http://elecraft.85.s1.nabble.com/KPA100-diodes-blown-tp2773055p2825412.html
sort. Perhaps while you were operating and a thunderstorm was nearby -
Do you have lightning surge suppressors on your antenna feedlines. If
you do not, I highly recommend them. I know they are expensive, but so
is a repair to your equipment. The surge suppressors will not guarantee
catastrophes if you have a good grounding system in your shack. See the
> 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" <
[hidden email]>
> To: "Brett Gazdzinski" <
[hidden email]>
> Cc: <
[hidden email]>
> 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
>>>
>>>
>
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