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Re: Multiiturn loop antanna
Yes, but what makes you believe the efficiency will be the same?? Adding loops raises the impedance which means the same power will have a higher voltage and lower current after matching.? This in turn means the I2R losses will be lower in spite of the higher resistance.? Here is an example.?
A 2 turn loop has four times the impedance so the current will be a quarter.?? The resistance will double.? The resulting I2R losses will be (1/4)^2*2 or 1/8 the losses compared to a single turn loop if the same conductor is used.?
Of course if you are using a single turn loop for transmitting it is likely to be something substantial such as copper pipe.? That makes it hard to build with multiple turns.? But I don't think paralleling turns would do what you expect.? Then there are the losses in impedance matching if needed.
Rick
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Re: Multiiturn loop antanna
A thought or two to consider: ?If you make a small 1-turn loop that is 50% efficient, then half the power you feed into it gets turned into RF that radiates.? If you make a small 2-turn loop and manage to keep the efficiency at 50%, the best it can do is radiate the same.
In order to get a better radiator, either the efficiency must go up (less losses), or the antenna can be made more directional to concentrate some of that energy in a particular direction.? I don't think you can change the directionality of an electrically small loop by using the same basic coil form.? Any electrically small round loop in air has pretty much the same directionality to it.
So the thing you need to concentrate on, is cutting the I*R losses.
Connecting the turns in parallel, rather than series, may help with that.
The different number of turns can affect the impedance seen by whatever drives the antenna, so it might affect your ability to match the antenna and get power into it.
A large loop antenna (i.e., circumference comparable to a half wavelength or more) plays by different rules than a small loop.? In a small loop where the total wire length is short, the current in each turn is the same, so their effects complement one another.? In a large loop, the currents could be out-of-phase between one turn and the next turn, resulting in rather different results (partial cancellation?).
Regards, Andy
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Re: Multiiturn loop antenna MFJ-936B on 40M
Hi Chris,
Along the same lines, I have an MFJ-936B loop tuner with all 4 pre-cut 10 Gage wires. If the 28' 40M wire is spread out properly it apparently gets 30% efficiency or so. I have the cross-t frame which is supposed to only handle up to the 13' 20-30M wire, however, I have wound the 28' wire on the frame in a spiral, using all the clips to keep the wire 2"-3" away from itself. The spiral is essentially in 3 progressively smaller loops (5' down to maybe 2'). It seems to work well and I have had no arcing, at least to 50 watts which is the max I use anyway. I have done Pactor/Winmor at 5 watts up to around 800 miles in the daytime, so it gets out. Do you have any feel for efficiency under these circumstances? The tuneup is not far off from what I see as a single big loop and it is much more convenient to use as a smaller spiral.? Others with this tuner might like this idea also.
Dave???? N7NZH???? Dewey, AZ
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Re: Got my AlexLoop Walkman antenna today!!!
Very good! Good to see the loop is performing for you!
Tonight, as last night, I'm getting WSPR* 'spots' on a loop long-path to VK-land on 40 meters at 4:30 PM CST ... the loop here is a Quarter-wavelength, 32 ft circumference, 8 ft per side tuned loop about 12 ft above ground out in the back yard.
Proof, again, that loop can and do work!
73, Jim WB5WPA?
* WSPRnet.org
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Ferrite Sleeve Loops Antennas (FSL) For Sale
If anyone is interested, I am in the process of building two 7.5" diameter
X 7.5" long Ferrite Sleeve Loop Antennas (FSL). In the past I have done many
experiments with this size FSL, and there is an article posted on this
sight covering those experiments.
?
I will be selling both of them and will either build them as single band,
or dual band. With the single band units I can build?them for LW, or MW
coverage. With the dual band units they will cover both LW and MW bands.?Based
on my past experiments I know that they will perform equal to, or better than a
4' box loop. My method of building is using ferrite bars rather than?rods and
based on my experiments, I can not tell any difference in performance between
the?two methods. With the bars they are much lighter in weight and allow for a
much nicer looking build.
?
Both FSLs will have?Red Oak end pieces and will be mounted on a Lazy Susan
with Red Oak top and bottom. The variable capacitors that I will use are the
very small Russian high Q units, with a 3:1 turn ratio. The front panels will
have nice looking graphics.
?
The prices for the FSLs will be $400 for MW band coverage, $435 for LW
coverage and $475 for dual band coverage, plus shipping cost. These will be
built first class, no junk. At this point I have most of the mechanical?work
completed and the ferrite bars have been epoxied to the substrates?and covered
with fiberglass and are?ready to be wound.??
?
These maybe the last that I build, although I still have materials to build
more.
?
