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I think my reasoning in post 2 was also incorrect. The idea that the JFET has an extremely high input impedance may apply to low frequencies, but probably not at RF. I was told on another forum that I need to look at power, something I cannot do if there is total reflection, so there has to be some finite input impedance at RF just like mosfets have.

My plan now is to build the amp without the antenna/tank part, then drive it with a signal generator using a multi-tap xfmr to try to figure out the actual input impedance based on the power that comes out as I change taps. Once I know the approximate input impedance, I can then match the known tank impedance to that value. Like I said before, there is reference to the BF998 having a 2kΩ input, but I'd like to know for sure.

What a trip lol

I will probably let this thread rest until I have a working amp, and then report on what I did to get there. I am way out of my depth on this one, could have just followed someone else's schematic and been happy with the result lol.

Edit: and I just had my koolaid pissed in again. Read a forum post on eev that states the mosfet I am using has the lowest NF at the highest gain and reducing the gain using gate 2 screws up the NF. Same post mentioned not using tanks because the insertion loss adds directly to NF, something I hadn't considered. Maybe I can use litz wire on ceramic or borosilicate as a form to lower the insertion loss. I don't know. The more I dig, the worse my idea looks, but this is more for learning than anything else, so whatever happens, happens. Starting to realize the best front ends don't come easy!

<blockquote data-quote="brandon7861" data-source="post: 848944" data-attributes="member: 53724">I think my reasoning in post 2 was also incorrect.&nbsp; The idea that the JFET has an extremely high input impedance may apply to low frequencies, but probably not at RF.&nbsp; I was told on another forum that I need to look at power, something I cannot do if there is total reflection, so there has to be some finite input impedance at RF just like mosfets have.My plan now is to build the amp without the antenna/tank part, then drive it with a signal generator using a multi-tap xfmr to try to figure out the actual input impedance based on the power that comes out as I change taps.&nbsp; Once I know the approximate input impedance, I can then match the known tank impedance to that value.&nbsp; Like I said before, there is reference to the BF998 having a 2kΩ input, but I&#039;d like to know for sure.What a trip lolI will probably let this thread rest until I have a working amp, and then report on what I did to get there.&nbsp; I am way out of my depth on this one, could have just followed someone else&#039;s schematic and been happy with the result lol.Edit: and I just had my koolaid pissed in again.&nbsp; Read a forum post on eev that states the mosfet I am using has the lowest NF at the highest gain and reducing the gain using gate 2 screws up the NF.&nbsp; Same post mentioned not using tanks because the insertion loss adds directly to NF, something I hadn&#039;t considered.&nbsp; Maybe I can use litz wire on ceramic or borosilicate as a form to lower the insertion loss.&nbsp; I don&#039;t know.&nbsp; The more I dig, the worse my idea looks, but this is more for learning than anything else, so whatever happens, happens.&nbsp; Starting to realize the best front ends don&#039;t come easy!</blockquote>

[QUOTE="brandon7861, post: 848944, member: 53724"] I think my reasoning in post 2 was also incorrect. The idea that the JFET has an extremely high input impedance may apply to low frequencies, but probably not at RF. I was told on another forum that I need to look at power, something I cannot do if there is total reflection, so there has to be some finite input impedance at RF just like mosfets have. My plan now is to build the amp without the antenna/tank part, then drive it with a signal generator using a multi-tap xfmr to try to figure out the actual input impedance based on the power that comes out as I change taps. Once I know the approximate input impedance, I can then match the known tank impedance to that value. Like I said before, there is reference to the BF998 having a 2kΩ input, but I'd like to know for sure. What a trip lol I will probably let this thread rest until I have a working amp, and then report on what I did to get there. I am way out of my depth on this one, could have just followed someone else's schematic and been happy with the result lol. Edit: and I just had my koolaid pissed in again. Read a forum post on eev that states the mosfet I am using has the lowest NF at the highest gain and reducing the gain using gate 2 screws up the NF. Same post mentioned not using tanks because the insertion loss adds directly to NF, something I hadn't considered. Maybe I can use litz wire on ceramic or borosilicate as a form to lower the insertion loss. I don't know. The more I dig, the worse my idea looks, but this is more for learning than anything else, so whatever happens, happens. Starting to realize the best front ends don't come easy! [/QUOTE]

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