I was looking a tDick Cappels Receiver this how could it be changed to pickup 433 mhz and lower.

I wondering what changes need to be made I have a bunch of transmitters Id like to find what there outputting.

 

Try a SDR dongle.

 

Yes, an SDR dongle for a few $ on EBay or similar will give you a cheap spectrum analyser. Pretty easy to install the free software and have a play with.

 

Here is how I modified the detector for some impulse radio experiments an should work well at 433 MHz.. The Fairchild KSP10 has low base to collector capacitance and and Ft of 650 MHz, though that is specified at a higher current). Should be fine for pulse modulation or amplitude modulation, nearly impossible for it to detect FM.



Those SDR adapters are very fascinating.I ordered one but it arrived not working. Still trying to get a replacement or refund... Forgive teh digression.

 

Do you think a HE8050S would work for the KSP10
I have a 2N3709 maybe closer
I found a C1923 that maybe the one from what I read.
The 2 black dots with the cap what is that a crystal if so what value
found a MPSH10 looks like a match for KSP10

 

The device between the two black dots is a selectable capacitor that sets the low pass corner frequency of the detector's output. C = 1/(6.28 * 39k * Fc)

I think the KSP10 is Fairchild's version of the earlier MPSH10. (Now that Fairchild has been absorbed by ON Semiconductor which is a spin-off of Motorola I guess they can mark transistors from the same production line with both part numbers.)

 

I just noticed an omission in the schematic: The emitter of the KSP10 and the three capacitors are grounded.