 #8912
>>> 4 WB9JNZ Eric IL FTdx101d net control
>>> 5 K6VWE Stan MI K4D #193
>>> 6 W1NGA Albert CO K4 #1473
>>> 7 K1DIH Brian CT K4D #1274 relay
>>> 8 K7BRR Bill AZ K4D #704
>>> 9 WB7S Jerry WY K3s #11545
>>> 10 W5GGO Sid TX IC-746Pro
>>> 11 K1NW Brian RI K4D #863 remote
>>> 12 KF5DMC Paul LA FT-950
>>> 13 K6FW Frank CA K4 #1083
>>> 14 NS7P Phil OR K3 #1826
>>> 15 W9PCS Paul WI K4D #620
>>> 16 WN8A Jim MI K3 #3480
>>> 17 KO5V Jim NM K2/100 #7225
>>>
>>>
>>> ------------------------------
>>>
>>> Message: 3
>>> Date: Sun, 22 Mar 2026 21:16:50 -0400
>>> From: w2yf <w2yf.radio at gmail.com>
>>> To: elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] K3 high SWR at end of transmission
>>> Message-ID:
>>> <
>>> CA+_pMJZXt6kLYC8+L3kV8OP3ywWw5rRS6ayDqisakTywYaAD3Q at mail.gmail.com>
>>> Content-Type: text/plain; charset="UTF-8"
>>>
>>> Bob,
>>>
>>> I was hoping PTT-RLS would do the trick, as I was reading the description
>>> it sounded like it would solve the problem. Unfortunately, tweaking this
>>> parameter didn't fix it.
>>>
>>> I tested my KX3, different radio, different computer, different
>>> everything... it does the exact same thing... so maybe the whole K-Line
>>> does this.
>>>
>>> It is problematic when you have software releases of WSJT-X that have a
>>> feature to auto-shutoff transmit when SWR exceeds 2.5, but of course it
>>> shuts off every iteration since it appears the radio is giving incorrect
>>> SWR values at close of transmission.
>>>
>>> I thought this would be a great feature, especially when mobile and
>> antenna
>>> SWR can get a little edgy, but if the transmitter doesn't give correct
>> SWR
>>> values, that feature isn't useful.
>>>
>>>
>>> Brian,
>>>
>>> Thanks for the extra data point... so I'm not the only one.
>>>
>>> Tom, W2YF
>>>
>>>
>>> ------------------------------
>>>
>>> Message: 4
>>> Date: Sun, 22 Mar 2026 19:04:26 -0700
>>> From: kevin <kevinr at coho.net>
>>> To: Elecraft Reflector <elecraft at mailman.qth.net>
>>> Subject: [Elecraft] Elecraft CW Net Report
>>> Message-ID: <cfcaf448-2f4a-4d4a-872c-de8b6c0bc6ab at coho.net>
>>> Content-Type: text/plain; charset=UTF-8; format=flowed
>>>
>>> Good Evening,
>>>
>>> ? ?Twenty meters had little noise, with moderate QSB.? Without the QSB
>>> I would have missed some of you.? Forty meters had deeper QSB with more
>>> noise.? Both bands were not kind today.
>>>
>>>
>>> ? On 14050.5 kHz at 2200z:
>>>
>>> W0CZ - Ken - ND
>>>
>>> K4JPN - Steve - GA
>>>
>>> K6XK - Roy - IA
>>>
>>> K4TO - Dave - KY
>>>
>>> W8OV - Dave - TX
>>>
>>>
>>> ? On 7047.5 kHz at 0000z:
>>>
>>> K0DTJ - Brian - CA
>>>
>>> K6PJV - Dale - CA
>>>
>>>
>>> Until next week 73,
>>>
>>> ? Kevin.? KD5ONS
>>>
>>>
>>>
>>> -
>>>
>>>
>>>
>>>
>>>
>>> Escher https://www.youtube.com/watch?v=ldxFjLJ3rVY
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> ------------------------------
>>>
>>> Message: 5
>>> Date: Sun, 22 Mar 2026 22:06:29 -0400
>>> From: "Dave New, N8SBE" <n8sbe at densbe.com>
>>> To: Elecraft Reflector <elecraft at mailman.qth.net>, Elecraft K4
>>> <Elecraft-K4 at groups.io>, Main <main at elecraft-kx.groups.io>
>>> Subject: [Elecraft] Elecraft 80M SSB Net Report
>>> Message-ID: <449279ac4ea8dbbf2f45d003531e7e23 at densbe.com>
>>> Content-Type: text/plain; charset=US-ASCII; format=flowed
>>>
>>> 3803 kHz, 9PM ET Sunday (currently 0100Z Monday).
