If you have a link relevant to the group, please post it in the Links section. If you just put it in a message, it will get lost in the shuffle after a few...
713
doneirik
Jun 9, 2005 12:31 pm
Hi, The magnetic field strength of a loop antenna (for use in RFID)is given by the equation H = (I*N*R^2) / (2*sqrt(R^2+x^2)^3), where I=current N=number of...
714
dldorrance
Jun 9, 2005 3:02 pm
... Eirik, this answer is qualified; I am not an engineer. However, I think your very valid concerns about resonance and the materials the loop is made out of...
715
Andy
ingrahama
Jun 9, 2005 6:06 pm
... Maxwell's equations are your starting point. Now if only I could remember my Maxwell's equations ... it's been SOOO long ... The magnetic field is a...
716
Darren Hennig
phones414
Jun 10, 2005 3:37 pm
Erik: You are using a DC formula to try and calculate and apply a field strength to a situation where the formula does not necessarily apply. Andy is correct -...
717
doneirik
Jun 13, 2005 9:01 pm
Hi, First of all, thanks to all who answered my previous post on magnetic field strength. I still have some further questions regarding the use of the formula...
718
Darren Hennig
phones414
Jun 14, 2005 4:37 pm
Erik: We may be able to approach this from a different angle to prevent damage to your unit. What is its characteristic input impedance(s) available for the ...
719
Darren Hennig
phones414
Jun 14, 2005 6:48 pm
Erik: I think that I have a way to approach this problem from an ambient field strength standpoint. Free space impedance is 120*pi, or 377 ohms. Thus, since...
720
doneirik
Jun 14, 2005 6:49 pm
Hi Darren, My rfid reader has an RF output of 200 mW. The antennas have an impedance of 50 Ohm. Dimensions are from 30x30mm (PCB antennas with 3 windings) to...
721
dhennig2
phones414
Jun 14, 2005 7:22 pm
Erik: I don't understand what you are trying to do actually. BCB is broadcast band. If you are worried about BCB interference, a simple highpass filter or MW...
722
Bruce Carter
rbrucecarter
Jun 14, 2005 9:16 pm
Your link was broken. The actual link is: http://www.ahsystems.com/notes/RFconversions.php You put an extra "t" in RFconversions ... VERY good resource! I...
723
doneirik
Jun 14, 2005 9:25 pm
Hi Darren, Sorry if I was unclear as to what I wanted to do, and why I wanted to measure the current... I have an RFID unit with a selection of 50 ohm antennas...
724
Irv Ambler
irv42352
Jun 18, 2005 7:22 am
Ok Guys (& Girls?), I am in the process of building a 4 foot loop antenna for MW/AM Dxing. I read that guys "aim" their antennas towards a target country,...
725
gplynas
Jun 18, 2005 12:56 pm
Irv, The antenna is aimed according to what would be the "great circle route" to the country of interest. If you have a world globe, stretch a string from...
726
c.e.boyd
nooneboyd
Jun 18, 2005 1:01 pm
Hi Irv and all: You may have a look at DXAtlas at www.dxatlas.com It may well be exactly what you need for antenna alignment. Good listening: theboyd ... ...
727
Henry Kolesnik
wd5jfr
Jun 18, 2005 1:42 pm
Use a globe. There are programs that will draw a flat globe centered on your location. Thats what hams use to point their beams. Google for it. 73 Hank...
728
Andy
ingrahama
Jun 18, 2005 3:11 pm
Irv, There are a number of programs, and also some on-line resources that will give you the bearing to any location on earth, as the crow flies (great circle...
729
Darren Hennig
phones414
Jun 19, 2005 12:27 am
Irv: The best way is to use a program with a "great circle" bearing being given for the targets of choice. This is the actual direct a short-path wave would ...
730
John
coop1776
Jun 19, 2005 4:37 pm
I am interested in building an indoor loop antenna primarily for 6-7 Mhz or 41 , 49 meter band. I am new to this. I plan to make a spiral loop using about 560...
731
c.e.boyd
nooneboyd
Jun 19, 2005 4:52 pm
Hi John: Not to sound critical of your plan, but do you realize how heavy 560 of wire is going to make your loop? Even if you'll be using 32 gauge it will...
732
Jim Dunstan
norlink88
Jun 19, 2005 6:22 pm
... Hi, A tuned receiving loop for HF for 41 & 49 M bands is an excellent antenna and great improvement over the whip. However the characteristics of a small...
733
john nelson
jnelson123_us
Jun 19, 2005 8:55 pm
I have a 4' diameter loop that resonates at 7mhz and it is a single turn. jn ... __________________________________________________ Do You Yahoo!? Tired of...
734
John
coop1776
Jun 19, 2005 11:45 pm
sorry, that was a typo. It was supposed to say 60 ft of wire. ... heavy ... gauge it ... 6-7 ... spiral ... the ... connect it ... receiver. ... appreciated, ...
735
John
coop1776
Jun 19, 2005 11:47 pm
Thanks, I meant 60 ft of wire but will take your suggestion and use 16 ft. Is the tuning capacitor going to help? Should it be feed straight into the receiver...
736
Jim Dunstan
norlink88
Jun 20, 2005 12:25 am
... Hi, If you feed it directly into your receiver (eg no pre-amp) you will need to resonate the loop in order to get a strong signal. The easiest way to ...
737
Ken Javor
emc_c
Jun 20, 2005 12:40 am
Isn't it the loop diameter that is limited to a tenth waelength? From: Jim Dunstan <jimdunstan@...> Reply-To: loopantennas@yahoogroups.com Date: Sun, 19...
738
dldorrance
Jun 20, 2005 2:46 am
... John, you don't need to use so much wire. You may create a circular 40 meter receiving loop, using a single turn loop with a diameter of 3 to 6 feet. 6...
739
Jim Dunstan
norlink88
Jun 20, 2005 3:25 am
... The wave length of a loop is the length of the wire or the circumference. A full size loop, 1 wave length, is usually calculated 1004/F(MHZ), about 143'...
740
Ken Javor
emc_c
Jun 20, 2005 4:15 am
Thank you. From: Jim Dunstan <jimdunstan@...> Reply-To: loopantennas@yahoogroups.com Date: Sun, 19 Jun 2005 23:25:22 -0400 To:...
741
oene
oene51
Jun 20, 2005 3:24 pm
Just made a 5' loop and it resonates at 7.705. Maybe because it's scuare?...
