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+--- Thread: Pulling RF off the H-amp? (/showthread.php?tid=822)
Pulling RF off the H-amp? - b.e.wilson - 2014-08-20
I've ordered a kit, and I've put together the loops. After testing them, I think I'd like to use them in my shack, which means I need to find a place on the board to pull the RF out. I was thinking directly after the first gain stage, before the signal gets to the filters. Is there an accepted method of doing this? I'm hesitant to pull the signal off the board directly into a coax to the shack, and thinking I'd better use a buffer amp. It'd be nice if a tried and tested method was out there, rather than reinvent a method.
RE: Pulling RF off the H-amp? - Rob.Chouinard - 2014-08-20
I have about 50 ft of Sheilded Cat 5e between my controller and my amp. I even used direct bury cable (that I buried) and I have my amp and antenna in the back yard on the fence post.
RE: Pulling RF off the H-amp? - b.e.wilson - 2014-08-20
(2014-08-20, 01:24)Rob.Chouinard Wrote: I have about 50 ft of Sheilded Cat 5e between my controller and my amp. I even used direct bury cable (that I buried) and I have my amp and antenna in the back yard on the fence post.
Sorry, I wasn't sufficiently descriptive. I'm looking to pull out the RF off the antennas or off the amp board before the filter stages, so I can listen to the 30 KHz to 2 MHz segment. I figure this might be cheaper than buying a Wellbrook loop antenna. I'm mostly curious how to get the signal off the board without messing up the signal that goes to the controller board.
RE: Pulling RF off the H-amp? - RichoAnd - 2014-08-20
I suggest right after the HP-Filter.
Lower cutoff (-3 dB point) is 3KHz, and 50/60 Hz are attenuated significantly.
A 430-470 Ohm at that point is acceptable - this gives an attenuation of 20dB at the outlet.
Remember first stage amplifier ~ 0-30dB
Will we hear about the result?
RE: Pulling RF off the H-amp? - Bonzo - 2014-08-21
I don't want to be a spoiler - just take this as a warning if strange things happen:
For me the idea to split the VLF signal sounds like a potential source for unwanted common mode currents
resp. ground loops causing hum, noise and/or interference.
RE: Pulling RF off the H-amp? - b.e.wilson - 2014-08-21
(2014-08-21, 17:44)Bonzo Wrote: I don't want to be a spoiler - just take this as a warning if strange things happen:I'm a scientist. I'm pretty comfortable experimenting and dealing with negative results.
For me the idea to split the VLF signal sounds like a potential source for unwanted common mode currents
resp. ground loops causing hum, noise and/or interference.
RE: Pulling RF off the H-amp? - Bonzo - 2014-08-21
(2014-08-21, 17:58)b.e.wilson Wrote: I'm a scientist. I'm pretty comfortable experimenting and dealing with negative results.I see. Then the warning was of course mentioned only for the unexperimenced guys that intend to copy the idea!
RE: Pulling RF off the H-amp? - Einar - 2014-08-21
I would use a balanced amp. Opamps are cheap. With a balanced amp you are less likely to get in trouble with noise on ground since ground is not a reference potential. Ground noise can affect the signal you tap off, but worse is that it can sneak back into the BO system.
I'm a trouble shooter, and you would not believe how many problems we pin down to people believing that ground is the same in a system of connected devices.
RE: Pulling RF off the H-amp? - b.e.wilson - 2014-08-22
Yeah, I appreciate all the comments. I don't figure it will work just right the first time, and may take a while to figure out.
I need to get my boards built and get the system up and running first, so this will take a while.
RE: Pulling RF off the H-amp? - RichoAnd - 2014-08-22
To avoid ground loops, simply add a transformer on receiver site.