Hello Jim:
I don't know your Titan exactly, but here are a few things for you to check
out.
One, using your SWR bridge built into the exciter, while you have a 50 ohm
dummy load on the Titan, adjust the input coils of the Amp for minimum SWR.
I don't know if your model has a torroidal input, or individual tuned coils
for each band. One by one, adjust each input coil for minimum SWR.
The thru SWR, when the amplifier is bypassed, but the RF still enters and
exits your Titan, needs to be checked.
Normally, the higher you go in frequency, the more of an issue the bypass
SWR will be. If your rig sees a 1:1 match into the dummy load, without the
Titan connected, inserting the Titan in the bypass mode should also indicate
1:1 on each band. If the SWR is high on 10 meters, you may have to add some
small capacitance on the output cable to balance out the inductance.
If the input coils are adjustable, you should be able to obtain a fairly
close match, no tuner needed, either the built in tuner, or an outboard
tuner between the rig and the amp. If the SWR doesn't reduce with tuning,
or the amp uses a torroidal input, try a much longer length of high quality
RG 8 cable between the rig and amp, say 15 to 20 feet, and see if the SWR
does not indeed reduce.
Mount the SWR bridge coupler directly on the back of the amplifier, with a
double male connector on the RF output SO 239. Use whatever length is
necessary between the coupler output and your antenna tuner.
You may find the longer cable between the rig and the amp will solve your
problem if the amp input SWR will not reduce.
73 and Happy DXing,
Mike
W2AJI
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: <amps@contesting.com>
Sent: Sunday, September 24, 2006 5:02 PM
Subject: [Amps] Titan 425 Reflected Power
> I'm encountering a strange problem with my Titan. If I follow
> standard practice and achieve a 1:1 match with the exciter, then
> take the amp out of standby, the amp typically shows mismatch on
> the order of 1.5 or 2:1.
>
> 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.
>
> 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.
>
> 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.
>
> 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?
>
> 73,
>
> Jim Brown K9YC
>
>
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