[Elecraft] KPA500 and SWR above 1.5:1

[Geoffrey Downs]

Thank you Eric. That is interesting and impressive. I will be seriously 
considering a kit.

73

Geoff
G3UCK

----- Original Message ----- 
From: "Eric Swartz - WA6HHQ, Elecraft" <eric at elecraft.com>
To: "Geoffrey Downs" <geoffreywd at madasafish.com>
Cc: <Elecraft at mailman.qth.net>
Sent: Wednesday, May 11, 2011 7:10 PM
Subject: Re: [Elecraft] KPA500 and SWR above 1.5:1


> The KPA500 bases its SWR protection on reflected power level, not an 
> absolute SWR. The KPA500 is happy up to a 2:1 SWR at 500-W out. As long as 
> the actual reflected power is below that for a 2:1 SWR at 500W, it will 
> not reduce its power. This means you can operate into a higher than 2:1 
> SWR load at full amplifier gain if you reduce the amp's output power 
> slightly.
>
> The amp "soft-faults" and reduces output power by about 2.5 dB by 
> switching in an input attenuator at the 500W 2:1 reflected power point, 
> and it flashes a red LED to alert you to this so you can adjust driver 
> power (or SWR via an external tuner) down a bit. Once this is corrected 
> below this threshold by the operator, the KPA500 automatically goes back 
> to full gain. It also does this for minor overdrive conditions.
>
> Of course, for excessive SWR events (wrong antenna, open antenna etc), and 
> severe overdrive, the amp protects itself by immediately hard faulting and 
> going into bypass mode. After correcting the fault, just push the 
> operate/standby switch to get back on-line. While at Contest University, 
> our Italian representative surprised me by demonstrating this feature to 
> customers by pulling the coax from the dummy load while the amp was 
> transmitting. After I recovered from my surprise, I realized the amp was 
> perfectly happy and had protected itself as advertised :-)  But don't try 
> this at home, as he also received a minor RF burn to help him remember 
> this event..
>
> 73, Eric   WA6HHQ
> www.elecraft.com
> ====
>
> On 5/11/2011 9:24 AM, Geoffrey Downs wrote:
>> The manual says the bargraph shows green ("normal") up to an SWR of 
>> 1.5:1,
>> yellow ("marginal") from 1.5:1 to 2.1:1 and red ("excessive") above that.
>> Does this mean no inhibition of output  by the protection system (and no
>> need for it) up to 1.5:1 but progressive reduction of output above? If 
>> so,
>> will the amp operate without damage in the yellow zone and what %
>> reductions in output might be expected up to 2.1:1? Also in what 
>> conditions
>> of SWR does the intelligent 2.5db output reduction apply; and at what SWR
>> does output shut off altogether - ie the REFL HI fault condition.
>>
>> 73 to all
>>
>> Geoff
>> G3UCK
>
>