Tunable active magnetic loop antenna
Justtis
who has built and used same.
I need a quiet antenna like this and Wellbrook is just too expensive!
http://www.wellbrook.uk.com/index.html
elaich
news:dDU0m.52720$lB7....@newsfe19.iad:
Here's a simple one:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=10174
I had links to 2 Radio-Electronics projects on building a very nice small
amplified antenna, one for BCB, the other for shortwave, but typically, I
can't find them.
Justtis
necessarily have to be tunable.
I know what it's like to misplace things. I had a plan for a Wellbrook
1530 clone including the balanced broadband rf amp/control box but it's
nowhere to be found. Probably ended up in the shredder.
About 40 feet back from the house I'm running into all kinds of interference
from Bell and Cable wires running at right angles across the back. I'll
have to mount the unit somewhere between 20 and 35 feet away from the house
for the best quiet spot. Then with the new rotor I purchased for the
project, I can hopefully null out most of the rest of the interfering
garbage. The MFJ-1026 should remove near all of what's left. 'Got
everything ready for the build except the main part.
"elaich" <x@y.z> wrote in message news:h216if$kc6$1...@news.albasani.net...
cuh...@webtv.net
around and around like a windmill?
cuhulin
user
I have a 86cm tuned loop, that is better than the ALA1530 on an Akai tuner,
cause it mixes up radios stations with the ala..
here a calculator.
http://users.fulladsl.be/spb13810/
a wire of 15m will do for the 1500khz, but for 540Khz, you might need up to
20meter.
I have used hula-hoops, and think that is the most efficient loop, ...
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Shortwave transmissions in English, Francais, Nederlands, Deutsch,
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Wimpie
Hello Justtis,
When you want to make a tunable loop (so tuning at the loop, or very
close to it), you don't need an amplifier in most cases.
Tuning (with reasonable match) has the advantage of large signal
output for relative small loops and rejection of strong out of band
signals. Also it is easier to get a good balance to avoid conducted
interference traveling via the coaxial feeder to the loop antenna.
Disadvantage is that you have to tune when changing band or frequency
and the tuning unit is outdoors.
Active loops save you from tuning, but may result in inter-modulation
products due to strong signals. Also your receiver may suffer from
this (in that case you need some form of preselection).
From my own experience, loops do best up to the low HF. Above about 5
MHz, the performance difference between a loop and a vertical
capacitive antenna (stick) is minimal. Of course when mounted at a
rotor, the loop has the advantage of directivity for low elevation
signals.
Before buying any loop (or spending a lot of money on parts), first
try one to make sure it solves your problem. When you are interested
in one band only, you can make a provisional tuned loop yourself to
see the improvement over your existing antenna.
Try to get in contact with a radio amateur (HAM) group. Almost sure
people over there will share their knowledge. You may also post in
rec.radio.amateur.antenna
Another less known method is to make a thick single-turn un-tuned loop
with natural balun function in it (that are loops where the tubing is
cut at the top of the loop). An example of a small strip-ype loop is
given here: http://www.tetech.nl/divers/small_H_FieldLoop2.jpg . Go
the shack with low loss cable and do the tuning (and matching) in the
shack. For transmitting this is no good option, but for reception
only, this gives good results and you have the tuning/matching unit
indoors adjacent to your receiver.
Best regards,
Wim
PA3DJS
www.tetech.nl
Remove the obvious three characters in case of PM.
Telamon
"Justtis" <jus...@hotmail.com> wrote:
Why don't you build a passive loop antenna? A loop antenna around 50
foot circumference will not need amplification. You can build it out of
coax cable and split the shield halfway around the loop so it is shield
balanced. A loop this size as a square is only about 12 foot a side.
It's cheap and easy to build.
--
Telamon
Ventura, California
Justtis
model, mistakingly I chose to include "tuned".
Very good advice! Thanks for pointing me in the right direction.
My main receivers are: Icom R71A(Kiwa memory board installed), Icom R-75,
Kenwood TS-140(receive only), Kenwood R-1000, Drake R8.
Portables: Grundig Satellit E1, Grundig Satellit 800, Sony SW-55, Sony
ICF-2010, Sony ICF 5900W & 6500W. Many others waiting for a quiet
antenna.
