"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