Portland OR KATU 2.1 vs KOIN 6.1?
 

I live in Portland OR (45.5225 N, -120.7677 W) and have LOS to most of the local broadcast antennas. I get great signals for all stations except KOIN 6.1, which is odd because I get great reception on KATU 2.1, the tower for which is literally right next to the tower for KOIN 6.1. I'm using an outdoor directional antenna with high-quality coax to my Sony TV, and as I say I have great reception on all other channels.

Any suggestions as to why I'm having this problem?

What's the make and model of your existing antenna?

Longitude -120.7677 is east of The Dalles, OR. Can you post a link to your TV Fool report? Thanks

Antenna - ClearStream 2
 

I have the ClearStream 2 by Terrestrial Digital (http://www.antennasdirect.com/store/...V-antenna.html).

I should also say that during stormy (windy) weather, KATU (2.1) cuts up.

TVFool signal report
 

The Main situation is 21 Digital Broadcast Tv stations/channels that are Very Strong and less then 2 miles away !!

The first 9 Digital Broadcast Tv stations/channels are OVER THE TOP STRONG , SO STRONG that they are High Lite with RED in the the channel list !!
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If there are Any preamplifiers connected , All parts of the preamplifier Must be Removed Completely , remove the preamp , remove the power inserter , remove the preamp power supply.

Remove Any and All distribution amplifiers.

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The signal strength reception must be reduced.

As a first step to reduce signal strength.

Try this , antenna aiming situation ,
Turn the antenna around so the reflector screen is facing the Tv transmitters at about 78 degree magnetic compass direction.
The reflector screen will block some of the signal to reduce signal strength.

As a second step to reduce the RF signal strength and interference from multipath (reflected signals). From the metal antenna mast pipe or metal antenna mount stand , run a #10 copper ground wire to house electric service ground.

As a third step to reduce signal strength and interference from multipath (reflected signals) install a coax grounding block in the coax line and connect the coax ground block to the house electric service with #10 ground wire.

As a fourth step to reduce signal strength , install a variable attenuator in the coax down lead before any splitters. http://www.mcmelectronics.com/product/30-2118. $12.86

The short answer is "Move the antenna."

You are experiencing a multi-path due to some object in or near the signal's path. Since it is more evident during windy/wet weather, I will assume the antenna is probably behind a tree, the most common reason for this problem.

Antennas cannot resolve issues caused by unfavorable site selection so it's often necessary to, as our directions clearly state, "Before attaching the antenna to any surface, TEST RECEPTION in that area."

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Anyone reading this thread should not conclude that antenna system grounding is going to cost them signal strength.

While I fully agree that the mast and coax shield should be grounded, I recommend doing so for reasons of general electrical safety. Correct grounding practice does not reduce the antenna system signal output to the TV unless additional coax is used to reach the grounding block, and then the effect is negligible unless a great deal of extra coax length is involved.

I agree completely, the signal levels are so strong that the other measures suggested thus far are appropriate;

1. No amplifier should be used in this system.

2. Re- aim and/or move the antenna.

3. An attenuator is indicated. (I doubt a variable design is needed, or worth the added expense. I would try 16 or 32 dB of fixed attenuation)

http://forum.tvfool.com/showthread.php?t=901
http://www.amazon.com/Steren-16dB-In...ref=pd_sim_e_6

Properly grounding the system per NEC will have no material effect on received signal power.

Keep in mind that, for locations very close to and below the plane of the broadcast antennas' main radiation lobe, signal levels will be markedly below those forecast by LRI calculations. I've measured values up to 30 dB less than calculated when testing very close to the broadcast tower.

The OP is 1.7 miles away from the (imaginary) base of the antenna and about 1000' below the center of radiation. Most of the radiated signal is above his head and the numbers in the plot are incorrect in this type of situation.