A FET might be alright, definitely the ticket on short whip with a
high impedance .... I'm not sure what the impedances look like on a
(relatively) short untuned loop, I tried to measure one with my AMQRP
Antenna Analyst but I have way too much metal (heat ducts, pipes, etc)
in my basement to get an accurate reading so I need to wait a few more
weeks for the weather to warm up so I can take it outside in the free
and clear and get some measurements
I will say this though, expect a Wellbrook clone from me by the end of
April using a push-pull pair of 2N5109s (or similar) and perhaps a
pair of FETS depending on the impedances or the need for more gain
JR
--- In loopantennas@..., "Keith Browning" <kbrowning@...>
wrote:
How about a plain old FET to lower the loading?
Keith
----- Original Message -----
From: "jr_dakota" <SG2112@...>
To: <loopantennas@...>
Sent: Friday, March 02, 2007 10:09 AM
Subject: [loopantennas] Re: Active loop antenna
You need strict 50 ohm input and output impedances for these MMICs to
work properly which is kind of hard to do with the first amplifier on
a broadband antenna ... On a tuned loop with a small pickup loop it
would probably be alright but a plain ol' RF transistor would work as
well or better
You also have to be real careful applying a 1 Ghz amplifier for use in
the HF range because they have a tendency to 'go off' (Oscillate) in
the VHF range where you can't hear (And most people can;t see on their
scope) the result in the receiver but other than it's not working
right (Little or no gain, front end blocking, etc)
Personally I don't like to use them other than in transmitting amps
for the HF range, when you start getting into 2 Meters and up though
they are hard to beat because you can get decent gain and IP3 without
tuned circuits where the difference between a 2 1/2 turn inductor and
a 3 turn inductor can be several Mhz
JR
--- In loopantennas@..., "exnci2000" <awfhgm@> wrote:
Hi,
On minicircuits.com catalog,there are some interesting mololithic Rf
amplifier ERA/MAR series offering good IP3.I would like to know if you
have some schematich diagram to homebrew an active broadband loop
antenna from 100 Khz to 30 Mhz !!
Best regards
Franco
Italy.-
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