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Could this design be adapted to have the power supply through the coax?

Cor Beijersbergen van Henegouwen

For a simpler and better acitve dipole that really works, I
have one, try
<>
The acitve parts, 2 each , J310 JFET and a 2N5109 won't break the
bank are are much easier to setup then Dallas's other active antenna.

Will

At 06:12 AM 5/31/2007 +0000, you wrote:

--- In
<mailto:loopantennas%40yahoogroups.com>loopantennas@..., Jim
Dunstan <jdunstan@...> wrote:

At 05:19 PM 5/30/2007 +0000, you wrote:

From personal experience I can say antenna works well at 27MHz.

Are you speaking of the active whip that he mentions works well at SW
too? As this one needs a ground rod its one of the antenna's I wont be
able to use (4th floor apartment building no lighting rods etc either...)

Hi,

In the article on the active antenna the author shows two versions ... one
version is a mono pole, the one you mention that uses a ground rod. The
other version uses a dipole. The dipole version is really 2 complete 1
meter whip/amplifiers constructed as mirror images. This produces a
balanced system that does not need to be mounted at ground level. It is
the version you would require in your location in the 4th flr apartment.y

The active antenna was designed to provide reception at MW &LW bands ...
but a person who has used the system says it works well at 27Mhz ...
therefore I assume it works fine across the HF band as well.

Jim, VE3CI

--- In loopantennas@..., gandalfg8@... wrote:

In a message dated 30/05/2007 18:57:05 GMT Daylight Time, novost@...
writes:

We may never know if the _diodes_ had the potential for creating
RF noise because they were already bypassed with substantial-
looking disk ceramic capacitors, two of which are clearly visible
in his photograph and the wires for all are visible on the solder
side of the PCB - so it shouldn't be a great surprise that there
was little RF noise and that extra capacitors didn't reduce it.

------------------------

I was about to reply...
"C'mon, surely he ain't gonna make such an obvious mistake".....
but you're right:-)

I think you are seeing the capacitors he added. He says he added 1 mf
ceramic capacitors, and that the diodes were not noisy, because they
"did not reduce the noise at the lower end of the NDB". He apparently
measured or at least noted the noise; added capacitors and inductors;
noted no significant noise reduction; concluded the capacitors and
inductors really weren't needed for that particular R/S supply.

Bob

In a message dated 31/05/2007 16:04:34 GMT Daylight Time,
rblum@... writes:

I think you are seeing the capacitors he added. He says he added 1 mf
ceramic capacitors, and that the diodes were not noisy, because they
"did not reduce the noise at the lower end of the NDB". He apparently
measured or at least noted the noise; added capacitors and inductors;
noted no significant noise reduction; concluded the capacitors and
inductors really weren't needed for that particular R/S supply.



---------------------------------
Hi Bob

The point Len was making is that you can see the added capacitors on the
back of the board but that there are already capacitors across the diodes,
mounted as normal through hole components on the circuit boards, and that could
have been the reason there was no noise reduction in this example.
Whether or not the existing level of noise was considered acceptable does
not seem very clear, altough I get the impression it might have been, the
observation was only that it didn't change.

If you look at the lower photos in the reference given earlier you'll see
that Len is right.
The existing caps look, to me anyway, to be fairly small ceramic types but
they are definitely in circuit and part of the original construction.
You can see two of the original capacitors clearly, a bit of another less
clearly, and can also see from the rear photo that they are across the diodes,
in addition to the later ones mounted on the rear of the PCB.

regards

Nigel
GM8PZR

--- In loopantennas@..., Jim Dunstan <jdunstan@...> wrote:

At 05:19 PM 5/30/2007 +0000, you wrote:

From personal experience I can say antenna works well at 27MHz.

Are you speaking of the active whip that he mentions works well at SW
too? As this one needs a ground rod its one of the antenna's I wont be
able to use (4th floor apartment building no lighting rods etc either...)

At 05:19 PM 5/30/2007 +0000, you wrote:

From personal experience I can say antenna works well at 27MHz.

The main point with either twin lead or coax is bring the feedline
out at a right angle to the orientation of the antenna for at least
10'.

Will

Hi Will,

You are right it is important to take care when dressing antenna feed line, especially when dealing with a dipole (balanced) antenna in order to minimize antenna/feed line interaction which might disturb antenna balance. However the question was about the use of zip cord or speaker wire as a feed line .... and whether it would pick up RFI when it comes into the RFI polluted environment of the house/radio operating position; the assumption being that coax would be better.

