Loop Antenna Preamp
 

What are the advantages of a differential fet preamp over a single-ended fet
preamp? Does the diff amp have twice the output? Better SN ratio? Something
else? It seems like more work to try and find the center of the loop, I'm
just curious what the advantages are.

Thank you.

Al KA5JGV

http://members.cts.com/king/j/jlkolb/site/dif_fet.pdf
http://members.cts.com/king/j/jlkolb/site/fet_pre.pdf



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If it's a low-frequency loop, the advantage of balance is that you get
better rejection of local (near-field) voltage-noise fields. It's
less likely to matter when you get above a couple MHz. There are
similar considerations if you are wanting to use it for
direction-finding work, and in that case it could be of interest to
higher frequencies. You don't necessarily have to ground the center
of the loop to make things balanced.

Cheers,
Tom


"AL KA5JGV" wrote in message m...
What are the advantages of a differential fet preamp over a single-ended fet
preamp? Does the diff amp have twice the output? Better SN ratio? Something
else? It seems like more work to try and find the center of the loop, I'm
just curious what the advantages are.

Thank you.

Al KA5JGV

http://members.cts.com/king/j/jlkolb/site/dif_fet.pdf
http://members.cts.com/king/j/jlkolb/site/fet_pre.pdf



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In message , Tom Bruhns
writes
If it's a low-frequency loop, the advantage of balance is that you get
better rejection of local (near-field) voltage-noise fields. It's
less likely to matter when you get above a couple MHz. There are
similar considerations if you are wanting to use it for
direction-finding work, and in that case it could be of interest to
higher frequencies. You don't necessarily have to ground the center
of the loop to make things balanced.

True. In fact, forcing a centre-tap earth (ground) on a loop puts two
earths on the tuned circuit if the loop is tuned with a 2-gang capacitor
with the frame earthed. Not always good. A mechanical centre-tap may not
be an electrical centre-tap, giving unwanted resonances at HF.

Mike
--
M.J.Powell