Main listening interests: Ham 80/40 metre and utility stations(military,
gov't, marine, air etc.).
With the current lack of strong signals I'm trying to supply as near a noise
free signal as possible. Thus the magnetic loop design.
"Wimpie" <wima...@tetech.nl> wrote in message
news:631fb6d8-574a-4c18...@r36g2000vbn.googlegroups.com...
cuh...@webtv.net
at building supply stores.Wire is cheap too.
cuhulin
mi...@sushi.com
I use the ALA100 with home brew loops. Damn good, but you are right
that it is expensive. The ALA100 is the cheapest of the Wellbrook
products. They have some variants of it now. You need a good radio to
use an untuned loop since it delivers a huge amount of RF.
I suspect the ALA100 is just a wideband transformer and a common gate
amp. You can get North Hills wideband transformers on ebay. I have a
few of these transformers, but haven't got around to trying to make a
home brew wellbrook. I found half a dozen North Hills 1301LB
transformers in a surplus shop and wiped out their stock at $6 a pop.
Oh, and I'm being a jerk and hoarding them.
If you don't want to pay for a North Hills transformer, I suspect any
passive video over twisted pair transformer will do the trick.
I was thinking of using one unbal to bal to feed the source of a
depletion mode JFET, ground the gate, then use the balanced end of
another transformer as the load, tying the free end to the power
supply, bypassed to ground, and of course the other end in series with
the drain. Then feed the unbalanced side to the radio.
If you had enough of these transformers, you could probably make a
multicoupler using the same dcheme. Instead of one transformer in the
path of the source, use several.
There is some misconception that the Wellbrook loops are shielded. the
pipe that you see is the loop itself.
Telamon
<384ec149-4ef6-4ad3...@y7g2000yqa.googlegroups.com>,
"mi...@sushi.com" <mi...@sushi.com> wrote:
> On Jun 25, 5:29�pm, "Justtis" <just...@hotmail.com> wrote:
> > Anyone know of a good site offering build plans. �Prefer plans from someone
> > who has built and used same.
> > I need a quiet antenna like this and Wellbrook is just too
> > expensive!http://www.wellbrook.uk.com/index.html
>
> I use the ALA100 with home brew loops. Damn good, but you are right
> that it is expensive. The ALA100 is the cheapest of the Wellbrook
> products. They have some variants of it now. You need a good radio to
> use an untuned loop since it delivers a huge amount of RF.
< SNIP >
So stop whining about the cost and build a low cost passive loop. It if
works well but you still need further improvement it will at least tide
you over.
All the amplification does for you is allow the loop to be smaller,
which may mostly be a convenience depending on the environment.
Be sure to build a balanced loop that only responds to the magnetic
field.
--
Telamon
Ventura, California
Justtis
loop! Where did you get that from? Please re read the messages! You seem
to have run them together!!
"Telamon" <telamon_s...@pacbell.net.is.invalid> wrote in message
news:telamon_spamshield-4...@newsclstr03.news.prodigy.net...
mi...@sushi.com
<telamon_spamshi...@pacbell.net.is.invalid> wrote:
> In article
> <384ec149-4ef6-4ad3-9c8a-9377b3361...@y7g2000yqa.googlegroups.com>,
I saw your other post on the subject. Feeding a loop to a 50 ohm input
of a radio will not work well since once side of the loop will be at
ground. This is where the wideband transformer comes into play. You
can float the loop above ground if you have the transformer. It is
possible to do the same with a differential amp, but good transformer
would be lower noise.
~ RHF
- the pipe that you see is the loop itself.
Greater Surface {Effect} Area and
Relative Greater Signal Capture Area
over a single strand of Wire. ~ RHF
.
Justtis
<mi...@sushi.com> wrote in message
news:d0716a00-14b7-4769...@b14g2000yqd.googlegroups.com...
Telamon
<d0716a00-14b7-4769...@b14g2000yqd.googlegroups.com>,
"mi...@sushi.com" <mi...@sushi.com> wrote:
> On Jun 28, 6:17�pm, Telamon
> <telamon_spamshi...@pacbell.net.is.invalid> wrote:
> > In article
> > <384ec149-4ef6-4ad3-9c8a-9377b3361...@y7g2000yqa.googlegroups.com>,
> >
> > �"m...@sushi.com" <m...@sushi.com> wrote:
> > > On Jun 25, 5:29�pm, "Justtis" <just...@hotmail.com> wrote:
> > > > Anyone know of a good site offering build plans. �Prefer plans from
> > > > someone
> > > > who has built and used same.
