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KPA500 Faulting on high SWR on power rise

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ke9uw

Re: KPA500 Faulting on high SWR on power rise

https://www.digikey.com/product-detail/en/littelfuse-inc/CG21000/F10878-ND/2024360

Chuck Hawley
[hidden email]

Amateur Radio, KE9UW
aka Jack, BMW Motorcycles
________________________________________
From: [hidden email] [[hidden email]] on behalf of Chris Hallinan [[hidden email]]
Sent: Saturday, February 24, 2018 10:50 AM
To: [hidden email]
Cc: Wes Stewart; <[hidden email]>
Subject: Re: [Elecraft] KPA500 Faulting on high SWR on power rise

Not sure. I pulled the plug out and Googled the numbers on it. The plug
is labeled CG2 1000, which I think means it is a 1000V breakdown voltage.
It appears to be a Littlefuse device, according to Allied Electronics which
has the leaded version of the part for $2 ;)

Without knowing for sure, 1000V seems plenty for a 500W amp into
approximately 50 ohms load. Note I have the surge protector on the low SWR
side of the tuner which is mounted under an eve of the house. Probably not
ideal but that's another issue ;)

Chris

On Sat, Feb 24, 2018 at 11:06 AM, Don Wilhelm <[hidden email]>
wrote:

> Chris,
>
> What is the possibility that you have an HP suppressor body and a 200 watt
> Arc-Plug?
>
> 73,
> Don W3FPR
>
>
> On 2/24/2018 10:32 AM, Chris Hallinan wrote:
>
>> Hi Wes. Appreciate the feedback. I'm certainly not impressed by having
>> one
>> marked HP that is clearly not. See my earlier post: the surge protector
>> was my problem all along. It's arcing at about 300W.
>>
>>

--
Life is like Linux - it never stands still.
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Chuck, KE9UW

Jim Brown-10

Re: KPA500 Faulting on high SWR on power rise

In reply to this post by Bill K9YEQ

Someone should tell the electrons. UHF connectors have been standard on
legal limit power amps for as long as I've been a ham.

73, Jim K9YC

On 2/24/2018 1:46 PM, Walter Underwood wrote:
> The Amphenol voltage rating for UHF connectors is 500 V peak. So the connectors could be another weak point.
>
> https://www.amphenolrf.com/connectors/uhf.html

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Bob McGraw - K4TAX

Re: KPA500 Faulting on high SWR on power rise

I question the 4:1 balun being the correct nor best choice. Typical of that antenna the feed Z of the radiator is more likely 25 to 35 ohms. The 4:1 balun is presenting something like 10 ohms to the tuner. Worst case for high current and hi loss in the tuner causing heating. A 1:1 balun would seem more likely correct.

Many seem to "think" a 4:1 balun is correct when using open wire or a balanced line to "match the line".

Bob, K4TAX

Sent from my iPhone

> On Feb 24, 2018, at 8:59 PM, Jim Brown <[hidden email]> wrote:
>
> Someone should tell the electrons. UHF connectors have been standard on legal limit power amps for as long as I've been a ham.
>
> 73, Jim K9YC
>
>> On 2/24/2018 1:46 PM, Walter Underwood wrote:
>> The Amphenol voltage rating for UHF connectors is 500 V peak. So the connectors could be another weak point.
>>
>> https://www.amphenolrf.com/connectors/uhf.html
>
>
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Bob McGraw - K4TAX

Re: KPA500 Faulting on high SWR on power rise

In reply to this post by Jim Brown-10

Yes and in years past AM legal limit PEP power was about 3KW. PL-259's were used on these transmitters and Johnson KW Matchbox type equipment.

Bob, K4TAX

Sent from my iPhone

Rick WA6NHC-2

Re: KPA500 Faulting on high SWR on power rise

In reply to this post by Bob McGraw - K4TAX

In my case, the 4:1 was shown as correct by comparing to a 1:1 (for me). I was able to find more usable bands with the 4:1 (meaning closer matches).

If the dipole is single band only, using a 75 ohm feed (choke at the transition from feed to antenna) is best. A resonant dipole is closer to 72 ohms, ignoring local conditions, one of which is elevation above ground. Inverted vee systems are lower impedance so 50 ohm is the proper choice (again, single band only).