The main point was addressing the question. Properly dressed and terminated balanced feed line is definitely more immune to RFI than a standard properly terminated unbalanced coax feed line. This is true at audio and RF frequencies. Would you agree?

Jim, VE3CI

At 9:35 am ((PDT)) Tue May 29, 2007, gfreport wrote:

Posted by: "gfreport1" gfreport@... gfreport1
Date: Tue May 29, 2007 9:35 am ((PDT))

This one is uses cheaper parts.
<>

Note that of the second power supply here, 12 volt AC/DC #273-1776,
Dallas says; "It turned out that the diodes in this power supply were
not noisy like the diodes in the bridge I used for the 24 VDC supply",
giving as the reason; "because bypassing them with the 1 mF
capacitors did not reduce noise at the lower end of the NDB"
(Aeronautical Non Directional Beacons are at 200 - 500 KHz.)

We may never know if the _diodes_ had the potential for creating
RF noise because they were already bypassed with substantial-
looking disk ceramic capacitors, two of which are clearly visible
in his photograph and the wires for all are visible on the solder
side of the PCB - so it shouldn't be a great surprise that there
was little RF noise and that extra capacitors didn't reduce it.


Regards, LenW

In a message dated 30/05/2007 18:57:05 GMT Daylight Time, novost@...
writes:

We may never know if the _diodes_ had the potential for creating
RF noise because they were already bypassed with substantial-
looking disk ceramic capacitors, two of which are clearly visible
in his photograph and the wires for all are visible on the solder
side of the PCB - so it shouldn't be a great surprise that there
was little RF noise and that extra capacitors didn't reduce it.



------------------------

I was about to reply...
"C'mon, surely he ain't gonna make such an obvious mistake".....
but you're right:-)

Not sure if I'd describe them as "substantial" but definitely fitted, you
can even see part of a third one in the bottom photo if you look carefully.

How odd.

regards

Nige
GM8PZR

Here is an interested active antenna:



Has somebody in this group built one?
---
timo

Richards,

The MFJ-956 and MFJ-16010 tuners are both intended for use with random
length wire antennas... not loops. MFJ does make loop tuners. The
MFJ-933 and -935 but they are not Z-match designs. Those tuners are
meant to be mounted at or _very_ close to the loop.

Using any tuner remotely located from the loop (including the Z-match)
will distort the loop pattern since the feedline becomes part of the
loop. With close-spaced wire like speaker cable there will be greater
signal loss than with wider spaced wire like 300 Ohm twinlead or 450
Ohm ladderline. I follow a very loose rule of thumb that says the loop
circumference should be a minimum of 4 times the length of the
feedline. That seems to ensure that the loop does not simply act like
a short circuit at the end of the feedline. The greater the loop
circumference the more signal capture area it will have... and that's
the name of the game. The tuner is simply used to enable a reasonably
efficient transfer of that energy to the receiver.

The Z-match is not difficult to build. Mine uses one 365pF variable
cap, 1 dual-365pF variable cap, the coil wound on a T80-6 toroid and a
DPDT switch to choose between the two output link windings. I believe
I used the design on G3YCC's web page as a guide. The whole thing is
build into a black plastic enclosure from Radioshack. The caps and
toroid were ordered from Ocean State Electronics.

It's certainly much cheaper to build one of these than to buy an MFJ
tuner... and, IMHO, it's much more flexible in use for receiving. I
have used mine for transmitting also but the caps limit power handling
to a max of about 5 watts.

73,

'Bear' NH7SR

At 05:54 PM 5/29/2007 +0000, you wrote:

Try these:
This is the better, but the FET is very pricy.

<<>>

OK...

There are some issues I see with my VERY little experience (basically,
none) with building circuits but I will see if I can make a try.

Why is there a gas discharge tube in the dipole? And if you use
speakerwire for the connection between antenna and receiver, wont it
pick up noise inside the house?

Hi:

Let me help with your questions .... the short (1 meter) antenna is
connected to the FET in either a mono pole or dipole version of his
circuit. The gas discharge tube is a safety device that will discharge any
DC static build up to ground. It provides no function to enhance
reception. As I mentioned he shows 2 versions of his antenna/amplifier ...
the first is single ended (mono pole) and should really be mounted right on
the ground next to the ground rod. The second version is a dipole ...
which will allow the antenna/amplifier to be mounted away from ground.

