Picket Fencing Problem

Stylishxone767 · Apr 10, 2016

I experience bad picket fencing while moving in my car on both bands. It doesnt seem to matter how close I am to the repeater. My antenna is a TRAM 1181 dual band that had a magnetic mount. Could the antenna be the root of the problem? Or is this a common problem for everyone? Im a brand new HAM and am learning so id appreciate the help.

popnokick · Apr 10, 2016

Is it from the same repeater on both 2M and 70cm? Picket fencing is usually associated with multi path reflections coming from the same site... and goes away quickly when you move more than a wavelength in any direction. I'm wondering if what you are experiencing is really picket fencing, or simply weak signals. If the choppiness you're hearing is constant... and on either 2M or 70cm... and coming from any / all repeaters you are working... it's not picket fencing, but most likely just poor signal strength. If it's poor signal strength then a boatload of other question apply. For starters:
- Where is the antenna located on your vehicle?
- What radio do you have?
- What coax are you using?
- Does this happen with both simplex and repeater QSOs?
- Does it happen on both 2M and 70cm QSOs?
- Do you have another radio that you can check with, e.g. an HT, mobile rig, or base radio / antenna?

K5MPH · Apr 10, 2016

Have you checked the swr's to see if you have an antenna problem and also how is the antenna mounted.....

Stylishxone767 · Apr 10, 2016

No its not from the same repeater. The antenna is located in the middle of the roof of my car, a Ford fiesta so its a small roof. Dont know what effect that causes. The radio is a cheap one, a QYT KT8900. I thought it might be the problem but I always like to think its an antenna issue first and foremost. I think its your standard RG58 cable but its brand new so I didnt think it would be a problem. I have only had a couple QSO's but they were when I was stopped. And no I dont have anything else yet.

Stylishxone767 · Apr 10, 2016

kb5zcs said:
Have you checked the swr's to see if you have an antenna problem and also how is the antenna mounted.....

No I havent yet. I ordered by first SWR meter yesterday. Does a bad SWR cause picket fencing when your simply listening, not transmitting?

K5MPH · Apr 10, 2016

It will help to see if you might have an antenna problem and also can you try another antenna.....

prcguy · Apr 10, 2016

I think picket fencing is the most likely problem and it would happen with just about any antenna you use. The problem is due to your surroundings and not your antenna. Its most common in heavy urban areas with lots of tall buildings, big metal water tanks/towers, steel bridges or many things that reflect radio waves so they arrive at different times to your antenna.

The fading is not due to a weak signal but rather two signals arriving out of phase to the point of canceling each other and that is usually affected in 1/2 wavelength spacing as your car moves. If your on 2m and you move your car to find a null spot, the next null should be 1/2 wavelength away or about 3.2ft. At 440MHz the spacing would be about every foot from null to null.
prcguy

popnokick said:
Is it from the same repeater on both 2M and 70cm? Picket fencing is usually associated with multi path reflections coming from the same site... and goes away quickly when you move more than a wavelength in any direction. I'm wondering if what you are experiencing is really picket fencing, or simply weak signals. If the choppiness you're hearing is constant... and on either 2M or 70cm... and coming from any / all repeaters you are working... it's not picket fencing, but most likely just poor signal strength. If it's poor signal strength then a boatload of other question apply. For starters:
- Where is the antenna located on your vehicle?
- What radio do you have?
- What coax are you using?
- Does this happen with both simplex and repeater QSOs?
- Does it happen on both 2M and 70cm QSOs?
- Do you have another radio that you can check with, e.g. an HT, mobile rig, or base radio / antenna?

Stylishxone767 · Apr 10, 2016

Does rain or snowfall cause picket fencing?

nd5y · Apr 10, 2016

OP's problem might not be normal picket fencing or loose connection noise.
Some Chinese radios have problems with PL/DPL decode, audio rapidly cutting in and out, and other pulse type noises. Sometimes it even happens on strong signals. He needs to have an experienced ham listent to it.

nd5y · Apr 10, 2016

Stylishxone767 said:
Does rain or snowfall cause picket fencing?

No. At least not at VHF/UHF.

mmckenna · Apr 10, 2016

Stylishxone767 said:
The radio is a cheap one, a QYT KT8900.

Does it happen all the time, or just when you are in down town type areas?

I'd consider your power source, too. How are you feeding power to the radio?

