• Anyone around North Buffalo or Tonawanda with a RR scanner picking up interference?

  • Pertaining to all railroading subjects, past and present, in New York State.
Pertaining to all railroading subjects, past and present, in New York State.

Moderator: Otto Vondrak

  by videobruce
Specifically between 160.80 and 161.25 MHz in the area in the title preferably using a roof antenna.
The interference sounds like motorboating signal that drifts around between those two frequencies. Not constant, comes and goes, all times during the day and evening.
I can not pin it down except possibly around the Zoo (for a base reference). I've picked it up traveling on the '33' almost out to Cheektowaga.
This is receivable on 4 different 'scanners' including one that is digital.
It's not NXDN and the signal strength does vary somewhat. I don't believe it is not intermod related.

Take a look and listen below;
2004 starts to drop out 35s in.MP3
peak spike 1.png
peak spike 2.png
You do not have the required permissions to view the files attached to this post.
  by clearblock
I have many years experience in RFI investigation and never heard anything quite like that. So it apparently is a drifting signal affecting a discrete frequency vs a broadband noise?

It there any apparent on/off cycle when the signal is active? If it is heard over a wide area, it must be high power so I would suspect some sort of industrial equipment that uses RF for heating. This normally has an on/off cycle while the machine is in use. I had 2 cases back in the 70s where it was heat sealing equipment used to seal seams in plastic products. In both cases, in different areas, it happened that the RR frequencies were what was affected.

Other possibility is a radio transmitter where the RF power amplifier stays keyed and goes into self-oscillation when the transmitter is not keyed. This results in the interference on and drifting around continuously when the transmitter is not keyed and then it goes away while the transmitter is keyed on its proper frequency and returns when it is not keyed.

So times of operation and and apparent operating cycle can be a clue. Driving around while monitoring signal strength is the only way to narrow down the source location. What you a hearing certainly could be some type of industrial RF welding or sealing equipment.
  by videobruce
Correct, it's not broadband noise.
There is really no pattern to it. In the past4 or 5 days, it seem to have shifted downward in frequency that isn't affecting the specific frequencies I monitor, so I can't tell when it is active unless I program some of the other frequencies where it is receivable.

I'm tiring to build a 3 element Yagi antenna, but the specs are conflicting for the length and spacing of the elements depending on which 'calculator' one uses. :(
  by clearblock
Sometimes use of the null off the ends of a horizontal dipole can give a reasonable indication. There is the 180 degree ambiguity but the null is fairly sharp. Even a handheld radio held horizonal will give somewhat of a null with the antenna pointed at or 180 degrees away from the source. Once you have bearings from 2 locations the 180 ambiguity should no longer be a factor.

More observations of signal strength when driving around can also help narrow down the search area to then drive an organized search pattern. But, in a built up urban area, reflections and blocking by buildings can sometimes throw you off with both signal strength and directional antenna observations. With an intermittently active signal it can be very frustrating.
  by videobruce
I'm going to try to build this 3 element 'tape measure' yagi, but I don't have exactly high hopes for it due to so many variations of the dimensions. :(
  by videobruce
There are probably 6 if not more plans for this type of antenna for the same purpose and it seems that everyone has different specs (for the same frequency (146MHz) :(
  by videobruce
Ok, I built the antenna without any balun or matching 'U', just a straight run of RG-58 cable to a BNC fitting and a BNC to SMA adapter.
Using a RF Explorer which I felt would be the best choice for portability and still give me a 'spectrum' to scan since the interference is not set on a single frequency. The 'receive' results are very poor compared to the stock telescoping 'whip' antenna that is supplied with the unit. I barely get any readings including just baseline noise. It's just a flat line for the most part with a few minor peaks here and there. I noticed this right away inside.

I first confirmed the jumper cable and the solder points, both are good. I rechecked the Explorer with their antenna and all is well. The test was done outdoors on a 2nd floor porch moving around and doing a 360 circle. This is aiming the antenna for max signal, not off the rear for a null which in no way would work unless I was less than a few hundred feet from the source. Of course the interference was not present at the time. :(

I'm going to run some more tests and report back.
  by clearblock
With a Yagi, you always go for the peak since there is often a minor lobe off the back and minor nulls are off the back corners and really of no value. Whatever dimensions you picked should work unless you are concerned about use for transmitting on 147. Since the design frequency is 147, the pattern and impedance will be degraded at 161 but not enough to affect the basic directional characteristics you need.

The RF Explorer sounds like an excellent choice for the purpose.
  by videobruce
The problem was I forgot to check resistance between the center and the shield of the cable I made which I normally do with a DVM. I checked the center and the shield separately, but not across the center and the ground. There was a dead short at the BNC connector which I replaced (I always have spare connectors).

After rectifying my mistake, the yagi seems to be ok, thou the testing location gave many 'false' peaks due to reflection off the house. The local US weather service on 162.55 makes a nice test signal. :wink:
  by videobruce
It was asked if I noticed changes in the pattern of the interference with any weather changes. Up to a couple of weeks or so ago, there wasn't since there weren't any real changes in the weather,
from last weekend to now the interference has completely stopped, or at least drifted outside of the frequency area of interest. Nothing as far as I can tell. The temperature has dropped 20+ degrees overall 4 or 5 days ago and we have had some, but not much rain. Before, we were in a dry spell and in the upper 80's during the day. Now it's mid fifties and mid 40's at night.

That can't just be coincidence. Any thoughts on this??
  by clearblock
Electrical interference from power lines is very weather sensitive but it is always broadband noise not a discrete frequency signal. Loose hardware is worse in dry weather and bad insulators or tree contact is worse in wet weather.

Some swimming pool heating and other associated equipment is notorious for RFI and it will be seasonal and possibly temperature related. But it normally only affects a small area like within a block or two of the source.
  by videobruce
The neighbor has a built in pool, I did consider that, but your right, no way something like that would be picked up 2 miles away. Besides, that would be way too easy. :wink:
I have finally built that Yagi and did some initial tests, but can't find something that isn't there at the time. I plan on doing some field tests in a open area nearby using a constant known signal and see how that works.