The speaker wire or zip cord is a balanced feed line. His objective (he
goes to great lengths) is to completely isolate the antenna (1 meter in
length) from the amplifier and feed line. The amplifier is high gain, high
impedance input and low noise. He uses RF transformers to isolate the unit
from the feed line. In critical situations it is much easier to maintain
balance and isolation using balanced feed line instead of coax. Properly
terminated balanced line will not pick up RF ... eg noise. The reason is
that the noise signals are picked up at any point in the feed line in
exactly the same strength and phase. When the meet at the terminating
transformer winding they will be 180 deg out of phase and cancel each other
out .... eg no noise. This is not true in coax.

And finally, he speaks of just LW and AM, but my interest is in the
shortwave (60mtr tropical band is my main focus I want a new antenna for).

I do not know how well the unit will work on 60M tropical band. The
antenna and amplifier should be just fine .... the limiting factor will be
the transformers .... which are designed for LF/MW frequencies.

Jim, VE3CI

frederick1444 schreef:

Hi, I am looking for an effective antenna to use that will pull in
local AM stations more clearly, about all I hear on AM now is static. Do loop antennas work for FM stations? I would like better FM
reception too.

about 40 cm dia.

I have made FM loop with dia 86cm, good directivity.


Marc

--
--
Shortwave transmissions in English, Francais, Nederlands, Deutsch, Suid-Afrikaans, Chinese, Dansk, Urdu, Cantonese, Greek, Spanish, Portuguese, ...
Updated every 2-3 months.

Try these:
This is the better, but the FET is very pricy.

<>


OK...

There are some issues I see with my VERY little experience (basically,
none) with building circuits but I will see if I can make a try.

Why is there a gas discharge tube in the dipole? And if you use
speakerwire for the connection between antenna and receiver, wont it
pick up noise inside the house?

And finally, he speaks of just LW and AM, but my interest is in the
shortwave (60mtr tropical band is my main focus I want a new antenna for).

--- In loopantennas@..., "gfreport1" <gfreport@...> wrote:
<snip>

Thank you William, much appreciated.

If you have any additional info later about the power supply its most
welcome. I will also dive into those active dipoles. Ultimately its
about improving my reception, and learning some building skills =)

I might end up building both, so I'm sure to find out whats best for
my location.

Jeroen

Hi, I am looking for an effective antenna to use that will pull in
local AM stations more clearly, about all I hear on AM now is static.
Do loop antennas work for FM stations? I would like better FM
reception too.
Any antenna has to pass WAF (wife acceptance factor)so smaller is
better, no 4,5 or 6 foot antennas please.
Would a 8 inch or longer ferrite bar provide better reception?
Forgive all the newbie questions, just getting into a nice componet
stereo system, but have already learned that even a good vintage tuner
(Sansui TU 717)cann't pull in stations without a decent antenna. Most
of the mass produced antennas I have investigated either don't seem to
work or cost an arm and a leg.
Any suggestions greatly appreciated.
PS I live in a valley surrounded by hills in Petaluma, Ca.
Thanks Frederick.

OK -- yet most Z match tuners seem to be home brew. Does
either my MFJ-956 or MFJ-16010 tuner qualify? Or do I need
something else? IS there an inexpensive commercially made
one that works for cheap? If not cheap, for a lot?

Thanks - I will Google around on this...

Given what you say, I could make a loop on the outside of my deck railing, which would be 20 feet by 5 feet, and all be about ten feet
above ground. From your comment that would be a decent loop, and
tunable in the shack with a z match tuner (assuming I figure out
what one is and how to get or make one....) Hmmmm... I like this
prospect.

/// Richards ///
===========================================================

Michael Hebert wrote:

Richards,

Like Jim Dunstan said the loop doesn't need to have a tuning cap. You
can use a simple wire loop with a remote tuner. Google for "Z-match"
and you will find a simple and very capable tuner. If you need to run
anything longer than 20' or so for a feedline you can use 450 Ohm TV
ladderline (if you can find it) or make some ladderline with #20 wire
spaced an inch or so apart. That should be good for upwards of 50'
with very little loss. I have even used runs of 20' of 300 Ohm foam
filled twinlead with good success.

Loop size?? Whatever you can erect!! I have used square loops with
sides as small as 2' and as large as 25'. The Z-match tunes them all!

