[BC] BE tuner and such

[Ronald J. Dot'o Sr.]

 Comments embedded below.

 Ron D

Ronald J. Dot'o Sr. wrote:

In the past I've adjusted the ATU with a bridge to a 50 ohm, 0J
match but the TX didn't like it when I applied power, as I guess
things change under full power, so I adopted this method which
doesn't require the test equipment and works for me.

 On a single tower (Non-D) station, you should NOT be seeing such a
 difference from the bridge. One (or more) things must be happening.

 A. Transmitter output is not 50j0. Some of the boxes seem to like a
 slightly capacitive load. Component failure can cause output
 network
 mismatch. (have an Omni that only likes 41 -j14 due to bad chip
 caps)

[After I got the TX to match the tower I would have liked to read the
ATU input values for future reference but the owner was in a rush to
 get back on the air, so I didn't.]

 C. Bridge leads are introducing too much inductance, (this
 be a problem at a 50j0 point)

[ I connect the long lead, clear of any obstructions, to the
 measuring point and then short it to ground with a very short clip 
lead and
 balance the bridge, remove the cliplead and then do the reading so 
the leads should not be a problem.]

D. Bridge is not calibrated, this is easily verified by measuring a
 known 50j0 ohm resistor, other values can be checked as well.

 [I have a GR 100 ohm precision resistor that came with the GR 916A
 bridge and measures 100 ohms exactly.  The bridge reads 100 ohms and
 0 J with the resistor.  FWIW I have two 916A bridges and they both
 read the same.  I have read towers that were previously read by 
consulting
 engineers and got the same readings so I guess all is in order :-).]

 E. Someone overlooked a range shifting switch in the wrong
 position. (Of course I've never done that myself..)

 [I'm not sure what you mean by a range shifting switch but if it's
 there I've probably done it. ;-)  Do you mean the C/L switch on the
 bridge?  I follow the bridge manual faithfully and get the readings
 expected.  I tend to hang with Burt Weiner's explanation of lumped
 constants (I hope that's the proper term and doesn't confuse things)
 downrange that keeps a 50J0 ATU input from working and adjusting the
 ATU so that the TX sees 50J0 at the TX output connector.]

 F. Something is just really screwed up!

 [Well, the TX seems happy for several years now with minimum
 reflected
 and the occupied bandwidth measurements are all good so I'll just
 let sleeping dogs lie.  As we used to say in SAC: "If it ain't broke
 then
 don't fix it!".]