High swr seen by the exciter points to the cathode circuit tuning. It
may need to be adjusted if there are two input circuits for 80 and 75.
Typically the Q of that cathode tuned circuit is very low so it covers
the full band decently.
How are you tuning, for maximum out or by grid and plate currents?
Tuning by DC meters alone can get you a long ways from proper matching
and proper output. Tuning for maximum smoke out of the coax connector
gets the best results from a GG linear in my experience.
73, Jerry, K0CQ
On 11/24/2010 4:21 PM, CSM(r) Gary Huber wrote:
During the past weekend I participated in the phone Sweepstakes and observed
high VSWR on my OMNI-VII while driving my Titan 425 using the published
settings for 75 meters when operating between 3.8 and 3.9 MHz.
The manual suggests; BAND 75, TUNE 5.5, LOAD 7.5, FREQ 3.9 MHz. but with BAND
75 selected the load control was near 10 and the driver VSWR was nearly 10 to 1!
By switching the Titan bandswitch to 80, the LOAD setting became 3, TUNE stayed at
5.5, FREQ stayed at 3.8 – 3.9 and the VSWR dropped to 1.1 to 1.
Over the twenty plus years I’ve had this Titan 425-E as the original owner, I had seldom used
it on 80 and even less on 75 so I had not observed the high VSWR. A new OMNI-VII with its
“High Current” notification and shut-off protection got my attention to the fact and
drove me to the solution.
Best regards,
CSM(r) Gary Huber - AB9M
9679 Heron Bay Rd
Bloomington, IL 61705
(309-662-0604)
www.csm-gh.com
glhuber@msn.com
gary.huber@us.army.mil
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