I have been following the antenna discussion and a lot of people
point to the low noise antenna web site
(http://www.anarc.org/naswa/badx/ante...e_antenna.html).

This site recommends a 9:1 impedance transformer. That matches
impedance, but you also lose 3:1 on your antenna voltage. I can put
a JFET in a box and get the same ratio, but without the voltage loss.
Other than the voltage needed, what would be the down side? The
power is so small, 4-AA batts will run it for a year, even if I
forget to flip the switch.

There are good JFETs that are a least as "flat" in response as the
transformer.

I always check the "prior-art" before I build something. But I will
be trying both this break.

TIA,

Steve.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA

steven, i dont know the answer to your question but i am sure that if
you show us the details on your JFET in a box gadget then several of us
will run to build one. lots of testing will follow with much discussion
and maybe even a flamefest! lots of fun will be had by all.

"Steven Swift" wrote in message
...
I have been following the antenna discussion and a lot of people
point to the low noise antenna web site
(http://www.anarc.org/naswa/badx/ante...e_antenna.html).

This site recommends a 9:1 impedance transformer. That matches
impedance, but you also lose 3:1 on your antenna voltage. I can put
a JFET in a box and get the same ratio, but without the voltage loss.
Other than the voltage needed, what would be the down side? The
power is so small, 4-AA batts will run it for a year, even if I
forget to flip the switch.

There are good JFETs that are a least as "flat" in response as the
transformer.

I always check the "prior-art" before I build something. But I will
be trying both this break.

TIA,

Steve.
Unless you very carefully select your JFET, you will experience intermod
and crossmod. In order to avoid this the devices used are those designed for
CATV applications where the IP3 is very high. This also requires a lot of
current to bias them properly.
For short active whips you might get by with something less, but for a
random wire, there is a lot of signal, and precautions need to be taken.
I would go with the 9:1 transformer- but wound on a binocular core not a
toroidal core- there is a near 10X increase in BW by doing so.
Dale W4OP

SS,

I look forward to Reading More about Your Idea and Design
for using a JFET Amplifier in lieu of a Balun for a "Low
Noise" SWL Antenna.

FWIW: If the 'stated object' of the Balun in a "Receive
ONLY" SWL Antenna is simply to Match the Impedance of the
Antenna to the Lead-In-Line.

NOTE: This type of Antenna does NOT require the Power Handling
Capabilities of a BALUN that can transform a few Watts to a Hundred
or more Watts of RF Power for Transmitting.

Then a JFET Amplifier placed 'between' the Antenna Element and
the Lead-In-Line could work as an Impedance Matching Device.

Plus the JFET Amplifier could provide an Additional Level of Signal
Amplification that a Balun could not.

But REMEMBER - The Balun as a "DEVICE" serves several purposes in
the "Low Noise" SWL Antenna Design and Configuration as presented
in writing by John Doty:
GoTo= http://www.anarc.org/naswa/badx/ante...e_antenna.html

* Impedance Matching between the Antenna Element and Lead-In-Line.

* Isolation of the Antenna Element and Lead-In-Line.

* A Remote (Low Noise) Grounding Point for the Antenna & Ground
System.

* Improved Antenna Lightening Protection and Electrical Safety.

You JFET in a Black Box would have to be able to accomplish these
same things to provide the same level of benefits that the Balun
does in the "Low Noise SWL Antenna Design and Configuration as
described by John Doty:
GoTo= http://www.anarc.org/naswa/badx/ante...e_antenna.html

* So First this JFET Amplifier would have to be "Located"
at the 'junction' of the Antenna Element and Lead-In-Line.

* Provide for Isolation of the Antenna Element and Lead-In-Line.

* Provide for a Remote (Low Noise) Grounding Point for the
Antenna & Ground System.

* Provide for Improved Antenna Lightening Protection and Electrical
Safety.


