Hi Stefan,
Ok, I recognized the problem with the foto and had to resend my mail without:-)
Meanwhile my tx is back on the air.
I think the methode with the bulb is ok for mf as it works also well on sw
bands.
Key down without load?
In this case I have an Input of only 10 watts versus 120 with load...
Transformer stays at very moderate temperature even when I operate with 25
volts/25 amperes.
Before I used t130-2 which got very hot..
73, df5qg
Christian Groeger
Stefan Schäfer <[email protected]> schrieb:
>Hi Christian,
>
>> -------- Originalnachricht --------
>> Betreff: Re: LF: MF PA
>> Von: "C. Groeger"<[email protected]>
>> An: [email protected]
>> Cc:
>>
>> Hi Stefan,
>> Thanks for these infos!
>> This is always helpful because I'm not a really good technican. Everything I
>> built was a mixtiure of my ideas and stuff from the net...
>> Output power is 100 w, measured with a 100 w bulb, matched to 50 ohms via
>> transformer. Thus efficiency is ok, I think.
>> The overall setup is:
>> Vxo/xo 10 mc/10.24 mc, mixer, Fd,
>> PreDriver 2n2219, Driver irf640, pa 2 x irf 540.
>> I have attached a foto...
>> 73, df5qg
>>
>
>There is no photo attached. Note that attachments on this reflector must
>not exceed 400 kB (or so). Otherwiese the email is rejected. Better use
>a dropbox link for large attachments, so people can decide if they want
>to have a look at it before downloading all the stuff.
>
>Well, 100W out at 120W in is 83% efficiency. And 20W losses can't be a
>problem for 2 TO-220 FETs as long as you use a suitable heat sink and
>reasonable thermal coupling.
>
>But i'm not sure how you measure 100W RF power with a 100W bulb. Is
>there no reactive component of the impedance of that bulb when running
>at 475 kHz?
>
>Take a look to the gate voltage, be sure that it is a real rectangular
>wave. Also run the PA in CW-key-down without connecting a load or a low
>pass filter and check if the output transformer becomes warm or hot.
>Maybe the core material is not suitable or the number of primary turns
>is to low? I don't expect overvoltage problems from a 100V FET at 12V
> DC supply voltage. Just some ideas...
>
>73, Stefan/DK7FC
>
>
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