If anyone is interested in one of these please contact me off list at
everettsharp? A O L and?I will?configure them to your specification.
?
Everett N8CNP
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Re: Multiiturn loop antanna
Merry Christmas everyone,
Does anyone know if a multi-turn loop antenna has the same or similar performance as a single turn anttenna. eg 2 turns vs 1 turn.
At best they can be similar. The intra-winding (between turns) capacitance will cause the parallel resonance to be lower. The turns should be spaced at least two conductor diameters apart. I described this in my 2-part series on loop antennas in QEX many years ago. Ribbon cable is a very bad idea. Chris Trask N7ZWY / WDX3HLB Senior Member IEEE
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Re: Multiiturn loop antanna
In loopantennas@..., <goodgun@...> wrote : > Does anyone know if a multi-turn loop antenna has the same or? > similar performance as a single turn anttenna. eg 2 turns vs 1 turn. >? > 73's > Colin ZL1BTT
Your question is rather vague, but perhaps the following document may be of help.
Quote from page 6 of that document: "The fields radiated by an electrically small loop antenna can be increased?by adding multiple turns. For the far fields, the added height of multiple?turns is immaterial and the resulting far fields for a multiple turn loop?antenna can be found by simply multiplying the single turn loop antenna?fields by the number of turns N."
The radiation increase isn't free, however. You need to think about the loss you are adding as well by introducing the extra turns. The total conductor length is increased, and the current distribution in the multi-turn structure will not be uniform due to proximity effect (which increases ohmic loss).
I think a carefully-engineered multi-turn loop could be more efficient than a single-turn loop for certain frequencies.?
Best regards, qrp.gaijin@...
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Multiiturn loop antanna
Merry Christmas everyone, Does anyone know if a multi-turn loop antenna has the same or similar performance as a single turn anttenna. eg 2 turns vs 1 turn. 73's Colin ZL1BTT
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Re: Box Loop Antenna to Car Radio
The radios I grew up with, and a lot of aftermarket radios, use a Motorola connector. Newer car radios, especially the multi-function radios that are now common, use what is called a FAKRA connector. These are smaller coaxial connectors with locking tabs and color coding for the application (AM/FM, satellite, gps, etc). They are also 50 ohm impedance. You can find FAKRA-to-Motorola pigtails on Ebay and at
Installer.com also listed amplified whip antennas at that link. They'd be a lot easier to install than a loop. You could also roll your own, such as the PA0RDT mini-whip.
Dave Sarraf
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Re: Box Loop Antenna to Car Radio
The whip antenna acts as if it is a low value capacitor, say 10 pF or so. The capacitance of the cable would form a capacitor divider and most of the signal from the antenna would be lost.
A box loop with either an amplifier or a low impedance coupling loop can drive normal coax without excess signal loss.
Car antenna plugs are available on ebay.
<>
These are sometimes called Motorola connectors
A premade radio antenna to BNC cable along with an adapter from BNC to the connector type on the loop, along with a BNC extension might be the easiest approach.
<>
John
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On 12/19/2014 9:23 AM, hmholden69@... [loopantennas] wrote:
I would love to try my 3 Ft.Box Loop antenna with a car radio, but not
sure how to interface the two. I have been told that the normal cable
from the car antenna to the radio is a special low capacity type. Any
ideas on how to hook up a loop to a car radio in the shack? I have an
especially good car radio that I would like to MW DX with using my box loop.
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Got my AlexLoop Walkman antenna today!!!
I got my AlexLoop Walkman antenna in the mail today ( FYI $339.95 On Sale HRO but GigaParts matched price). I am absolutely BLOWN AWAY at how well this small 36" loop woks. In less than a few minutes I was working stateside stations on 20M. My first contact was WIAW / Portable 4 in Georgia with 5/9 report. As well as several other stations. I am blown away at how well this small antenna performs!!!! I have a MicroTune AlphaLoop on the way as well to compare the two. This is my first loop antenna experience and I am impressed!!!! Danny KJ4FH, New Bern, NC
----- Sent from mBox Mail Hotmail for iPhone and iPod Touch
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Re: Box Loop Antenna to Car Radio
Hi,
??? There is a fair chance you would overload the radio
as I believe they are designed
for a small whip type antenna. !!!!!
Others may know differently, take care.
???????????????????????????????????????????????????
72, Brian, G0NSL.
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Sent: Friday, December 19, 2014 5:23 PM
Subject: [loopantennas] Box Loop Antenna to Car
Radio
?
