"Brenda Ann Dyer" wrote in message ...
"Mark Keith" wrote in message
om...
"Brian" wrote in message
hlink.net...
I'm guessing 10-365pf would cover the majority of the broadcast band.


Brian

I bet it takes double that. He will need a "dual" 365pf cap to cover
the whole band with one cap, and no switching.

Why would this be the case, when a standard AM radio covers the entire
broadcast band with a single 10-365pf variable??

Q of the circuit? Not really sure. I don't build AM radios. But in
judging from my loops, I'd be surprised to see one tune the whole band
with a single 365pf cap. I'm fairly sure neither of mine would. If I
dumped one of the gangs of my dual 365 cap on my 16 inch loop, it
WOULD NOT cover the whole BC band. When you build a loop, you build it
around the cap. IE: adjust the number of turns to give the desired
range with the cap at hand. If you can get a loop to cover the whole
band with a single gang cap, more power to you. But I'd have to see it
to believe it. It ain't happening here. MK

Mark Keith wrote:
"Brian" wrote in message hlink.net...

I'm guessing 10-365pf would cover the majority of the broadcast band.


Brian


I bet it takes double that. He will need a "dual" 365pf cap to cover
the whole band with one cap,


Resonance in a circuit happens when inductive reactance equals
capacitive reactance. They're both measured in ohms. There is NO
magic capacitance for covering the broadcast band. The PROPER
capacitance is the one that matches the antenna/coil over it's
intended range.


So, resonance occurs at:
Xl = Xc

That can also be said as:

f = 1 / [2 * pi (sqrt LC)]

http://www.electronics-tutorials.com.../resonance.htm




mike

"Mark Keith" wrote in message
om...
"Brian" wrote in message
hlink.net...
I'm guessing 10-365pf would cover the majority of the broadcast band.


Brian

I bet it takes double that. He will need a "dual" 365pf cap to cover
the whole band with one cap, and no switching. With the dual cap, you
solder the two gangs together, and end up with 730 pf. But the min
value will be larger with the dual cap, and will reduce the upper
range a bit. IE: two 10-365pf caps, will give a 20 pf min, instead of
10. This shouldn't keep you from tuning the whole BC band, but if you
rig a way to switch to only one gang, you can increase your upper
range even farther. My 44 inch per side loop uses a triple 365pf
cap.It also has five smaller value gangs "maybe 25-50 pf each??" ,as
well for eight gangs total. With that cap, and a switch which I mount
of the side of the cap, I am covering from 450 kc to 2300 kc in two
ranges. My 16 inch round loop uses a plain dual 365pf cap. No extra
gangs. It covers from 500-2000kc with no switching. I really have my
doubts a single 365pf cap will cover the whole BC band. To cover the
low end, you will need more turns to tune with the small value cap.
This in turn will reduce the upper range due to the extra turns in
themselves, and also the extra stray capacitance you will see from the
extra windings. If you tune for 540 kc at the low end, I doubt you
will be able to tune 1600. I'm taking a wild stab, and guessing your
upper range might be 1000 kc or so ?? MK


Mark,
Gangs in the capacitor is not the issue when trying to cover the AM
broadcast band.
It is the ratio of highest to lowest capacitance that is of concern.

If I assume the highest frequency is 1710 kHz and the lowest is 520 kHz. The
ration of highest to lowest frequency is 3.29.

Square this number to get 10.82.

The ratio of high to low capacitave needed is 10.82 but this must also
include stray wiring capacitance.

A 10-365 pf capacitor has a ratio of 36.5. More than enough to cover the
band if the stray capacitance is low enough.

A 10-365 pf capacitor will work if the stray capacitance is less than 28 pf.

Once you have the a sufficient range of capacitance, you just need to make
sure your loop has the proper inductance to match that capacitance.

If you need 700 or 1000 pf to tune a loop to the AM band, then it indicates
the inductance of your loop is lower and you are just using more
capacitance to offset the condition.

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

Going back to the initial question in the thread. If the tuning capacitor
supplied with the kit could cover the entire AM band with the kit's coil,
then it should also cover the entire AM band with a different coil/loop. It
is just a matter of getting the inductance right.


craigm

"craigm" wrote in message ...
"Mark Keith" wrote in message
om...
"Brian" wrote in message
hlink.net...
I'm guessing 10-365pf would cover the majority of the broadcast band.


