[Elecraft] Tuning Random-Length Wire Antenna with K3 Internal Tuner??

Sun Dec 13 14:19:53 EST 2020

Examining the KAT3A circuit board, I doubt it can handle more than 
1000 volts that a worst case random wire -- or a fault -- could cause 
at the output of the KAT3A tuner when the K3 is producing full rated 
output. But its unlikely that the KAT3A can produce full rated K3 
output because of inevitable low tuner efficiency at high VSWRs. 

I've never connected an antenna with a greater than 10:1 VSWR to 
my KAT3A tuner. I would never intentionally do that because of the 
stress it would could cause to the tuner components from high voltage 
and/or high current and inevitable poor tuner efficiency when feeding 
very high VSWR. 

Hopefully the K3's very fast acting excess VSWR detection turns down 
its output power before damage occurs. The K3's excess VSWR 
protection is very effective at preventing damage when the tuner is off. 

A better solution to extreme VSWR that can be caused by a truly random 
length antenna is to use one of the proven commercial multiband wire 
antennas. Just one example of a simple eight band wire antenna that 
definitely will not damage a K3: 

www.dxengineering.com/parts/pez-ef-allbandkw 

73 
Frank 
W3LPL 

----- Original Message -----

From: "Walter Underwood" <wunder at wunderwood.org> 
To: "Elecraft Reflector" <elecraft at mailman.qth.net> 
Sent: Sunday, December 13, 2020 6:45:34 PM 
Subject: Re: [Elecraft] Tuning Random-Length Wire Antenna with K3 Internal Tuner?? 

I think you just proved my point. The KAT3A does not have a lower power rating for larger SWRs. That would indicate that it can handle the rated power over the entire rated SWR range. If extreme SWR at full power would exceed the component ratings, the specs would say that. 

This is the entire set of specs for the KAT3A: 

• Maximum impedance match: 10:1 SWR 
• Maximum power handling: 110 watts 

https://elecraft.com/collections/kat3a_model/products/kat3a-100w-atu 

I just curious why people would think that Elecraft publishes specs that their equipment does not meet. That is a pretty strong accusation. 

No, I didn’t check out TLW, but I have a solid understanding of transmission lines and conjugate matches, even though I only got a B- in my fields and waves class at Rice. 

wunder 
K6WRU 
Walter Underwood 
CM87wj 
http://observer.wunderwood.org/ (my blog) 

> On Dec 12, 2020, at 11:12 PM, David Gilbert <ab7echo at gmail.com> wrote: 
> 
> 
> Seriously?? Why do you think that Elecraft's tuners (like just about every other one) have max power ratings that differ depending upon the SWR? For example, for the KAT500 has a max power rating of 1000 watts into a 3:1 SWR but only a 600 watt rating into a 10:1 SWR??? It can match both SWRs, but not handle the same power at both. 
> 
> Did you bother to check out TLW like I suggested? 
> 
> Dave AB7E 
> 
> 
> 
> On 12/12/2020 8:59 PM, Walter Underwood wrote: 
>> Of course there are high voltages or currents in some tuning solutions. Why do people think the Elecraft ATU would not be designed to handle those? 
>> 
>> wunder 
>> K6WRU 
>> Walter Underwood 
>> CM87wj 
>> http://observer.wunderwood.org/ (my blog) 
>> 
>>> On Dec 12, 2020, at 7:36 PM, David Gilbert <ab7echo at gmail.com> wrote: 
>>> 
>>> 
>>> A matched conditon does NOT prevent the components of the tuner from seeing high voltages and/or high currents. Check out TLW ... the transmission line application that comes free with the ARRL Antenna Book. Pick a load that gives a high SWR and then click on the "Tuner" button for the application to draw one of four different tuner configurations for you. The app will tell you what the voltages across each component are, and also the power loss (i.e., heating effects) in each one. 
>>> 
>>> 73, 
>>> Dave AB7E 
>>> 
>>> 
>>> 
>>> 
>>> On 12/12/2020 8:18 PM, Walter Underwood wrote: 
>>>> Tuning happens at low power, so transients are small. After it is matched, why would the K3 ATU not be rated for full power over the full SWR range? 
>>>> 
>>>> Other components might fail, of course. Amphenol UHF connectors are only rated for 500 V. 
>>>> 
>>>> wunder 
>>>> K6WRU 
>>>> Walter Underwood 
>>>> CM87wj 
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