[eagle] Re: 70 cm Receiver IF Spurs - Problem Solved

Lyle Johnson kk7p at wavecable.com
Sun Jun 17 21:23:48 PDT 2007


Hello Juan!

> The uglier this gets the more interesting I find it!  I hope no one is
> getting disheartened.  After all, this is why we all got involved in the
> first place, isn't it?  If it was easy it would be boring.

No one is bored... :-)

> I just cooked up an idea for a noisy power source that could be used during
> payload development and test.  I stuck my write up and a block diagram at
> the end of my current log.  
> 
> Here's the link:
> http://www.juanr.com/pages/hobbies/ham_radio/Eagle/Spur_Suppression.htm
> 
> What do you think?

It would be nice to be able to add to the bench supply output a noise 
source capable of a volt or more at whatever current the D.U.T. might 
require.  Maybe an amplifier we can feed with a function generator to 
simulate a sawtooth or ??? waveform from a few kHz to a few tens of kHz 
to better simulate the assumed dirty power source?

We really need to get an idea what to expect worst case from the S/C 
power system.

> Shielding the CAN-Do inductor obviously won't solve all these problems but
> it might buy back 2 inches of space and that's worth the effort.

Yes, we need to shield this if we can.

> Lyle,
> 
> My suspicion is that the two VCOs on this receiver are also the most
> susceptible to radiated EMI from CAN-Do.  I can't say for sure but it looks
> that way to me.  Both are in metal cans soldered to ground.  The closest one
> was about 2 inches away from the CAN-Do inductor.  I've more than doubled
> that distance to 4-1/4 inches to get away from it.  That's a lot of EMI!

Indeed it is.  We should try and find a toroidal inductor to minimize 
radiation, then put a magnetic shield around it to suppress what the 
toroid radiates.

73,

Lyle KK7P



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