In a message dated 9/24/2006 9:12:51 P.M. Eastern Standard Time,
W4EF@dellroy.com writes:
> I'm encountering a strange problem with my Titan. If I follow
> standard practice and achieve a 1:1 match with the exciter, READING WHAT
SWR METER? IN THE RADIO? then take the amp out of standby, OK SO YOU HAD
THE AMP MAKING POWER IN THE FIRST SENTENCE AND NOW YOU ARE BAREFOOT? the amp
typically shows mismatch on
> the order of 1.5 or 2:1. THE SWR METER ON THE AMP?
OK, SO IF THE SWR METER ON THE AMP IS BEFORE THE ANTENNA CHAGE OVER RELAY
YOU COULD HAVE AN IMPEDENCE BUMP IN THE ANTENNA RELAY. DIRTY CONTACTS OR
SOMETHING.
> If I then re-tune the antenna for minimum reflected power on the
> Titan, the VSWR at the tuner, and also at a Bird inserted right
> after the Titan, shows a mismatch of 1.5 - 2:1. The mismatch seems
> to be greater at higher frequencies.
>
OK, SO THE TITAN AMP SWR BRIDGE DOES NOT AGGREE WITH THE OTHERS, COULD BE
BECASUE OF WHERE IT IS POSITIONED IN THE BLOCK DIAGRAM OF THIHGS.
> The bridge in the tuner and the Bird are consistent -- that is,
> when the bridge in the tuner shows a match, so does the Bird, 12
> inches of RG-8 from the Titan's output connector.
THEY BOTH SEEM ACCURATE DUE TO THIER LOCATION IN THE BLOCK DIAGRAM.
> I have three different tuners -- a Ten Tec 229B, a Ten Tec 238A,
> and Drake MN2000. It happens with all of them. I've traded cables,
> made them as short as possible, changed the switch that switches
> between the tuners (from a B&W to an Alpha Delta). The exciter is
> going through the Titan to get to the antenna for tuneup. I've
> traded Birds. I've eliminated the Bird. All of the cables are RG-8,
> all are short.
> So you say, go with the bridges. BUT: Grid current in the Titan
> tends to be much lower when the Titan bridge indicates zero
> reflected power, and rises rapidly when I don't. And grid current
> is the big NO-NO in 3CX800A7's, the output tubes in the Titan. I am
> careful to keep grid current down to an indicated 30 mA for the
> pair (120 mA is absolute max). I can't get close rated power
> without excessive grid current unless I tune the antenna for zero
> reflected indicated on the Titan.
>
I GUESS YOU KNOW THAT REGRDLESS OF THE FACT THAT YOU CAN "SIMULATE" A 1 TO 1
SWR WITH A TUNER, YOU STILL HAVE AN SWR ON YOUR ANTENNA SYSTEM THAT YOU CAN
NOT CHANGE.?????
> The SWR indicator in the exciter (TS850) also agrees with the Bird
> and the bridge in the tuner -- IF I bypass the amp's RF circuitry
> and connect the radio direct to the tuner (or through the
> switches). This points to the RF path within the Titan between the
> SO-239 output connector and the final output stage. Has anyone
> encountered this before? Any fixes?
I AM WONDERING HERE IFWHAT YOU ARE ENCOUNTERING IS A MISMATCH TO THE INPUT
CIRCUIT OF THE AMPLIFIER AND NOT THE ANTENNA. IF YOU CAN ACHIEVE MAXIMUM
OUTPUT FORM THE AMP THEN A BIT OF SWR ON THE INPUT TO THE AMP SHOULD NOT BE OF
ANY CONSEQUENCE, NAYBE IT IS JUST ME BUT I AM FINDING IT HARD TO UNDERSTAND
JUST WHAT YOU ARE SAYING, BUT I THINK I KNOW BUT THEN I HAVE NY DOUBTS. I
HAVE
OWNED 3 TITAN AMPS IN THE PAST
DOES ANY ONE ELSE HAVE A PROBLEM FOLLOWING THIS THREAD?
AS A FINAL THOUGHT, AN SWR OF LESS THAN 2 TO 1 BEFORE THE INPUT OF AN
AMPLIFIER THAT IS MAKING FULL POWER OUTPUT AT OR BELOW SAFE GRID CURRENT LEVELS
BARES NO CONCERN IN MY OPINION. WITH A GOOD ANTENNA TUNER PRESENTING A 1 TO 1
SWR TO THE OUTPUT OF THE AMP, YOU CAN'T ASK FOR BETTER. HOWEVER YOU STILL
CAN'T CHANGE THE SWR OF FEEDLINE/ANTENNA SYSTEM AFTER THE TUNER.
I DON;T KNOW IF ANY OF THIS HELPED, BUT IF I HAVE MISSED SOMETHING, PLEASE
TRY AGAIN. 73 Lou
> 73,
>
> Jim Brown K9YC
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