Brian

I bet it takes double that. He will need a "dual" 365pf cap to cover
the whole band with one cap, and no switching. With the dual cap, you
solder the two gangs together, and end up with 730 pf. But the min
value will be larger with the dual cap, and will reduce the upper
range a bit. IE: two 10-365pf caps, will give a 20 pf min, instead of
10. This shouldn't keep you from tuning the whole BC band, but if you
rig a way to switch to only one gang, you can increase your upper
range even farther. My 44 inch per side loop uses a triple 365pf
cap.It also has five smaller value gangs "maybe 25-50 pf each??" ,as
well for eight gangs total. With that cap, and a switch which I mount
of the side of the cap, I am covering from 450 kc to 2300 kc in two
ranges. My 16 inch round loop uses a plain dual 365pf cap. No extra
gangs. It covers from 500-2000kc with no switching. I really have my
doubts a single 365pf cap will cover the whole BC band. To cover the
low end, you will need more turns to tune with the small value cap.
This in turn will reduce the upper range due to the extra turns in
themselves, and also the extra stray capacitance you will see from the
extra windings. If you tune for 540 kc at the low end, I doubt you
will be able to tune 1600. I'm taking a wild stab, and guessing your
upper range might be 1000 kc or so ?? MK


Mark,
Gangs in the capacitor is not the issue when trying to cover the AM
broadcast band.
It is the ratio of highest to lowest capacitance that is of concern.

Of course. I've already noted that.

If I assume the highest frequency is 1710 kHz and the lowest is 520 kHz. The
ration of highest to lowest frequency is 3.29.

Square this number to get 10.82.

The ratio of high to low capacitave needed is 10.82 but this must also
include stray wiring capacitance.

A 10-365 pf capacitor has a ratio of 36.5. More than enough to cover the
band if the stray capacitance is low enough.

If you say so. It would depend on the spacing of the wires to a large
degree.
I'm just saying most all the loops I've built so far need a wider
range cap.
If they are getting by with a single 10-365 cap, I'd like to see the
loop, the size, winding spacing , etc..I bet it will be quite
different than the ones I build. Most of my loops are the standard
solenoid type loops. The spacing varies, but on my 44 inch per side
loop, the ratio is pretty wide, maybe 5 to 1.
It's smaller on my small loop, as it uses thick wire, that is closer
together as far as the ratio.

A 10-365 pf capacitor will work if the stray capacitance is less than 28 pf.

The stray capacitance of my large loop is appx 9 pf. "assuming
rjloop3.exe is fairly accurate as a calculator. It seems to be." .

There is no way in heck a 10-365 pf cap would cover the whole BC band
on that particular loop. I can tune up to about 2300 kc on the upper
end if I use a single low value gang. "I have a switch". According to
my calculations, if I used only a single 365pf, my lower limit would
be appx 810 kc. I calculate a dual 365pf to drop down to about 580 kc.
I calculate needing 1220 pf at 450 kc. And this is pretty close to
what I'm using. As you can see, yea, I'm using a multi-gang cap, which
is switchable to allow a low value for the high end, but my loop also
covers a wider range than just the BC band. 450-2300 kc in two ranges.
My 16 inch round loop uses a dual 365 pf cap, which I assume is maybe
20-30 min-730 high value. With that particular loop, it covers from
500 to 2000 kc.
I built a loop a while back for another poster of this group. It was a
diamond loop on a 30 inch frame. It used a multi-gang cap with a dual
365 pf, and a bit extra in three other small gangs. That loop covered
540 to 1830 kc.

Once you have the a sufficient range of capacitance, you just need to make
sure your loop has the proper inductance to match that capacitance.

Of course.

If you need 700 or 1000 pf to tune a loop to the AM band, then it indicates
the inductance of your loop is lower and you are just using more
capacitance to offset the condition.

Maybe so, but all the loops I've built need that range, and I always
build the loop around the cap at hand. I haven't looked at the loop
he's considering, but it must be quite a bit different than the box
solenoid type loops I've been building. Maybe a smaller pancake type
loop? I'd have to look at it.

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

Going back to the initial question in the thread. If the tuning capacitor
supplied with the kit could cover the entire AM band with the kit's coil,
then it should also cover the entire AM band with a different coil/loop. It
is just a matter of getting the inductance right.

It's quite possible I guess, if the loop specs fits that low a range
to allow whole band coverage. None of mine do though. BTW, by whole
band coverage, I am including the new upper range also to 1700 or
whatever it is... All mine go higher than that. My large loop is a
diamond, 5 turns, 44 inches per side. The PVC cross support is 5 ft
across. It's here in the room and rotates. It's a kick butt loop. Very
sensitive, and very balanced. I'm not saying a loop can't be made to
cover the whole band with a single 10-365. I'm just saying that for
the average "box" type loops many will try to build, I don't see it
happening. I guess just general box/diamond loop info from what I see
here...:/ MK

= = = "Brian" wrote in message
= = = hlink.net...

