[Lowfer] Receiving Loops

[Chris Trask]

>
>Gentlemen,
>   I have been monitoring LF for several years using the AMRAD E-Field
>Probe. It has given me what I believe are good results but I would like to
>try building a Loop. Several years ago, I built a large multiturn receiving
>loop that was remotely tuned with varactor diodes. Actually this was my
>first antenna on LF and I thought it was performing well until I built the
>AMRAD E-Field Probe. The probe outperfoms the loop in every way. What are
>your opinions on a good receiving loop ... I found the specs on this one,
>what do you think?
>

     I've published a number of papers on receiving loop antennas as well as a recent one on a transmitting loop.  Of the receiving loops, I found that this one gave the best overall performance:

    http://www.home.earthlink.net/~christrask/Paper011.html

It can be easily adapted to LF by increasing the number of turns on the transformers and the transformer core materials.

>
> http://imagenisp.ca/jsm/burhans.html
>

     I like the way that VE7SL made use of parts available from Mouser, especially the use of audio transformers for the LF band.  I think I have some of those and I'll have to do some thorough testing of them to see what their performance limitations are as they could be very useful for the design of LF receiving antennas.  I also like the way that he conserved the DC power consumption of the amplifier, though it seems that the 6.8mH choke should be a much higher value.  

     But, using the braided shield of the coax as the shielded loop outer conductor is a bit questionable as the noise immunity performance is very dependent on the skin effect properties of the shield.  This could be remedied by removing the braid and then using 1/2" copper tubing, which can be attached by way of PL-259 reducers as I demonstrated in the paper I mentioned above.  It would also overcome the problems he mentioned in using hardline (aka semi-rigid) coax.

     I don't think much of his bias tee.  He could have made a much better one by way of those Mouser audio transformers, such as #42TM030-RC, provided that it will handle the frequency range.

     Overall, it's a fairly good design, better than most of the ones I've seen.






Chris

     ,----------------------.       High Performance Mixers and
    /    What's all this     \    Amplifiers for RF Communications
   / extinct stuff, anyhow?  /
   \  _______,--------------'           Chris Trask / N7ZWY
  _ |/                                  Principal Engineer
 oo\                                  Sonoran Radio Research
(__)\       _                             P.O. Box 25240
  \  \    .'  `.                     Tempe, Arizona 85285-5240
   \  \  /      \
    \  '"        \                 IEEE Senior Member #40274515
     .       (  ) \
      '-| )__| :.  \              Email: christrask at earthlink.net
        | |  | | \  '.       http://www.home.earthlink.net/~christrask
       c__; c__;  '-..'>.__

                       Graphics by Loek Frederiks