ABOUT - THE "LOW-NOISE" SWL ANTENNA:
When an OutSide/OutDoor is your First Option.
- But Before You Start:
- - Read about the "Low Noise" SWL Antenna
- - - created and written about by John Doty

* "LOW NOISE SWL ANTENNA"
http://groups.yahoo.com/group/SWL-AM...enna/message/2

* "LOW NOISE SWL ANTENNA"
http://groups.yahoo.com/group/SWL-AM...na/message/119

* "Two Reasons to use a Balun (Matching Transformer)
with a Receive Only Antenna"
http://groups.yahoo.com/group/SWL-AM...na/message/150

* "Understanding the Random Wire Antenna...
- - - And Building a Better One !"
http://groups.yahoo.com/group/SWL-AM...na/message/200

* "An OutSide Ground for Better Safety and more..."
http://groups.yahoo.com/group/SWL-AM...na/message/206

* "Am I Missing Something ? ? ? YES a Matching Transformer!!!"
http://groups.yahoo.com/group/SWL-AM...na/message/314


REMEMBER: The Antenna is 55.5% of the Radio/Receiver
and Antenna/Ground Reception Equation
http://groups.yahoo.com/group/SWL-AM...na/message/288


WHE "SWL Antennas and AM & FM Antennas" eGroup on YAHOO !
- When You NEED to Contemplate the
- - "Aerial High" and the
- - - "True Meaning of Ground".


iane ~ RHF
All are WELCOME at this "Antenna Ashram"
+ Who Seek Better Reception
+ + And a Clear Understanding
+ + + From That Which Transcends the Ether and Beyond.
..
..
= = = (Steven Swift)
= = = wrote in message ...
I have been following the antenna discussion and a lot of people
point to the low noise antenna web site
(http://www.anarc.org/naswa/badx/ante...e_antenna.html).

This site recommends a 9:1 impedance transformer. That matches
impedance, but you also lose 3:1 on your antenna voltage.
I can put a JFET in a box and get the same ratio, but without
the voltage loss.
Other than the voltage needed, what would be the down side?
The power is so small, 4-AA batts will run it for a year,
even if I forget to flip the switch.

There are good JFETs that are a least as "flat" in response
as the transformer.

I always check the "prior-art" before I build something.
But I will be trying both this break.

TIA,

Steve.

..

The summary from emails is:

1: Fet will be overloaded and generate lots of intermodulation.
2: I have to choose the fet very carefully (I have thousands to select
through).
3: Need bandpass filters.

I think I still to build a box and give it a test.

Won't take much time.

Steve.

(Jim) writes:

steven, i dont know the answer to your question but i am sure that if
you show us the details on your JFET in a box gadget then several of us
will run to build one. lots of testing will follow with much discussion
and maybe even a flamefest! lots of fun will be had by all.

--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA

"Steven Swift" wrote in message
...

The summary from emails is:

1: Fet will be overloaded and generate lots of intermodulation.
2: I have to choose the fet very carefully (I have thousands to select
through).
3: Need bandpass filters.

I think I still to build a box and give it a test.

Won't take much time.

Steve.
The problem with filters in front of the FET (and this is where they must
be in order to tame the IM), is that their input Z will load the wire
defeating the purpose of having a hi Z FET in the 1st place. A single
parallel L-C trap might afford some protection from the worst offender- but
seems like a lot of trouble.

Dale W4OP

Looks pretty ugly. I put a scope on the antenna and saw about 4 volts of
signal + noise. It would be really hard to make a FET follower that didn't
get messed up with this. And then-- can the radio really take this much noise.

Looks like the 9:1 with low noise methods is still a pretty good idea.

Thanks, newsgroup R.R.S.

Steve.


"Dale Parfitt" writes:

"Steven Swift" wrote in message
...

The summary from emails is:

1: Fet will be overloaded and generate lots of intermodulation.
2: I have to choose the fet very carefully (I have thousands to select
through).
3: Need bandpass filters.

I think I still to build a box and give it a test.

Won't take much time.

Steve.
The problem with filters in front of the FET (and this is where they must
be in order to tame the IM), is that their input Z will load the wire
defeating the purpose of having a hi Z FET in the 1st place. A single
parallel L-C trap might afford some protection from the worst offender- but
seems like a lot of trouble.

Dale W4OP


--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA