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Specan log detector and power regulators

 

Hi, I am starting to build a 'specan' (?)

Mainly because I have a prototyping shield spare I will be using one.? It also has an SOIC 14 footprint.? I was wondering whether I could put the AD8307 on the shield.?

Would that introduce too much noise from the MCU?

What about if I were to shield the area of the board that contains the log detector?

Second Question:? Ashhar Farhan used an external 5v regulator for the arduino (separate from the regulator for the AD8307) but the arduino has a regulator on board.? Is there a good reason for by-passing the arduino's regulator?

thanks & 73

Ellis G7SAI
 

The data sheet of the AD8307 gives a supply filter circuit that is good enough to be used with the output of the arduino
Keep in mind the AD8307 goes to 500MHz, good shielding is important for the low end of the power range.
If the shield has a massive ground plane at the side of the arduino it may work but if its a thru hole shield without proper ground plane probably not.
--
HBTE Files section:?/g/HBTE/files
Erik, PD0EK
 

Thanks Erik,

I'll stick with keeping the AD8307 on its own shielded daughterboard.? I have some feedthrough capacitors so I may use some of them to keep as much noise out of the detector.

73 de Ellis G7SAI
 

I have used the 8307 in several projects, and found it to be an extremely sensitive device.? To get a good noise floor you really should shield the? 8307 stage. I have etched my own double sided boards, or have had them made. If you wish I can send the gerber files for ones I hade made by oshpark.? The separate regulator also goes a long way to reducing any noise from the Arduino which can raise the noise floor. I found that good shielding and layout can lower the noise floor by almost 10 dB.? If you want I can post the Gerber files for a small board with regulator I hade made by OSH Park, files should be OK for most of the other board houses.
--
DuWayne,? KV4QB
 

Post it in any case, someone else in the future may find it useful.

On Tue, 24 Aug 2021 at 18:50, DuWayne Schmidlkofer <duwayne@...> wrote:
I have used the 8307 in several projects, and found it to be an extremely sensitive device.? To get a good noise floor you really should shield the? 8307 stage. I have etched my own double sided boards, or have had them made. If you wish I can send the gerber files for ones I hade made by oshpark.? The separate regulator also goes a long way to reducing any noise from the Arduino which can raise the noise floor. I found that good shielding and layout can lower the noise floor by almost 10 dB.? If you want I can post the Gerber files for a small board with regulator I hade made by OSH Park, files should be OK for most of the other board houses.
--
DuWayne,? KV4QB

 

Thanks DuWayne,

This build is going to be dead bug style, but I will doubtless be using the 8307 again.

Is your pcb for the dip package or the smd version?

73 Ellis G7SAI
 

Hi Ellis,
I too am making a "specan". I have the log detector working on a separate board(using it as a sweeperino), but not far along enough in testing to put the shields on.? I left open tracks on the top layer to solder the shields.
I'm curious if you have made the 100MHz 2nd oscillator yet.? I've built 2 and have burned Q1 both times.? I've checked and double checked the circuit board and pin outs. to now avail. Need some help here.
Andy KM4TRT

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