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Box Loop Antenna to Car Radio
I would love to try my 3 Ft.Box Loop antenna with a car radio, but not sure how to interface the two. I have been told that the normal cable from the car antenna to the radio is a special low capacity type. Any ideas on how to hook up a loop to a car radio in the shack? I have an especially good car radio that I would like to MW DX with using my box loop.
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What's a Good Tripod to get for the AlexLoop Walkman Antenna?
What is a good-Looking?Well-fitting "Tripod" to?purchase for the AlexLoop Walkman Portable Antenna?
?
Any photos or URL Links appreciated.
?
(prefer all black)
(prefer Weatherproof)
(be nice to have a carry bag but NOT necessary)
?
Danny Garris - KJ4FH
New Bern, NC
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Re: Active loop antenna
Cant pm u Frasier ? Only partial email address
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Re: Quick and easy AM broadcast antenna
One more thing that was implied but not stated: The radio will pick up most efficiently at resonance, which requires both the inductance and the capacitance of the final (tuned circuit+antenna system) to be matched {Fr = 1/(2*pi*sqrt(L*C))}. If you increase the inductance of the antenna beyond the range of the variable capacitor (either external or internal varactor) you don't buy yourself anything except worse performance (the loop will act as a pre-selector and mute the signal of interest). Make sure you keep the inductance of the antenna system roughly the same, which means as stated earlier in this thread increasing the area enclosed by the loop if you increase the number of turns. Inductance increases roughly by the square of the number of turns so you need to increase the area accordingly (as stated earlier in the thread).
73s, Bob Cavanaugh - AG6YK
On Monday, December 8, 2014 11:12 AM, "'Richard (Rick) Karlquist' richard@... [loopantennas]" wrote:
?
Increasing the number of turns increases signal VOLTAGE
but also increases inductance. If the radio electronics
are resonating out the inductance, you don't want to mess
with the value of inductance. (If the radio electronics
are NOT resonating out the inductance, no wonder you have
such poor sensitivity). If you double the diameter, but
use 70.7% as many turns the inductance will remain the
same. You can also make the loop taller but not wider.
This will still give you more pickup area but will not
exceed the space behind the radio.
Rick N6RK
On 12/8/2014 10:57 AM, ceeohtoo@... [loopantennas] wrote:
>
> Shoul! dn't just using more turns on the stock form intercept more
> signal and improve the SNR? And how about more turns AND also changing
> to a larger antenna form to wind turns on? Since it's a shelf stereo,
> I'm size limited on space for spinning the antenna around to the best
> reception.
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Re: Quick and easy AM broadcast antenna
Assuming this is a typical digital AM
receiver, the original ferrite "loop" antenna is untuned and feeds
an FET RF amplifier as a broadband antenna.? That's why it's not
particularly sensitive.? Good results can be obtained winding
about 5 turns of hook-up wire around the existing coil (no direct
connection) to serve as an inductively-coupled pickup.? The ends
of the added pick-up coil can then be used as the connection point
for a simple dipole or another loop.? A long wire can be connected
to one lead of the added pick-up coil, but the remaining lead
should be grounded.
Regards,
Dexter
On 12/8/2014 11:32 AM, Gordon Quickstad ceeohtoo@...
[loopantennas] wrote:
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Show quoted text
?
THE STORY:
I bought a new Sharp compact stereo and the AM reception
is worse than horrible with the supplied
8-loops-of-wire-on-a-plastic-form "AM antenna." My 20 year
old Aiwa that I replaced had the same exact plastic
antenna but with 6 loops of wire.
I went to Goodwill and bought a $3.99 clock radio
thinking I'd take the ferrite rod antenna out, wrap some
wire around it, and voila, plug it in as an external
antenna. While looking closely inside, I see that the
ferrite rod is actually connected to the tuning
capacitor and is part of a resonate circuit so I put the
the radio back together, checked it for working again,
and I'll use the in-store credit to buy a shirt.
GETTING CLOSE TO THE QUESTION:
Last night I got on Ebay and found 200' of 10/46 Litz
wire for $7 and ordered it.? This hair-brained idea is
to wind the small Litz wire on the stock wire - loop
form and get better reception (more turns is better,
right?)
THE QUESTION:
Can I use 200' of small Litz wire, when it arrives,
in place of the supplied antenna of the short 8 wire
loop and get better AM reception? I really don't want to
have an antenna that I have to tune with an external
capacitor.? Of course I'm OK with spinning it around to
adjust for maximum signal.
Thanks in advance.
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Re: Quick and easy AM broadcast antenna
I had the same problem with a $150 Sony stereo. The AM reception is really terrible. I live east of Los Angeles and the AM band is chock full of stations but the stereo will hardly pick up any except the 50000 watters. Also it acts like there is no AGC. High power stations like KFI come in only fair and weaker ones like 10000 watts are too poor and noisy to listen to. The volume must be turned up high to hear them like the 50 kW stations. Then you have to remember to back down the volume before changing stations.
