anothr ant tuner question
 

Geee-----we're on a roll! Thanks for good info on my previous query. Now,
a new one:

Just put a small MFJ -949E tuner into my antenna system.

Thing works great. The only weird thing is I notice the tuning is extremely
"tight" and "goosey". The slightest movement of the variable caps produces
jumps in meter readings. Having said that, I can still manage with it.

Years ago, this kind of tuning effect was from hand capacity, when just
about everything in the shack was RF hot.

However, this isn't what we're dealing with here. Once my controls are set,
touching around the tuner anywhere doesn't alter anything. So, it's not
hand capacity/coupling.

What is this effect indicative of? Just curious.

anothr ant tuner question
 

In article ,
RB wrote:

Geee-----we're on a roll! Thanks for good info on my previous query. Now,
a new one:

Just put a small MFJ -949E tuner into my antenna system.

Thing works great. The only weird thing is I notice the tuning is extremely
"tight" and "goosey". The slightest movement of the variable caps produces
jumps in meter readings. Having said that, I can still manage with it.

Years ago, this kind of tuning effect was from hand capacity, when just
about everything in the shack was RF hot.

However, this isn't what we're dealing with here. Once my controls are set,
touching around the tuner anywhere doesn't alter anything. So, it's not
hand capacity/coupling.

What is this effect indicative of? Just curious.

Any of several things.

This could indicate that your caps have noisy (dirty or oxidized or
burned) sliding contacts to the stator.

It could indicate that the caps have a somewhat "sticky" bearing
arrangement, which is subject to both stiction and some amount of
backlash and overshoot.

It could indicate that you are attempting to tune a highly reactive or
otherwise-difficult load, and have one or both of the caps set to a
low-mesh (and thus high-reactance) setting. If the rotor and stator
plates in those caps have the same radius throughout (I can't tell
from the picture), then when the caps are mostly un-meshed, a very
small change in the position of the rotor can make a proportionally-
large change in capacitance and change the reactance (and thus the
matching) quite a lot.

There can be a definite advantage to using air-variable caps which
have plates (on either the rotor or stator) which are tapered in
radius, from one end of the rotation to the other... it makes the
adjustments at the mostly-unmeshed, low-capacitance end rather less
critical. Take a look at a typical "broadcast variable" capacitor
from an older AM radio set, and you'll probably see this sort of
construction.

With a C-L-C T-match tuner, it's usually possible to achieve a match
at several different settings of the controls. If you've achieved a
match, and find that both of the caps are set up to a fairly-far-
unmeshed setting, try switching the inductor down to the next-lower
inductance setting, and then tweaking both caps in the direction of
greater mesh (more capacitance, lower reactance). This may boost your
tuner's electrical efficiency, and may also make the tuning less
critical and "jumpy".

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

anothr ant tuner question
 

RB wrote:
Geee-----we're on a roll! Thanks for good info on my previous query. Now,
a new one:

Just put a small MFJ -949E tuner into my antenna system.

Thing works great. The only weird thing is I notice the tuning is extremely
"tight" and "goosey". The slightest movement of the variable caps produces
jumps in meter readings. Having said that, I can still manage with it.

Years ago, this kind of tuning effect was from hand capacity, when just
about everything in the shack was RF hot.

However, this isn't what we're dealing with here. Once my controls are set,
touching around the tuner anywhere doesn't alter anything. So, it's not
hand capacity/coupling.

What is this effect indicative of? Just curious.

I suspect it is caused by an effective Hi-Q load on the antenna side of
the tuner. That could be a high reaactive component or a low resistive
component of the input impedance to the coax.

What kind of antenna and transmission line are you using?

I run a 140 foot long center fed doublet withh 600 ohm open wire tuned
feeders and observe the same type of indications on 60 meters. The
resistive component of the input impedance is 10 ohms with 15 ohms of
inductive reactance. It's not a problem, just sharp tuning.