For this example of multiband use AND open wire feed (for dramatically lower feed loss at high SWR) which alters the impedance of the system and the length of the feed matters; one can use an analyzer to find which transformer works best or simply try both.

The 4:1 presents a bit more device loss compared to a 1:1, but if it also provides near resonance on more bands, so that loss is negligible.

With open line (75-600 ohm typical) you don’t match the line with the balun, you match what the SYSTEM presents, antenna and feed.

Rick WA6NHC

Smell Czech correction happen

> On Feb 24, 2018, at 7:30 PM, Bob McGraw K4TAX <[hidden email]> wrote:
>
> I question the 4:1 balun being the correct nor best choice. Typical of that antenna the feed Z of the radiator is more likely 25 to 35 ohms. The 4:1 balun is presenting something like 10 ohms to the tuner. Worst case for high current and hi loss in the tuner causing heating. A 1:1 balun would seem more likely correct.
>
> Many seem to "think" a 4:1 balun is correct when using open wire or a balanced line to "match the line".
>
> Bob, K4TAX
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Mark Goldberg

Re: KPA500 Faulting on high SWR on power rise

In reply to this post by Bob McGraw - K4TAX

There are a lot of factors that determine what the best choice of Balun is.
Unless it is a resonant antenna, the impedance is not purely resistive,
usually far from it. It can be almost anything. The feedline length will
affect what the impedance is at the tuner. The tuner, if you have one, will
select, or you will select the configuration and values of inductance and
capacitance that provide the correct match. Those components, especially
the inductors have losses and heat up. You don't generally know what those
losses are and they vary from part to part.

The tuner It can often match with a 1:1, 4:1 and other baluns, as long as
the impedance seen by the tuner is within it's range. The claims that a
tuner can tune 10:1 or 3:1 are not that useful, except for a general
comparison. They can't match every possible impedance, inductive,
capacitive or whatever within that range. Depending on the manufacturer's
choices of values, they may be able to match a higher SWR if it is very
inductive, rather than capacitive, for example. The optimal match will also
be determined by the losses. You may be able to get a match, but 50% of
your power may be absorbed by the tuner, with smoke eventually being let
out.

I use a homebrewed dual core switchable 4:1 / 1:1 currrent balun. Most of
the time, the tuner can match my Horizontal loop with the switch in either
position. It may result in a lower SWR in one position or the other and I
usually choose the position that results in the lowest SWR after the tuner
matches. In a few cases, after transmitting for a while, the tuner will try
to retune. I believe that is likely due to an inductor heating up in the
tuner and changing value. That tells me the losses are likely high and I
try the other switch position and see if it stays tuned. If you know what
impedance your antenna system and feedline present to the tuner, you may be
able to choose an optimal balun. In my case, with so many bands, there is
no single best choice. I choose whatever works best on that particular
frequency.

73,

Mark
W7MLG

On Sat, Feb 24, 2018 at 8:30 PM, Bob McGraw K4TAX <[hidden email]>
wrote:

> I question the 4:1 balun being the correct nor best choice. Typical of
> that antenna the feed Z of the radiator is more likely 25 to 35 ohms. The
> 4:1 balun is presenting something like 10 ohms to the tuner. Worst case for
> high current and hi loss in the tuner causing heating. A 1:1 balun would
> seem more likely correct.
>
> Many seem to "think" a 4:1 balun is correct when using open wire or a
> balanced line to "match the line".
>
> Bob, K4TAX
>
>

Don Wilhelm

Re: KPA500 Faulting on high SWR on power rise

In reply to this post by Rick WA6NHC-2

Rick and all,

Whether that is true or not depends on the length of the radiator and
feedline relative to the frequency. Read my "Antennas" article on my
website www.w3fpr.com.

There is good reason that the Elecraft BL2 is switchable between 1:1 and
4:1.

73,
Don W3FPR

On 2/24/2018 10:53 PM, Rick Bates (WA6NHC) wrote:
> In my case, the 4:1 was shown as correct by comparing to a 1:1 (for me). I was able to find more usable bands with the 4:1 (meaning closer matches).
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