Anyway I "solved" it with an external outside active antenna. But I was still not happy. The no AGC problem bugged me so I now use a $100 Drake PRN 1000 100 kHz - 30 mHz SW AM only receiver with the active antenna and feed the audio to the "portable" input.
You can use the extra little loop to couple another antenna with some wire connected to it to your rx by placing the two loops close together and changing the orientation for best reception. Maybe that will help without spending a bunch of $$$.
Don KPC6NDB
Upland, CA
34.10 -117.63 1250ft
FRG-100B FunCube Dongle Pro+
ICF2010 Perseusx3 WR-G31DDC
R70 R71A w/250Hz R75x2 w/250Hz
SDR-IQ SPR-4 SSR-1
SR-AF & LPF DSP599zx MFJ-784B
HD-1418 AF-1 MSB-1
PA0RDT Mini-Whipx2 @ 25ft
RYO Active Antenna @ 25ft
ALA100Lx2 Z1501F @20ft w/9ft Whip
Solarcon A-99
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Show quoted text
On 08-Dec-14 08:32, Gordon Quickstad ceeohtoo@... [loopantennas] wrote:
THE STORY:
I bought a new Sharp compact stereo and the AM reception is worse than
horrible with the supplied 8-loops-of-wire-on-a-plastic-form "AM
antenna." My 20 year old Aiwa that I replaced had the same exact plastic
antenna but with 6 loops of wire.
I went to Goodwill and bought a $3.99 clock radio thinking I'd take the
ferrite rod antenna out, wrap some wire around it, and voila, plug it in
as an external antenna. While looking closely inside, I see that the
ferrite rod is actually connected to the tuning capacitor and is part of
a resonate circuit so I put the the radio back together, checked it for
working again, and I'll use the in-store credit to buy a shirt.
GETTING CLOSE TO THE QUESTION:
Last night I got on Ebay and found 200' of 10/46 Litz wire for $7 and
ordered it. This hair-brained idea is to wind the small Litz wire on
the stock wire - loop form and get better reception (more turns is
better, right?)
THE QUESTION:
Can I use 200' of small Litz wire, when it arrives, in place of the
supplied antenna of the short 8 wire loop and get better AM reception? I
really don't want to have an antenna that I have to tune with an
external capacitor. Of course I'm OK with spinning it around to adjust
for maximum signal.
Thanks in advance.
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Re: Quick and easy AM broadcast antenna
Increasing the number of turns increases signal VOLTAGE
but also increases inductance. If the radio electronics
are resonating out the inductance, you don't want to mess
with the value of inductance. (If the radio electronics
are NOT resonating out the inductance, no wonder you have
such poor sensitivity). If you double the diameter, but
use 70.7% as many turns the inductance will remain the
same. You can also make the loop taller but not wider.
This will still give you more pickup area but will not
exceed the space behind the radio.
Rick N6RK
toggle quoted message
Show quoted text
On 12/8/2014 10:57 AM, ceeohtoo@... [loopantennas] wrote:
Shoul! dn't just using more turns on the stock form intercept more
signal and improve the SNR? And how about more turns AND also changing
to a larger antenna form to wind turns on? Since it's a shelf stereo,
I'm size limited on space for spinning the antenna around to the best
reception.
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Re: Quick and easy AM broadcast antenna
Thanks for the help.
To expand a little, the problem is poor signal to noise ratio on (probably) all stations. ?Other old discrete electronics portable radios that I own in the same location pull in the stations clearly with their ferrite antennae. ?I bought the Litz wire because I'm thinking that using low-loss Litz wire on the stock antenna form, and lots of turns, will help. ?I didn't know that using a physically larger loop would give 6db in itself. ?Yes, you're right, both the AM and FM electronics on the radio are in a very small shielded enclosure right where the antennas plug into in back and it's about "chip" sized (I saw it when I had to fix the CD changer on the newly purchased system because A. I'm mechanically inclined and B. don't like waiting for repairs, so I took the risk and broke the warranty and went inside with success but no future warranty).
Shouldn't just using more turns on the stock form intercept more signal and improve the SNR? ?And how about more turns AND also changing to a larger antenna form to wind turns on? ?Since it's a shelf stereo, I'm size limited on space for spinning the antenna around to the best reception.?
There are some neat talk programs on AM because air time is so cheap so I do like to break away from the typical FM fare but can't stand just 50% signal with 50% static noise which I currently have.
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Rick Collins
Everett N4CY
Dexter
Don