[Elecraft] KX1 - very quiet on 30m and 20m

Thu Mar 19 08:53:41 EDT 2009

Don,

thanks for that information.

Here's what I have. TX appears fine. With 12.3V supply I get the  
following output: 80m 3.3W; 40m 2.9W, 30m 3.8W, 20m 3W. All measured  
by an Oakhills Labs QRP meter and a 50 Ohm dummy load.

The RX seems to have a problem. I have done a careful check of all  
trimmer settings.

Measuring across the volume control (all controls fully clockwise);  
XG2 set to 50 microvolts (battery checked!); Fluke 175 true RMS meter  
(by a lucky coincidence):

40m: 163mV with earbuds connected; 185mV without
20m: 140mV with earbuds connected; 158mV without

Leaving the earbuds in, I then tried injecting the XG2 directly on the  
junction of L6 and the top of the RF gain pot. The difference in audio  
level is dramatic, particularly on 20m, but I still don't get anywhere  
near your figures:

40M: normal antenna input 163mV; direct to top of RF gain pot 275mV
20m: normal antenna input 140mV; direct to top of RF gain pot 550mV -  
getting closer!

Other checks I've done:
- Made sure that the break in the PCB and subsequent link is OK for  
the addition of the KXB3080
- Checked L6 for continuity
- Checked connections to KXB3080 - and ensured that A & B are as shown  
in the manual i.e. B goes nearest to T1.
- Checked all voltages on U6 - within spec
- Checked connections of T2 and re-soldered joints (this was supplied  
by the Mychael)
- Checked L3 is the later version with the right number of turns

This feels like it may be a problem with the pin diode switches, but  
that still doesn't really explain why I can't get anywhere near your  
0.8V figures across the audio pot.

73 Bob G3YIQ

On 18 Mar 2009, at 23:39, Don Wilhelm wrote:

> Bob,
>
> OK, I finished the KX1 up to the point where I am able to give you  
> some numbers.
> With a 50 uV input at 7040 from my XG2 signal generator, I find  
> 0.866 volts measured across the AF Gain control (control set to  
> maximum) with a high impedance load at the headphone jack.  If I  
> plug in headphones (Sony MDR series), the voltage drops to 0.836  
> volts.
> Of course, the AGC should be active which will keep the voltage down  
> a bit.  The KX1 has the KXB3080 option installed, and the receiver  
> front end is a little more sensitive than either the original KX1 or  
> with the KXB30 installed.
>
> With a 1 uV input, I read 38 to 40 mV at the same point - AGC should  
> not be as active at that level.
>
> The voltage readings were obtained with a Fluke True RMS reading DMM.
>
> 73,
> Don W3FPR
>
> Don Wilhelm wrote:
>> Bob,
>>
>> I can't give you a measurement number right away, I do not have a  
>> working KX1 here at the moment, but that value may be possible  
>> tomorrow or Friday.
>> If you do not hear quite a loud signal with the 50 uV output from  
>> the XG2 (or XG1  with a 20 meter crystal) - with the RF Gain at  
>> full clockwise and the AF Gain between 25 and 35% of rotation, then  
>> there is something wrong.
>>
>> How is the transmit power output?  If that is OK, then the low pass  
>> filter is likely OK, and you might want to look at T2.
>>
>> The KX1 audio is not super strong, and having good volume does  
>> depend on using sensitive headphones.  If your headphones do not  
>> have an sensitivity rating greater than 108 dB/mW, then your  
>> headphones may be the major problem, see the KX1 manual page 62.
>>
>> 73,
>> Don W3FPR
>>
>> Bob Jones wrote:
>>
>>> I've just completed a KX1 build with the 80/30m option and auto atu.
>>>
>>> It works on all bands but 30m and 20m require the volume control  
>>> to be fully clockwise and even then it's quiet. I've carried out  
>>> the recommended checks and everything appears to be fine.
>>>
>>> Having read the previous posts on 'low audio' there's an element  
>>> of subjectivity regarding what this means.
>>>
>>> Does anyone know of a definitive measurement I can make to see if  
>>> this radio is working as well as it should?
>>>
>>> For example, I have the XG1 and can inject a 14.060 MHz signal at  
>>> 1 microvolt or 50 microvolts. With the bandwidth set to maximum,  
>>> what level of signal should I expect on the input or output of the  
>>> audio amplifier, or at any other point in the circuit?
>>> Any advice gratefully received.
>>>
>>> Bob, G3YIQ
>>>
>>>
>>>
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