[Elecraft] Weird EMI issue... part deux

[Joe Subich, W4TV]

> I've noticed that when I'm tuning around 4.8 MHz to 5.3 MHz, 
> I can hear EMI in the form of a motorboat sound whenever I 
> turn a front panel knob.  It's most apparent when spinning 
> VFO A or VFO B knobs, but also occurs when turning the filter 
> knobs. 

I have a slight bit of noise when tuning only in that area. 
I believe it to be entirely normal.  I recall  Wayne saying 
somewhere that the DDS operated in the area of 5 MHz and that 
was synthesizer switching noise.  

In my case, the noise is about S1 on an S-meter that was 
calibrated to the XG-2 and is in "abs" mode.  In my case 
the noise is only audible in the main Rx with VFOA or XIT/RIT 
when XIT/RIT is enabled ... or in the sub RX with VFOB or 
XIT/RIT when XIT/RIT is enabled.  The noise is masked by 
band noise with an antenna connected.  It is audible only 
from 4.900 to 5.100 and only noticeable from 4.940 - 5.050 
unless one it looking for it. 

As you say, it is not present when the VFO or RIT knobs are 
at reset ... it is not a problem here. 

73, 

   ... Joe, W4TV 
 
 





> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of James Sarte
> Sent: Saturday, February 28, 2009 5:27 PM
> To: Elecraft at mailman.qth.net
> Subject: [Elecraft] Weird EMI issue... part deux
> 
> 
> OK gang, I don't know what to do at this point and you're my 
> last line of defense before sending this rig back to Elecraft 
> engineering for analysis.
> 
>  
> 
> I'll sum it up briefly:
> 
> This is rig #2730.  I bought it in kit form, and assembled it myself.
> 
> It has a sub receiver, 100w amp, KDVR3, KAT3 tuner, 
> transverter, plus a full complement of filters on both receivers.
> 
> I also have a single general coverage receive module 
> installed on the sub receiver.
> 
>  
> 
> This is the problem:
> 
> I've noticed that when I'm tuning around 4.8 MHz to 5.3 MHz, 
> I can hear EMI in the form of a motorboat sound whenever I 
> turn a front panel knob.  It's most apparent when spinning 
> VFO A or VFO B knobs, but also occurs when turning the filter 
> knobs.  If I don't touch anything, no noise occurs.  I can 
> also hear this noise faintly when I'm around 3 MHz.  There is 
> no front-panel generated noise anywhere else from .5 to 54 
> MHz other than 3 and 5 MHz.  Also, if I don't have the sub 
> receiver on and I'm only listening to the main receiver, the 
> EMI noise isn't as loud when the pre-amp is on.  If I turn 
> the pre-amp off, the EMI generated from spinning knobs 
> increases in volume.  When I spin a knob and hear this noise, 
> I can also see the S-meter move in correlation with the 
> noise; spiking at S-7 from time to time.  This tells me that 
> this is locally generated interference, and occurs somewhere 
> within the K3's circuitry.  Turning the pre-amp on or off has 
> no effect on the sub-receiver; the noise is still present.  
> 
>  
> 
> Here's what I've done:
> 
> I've replaced the SUBIN board because I thought it was only 
> the sub-receiver being affected at one time, but it didn't 
> help. I've also swapped mixers and synthesizers with no 
> positive result. I've disassembled and reassembled the entire 
> front panel 4 times already, and cannot find anything wrong.  
> I've traced circuits on the sub receiver and SUBIN boards and 
> everything checks out.  I've also swapped TMP cables around 
> with no improvement. I've also removed just about every 
> module except the transverter and KAT3 hoping to eliminate a 
> problem module, but the problem still remains.  I've also 
> checked every screw and washer throughout the radio, and they 
> all match the assembly instructions.
> 
>  
> 
> I'm starting to think that there may be an isolation problem 
> with the main RF board at this point.  BUT, since I was not 
> able to test the rig without the KAT3 tuner or removing the 
> transverter board, I cannot be 100% sure.  
> 
> Is there anything else I can check before sending the rig 
> back to Elecraft???
> 
>  
> 
> Apart from this problem, I have not experienced any other 
> issues with this radio.  In fact, it works PERFECTLY well.. I 
> should probably tell myself to live with this noise, but 
> after spending 4k, I don't want too.
> 
>  
> 
> Suggestions people?  Please help a fellow ham out.
> 
>  
> 
> 73,
> 
> James KC2UEE
> 
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