Hi Doug:
It turns out that the fuses AMRAD specified were way too high in current
to keep the transformer from being smoked. The only fuses that work are
self resetting types. I've added them on the primary and secondary
side of the transformer but have not yet reinstalled the antenna. I get
requests every now and then for someone to build that AMRAD antenna.
Are you still making them?
Just sent an email to Chris Trask asking about his push pull design.
My interest in active antennas is for the low frequency area where
quarter wave wire antennas are not practical.
For HF you can't beat wire antennas. Active antennas, either whip or
loop do not work as well as wire.
http://www.prc68.com/I/WireAntenna.shtml
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.End2PartyGovernment.com/
k4...@aol.com wrote:
Hey Brooke,How are you doing? Are you still using that AMRAD antenna
preamp I made for you several years ago? It's been several years
since we emailed each other and I have lost contact with you until
now. Last time I heard from you, your wife had run over the coax with
the lawn mower and cut it into! Just curious if that thing was still
working. 73's. Doug, k4cle.
Connected by DROID on Verizon Wireless
-----Original message-----
From: Brooke Clarke <bro...@pacific.net>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Sent: Fri, Aug 26, 2011 16:39:01 GMT+00:00
Subject: Re: [time-nuts] Active LORAN antenna
Hi Ulrich:
You might consider the AMRAD active antenna that they designed for
the136 kHz ham band.
http://www.prc68.com/I/LF-Ant.shtml
or the McKay Dymec DA-100 active whip.
http://www.prc68.com/I/DR33.shtml#DA100
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.End2PartyGovernment.com/
Ulrich Bangert wrote:
Gentlemen,
my friend Frank and I both miss the matching actice antenna for our
Standford Research FS700 Loran frequency standards. We also do not
have a
schematic of it. Nevertheless we have tried to re-engineer the circut
from
the part's list and the circuit description in the FS700 manual. Our
result
is shown in the accompanying schematic.pdf.
The generator in the left in conjunction with the 10 k resistor
represents
the expected high footpoint impedance of the very short (3 m)
antenna. The
VDD in the right in conjunction with the 100 ohms resistor represents
what
it believed to be inside the FS700.
Not shown here is a 100 k resistor that may be included between the
filter
output and the 7 k resistor to form a 30 dB divider together with it.
Also
not shown is a 390 micro henry inductance which's impact is not to be
found
in the circuit descripion. Also not shown is a small neon bulb for
overvoltage protection.
The ac analysis shows that the overall filter function is well around
100
kHz. But it seems as if the fet (a 2N5991 in the original) would not
have
enough gain to counteract the overall damping included in the front end
let
alone to deliver some additional gain for the receiver's front end.
We both feed the receiver currently with dipoles for 80 m ham radio
and a
resistor that makes the receiver think the active antenna is connected.
The
receiver has a possible total of 130 dB gain and my receiver says it
uses
94
dB gain while Franks receiver says it uses 102 dB gain. The noise margin
is
also a bit better on my location. However, if one looks at the manual
f.e.
at page 17 one could get the impression as if a receiver gain of 75
dB may
be considered much more normal as our values. Instead of improving the
reception everything gets even worse if the active antenna is
connected. I
should also note that my qth is only 200 km away from SYLT (our German
Loran
station) while Frank is even 70 km nearer to it.
Questions:
1) Anyone an idea what we are possibly doing wrong?
2) Anyone an idea for the 390 micro henry inductor?
3) Anyone own the original schematic?
TIA for your help
Ulrich Bangert
www.ulrich-bangert.de
Ortholzer Weg 1
27243 Gross Ippener
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