[time-nuts] Active LORAN antenna

[Bob Camp]

Hi

ESD is also an issue with outdoor active antennas. Even if you don't get a
lightning hit, anything sticking up into the air can get a pretty good
charge on it as the clouds go over. The blocking cap on the input to the
Trask amp really isn't needed with a monopole. It's also unlikely to survive
the summer. The real question is weather if fails open or as a short...

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Brooke Clarke
Sent: Friday, August 26, 2011 4:36 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Active LORAN antenna

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/


k4cle at 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 <brooke at pacific.net>
> To: Discussion of precise time and frequency measurement 
> <time-nuts at 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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