[hpsdr] Hermes/ANAN-10 RX spurious signals?

[Dick Lichtel]

I looks like the 10MHz noise can be reduced from an S7 to an S2 by 
placing shielding over the 10MHz osc area. I tied the shielding to 
ground via copper foil tape to the 10MHz Clock  SMA connector.

The 10MHz osc is directly below the ANT1 input on the amp causing the 
clock to couple with the RX input... which is why moving the Hermes 
board in and out of the cabinet changes the noise strength.

It might be possible to place a shield in a slot  above the Hermes board 
in the cabinet. I only needs to be about 2" in depth. I'm thinking that 
a piece of brass or copper  from ACE hardware could be cut down to size 
to fit. It is probably a good idea to coat the metal with something not 
conductive to be safe. I'll try this tomorrow to see if the results are 
similar to placing a small shield over to the osc. area.

I suspect a similar approach can be taken for the 25Mhz clock, but I 
have to look at the schematic and board layout in be sure.

I think it was a bad idea to have the Hermes board face up in the 
cabinet. The spurs probably wouldn't be there and we won't have to 
solder those tiny rf connectors. We would need to new face plates to 
mount the Hermes board backside up.

Dick KD4JP

On 11/12/2012 6:17 AM, Bruce Beford wrote:
> Thanks, Dick.
> I am glad you have had a chance to experiment with this a bit. I won't be
> able to work with mine for a week. Please keep us posted on your
> progress/observations.
> 73,
> Bruce, N1RX
>
> ________________________________________
> From: Dick [mailto:dick221z at gmail.com]
> Sent: Sunday, November 11, 2012 10:11 PM
> To: Bruce Beford
> Cc: hpsdr at lists.openhpsdr.org
> Subject: Re: [hpsdr] Hermes/ANAN-10 RX spurious signals?
>
> Since the position of the Hermes board in the case seems to affect the 10MHz
> spur, I tried putting the Hermes back in position and sliding bit of
> shielding over the A/D  area, about 1/2 spacing above, not grounded. This
> reduced the 10MHz spurs by about 2 S units. So it looks  like some shielding
> is needed over the analog section.
>
> I'll look into making something more practical that can be grounded later on
> in the week.
>
>
>
>
>


 1352771818.0