Right now I'm using my Z-match to tune an indoor loop strung around
two sides of my bedroom and tuned through about 10' of #22 speaker
wire. Yes, it's noisy but it works better than a random wire or dipole
from inside my 2nd floor urban apartment.

73,

'Bear' NH7SR

I wish I could find a simple design for a SWL loop antenna
that would cover, at least, say, between 5 and 10 MHz. Just
something simple I could stick up in the yard, maybe. All these
amplifiers, tuning capacitors, etc. Where is a simple loop?

Not easily done. Loops are inherently low impedance antennas, and when
you're well below the first resonance they look a lot like an inductor. As
you approach the resonance, they begin to look like a shorted transmission
line. I had to tackle this when I was designing my own active loops, and I
was able to devise a remote tuning and amplifier using the coax as both the
amplifier power and the tuning voltage. It became a 2-part series in QEX.

A 1M diameter loop made with 0.25" copper tubing (first resonance at
27.5MHz) will have an impdance of 0.5 + j110 ohms at 5MHz, 1.0 + j 230 ohms
at 10MHz, 1.5 + j450 ohms at 15MHz, and 25 +j1500 ohms at 25MHz. Not
exactly a linear relationship.

The same antenna can be used at 40M with just a 64:1 impedance
transformer (three 4:1 transformers in series) and a fixed capacitor, but
you will still need some sort of tuning somewhere in order to have it
function well over the entire band. Making the transformers so they will
have low loss is a real pain.

Chris

,----------------------. High Performance Mixers and
/ What's all this &#92; Amplifiers for RF Communications
/ extinct stuff, anyhow? /
&#92; _______,--------------' Chris Trask / N7ZWY
_ |/ Principal Engineer
oo&#92; Sonoran Radio Research
(__)&#92; _ P.O. Box 25240
&#92; &#92; .' `. Tempe, Arizona 85285-5240
&#92; &#92; / &#92;
&#92; '" &#92; IEEE Senior Member #40274515
. ( ) &#92;
'-| )__| :. &#92; Email: christrask@...
| | | | &#92; '.
c__; c__; '-..'>.__

Graphics by Loek Frederiks

I wish I could find a simple design for a SWL loop antenna
that would cover, at least, say, between 5 and 10 MHz. Just
something simple I could stick up in the yard, maybe. All these
amplifiers, tuning capacitors, etc. Where is a simple loop?

(Crying in my beer this holiday...) //// Richards ////
=================================================================

Jim Dunstan wrote:

At 02:34 PM 5/28/2007 +0100, you wrote:

At 12:06 pm ((PDT)) Sun May 27, 2007, Jim Dunstan wrote:

[big snip]
A tuned loop (about 3' in diam.) is my favorite receiving antenna when
living at the apartment on the 9th flr. I put mine on the balcony and tune
it remotely with 12 ft of 300 ohm twin lead fed into a Z-match antenna
tuner.

Does this mean there is no capacitor attached to the loop
and all tuning is done by the ATU? So the resistance of the
feeder is included in the loop resonance?

If so, you could get higher Q and hence more output by
tuning at the loop. OTOH, Q is one of those good things
one can have too much of. ;-)

Regards, Len

Hi Len,

You are correct on all counts. The original purpose of the arrangement was to provide a decent antenna for my SWL activity (Sony 7600 receiver) from 5mhz to 15mhz. The tuner sits inside the window looking out on the balcony. The operation is simple .... when it hits resonance the noise level goes up on the receiver .... that's it!! Compared to the whip antenna the performance is a quantum leap improvement, even if I bring the receiver/whip out on the balcony.

I also built transmitting loops for operation at the apartment, using the more traditional tuning/matching arrangements. They work fine .... when I tuned in to SW station (eg 15mhz ... close to 20M) I could NOT detect appreciable difference in performance listening to SW broadcast stations. Of course, this kind of tuning is not compatible with band hopping.

In order for a loop to be an effective SWL antenna it must able to be mounted remotely and provide a reasonable signal level across a very broad range (at least 5-15 mhz or more). In order to provide a reasonable signal across this broad spectrum the antenna either has to be remotely tuned or be broad banded with amplification at the source. My system is the first ... remotely tuned .... with the distance limitation of approximately 15-20 ft. with balance feed line. If you go beyond that distance the capacitance of the feed line starts to limit tuning range. It is also possible to tune such a loop with coax feed line but the distance is even more limited as coax represents greater capacitance.

Jim, VE3CI