I'm guessing 10-365pf would cover the majority of the broadcast band.

Brian


BRIAN,

Loop Inductance of about 240 uH with a Capacitance Range of 10-365 pF
provides Full Coverage of the AM/MW Broadcast Band: 530 kHz to 1710 kHz.

AM Loop Antenna Calculator - by Bruce Carter (Version 4, 5-19-2003)
http://www.mindspring.com/~loop_ante...loop_calc4.htm
NOTES:
* Enter Edge Length (Inches) is the Distance
of One Side of a Square Loop Antenna.
* Enter Loop Width (Inches) is the Distance
between the First and Last Winding. (Depth)

Check-Out the "Loop Antenna Information Forum" eGroup on YAHOO!
LOOPS= http://groups.yahoo.com/group/loopantennas/

jm2cw ~ RHF

..

Oh, if you mean the capacitance of the one in the kit, I really don't know.
I found the manual online, but didn't see any details for the capacitor.


Brian

"Brian" wrote in message
hlink.net...
Anyone know if the variable cap, that I'm assuming is included in this
kit,
will suffice for the bc band loop I want to build?


http://www.radioshack.com/product.as...uct%5Fid=28-17
9

I see a loopstick in the kit and they usually use a 365-pF cap to tune one
of those. Bear in mind the cap is probably a chintzy little thing with a
tiny knob. Check oselectronics.com (#BC14400, $10.95. p 96 of online
catalog) and tubesandmore.com (Antique Radio Parts, #C-V365, $11.95 and
probably the same cap). For what the kit costs I think you could get a
better cap, if that's all you need.

"PM"

"Brian" wrote in message
hlink.net...
Anyone know if the variable cap, that I'm assuming is included in this
kit,
will suffice for the bc band loop I want to build?


http://www.radioshack.com/product.as...uct%5Fid=28-17
9



http://www.midnightscience.com/catalog5.html There's a nice one right at
the top of the page..

Yeah, I was just looking at that page a few minutes ago, thanks.


Brian

= = = "Brian" wrote in message
= = = thlink.net...

Anyone know if the variable cap, that I'm assuming is included
in this kit, will suffice for the bc band loop I want to build ?

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=28-179

Brian

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

BRIAN,

Since this is an AM & FM Radio 'Kit' it most likely uses a
"Miniature Poly-film Variable Tuning Capacitor" for AM & FM Bands
CAPS= http://www.oselectronics.com/ose_p98.htm
Part Number: BC-88

Ideal Variable Tuning Capacitor for miniature circuitry and use
as exact-duplicate replacement in current transistor receivers.
Tunes AM Band from 540Khz to 1600Khz and FM band from 88Mhz to
108Mhz. Rotates through a full 180°

Maximum Capacity:
AM/MW Antenna Section AM 21-152PF, Oscillator Section AM, 10-74PF.
FM Antenna Section FM 23-44PF, Oscillator Section FM, 14-23PF

Trimmer Capacity: variable to over 12PF.
Trimmer adjustment on rear of case.

Completely enclosed to clear polyethylene
plastic case to protect plates.
Includes calibrated dial, screw, and knob.
Small size, 3/4" Square x 1/2" Deep.


BETTER ALTERNATIVE:
AM/MW "Only" Tuning Capacitor: (Good for AM/MW Loop Antennas)
For your Loop Antenna 'Project' you may wish to consider a Capacitor
that is specifically designed to work within the Band Range of the
AM/MW Broadcast band.

"Miniature 1 Gang Poly-Film Variable Tuning Capacitor For Broadcast Band"
CAPS= http://www.oselectronics.com/ose_p98.htm
Part Number: BC-280

Tunes AM band from 540 kHz to 1600 kHz. Ideal Variable Tuning
Capacitor for miniature circuitry and use as exact-duplicate
replacement in current transistor receivers.
Works great in crystal radio sets. (Loop Antennas)
- Rotates through a full 180°
- Maximum Capacity: Single section tunes from 10-280pf.
- Completely enclosed in a clear polyethylene
plastic case to protect plates.
- Includes Calibrated Dial, Screw, and Knob.
Small size, 3/4" Square x 1/2" Deep.

REQUIRES: Loop Antenna Inductance of about 350 uH
when using a Variable Capacitor Range of 10 to 280 pf.

"AM Loop Antenna Calculator" - by Bruce Carter (Version 4, 5-19-2003)
CAL= http://www.mindspring.com/~loop_ante...loop_calc4.htm

Check-Out the "Loop Antenna Information Forum" eGroup on YAHOO!
LOOPS= http://groups.yahoo.com/group/loopantennas/

jm2cw ~ RHF

..