Hot rodding AA5 radios
 

If we are talking about a ferrite loopstick antenna, and if the coil is
wound on a cardboard former, the coil can be slided on the form to peak the
sensitivity on the lower end of the band. The trimmers peak the high end of
the band, and if the tuning capacitor has slits in the outer plates,
sections of these plates are bent to peak the sensivity in the middle of the
band, typically at 1000kHz. This is known as three-point tracking.
With some loopstick antennas, this is not an option because the wire is
wound directly over the ferrite form.

Pete

wrote in message
oups.com...

craigm wrote:
wrote:
Most of the mass-produced radios lack the RF coil to properly match the
ferrite antenna. As you adjust the oscillator coil you will find a spot
where the gain of the circuit is optimum. You are not adjusting the
ferrite antenna: you are matching the oscillator to wherever the
ferrite is tuned to. This will produce stronger signals. Try it.


That would do winders for dial accuracy.

************************************************** **********************************
Actually, this type of radio doesn't have good dial accuracy out of the
box, so the tuned version is not much different than the original as
long as the tuning device is adjusted.
This adjustment is made to have the oscillator 455 khz higher than
whatever the ferrite is tuned to. Since there is no easy way to adjust
the ferrite, adjust the oscillator coil until it is 455 khz higher than
the antenna (ferrite) coil. You will find a spot where the signals are
the loudest. This is where the correct difference frequency is 455 khz
and the gain is maximum through the IF. For example, if the station you
want to receive is at 600 khz, and the antenna is tuned to 610 khz due
to manufacturing tolerances, the oscillator must be tuned to 1065 khz
to have the correct difference frequency. Since the oscillator is the
only thing that can be adjusted, you adjust it. The IF is happy: all it
wants is a 455 khz signal. The increase in gain is especially
noticeable from 550 to 700. All the radios I have tuned could easily
add the new 1600 to 1700 frequencies. The 455 khz IF coils are quite
stable: I haven"t run into any that needed adjusting.

Hot rodding AA5 radios
 

I dont really know what I am thinking (m II will probally have something
to say about that,Haw Haw Haw) but wind some wire around a piece of
cardboard and see if you can attach that to your AM/ferrite core radio
antenna input.Who knows? it might help somewhat.
cuhulin

Hot rodding AA5 radios
 

Pete KE9OA wrote:
If we are talking about a ferrite loopstick antenna, and if the coil is
wound on a cardboard former, the coil can be slided on the form to peak the
sensitivity on the lower end of the band. The trimmers peak the high end of
the band, and if the tuning capacitor has slits in the outer plates,
sections of these plates are bent to peak the sensivity in the middle of the
band, typically at 1000kHz. This is known as three-point tracking.
With some loopstick antennas, this is not an option because the wire is
wound directly over the ferrite form.

************************************************** *********************************************
The above is a much better tracking method if you have air variable
tuning capacitor, and the right kind of loopstick. The radios I was
referring to are the cheapies that use the tiny sealed variable cap,
glued loopstick coil, and made in the last 30 years. These radios only
permit one adjustment to improve alignment: the oscillator coil. I
don't recall when the industry abandoned the air variable, but I think
it was around 1975. Those radios might need a different method of
alignment as they might still have coils and trimmers long gone from
the scene. I have a few 365 mmfd 2-gang variables in my junk box that I
am thinking of putting on ebay because of the high prices they fetch
now. Does anybody still make them?

Hot rodding AA5 radios
 

"Pete KE9OA" wrote in message
...
If we are talking about a ferrite loopstick antenna, and if the coil is
wound on a cardboard former, the coil can be slided on the form to peak
the
sensitivity on the lower end of the band. The trimmers peak the high end
of
the band, and if the tuning capacitor has slits in the outer plates,
sections of these plates are bent to peak the sensivity in the middle of
the
band, typically at 1000kHz. This is known as three-point tracking.
With some loopstick antennas, this is not an option because the wire is
wound directly over the ferrite form.

Pete


It's worth mentioning that perfect oscillator - RF tracking won't happen on
typical radios which have the same profile on both the oscillator and RF
sections of the tuning capacitor. It can be correct at two or three points,
but it's going to be off a bit between those points. There's a wider
frequency for the RF stage to cover than the oscillator stage and three
point tracking is the best economical comprimise for most radios. Alot of
the AM radios (not multiband) of the past had different profiles cut on each
of the sections of the tuning cap, but I don't know if that's done with the
common plastic dielectric tuning cap. I imagine anything beside a constant
radius profile would put a radial stress on the dielectric film, which might
be a problem. But I don't know for sure. It's been years since I've taken
one of those things apart, and I don't remember the profile of the plate.

I've aligned a few radios and I haven't noticed much consistant problems
with the factory alignments, but I don't get real fussy about oscillator -
RF tracking. Getting the best dial tracking is more important to me. I
figure getting it right somewhere near the high end and low end is about as
good as it gets. Getting it perfect at the extremes would just knock it off
more somewhere else.

Frank Dresser

Hot rodding AA5 radios
 

I've uploaded a graph illustrating oscillator - RF tracking error to the
group alt.binaries.pictures.radio.

Frank Dresser

Hot rodding AA5 radios
 

alt.binaries.pictures.radio
I have that site in the same webtv Save Folder (it amounts to computer
Bookmarks,more or less,computer wise anyway,buku thousands of them) I
have in this here (and buku others too) rec.radio.shortwave thingy in.I
will check it out.
cuhulin