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I made a high input impedance JFET CS amp as the 1st amplifier stage for a 60kHz Loopstick Antenna. I am using an RF JFET (J211) and ceramic capacitors.

enter image description here

The only signal I see is a 60Hz sine wave that is present even when the amplifier is turned off.

I am unsure what to do at this point. I dont know if a I need a larger Antenna or if I am doing something wrong in trying to detect this signal. WWVB is particularly weak where I'm at as well.

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  • \$\begingroup\$ What you should do is test your amplifier with a signal generator that generates a signal you can see, and that you can gradually turn down to the levels you expect to get from the antenna. But if you're seeing a lot of 60 Hz, then you have grounding issues that you need to address first. \$\endgroup\$ – Dave Tweed Jan 30 '16 at 2:11
  • \$\begingroup\$ How do you know that the antenna is tuned correctly? Test with a signal generator and a transmitting loop, some distance away, and check that the received signal peaks near 60 kHz. If you see mains buzz... Are you powering this from the mains - try a battery? Note that the expected voltage from WWV may be only a few tens of micro volts. \$\endgroup\$ – tomnexus Jan 30 '16 at 5:37
  • \$\begingroup\$ Those 10 microfarad caps are way way too big .Try 10 nanofarad and you will see a little less 60HZ so it might be easier to see your 60KHz \$\endgroup\$ – Autistic Jan 30 '16 at 9:20
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First, you'll need to check your gnd, then decouple your +12V power supply to get rid of that 60hz mains humm.

Next, Let's try to bias that depletion-mode JFET to around -1.5Vgs to keep it operating well within its linear region.

Finally, add a 60Khz tank between Vpos and your drain to narrow the bandwidth of your amp.

I'm envisioning something like:
Modified Preamp

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  • \$\begingroup\$ If you want a little more gain (and narrower bandwidth) from this circuit, you could place another 60Khz tank between the incoming signal trace & the 3M pull-down/bias resistor. \$\endgroup\$ – Robherc KV5ROB Jan 30 '16 at 5:45
  • \$\begingroup\$ I just revised the diagram due to improper placement of a gate bias resistor & changed coupling capacitors' values to match @Autistic 's suggestion from OP comment. \$\endgroup\$ – Robherc KV5ROB Jan 30 '16 at 14:08
  • \$\begingroup\$ It works! I tied 2 of theses amplifiers together and I am able to see a 20mV 60kHz On/Off signal. Thats pretty good considering I cant get FM radio or cell phone reception where I am at. \$\endgroup\$ – Tony Feb 8 '16 at 0:46
  • \$\begingroup\$ @Tony if you want, we could probably come up with some similar preamps for AM/FM radio frequencies & see if you can pull a few of those in. Cell phoes, however, (according to Wilson Cellular) use TDMA algorythms, so even with better signal amplification, the time delay would likely be too long for a cell tower to accept your link. \$\endgroup\$ – Robherc KV5ROB Feb 8 '16 at 15:41

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