6700 locks in transmit mode

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  • Updated 10 months ago
I have a 6700 that was recently repaired and calibrated by Flex however when transmitting at power levels about approximately 10 or 20 W the radio gets stuck in TX while in tune mode. It would seem to relate to too much reflected power since the antenna does not appear to be effectively tuned by the internal ATU. How effective is the tuner that is built in? Looks like I have an untuned vswr of around 2.7 to 1 so I would have thought the tuner would handle this. Seen this behavior on 3880.

Is it common to have the radio lock into TX mode when seeing relatively high reflected power?
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Gary Schulz

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Posted 10 months ago

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Bill -VA3WTB

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If the antenna is too far out of tune, then the ant tuner will only do so much.
Nothing like locking in tune is common, it all depends on your station and how much  RF the radio is dealing with.

A good place to start is trimming the antenna for a better SWR.
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The spec for ATU says:
VSWR Range: 8.3 - 300 Ohms (80m – 10m) 6.7 - 150 Ohms (160m and 6m)

From 13.1 of the 6000 Series Hardware Reference Manual


For a 2.7::1.0 SWR the ATU should work.  Perhaps some common-mode RF into the 6700?

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My 6700 is also at Flex getting re calibrated because of frequency instability apparently due to oscillator failure .

How long did you own your 6700 before it required re-calibration?
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Gary Schulz

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I don't know if it required re-calibration per se, this was just part of the repair procedure.  This radio had some issues with the TR switching on both Ant 1 and Ant 2 ports since it was new so they replaced some surge suppression diodes and some transformer (balun?) that was related to the 2 meter band...  Now I have this major issue with the TX locking up and the only way to stop it from transmitting is to turn off the power supply.  Will not respond to anything else...
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Jim Gilliam

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Don't confuse high SWR with transmission line radiation. Grounding, not using a BALUN, etc. causes RF in the shack.