Re: Availability of Mag Loop and other stuff...

Ian Reeve
 

Spent some time with a low budget may loop made from straight pieces of thick aluminium strip bolted in a hexagon shape with a remote tune function fed by a separate coax cable from a 12v supply.Deliberately designed to add a little resistance to the "loop" to reduce the spacing on the variable tuning capacitor,it worked.Hanging it from a tree branch it proved to receive signals two s points below my half size windom.Transmit showed a similar pattern.No efficiency figures for either antenna,just receive and transmit reports.The transceiver used a k3 at 100 watts at the input to the power/swr meter.There are some very fancy loops around at equally fancy prices but it seems to me a loop of copper pipe( 6 or 8mm diameter central heating radiator supply) of 1 meter overall diameter would be a good starting point.I understand that the lest resistance in the loop is paramount and therefore a massive voltage will be across the tuning capacitor which ideally needs to be of the vacuum sort.Either way the loop is resonant over a very narrow band and a being directional,useful to reduce troublesome qrm.As to efficiency,I will leave the calculations to the folks who know.


From: BITX20@groups.io <BITX20@groups.io> on behalf of Jack Purdum via Groups.Io <jjpurdum@...>
Sent: Sunday, June 2, 2019 5:35:38 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Availability of Mag Loop and other stuff...
 
"However taking peoples money with inaccurate or extravagant claims should not be a hobby, though it is often a vocation people pursue."

Taking people's money? I'm not selling anything. My real goal is to get people constrained by HOA's or spouses back on the air.

Jack, W8TEE


On Sunday, June 2, 2019, 12:10:18 PM EDT, ajparent1/KB1GMX <kb1gmx@...> wrote:


Arv,

The problem of online RX or for that fact QRSS and WSPR sites is antenna alignment.
If you antenna is not "aimed" that way the result is it could have been a long path or worse
"off the side".  They do help with "have you been heard" and allows estimating propagation 
in a given direction but comparing A and B antennas requires care for both aim and
time of comparison as propagation is a transient thing.

MY 0.02$ on hobby, it is!  However taking peoples money with inaccurate or
extravagant claims should not be a hobby, though it is often a vocation people
pursue.  When people want to enjoy the hobby and are limited in time and budget
accuracy and good explanation is helpful.  When one expends time and money
on a course of action or material its desirable to understand what the outcome
may be or the limitations.

So every time a new antenna fad hits we have this.  Loops are indeed useful.
They are compact, self contained, and in some cases can help with local noise.
The yabut is they are very narrow band if they are as efficient as possible and
that leads to remote tuning as they are touchy and requiring SWR monitoring.
Being small antennas they are still low gain and therefor not the ultimate radiator. 
However the idea that I can get a loop and conquer the world from my garden
is loaded for disappointment as even the cheapest loop cost hundreds of
dollars and they most expensive ones are not that much better.  I've looked at
commercial loops and they are in the range of 199$ to well over 500$  that is
a lot of money to get an antenna that may be only passable or worse that it
can't work indoors in a building with metallic handicaps (stucco with wire, metal
framing, aluminum siding,  and foil backed insulation).  You have to keep it a
reasonable distance away from the radio so RF problems do not result.

As to building ones own, a good design wants a vacuum variable and they
are NOT cheap.  Air variables of the dual rotor forma can work ok but still
if you have to buy one they are costly.  Also the cap used determines max
power and tuning range as it had to withstand very high voltages even
at QRP levels.

That said if your junk box can full the need its interesting to experiment with Loops.


Allison

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