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Author Topic: IC-718 / AH-4 / High Noise Floor  (Read 7793 times)

Posts: 12486

« Reply #15 on: March 09, 2012, 07:05:08 AM »

I've used the AH-4 with several Icom rigs and about 80 feet of wire as an antenna on many occasions. Each time the AH-4 antenna worked quite well. However, I did use about 6 or 8 20 foot radials (more would be better) and not a single ground rod.

Regarding sodium and mercury vapor lamps. They are generally fine UNTIL they begin to go bad. These lamps have a slow and agonizing death ---- slow for them and agonizing for any ham operating HF near them. I live in a relatively quiet RF neighborhood for many years. My neighbor installed sodium vapor flood lights and they were fine. However, as they approached retirement they would go through a cycle of light, flickering, off, then on again. The timing of this cycle was identical to and coincided with the S9 noise generated on every ham band. When the lamps finally died the noise went away. When they were replaced about 4 or 5 years ago there was no noise. However, one lamp is beginning to go and I can see the noise pop up on my Flex 5000 panscope and disappear consistent with its "cycle".

Harry WE1X

I wonder if these are actually Metal Halide lights. They are somewhat yellow like a sodium (but whiter) but have about 1/2 the life expectancy.  They are somewhat less efficient and usually are higher wattage to make up for it too. They also use a different ballast type.
« Last Edit: March 09, 2012, 07:09:26 AM by W8JX » Logged

Ham since 1969....  Old School 20wpm REAL Extra Class..

Posts: 19

« Reply #16 on: March 12, 2012, 10:15:25 AM »


So this weekend I stuck my 10m dipole in the trees. No noise. But 10m band conditions were pretty lousy this weekend.

So I cut my long wire in half. The half I took out was the half I had in free space so although the length was cut in half, the length in trees / length in free space ratio went way up. No AM broadcast QRM at multiple harmonics, noise was way down, non existent on 10m and on the other bands I'd probably attribute it to band condition noise given the environmental conditions in the midwest. Not to throw fuel on the "bet you trees cause noise fire" but  I don't believe that to be the case. Now I may change my tune when things warm up and the sap starts running but any vegetative noise was far overshadowed by cutting the length of the very sensitive signal gatherer.

Made my first contact on 40m. Got a 5/9 with 70 watts from Little Rock Arkansas, about 600 miles away.

Now I better add those radials....

Posts: 17417

« Reply #17 on: March 12, 2012, 10:24:33 AM »

Your original wire was a quarter wavelength on about 1.2 MHz.  No wonder it picked up
a lot of BCB stations!  They were probably overloading your receiver and mixing to create
all sorts of products.  A quick test is to add an attenuator to the front end and see if
the noise level goes down faster than the attenuation.  A high-pass filter in the feedline
to reject the broadcast stations should solve matters (or an old-fashioned T-network
antenna tuner as a quick test, since it will act as a high pass filter.)

The shorter wire is no longer resonant in the BCB, so it doesn't pick up as much RF,
and your receiver front-end is no longer generating as much junk due to overload.

Posts: 310

« Reply #18 on: March 12, 2012, 07:00:24 PM »

Just for info the AH-4 does a wonderful job tuning a 135' doublet fed with ladder line.
One side of the ladder line to the HOT of the tuner and the other side to the GROUND of the tuner.
Blows the socks off any random wire or longwire......
Also does well with loops, ladderline fed or direct.
This is my experience....Love my AH-4. Too bad ICOM did such a bad job with it's documentation.
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