Interference or...

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temchik

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Hi All,

I am trying to hang an antenna and I am experiencing some interference in the location I chose for it.

This is a temporary solution just to get a simple Slim Jim antenna from N9TAX outside of the house so I didn't want to mount anything permanently on the roof and the ground rod is right there... However. When the antenna is in place on the side of the house I connected it to a handheld transceiver and on 2m the receiver opens up with static and noise. Move about 5 feet in each direction and it stops. Another less sensitive HT doesn't open but it won't reach the repeater either from this location.

I am guessing there's some strong interference right in this location. The weird thing is - It does not matter if the antenna is touching the house or not, I can move away about 3-4 feet in each direction and the noise is still present. What could be producing such strong interference in an area about 5 x 5 x 5 feet right next to the house? Or I should move to another location and not deal with it?

Thanks!
 
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mmckenna

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Easiest solution is to move the antenna.

What is on the other side of the wall from the location where the interference is happening? Any phone lines, cable TV, WiFi, routers, etc?
 

temchik

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There is not much in that immediate location, maybe some power, but that shouldn't fill a 5x5x5 block of adjacent air with noise... I do have a WiFi router nearby in the vicinity, almost the same horizontal plane and it's a "long-range" version... Hmm
 

mmckenna

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There is not much in that immediate location, maybe some power, but that shouldn't fill a 5x5x5 block of adjacent air with noise... I do have a WiFi router nearby in the vicinity, almost the same horizontal plane and it's a "long-range" version... Hmm
WiFi routers and associated cabling are well known for being RF noise generators. Moving your antenna to a different location would be the easiest way to address this. Many consumer electronic products are RF noise makers. If you read the FCC Part 25 disclaimers that come with them, you'll see suggestions about moving antennas and the like to reduce interference issues.
 

temchik

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It's not the router, unplugged everything in the vicinity, nothing changed. Here's what's happening in details, let's my both HTs - HT1 and HT2:

- Connected HT1 to the antenna directly, antenna in my hand (yes, I know, I probably attenuate it as well). I move around the small area near the ground rod about 5x5x5 in all directions. In some portions HT1 opens up with noise and static. Not loud, not like the SQL0 setting does. Sounds like a faint signal. Move about and it stops and restarts but certain areas are clear.

- Connect HT2. Nothing.

- Hang the antenna on the wall, connect HT1 - noise. HT2 - nothing. Try to key up the repeater, HT1 reaches the repeater, receives confirmation beep and goes back to faint static. HT2 seems to reach the repeater, but does not receive the response!

- Found a place where HT1 is silent, way higher than the original spot and a bit away. Hang it, check up there, no noise, seems to be good.

- Run the coax down, connect HT1, no noise, key up the repeater, it responds, repeater stops transmitting and.... back to static! Switch to another frequency or turn off and on - no static until there is a transmission from the repeater. Right after the transmission - static.

- Try HT2 - works as it should, but, quite frankly, I cannot hear any difference between the whip antenna on HT2 and the Slim Jim about 15 feet in the air.

- This all only happens on 2m bands, 70cm is unaffected

So, there you have it, it's possible HT1 is defective, but it does not exhibit this behavior anywhere else but this particular spot. Stock antenna is not as sensitive, but HT1 goes crazy with the stock whip antenna in that spot as well, just not sensitive enough to completely open up... I left it on while I was checking with HT2 and HT1 went on with clicks and pops at random times with the stock whip

Thanks!
 

temchik

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No, it doesn't sound like the raw squelch 0, much more quiet and distinct
 

khooke

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it does not exhibit this behavior anywhere else but this particular spot. Stock antenna is not as sensitive, but HT1 goes crazy with the stock whip antenna in that spot as well, just not sensitive enough to completely open up... I left it on while I was checking with HT2 and HT1 went on with clicks and pops at random times with the stock whip
Is it possible that in this specific spot (I assume you're talking about some place in your house) the HT is near something electronic that is generating the noise? In these A vs B comparisons are you moving the location of the antenna around, or are you moving around, attached via coax to the antenna?

I guess either way, if you can't find what's causing the interference in that spot so you can't turn the device off or move it, then the easy answer is just don't use your HT in that location... avoid the interference. Almost everything electronic in your house generates some noise to some degree, it's probably easier to avoid it if you can, rather than fix it if you can't work out where it's coming from?
 

temchik

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Ok. I have experimented a lot with this antenna, moved it around everywhere, location actually does not matter at all. I have recorded a couple of videos, not sure it will let me post links, but here they are

N9TAX SlimJim Antenna: http://youtu.be/d86BGgz6UNU


N9TAX SlimJim Antenna: http://youtu.be/SHSYiZwv_mI

Anybody has any comments on this? Sounds like mututal incompatibility between this particular antenna and this particular radio. However, I have gotten good reports on actual TX and RX is good.

Another HT is silent, but audio reports are not great, much lower than with stock whip antenna
 

autovet

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Slim Jim Noise

I have the exact same problem. I put a Ringo Ranger 1/4 wave dual band in the exact same spot and had no interference what so ever and it ran circles around the Slim Jim antenna. I returned the Slim Jim antenna and got a second one. Same exact problem. It only happens on certain days about 50% of the time. At my home I can hang it anyplace on my property and still have about 5db noise. Your not the only one with the problem. My suggestion is to use a different type of antenna.
 

nanZor

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Anybody has any comments on this? Sounds like mututal incompatibility between this particular antenna and this particular radio. However, I have gotten good reports on actual TX and RX is good.
I remember doing much the same thing in the 80's with my handheld after spending a lot of time mounting a j-pole 30 feet high to a Yeasu FT-470 dual bander. Result was the same as yours!

Handheld radios, be they two-way or scanners, are not designed to cope with anything better than the usual whip. They don't have the front-end bandpass filtering to deal with it. What you end up with is overload, desense, intermod and images. Of course there is the guy out in the boonies where this isn't a problem, but for most of us it is.

This is made even worse by using a J-pole, which is inherently unbalanced and needs lots of common-mode choking near the feedpoint such as a handful of RS #273-105 chokes or equivalent.

In some cases, due to the very poor common-mode current situation, the entire antenna including the outside of the coax is acting more like a long-wire. Since the handheld radios, especially these ultra-cheap ones (no disrepect as I have a few myself) can also suffer from interfering with itself as the display, cpu etc can put this noise onto the coax shield, head up towards the antenna, and back down inside.

Some solutions to try are

1) Use ferrite chokes near the feedpoint transition from coax to the j-pole.

2) Try a different antenna such as a quarter-wave groundplane (these also benefit from chokes), or better yet, turn that antenna into a vertical dipole fed in the center with the coax running away from it horizontally for a few feet before any vertical runs back down to the ground.

3) Abandon the idea of using handhelds with large antennas, and use a mobile radio instead, which has the room for at least some bandpass filtering better than our $12 ht's. :) Still no guarantee, but usually waaay better than the handheld.

In my case way back when, I resorted to building a "paint can cavity" (courtesy old HamRadio magazine article) for 2M. Not very practical, but it worked to prove that using an HT with a large unbalanced external antenna with a long run of coax was a bad idea.
 
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autovet

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LED light interference

After pulling my hair out trying to get the noise out of my radio attached to a slim Jim antenna I figured out what the interference was. It is caused by the LED lights in my home. Turn them all off....noise goes away and the antenna works great. Hope this helps someone.
 
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