>>>
>>> Thanks to the following check ins (w) and relays (rel):
>>>
>>> Call St Radio/Amp Name
>>> 1 N8SBE RI/MI K4D/KPA500 remote via K1AV and K8CGS MI Dave
>>> (w),(op)
>>> 2 WB9JNZ IL FTdx101d/KPA1500 Eric
>>> (rel),(w)
>>> 3 K8CGS MI K4D/KPA500 Greg (w)
>>> 4 K1DIH CT K4D/Tokyo Hi-Power Brian (w)
>>> 5 KE8TRL MI IC-7300 Blaine (w)
>>> 6 K4TM VA IC-7300mkII Cary
>>> (c/o),(w)
>>> 7 W9PCS WI K4D/KPA500 Paul (w)
>>> 8 AE1E TX K4D/KPA1500 Ken (w)
>>> 9 WM6P GA K4D/KPA1500 Steve
>>> (rel),(w)
>>> 10 WA1MAD MA KX3 15W Mike (w)
>>> 11 K1AV RI K4D/KPA500 Peter (w)
>>> 12 K1JIW MA FT-710 Harlan
>>> (c/o),(w)
>>> 13 W4CBS FL K4/Mercury IIIS Don (w)
>>> 14 N1QWI MA FT-450D Daniel (w)
>>> 15 VE1BAC NB FTdx101mp Brian
>>> (c/o),(w)
>>>
>>> (Entries with (c/o) indicate a 'one and done' station that checked out
>>> during the 1st round. (n/h) failed to respond during initial (was only
>>> checked into Netlogger) or subsequent rounds. (p) indicates a portable
>>> station. (m) indicates a mobile station.)
>>>
>>> We had a total of 11 check ins this week (including the NCS). Thanks to
>>> all the stations that helped with relays, and a big thanks to Peter,
>>> K1AV and Greg, K8CGS who hosted my K4D to their K4D connection from
>>> Michigan to Rhode Island and SW Michigan while my 80M antenna is down
>>> for construction at my QTH. I hope to see all of you again. The net
>>> concluded at 9:52 PM ET.
>>>
>>> We have a really great group of folks checking in, and I encourage
>>> everyone in the Midwest and adjoining areas to check in next week.
>>>
>>> As a reminder, if you go to https://netlogger.org at the net starting
>>> time and look for the 80M Elecraft SSB Net, you should see the frequency
>>> we are using that evening, if we must QSY due to busy frequencies.
>>>
>>> Also, check out https://hams.live to find out how to set up a multi-SDR
>>> receiver on your PC, which greatly aids in hearing folks during poor
>>> propagation or high noise levels.
>>>
>>> Also, also, please check out https://mikeg-dal.github.io/QK4/ for the
>>> latest QK4 K4/K4D remote software for Windows. This is currently Beta,
>>> so some things are not complete, yet, but I think you will find it quite
>>> interesting.
>>>
>>> 73,
>>>
>>> -- Dave, N8SBE
>>>
>>>
>>> ------------------------------
>>>
>>> Message: 6
>>> Date: Mon, 23 Mar 2026 09:45:25 -0400
>>> From: Ronald Motyl <rjmotyl at gmail.com>
>>> To: elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] Elecraft Digest, Vol 263, Issue 15
>>> Message-ID:
>>> <
>>> CAPQ7QJm-GhwYBVrVfaaBnnNCLvqfitKDU4RS9K4c7-FNrq0Dow at mail.gmail.com>
>>> Content-Type: text/plain; charset="UTF-8"
>>>
>>> I've also seen the same issue with KX3 in DATA mode, WSJT-X improved, FT8
>>> (w/ Grid Tracker & L4OM, FWIW). Using the AX3 antenna connected with ?
>> 10'
>>> RG-8X.
>>>
>>> This was using KX3 direct and with the KXPA100.