KB0VWG · Apr 10, 2016

Does the picket fencing happen when you are not moving? If it still happens then I would believe it has to do with the antenna most likely. Listen to the weather broadcast on 162.xxx and see if happens when stationary or mobile.
kb0vwg
wqoi992

prcguy · Apr 10, 2016

He mentioned its when he's moving. Some radios have better limiters and go into quieting very quickly when signal levels get above a certain point where others have a wide range where signals can be noisy before quieting. I noticed this when switching from a UHF Motorola Spectra to a BK mobile in the same vehicle with same antenna. I never noticed picket fencing on the Motorola but it was very noticeable on the BK. A quick check on a service monitor revealed the problem, which was in the BK radio design.
prcguy

KB0VWG said:
Does the picket fencing happen when you are not moving? If it still happens then I would believe it has to do with the antenna most likely. Listen to the weather broadcast on 162.xxx and see if happens when stationary or mobile.
kb0vwg
wqoi992

KC4RAF · Apr 10, 2016

I agree with "prcguy".

When in motion, it starts to picket fencing, then that's a clear case of signals being out of phase. If you're stop/stationary, and the signal is clear without the picket fencing, then what else could it be? (that's not taking in to account of bad connections or loose ones.)

wyShack · Apr 11, 2016

A couple of suggestions- first tune into you local weather channel (162.xxx Mhz) and see if you still have a problem. also can someone else drive while you do some experimenting? If so watch the signal meter and see if it also 'jumps' up and down. if the answer is yes to both, I would suspect a problem in the antenna, coax or more likely connections. Does vehicle speed make a difference (should if it is 'real' picket fencing)? does the radio front panel flicker (power cable connection)? Do you have a meter and a way to check the coax while moving? most of the time a problem like this is 'solved' by a process of elimination and the 'answer' is obvious -AFTER it is identified.

Good luck and never stop learning

73

majoco · Apr 11, 2016

Again, what PRCguy said +1.

It was a common problem with VHF FM car radios when they first came out. The broadcaster went to circular polarisation and the problem went away.

kayn1n32008 · Apr 11, 2016

Are you using any sort of cheap usb charger when this happens? Try with and with out if you are. I have one and it plays havoc on vhf. So mich so i cant use it when talking on vhf

Stylishxone767 · Apr 11, 2016

wyShack said:
A couple of suggestions- first tune into you local weather channel (162.xxx Mhz) and see if you still have a problem. also can someone else drive while you do some experimenting? If so watch the signal meter and see if it also 'jumps' up and down. if the answer is yes to both, I would suspect a problem in the antenna, coax or more likely connections. Does vehicle speed make a difference (should if it is 'real' picket fencing)? does the radio front panel flicker (power cable connection)? Do you have a meter and a way to check the coax while moving? most of the time a problem like this is 'solved' by a process of elimination and the 'answer' is obvious -AFTER it is identified.

Good luck and never stop learning

73

Speed would be a factor over 10mph. It takes no time at all for the problem to start. No the screen does not flicker or show any other obvious signs of a a power drain. I ordered a new antenna because the TRAM antenna I have sucks either way so im upgrading. Ill see if there is any difference then

nd5y · Apr 11, 2016

Stylishxone767 said:
Speed would be a factor over 10mph. It takes no time at all for the problem to start.

Does the noise sound like this?
https://www.youtube.com/watch?v=jl40YU3Jsc4

Sort of like a geiger counter?
https://www.youtube.com/watch?v=upPiJ9vOYiY&nohtml5

DanoScan · Apr 27, 2016

PRCguy has the right answer. Enough about antennas, cables, power supplies, etc. The closer you are to the repeater, the less picket fencing will occur. And yes, the Chinese radios have a problem with it more than the higher end models. But eventually, everyone will run into picket fencing while mobile at some point. He's dead on about null spots. I can move my car just a foot, and have no problems. (As long as I stay in that spot)! Certain parts of town, you will find picket fencing all the time. Some places, you don't hear it. It also pays to be in a repeater that is very high off the ground. Here we have (Say two) repeaters just a mile apart. One is on a 300' building. The other is on a 600' tower. I get way less picket fencing in a certain area with the 600' tower. The 300 footer makes me want to pull my hair out trying to have a QSO. I find it necessary to pull over, find the null spot and finish my QSO. So, the problem is NOT solvable. It is something we all have to accept.

Picket Fencing Problem

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