> > > > I need a quiet antenna like this and Wellbrook is just too
> > > > expensive!http://www.wellbrook.uk.com/index.html
> >
> > > I use the ALA100 with home brew loops. Damn good, but you are right
> > > that it is expensive. The ALA100 is the cheapest of the Wellbrook
> > > products. They have some variants of it now. You need a good radio to
> > > use an untuned loop since it delivers a huge amount of RF.
> >
> > < SNIP >
> >
> > So stop whining about the cost and build a low cost passive loop. It if
> > works well but you still need further improvement it will at least tide
> > you over.
> >
> > All the amplification does for you is allow the loop to be smaller,
> > which may mostly be a convenience depending on the environment.
> >
> > Be sure to build a balanced loop that only responds to the magnetic
> > field.
> >
>
> I saw your other post on the subject. Feeding a loop to a 50 ohm input
> of a radio will not work well since once side of the loop will be at
> ground.
It works very well. I have several loop antennas.
> This is where the wideband transformer comes into play. You
> can float the loop above ground if you have the transformer. It is
> possible to do the same with a differential amp, but good transformer
> would be lower noise.
The transformer is not necessary for a connection to the coax or a
balanced amplifier input.
You could clamp a few ferrite cores around the coax lead-in to the radio
at the antenna connection to block noise coming from the radio if you
don't already have the radio plugged into a EMI noise suppression power
strip.
--
Telamon
Ventura, California
mi...@sushi.com
<telamon_spamshi...@pacbell.net.is.invalid> wrote:
> In article
> <d0716a00-14b7-4769-af44-d505168ff...@b14g2000yqd.googlegroups.com>,
Er, is there a reason you don't want to do this correctly?
The thing with shortwave is you can toss out a piece of wire and get
something. It is all a matter of digging the signal out of the noise.
In any event, the transformers are easily purchased on ebay. Or in
surplus shops if I don't beat you to them.
Telamon
<bd5a3613-d3e8-46fd...@b15g2000yqd.googlegroups.com>,
"mi...@sushi.com" <mi...@sushi.com> wrote:
> Er, is there a reason you don't want to do this correctly?
You don't need a transformer to "do it" correctly.
> The thing with shortwave is you can toss out a piece of wire and get
> something. It is all a matter of digging the signal out of the noise.
> In any event, the transformers are easily purchased on ebay. Or in
> surplus shops if I don't beat you to them.
Yeah, that's what people do and then post complaints here.
I'll let you in on a little secret. In order to be successful you have
to remove obstacles not create them. You don't need to transform an
impedance that close to the coax impedance.
--
Telamon
Ventura, California
dave
BalUn?
Telamon
dave <da...@dave.dave> wrote:
The transformer type would be a BALUN but it is not needed.
The loop and lead in are all made of the same 50 ohm coax. The shield
of the lead in and both sides of the loop are all connected together.
The shield is opened halfway around the loop so the shield is balanced
around the loop. One side of the loop center conductor is connected to
the lead in center conductor. The other side of the loop center
conductor is connected to the joined shield connection.
The split shield picks up the far electric field equally and at
opposite polarity so it is canceled. The coax center conductor has
current induced in it from the magnetic field since it is shielded from
the electric field. For the size of the loop the output will be less
compared to an antenna that uses both fields to generate a signal to
the radio but it also does a better job of canceling local noise
sources provided the noise source is far enough from the antenna that
its electric field will be canceled by the balanced shield.
The result is a generally lower noise floor. Since I live in suburbia
noise is a bigger issue than picking up the signal.
In reverse order of preference:
1. Common mode antennas are near worthless around here.
2. Hertzian voltage antennas perform a little better than common mode.
3. Any type of hertzian closed loop antenna performs better than the
voltage type.
4. The hertzian balanced shield loop antenna works better than 1 thru 3
above.
You will notice a trend in a certain antenna parameter in the order of
preference above. I'll leave it as an exercise for the reader to
discover it.
--
Telamon
Ventura, California