[Elecraft] KPA 500 Power Amp.

Wed Dec 25 15:20:44 EST 2024

Antenna gain — model it, that will ball park it.   It will show gain and losses; add line and mismatch figures; now you know, stay under that.   I change output between my SteppIR dipole (resonant) and 160m L (3:1, tuned, lower take off) both ~100’ of coax, to stay within limits. 

Heat — watch the temps, which I’m more aggressive than the amp-ware chooses (60’s C max is my choice); simple enough to make a habit. 

ERP limits — no thank you, my SteppIR presents different gain per band (posted gain is ‘hopeful’ free space and actual depends in part on height above ground, per band, which is a lot more modeling of a very complex antenna) and this ability appears to be beyond most hams.  It doesn’t work with the dumbing down of the licensing tests. 

Just don’t poke that bear. I moved in part (LARGE expense) to a place to raise antennas (new home, state and propagation).

I (and many others) paid a lot for the legal limit amps and near double that again for the antenna.   If others can’t do the same, it’s not leveling, it’s crippling those who can.   What then is the lowest common denominator, an HOA confined wire in the attic or damp washrag for an antenna ERP?

I can’t count the times that 1500 watts and 12 dB of gain was just barely enough to work the DX I heard.  Plus I rather enjoy being able to work through EU/JA walls and that requires high ERP; nothing beats gain, no matter how you get there.

I clearly have little patience for QRP, life is too short for that; loud is less aggravating. 

Merry Christmas,
Rick nk7i

> On Dec 25, 2024, at 10:31 AM, Bob McGraw <rmcgraw at benlomand.net> wrote:
> 
> My major concern, based on my actual measurements, is that operating a power amp of this type and design at reduced to significantly reduced power nets very poor efficiency.  In fact, my KPA500 at certain power levels below 500 watts will actually have higher heat dissipation than if operated at rated power. With this known, we all understand that heat is one of the most detrimental factors regarding solid state circuits and components.   I find many instances where hams operate at lower power with the thinking "it will save my tubes or transistors, etc."  Based on measurements, this thinking is far from accurate.   I refer it to "old ham lore".
> 
> As to operating on 60M, the US power limit is 100 watts ERP (Effective Radiated Power) with reference to a 1/2 wave dipole. Unless one actually knows the loss and gain of the antenna system, just operating at 150 to 200 watts is a blind shot in the dark. Do you know the gain or loss of a specific antenna?  Loss in a feedline is relatively easy to determine.   Gain or loss in the antenna is quite a challenging project.   Of course who is going to know?  That is not important.  But what is important, one must be thoughtful of others, those that do operate within legal power limits.   Just because you can, is no sign you should do so.    It just isn't the ham radio way.   The methodology is different for 30M where the PEP is 200 watts.   Add a 6 dB gain antenna and one has 800 watts ERP.   60M is not like that.
> 
> Perhaps the regulations should be re-written such that legal limit power is 1500 watts ERP in place of 1500 watts PEP.  That certainly would put all folks on a level playing field.   After all, FM broadcast and TV stations power is sated in ERP values.  I go back to changes when AM power was defined as 1 Kw DC input to the final stage.  That was changed to a power of 1500 watts PEP. With AM that equates to a carrier of 375 watts modulated 100% for 1500 watts PEP.
> 
> While electricity may be cheap, the abuse and failure of solid state devices operating at high temperature is not cheap.  Just something to think about.
> 
> 73
> 
> Bob, K4TAX
> 
> 
>> 
>> 
>> 
>> ----------------------------------------------------------------------
>> 
>> Message: 1
>> Date: Tue, 24 Dec 2024 21:17:55 +0000 (UTC)
>> From: Wilber Bandemer <bandemerw at aol.com>
>> To: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>
>> Subject: [Elecraft] KPA 500 Power Amp.
>> Message-ID: <1476882602.6827589.1735075075108 at mail.yahoo.com>
>> Content-Type: text/plain; charset=UTF-8
>> 
>> KPA 500 will not transmits on 60 meters. Please tell me what is wrong and what should I do to fixed this problem?73Wilber AB5WW
>> 
>> ------------------------------
>> 
>> Message: 2
>> Date: Tue, 24 Dec 2024 13:32:23 -0800
>> From: jerry <jerry at tr2.com>
>> To: Wilber Bandemer <bandemerw at aol.com>
>> Cc: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] KPA 500 Power Amp.
>> Message-ID: <b69f1bd595b09352c8ff823dfa70bca8 at tr2.com>
>> Content-Type: text/plain; charset=US-ASCII; format=flowed
>> 
>> Why use it on 60M?  Legal limit is 100W ERP on that band.
>> 
>>                  - Jerry, KF6VB
>> 
>> 
>> 
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