View Full Version : Quirky FM-6

03-15-2010, 08:49 PM
For the past couple of weeks after modifying the rotor to fit my FM-6 properly (weight distribution) I have noticed some odd effects, mainly, the front seems to have now become the rear, as far as reception goes.

Here is an example. Right now the antenna I "think" is pointing SSW, and I am receiving stations from that direction relatively normal... BUT... this is the opposite direction to 95.9 KLZX @ 70 miles and I am receiving that station better, and good enough to get an HD Lock. When I point at KLZX directly, I get a solid signal but no HD lock or RDS. Opposite, I get HD. Same goes for the other Logan stations, all about 70 miles.

What gives? Which side of my FM-6 is now the front? Or is it the way it has always been, with the side of the antenna pointing SSW the front? See the attached picture...:duh:

03-15-2010, 09:11 PM
Adjacent-channel signals can inhibit HD reception. Check for them by tuning 200 kHz above and below the desired channel. At least one adjacent channel must be substantially free of interference to receive HD.

Your antenna looks awfully close to the air conditioner unit, if that's what that is. It may be detuning the elements. The FM6 F/B is already poor and needs all the help it can get. Raise it into the clear if you can.


03-15-2010, 09:16 PM
I was going to say the same thing Brian did. But also, the FM-6 and the ground plane antenna are both too close to each other and too close to the air conditioning unit. If that ground plane is used for transmit, the standing wave ration (SWR ) on it could be high enough to damage the transmitter.

Ideally, you want to have antennas elevated at least 5-6 feet above the nearest other metallic object, and the same distance from other antennas as well.

03-15-2010, 09:16 PM
Thx Brian. I still am having trouble figuring out which side of the FM-6 is the front. I am betting I am right, that its the side facing south-southwest. I am a bit stuck in the height side of things, I don't have a bigger mast, and I think the height requirements per my landlord would be broken.

03-15-2010, 09:17 PM
By the way, your FM-6 is indeed aimed SSW ;-}

03-15-2010, 09:19 PM
By the way, your FM-6 is indeed aimed SSW ;-}

Thats what I thought Russ, just had a brain fart. I am considering moving the ground plane antenna which is indeed transmitting...on FM of all places. 99.9 to be exact.

It only puts out 25 mW on FM but it is enough for me to receive it's harmonics all over the FM band on the receiver the FM-6 is attached to, the Sony.

03-15-2010, 09:27 PM
In that case, you'll have to move it a lot farther than 5-6'.

And even another foot or so of elevation above the air conditioner might be a big help.

But if you're transmitting constantly it's a wonder you get much of anything on the FM-6...

03-15-2010, 09:53 PM
Good thing the weather is good today :D. I moved the ground plane a good 8 feet from the FM-6. It now sits on the edge of the roof, and much lower than the FM-6 which is raised. It is still transmitting. I also re-included my 3 turn balun... the one Brian recommends with the coax. It was being used by the ground plane as I never got around to switching the coax around last summer.

Results... KLZX is still coming in and out of HD from off the back of the antenna (at 70 miles). The difference is, the harmonics on FM (from the ground plane) have gone down considerably.

It should be noted. During the 2009 Es season, I did not use the ground plane at all. It was replaced with a TV antenna during that time, but as Fall rolled around, I put the ground plane back up.