[Elecraft] K1 80/40 tx problem

[Igor Lána]

Hello Don,
thank you for advice.

I check L9 and L10 again a it looks like good 
(http://ok1tgi.nagano.cz/obrazky/K1/L9_L10.jpg) - 28 turns.
I check all condensators on FB for 80m band and everything is OK.

I made new measuring.
I removed out the DRV-ground jumper and checked waveshapes on DRV and PA 
pads.
Power supply 13,8V/3.5A, output power 0.1W, dummy load 15W Nagoya 0-500MHz.
Oscilloscop Createc SC-03, 9MHz
Current was 0,45A on 40m, 0,98A on 80m.

DRV 7MHz (150ns, 1V): http://ok1tgi.nagano.cz/obrazky/K1/DRV_7MHz.jpg
DRV 3.5MHz (150ns, 2V): http://ok1tgi.nagano.cz/obrazky/K1/DRV_3MHz.jpg
PA 7MHz (150ns, 5V): http://ok1tgi.nagano.cz/obrazky/K1/PA_7MHz.jpg
PA 3.5MHz (150ns, 20V): http://ok1tgi.nagano.cz/obrazky/K1/PA_3MHz.jpg

Yes, there isn't little bit nice sinusoid. But bigger surprise was measuring 
in multimetr mode.

DRV 7MHz = 650mV rms: http://ok1tgi.nagano.cz/obrazky/K1/DRV_7MHz_mm.jpg
PA 7MHz = 3.6V : http://ok1tgi.nagano.cz/obrazky/K1/PA_7MHz_mm.jpg
DRV 3.5MHz = 1V (?!): http://ok1tgi.nagano.cz/obrazky/K1/DRV_3MHz_mm.jpg
PA 3.5MHz = 14.9V (!!): http://ok1tgi.nagano.cz/obrazky/K1/PA_3MHz_mm.jpg

This is strange values, isn't it ?

But the biggest mystery - see lowest line on PA 3.5 MHz multimetr PA 
measuring - there is 7.177 MHz !!!
I also made short checking with better oscilloscop (200MHz) at work on 
friday. And it showed me the same problem. But I didn't have dummy load and 
I thought that is the reason.

Is the PA over-drived ? Does it work in class C correctly ?

I checked "POWER" signal on pin 6, connector J1
RX 2.2 V for both bands. TX 3.5MHz = 2.94V DC, 7Mhz = 3.17V DC.

L1-L8 are adjusted for the best RX. Attemps in TX are complicated. On 80m I 
can't setup higer otput that 0.5 W because current is too high. On 40m I can 
adjust maximum 1W output with 2.0 "menu level".

Now I don't have any ideas.

Igor OK1TGI

----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at embarqmail.com>
To: "Igor Lána" <ok1tgi at seznam.cz>
Cc: <elecraft at mailman.qth.net>
Sent: Sunday, September 26, 2010 7:33 PM
Subject: Re: [Elecraft] K1 80/40 tx problem


>  Igor,
>
> The waveshapes are normal.  They will not be anything like a sine wave 
> coming out of a mixer, but the fundemental RF voltage is still present, so 
> the waveform will be cleaned up by the bandpass filters and the PA Low 
> Pass Filter.
>
> Since you have excessive current draw, the first place to look is the Low 
> Pass Filter on the 2 band board.  Are the capacitors correct?  Are the 
> number of turns on the toroids correct?  Count the turns carefully, 
> counting each turn that goes through the center of the core - a straight 
> wire through a toroid is one turn, a full wrap around the core is two 
> turns.  Failure to realize that fact is a common builder error.
>
> 73,
> Don W3FPR
>
> On 9/26/2010 12:06 PM, Igor Lána wrote:
>> Hello friends,
>> I built a kit K1 80/40. Everything was no problem. All values of 
>> resistors
>> and DC voltages were OK. But in chapter 9, part "Band 1 Allignment",
>> transistor Q7 has been melted (2W at 80 m band).
>> I changed it and after that I measured current -  0.1 W on 3.6 MHz 
>> current
>> is 1.1A! On 7 MHz, is slightly better - 0.1W  is 0.4 A but the 2W is 1.3 
>> A.
>> After several attempts to find mistake, I tried to use the "Signal
>> Transmitter tracing" with DRV-ground jumper. Instead of RF Probe  I used 
>> the
>> old oscilloscop in multimetr mode. I performed the measurements to the 
>> point
>> 15. All values looked like okay, but from the point 10, I watched the
>> unstability.
>> I switched oscilloscop to the measurement curve mode. And on OSC it is 
>> not
>> pure sine wave. The point of MIX has been very vibrant.  ATTN is clean. I 
>> do
>> not know if  the problem is on 6-7 intputs U8 or output 4.
>> Please, see videos of measuring on youtube.
>> ociloscop 150ns time raster: http://www.youtube.com/watch?v=fYTOw9DWfKI
>> ociloscop 50ns time raster: http://www.youtube.com/watch?v=9mUunLQdBuU
>> ociloscop-multimeter: http://www.youtube.com/watch?v=oFaKCssXsA
>> In every video first part is on ATTN, second on OSC, and the third on 
>> MIX.
>>
>> Please, do you have some recommendations how or where to find the error?
>> Can Xtal X6 defective?
>>
>> Thanks
>> 73 Igor OK1TGI
>>
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