>>>
>>> Would a choke help resolve or reduce this issue?
>>>
>>> Is it unusual to see SWR jump / change that much during a transmission?
>>>
>>>
>>> Ron Motyl
>>> KJ2J
>>>
>>>
>>> On Sat, Mar 21, 2026, 14:17 Brian Collamer via Elecraft <
>>> elecraft at mailman.qth.net> wrote:
>>>
>>>> Hi Tom
>>>>
>>>> My KX3 does the same thing when using Hamlib with WSJTX....
>>>>
>>>> Brian
>>>> KB1OPD
>>>>
>>>> On Sat, Mar 21, 2026 at 12:04?PM <elecraft-request at mailman.qth.net>
>>> wrote:
>>>>
>>>>> Send Elecraft mailing list submissions to
>>>>> elecraft at mailman.qth.net
>>>>>
>>>>> To subscribe or unsubscribe via the World Wide Web, visit
>>>>> http://mailman.qth.net/mailman/listinfo/elecraft
>>>>> or, via email, send a message with subject or body 'help' to
>>>>> elecraft-request at mailman.qth.net
>>>>>
>>>>> You can reach the person managing the list at
>>>>> elecraft-owner at mailman.qth.net
>>>>>
>>>>> When replying, please edit your Subject line so it is more specific
>>>>> than "Re: Contents of Elecraft digest..."
>>>>>
>>>>>
>>>>> Today's Topics:
>>>>>
>>>>> 1. K3 high SWR at end of transmission (w2yf)
>>>>>
>>>>>
>>>>>
>> ----------------------------------------------------------------------
>>>>>
>>>>> Message: 1
>>>>> Date: Fri, 20 Mar 2026 20:01:44 -0400
>>>>> From: w2yf <w2yf.radio at gmail.com>
>>>>> To: elecraft at mailman.qth.net
>>>>> Subject: [Elecraft] K3 high SWR at end of transmission
>>>>> Message-ID:
>>>>> <CA+_pMJYDgoywTd=-vE=-
>>>>> 41EMnkS9QLnCbPHnYGah1ow6tOPzHA at mail.gmail.com>
>>>>> Content-Type: text/plain; charset="UTF-8"
>>>>>
>>>>> I've run into an interesting issue:
>>>>>
>>>>> I get a high SWR report from the SW; command on a K3 -- only at the
>> end
>>>> of
>>>>> a transmission cycle.
>>>>>
>>>>> Things I have tested:
>>>>>
>>>>> - Occurs on ANT1 or ANT2.
>>>>> - Occurs when LPA is engaged (5w) or PA is engaged (25w).
>>>>> - Always occurs, if transmission is 15 seconds long, or 3 seconds
>> long.
>>>>> - Occurs on antenna matched at 1.3:1 and a perfectly matched dummy
>>> load.
>>>>> - Occurs with ATU engaged and without ATU engaged.
>>>>> - Is only at the end of transmission as the transmission envelope is
>>>>> falling off
>>>>> - I have calibrated the transmitter, identical results as above.
>>>>> - All coax has been swapped -- identical results.
>>>>> - SWR throughout entire transmission is 1.1:1, but then when PTT
>> closes
>>>> it
>>>>> reports 20.9:1
>>>>> - Bar graph on K3 shows no SWR variance at all, from the bar graph
>>>>> perspective it is as if nothing is happening with SWR... this only
>>>> appears
>>>>> when polled via the "SW;" command (via Hamlib).
>>>>>
>>>>> Is this a known bug in the K3 firmware? Is it symbolic of hardware
>> that
>>>> is
>>>>> on the edge of failure?
>>>>>
>>>>> The fact that it occurs only at the end of transmission and never
>>> during
>>>>> (regardless of length) is odd.
>>>>>
>>>>> Tom, W2YF
>>>>>
>>>>>
>>>>> ------------------------------
>>>>>
>>>>> _______________________________________________
>>>>> Elecraft mailing list
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>>>>> Elecraft web page: http://www.elecraft.com
>>>>>
>>>>> End of Elecraft Digest, Vol 263, Issue 15
>>>>> *****************************************
>>>>>
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>>> End of Elecraft Digest, Vol 263, Issue 17
>>> *****************************************
>>>
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