Author Topic: RF meters.  (Read 1929 times)

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Offline EvilLOON

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RF meters.
« on: May 31, 2015, 04:21:24 am »
So I have been looking for a cheap option to getting an RF meter.  Currently for massive RF I use any radio tuned to a static AM station.  I want to find something under the $50/€45 mark.  Im looking more for something  that can measure around 2.5GHz to probably 12GHz.  When I hunt around I see units well over the mark that I'm willing to spend.  I do not own a smart phone and i do have access to laptops and desktops.  What are everyone's recommendations?

The reason for this question.  We have electrical lines in the ground that are not shielded properly or failing.  I know the easily bleed into the AM range of radios.  Using a radio I can tell exactly where the line is in the ground. I just don't know what range the RF is being broadcast across.
 

Offline evb149

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Re: RF meters.
« Reply #1 on: May 31, 2015, 05:54:15 am »
The use of GHz frequencies probably does not make sense for this usage.  There are powerful AM broadcast band sources that exist and generate signals that the cables may pick up.  There generally aren't abundant powerful signals over 1GHz.  Anyway long lines will be more effective at picking up and radiating lower frequency signals than very small wavelength signals.  In theory they could be more efficient with the shorter wavelength signals but in pratcice that's less likely to be the case.
Anyway if the ground is somewhat conductive (as it often is -- that's why they GROUND electrical lines) then it will attenuate short wavelength (high frequency) signals much moreso than long wavelength ones (AM radio may work in a tunnel but FM radio and cell phones usually will not very well for this reason).
Also when the lines are in the ground the change in the environment itself will cause the signals not to couple well to the cable at the transition (due to the changed impedance and such) so the longer wavelength ones will be less affected in a short distance than will the short wavelength ones.

So beyond UHF TV signals I don't know what kind of powerful signals you may even have that the lines could have a chance of having picked up and also being able to be received after the lines are grounded.
The lower frequency the better your chance of having it work, so AM radio frequencies or frequencies even lower may be ideal practically.  Maybe up to the 10s of MHz, but I don't see much point in requiring anything higher than that except for specialized situations.



 

Offline EvilLOON

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Re: RF meters.
« Reply #2 on: May 31, 2015, 06:48:43 pm »
So more about the situation.  Due to financial constraints I live in something similar to a trailer park.  I used to work for the park and what was noticed time and time again were broken or corroded grounds on the power lines. In one specific situation I went to replace a photo cell on a street lamp. The photo cells attach to the bottom of the lamp posts. When grabbed the box the photocell sits in, I got the shock of my life. Traced the ground line back to the big box and found it green and crusty. I told the owners about it and they just said come up with a temporary fix.  So in typical jury-rigged fashion, I did a very generic bad fix.  We got a 4 ft(1.2m) grounding rod, drove it into the ground, and grounded the box directly to the grounding rod. When I got to take a quick look at the main power box's for the park I noticed plug fuses as the only fusing for the park.  I have since quit working for the park for other reasons.

Since that time I have attempted to setup a wifi connection for myself and my neighbor.  The distance the signal is being transmitted is about 75 ft(23 m).  I was using a traditional high output router and noticed the signal could not reach.  So I upgraded to 1 high-gain outdoor directional antenna/bridge/router ENH202.  The device seemed to work ok, but there was still massive signal loss at times. Checking signal strength it just looked pitiful on a graph.  So I went and I bought another ENH202 and just broadcast one to the other.  Once I did this, the signal stays strong  most of the time.  Bandwith between the 2 devices to the systems seems to be good.   

This lead me to breaking out an AM radio to look for RF interference.  I noticed when I stood over the electrical line between the 2 devices, I received huge RF bleed onto the radio.   All ranges in AM were being flooded with static. I'm curious at what ranges this static is being broadcast across. Specifically around the 2.5-5 ghz range.

http://www.engeniustech.com/business-networking/outdoor-access-points-client-bridges/9339-enh202-
 

Offline SeanB

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Re: RF meters.
« Reply #3 on: May 31, 2015, 06:54:08 pm »
More likely microwave oven leakage is the culprit, while the hash on the supply lines is probably all the bad connections on the mains feeders, combined with corroded connections and the leakage across insulators on the MV supply on overhead wiring.  The microwave ovens will still probably pass a leakage test, just that the leakage is cumulative with all the microwaves in the park, and you probably have the signal issues at around mealtimes and break times as people cook or warm food.
 

Offline EvilLOON

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Re: RF meters.
« Reply #4 on: May 31, 2015, 08:54:19 pm »
See that's what is strange, the signal dip happens almost all the time at random.  As far as microwave interference, I did have a Magic Chef vintage 83 microwave I was using forever.  That thing liked to knock out any RF signal within 300 feet when it was turned on.  I only got rid of it recently because I was tired of TV, WIFI, and even phone calls failing during microwave use. So Im at a loss  and can only blame the electrical lines in the ground.  I have even take a laptop over near the lines and watched the signal drop to not.  It's really strange.
 

Offline VK5RC

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Re: RF meters.
« Reply #5 on: June 01, 2015, 09:04:43 am »
RF interference is a complex field,  roughly half is radiative ie the interfering signal is picked up directly from the ether or conductive via power lines etc.  If a power line is underground and still radiating the soil must be very poorly conductive /dry.  The typical unit to use is a spectrum analyser,  big bucks for good gear but some not crazy units like the funcube dongle pro are around .
  Common sources of RF interference are smpsu,  arc welders,  internet over power line units and plasma tvs.
Your am radio is what most people use along with detective work,  my smpsu was a shocker,  S7 noise across a good chunk of the HF spectrum.
Whoah! Watch where that landed we might need it later.
 


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