[Elecraft] KPA100 diodes blown...

[Brett Gazdzinski]

Don,
Thanks for the info.
Everything connects through the station control, antenna's, receivers, 
transmitters, mod monitor, etc, it also has the T/R contactors, muting 
relays etc in it.

What I have done for the last 25 years is select the dummy load when not 
operating, which leaves the antenna's connected to nothing, and the homebrew 
receiver bridged with the 756 pro3 selected for the receiver (I only use the 
band scope in the icom).
The K2, as a transceiver, gets connected to rx position 5.

Nothing else has ever blown out when hooked up this way, and I have had many 
close strikes...

In that setup, you have a BIG antenna switch open (going to dummy load) 1 
inch spacing or more between things, plus the K2 antenna is also open 
(receiver switch selected to a short to ground from homebrew rx).

I have the kpa100 and the kat100 in one case, remote from the actual K2, 
hooked up to the antenna port all the time as its out of the way behind 
racks of big AM transmitters.

I think I will try the choke at the antenna 1 connector of the kat100.

That is another odd thing, that any voltage made it through the kat100 to 
take out the diodes in the kpa100....



Brett
N2DTS

----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at embarqmail.com>
To: "Brett Gazdzinski" <Brett.gazdzinski at verizon.net>
Cc: <elecraft at mailman.qth.net>
Sent: Saturday, May 02, 2009 9:41 PM
Subject: Re: [Elecraft] KPA100 diodes blown...


> Brett,
>
> I do not know how many other radios have wattmeters directly at the 
> antenna jack, so I really can't compare others.
>
> You can place a high value resistor (1k or greater - that is 20 times the 
> 50 ohm impedance) across the antenna and see if that helps.  An RF Choke 
> could also be used for the same purpose.  RFC10 (100 uHy) was removed from 
> inside the KPA100 because it can couple to parts of the base K2 and cause 
> out of band oscillations.  You could add an RF choke of 100 uHy or a 
> little greater across the antenna external to the KPA100 if you want the 
> protection it afforded back again.
>
> I am confused because you state that you disconnect the antennas when not 
> in use, but then you refer to the 3 turn winding in your homebrew 
> receiver.  The only certain cure for damaged diodes is to fully disconnect 
> the antenna connection when the K2 is not in use - I certainly hope you do 
> not operate during periods of thunderstorm activity, sine that is a 
> dangerous situation unless you have extensive (and expensive) lightning 
> protection (equal to that installed at a broadcast station) installed in 
> your ham station - a simple ground will not perform that function.  I have 
> never had a diode failure in my KPA100, but I disconnect the antennas and 
> connect a dummy load directly to the K2 when it is not in use.
>
> The 1N5711 diodes are a bit on the fragile side, but they do provide the 
> best voltage response vs. frequency curve.  If you want hardier wattmeter 
> diodes, you could replace them with 1N4148 diodes.  The accuracy of the 
> wattmeter may suffer by 5 to 10% (and that may be band dependent), and the 
> readings below 3 watts may not be as accurate and with the 1N5711s.  Since 
> you have to replace the diodes anyway, the choice is yours to make - just 
> be prepared to accept the consequences I have outlined if you decide to 
> use the 1N4148s, or if you choose the 1N5711s, understand that they are 
> more sensitive to static discharges and the take the necessary precautions 
> so they are not damaged.
>
> 73,
> Don W3FPR
>
> Brett Gazdzinski wrote:
>> I turned my K2 on after is sat a while, and hit the tune button to tune 
>> the antenna, and got crazy indications, D16 and D17 in the KPA100 are 
>> blown.
>>
>> Is there nothing that can be done about these diodes blowing so easy?
>> I need to order a set from Elecraft, but I leave all the other radios 
>> hooked up and nothing blows in them...
>>
>> I disconnect the antenna's, and select the dummy load, plus I usually 
>> have the homebrew receiver selected which has a 3 turn coil as an antenna 
>> input, which should look like a short to any voltage, but enough voltage 
>> must get through everything to blow the diodes in the K2...
>>
>> How are other radios protected against static buildup on the antenna?
>>
>> Brett
>> N2DTS
>>