Intriguing

One thing I found intriguing and that I was not aware of is if running in a fixed Xtal frequency or one of the frequencies in the VCO then all other frequency settings are still running in the background until that frequency is selected. I thought the frequencies only came to life when you switched them on. Makes me wonder if they could cause some type of interference in the background?

Gary.

Hi Gary,
Seeing this got the better of me, so I had a look. It seems that they do! However the voltage that they oscillate at while they are not selected is at least 10X less than while you are using that particular frequency, with the exception of the vco, which would be putting out the same voltage at all times. I have not found any evidence that the crystals cause any interference with other parts of the detector.

From what I have found the 5+ power supply rail is the biggest culprit of causing interference within the detector. It has a high speed switching inductor to raise the voltage 5v above the battery supply. This causes spikes on the 5v rail, which are picked up and amplified by the front end pre-amp, and also at the integrators. I have developed a real complex about this problem and I am trying to come up with a solution to stop it. I have found that running the 5+ rail from a separate battery makes the detector a lot stabler, but who wants to carry an extra battery around?
Cheers

Thanks mechanic for the reply and good you looked into the crystal ball so to speak if you pardon my pun.

The interference you speak off with the power supply rail I am yet to identify while operating but it must be there as you say.

Now another intriguing thing I was not aware of is if the GPM Gain was wound up 100% fully clockwise then it would be equivalent to a Gain figure around 200 on the GP4 series which has a max Gain figure of 15. That being correct and my math’s as well you would only need to wind the GPM Gain on 7.5% or lets say 10% to match the max Gain on the GP4’s and say around 5% on the GPM to run at a FP Gain setting of 8.

No wonder the GPM Gain can play havoc with hot ground.

Gary

Hi Gary,
If you have a look at the "sd2000 power supply noise" thread in modified ML detectors on gpoz about 1/3 down on the second page, are some pictures of the noise. Until you have it removed you will never have known it was there! There is not an elegant solution for this yet, however I think that Stefan is well along the way to solving it(fingers crossed).

Now as far as the gain goes, originally the gain of the 2000 was about 2, by adding the 500k pot,(gpm mod) max gain is 10.71 (I think anyway, somebody please correct me if I am wrong!)

Cheers

Ismael,

Could you add a reply to confirm Mechanic's thoughts (his last paragraph above) on my assessment of using your GPM Gain positioning in comparison too the Gain positions on the GP4000 and GP4500.

Gary

Thanks Ismael,

Therefore I can expect to increase my Gain by 7 times from its Standard setting to its Maximum setting.

Now being as thick as I am does this also mean I am increasing the Rx signal by the same?

Gary

Maybe you are not as thick as you think you are with no reply.