Running a Radio Transmission System

[SamTaylor]

Hey All,
I work to maintain a network of stream gauges to report water levels for flood prevention. We have a couple gauges (meaning everything from the sensor to the transmitter) that are acting really strange...and I'm hoping you can help me figure out why. During evening hours the transmissions aren't making it to the base station, but seem to work fine during daylight hours. Everything in the system has been replaced and the batteries are fully charged, but consistently this problem keeps coming up. Does this sound familiar to anyone? We're scratching our heads over here and I love to buy a drink for the one who can figure it out.

Thanks!

P.S. If this is the wrong spot to be asking this type of question, sorry. Maybe you can help me find the correct folks.

 

[dknguyen]

My dad did that same job. Except when he did it there were no meters or cell phones. There had to be someone physically there to record data and when a town flooded, the person would have to run to the phone booth in the next town over to call it in.

What's in the surrounding area? It couldn't just be somebody a radio amateur messing around with their project when they get home from work could it? Or a software setup issue?

 

[SamTaylor]

The temps can get as low as 0°/32°F but currently it's pretty warm. The problem persists in the summer, but it's not as bad.

 

[dknguyen]

The temps can get as low as 0°/32°F but currently it's pretty warm. The problem persists in the summer, but it's not as bad.

Yeah, I just noticed Utah. Probably not too cold.

What frequency band?

 

[dr pepper]

Low and medium frequencies are affected by atmospherics once it goes dark.
This tends to be more on long range transmissions where the signal bounces off the outer atmosphere though.
The frequency the system operates on is important, do you know what it is?
As already mentioned something could be switched on causing interference, one would hope it isnt a ham though.
There are 4 things that spring to mind to improve the setup, improve the antenna, increase the transmit power, place a repeater inbetween both ends, and change the frequency.

 

[chemelec]

All the Creeks and Rivers in Canada are monitored by a government agency and these graphs are Readily available.

 

[SamTaylor]

Low and medium frequencies are affected by atmospherics once it goes dark.
This tends to be more on long range transmissions where the signal bounces off the outer atmosphere though.
The frequency the system operates on is important, do you know what it is?
As already mentioned something could be switched on causing interference, one would hope it isnt a ham though.
There are 4 things that spring to mind to improve the setup, improve the antenna, increase the transmit power, place a repeater inbetween both ends, and change the frequency.

Our frequency is 170.275. We have done quite a bit of work to improve the site with amplifiers and we can try to add a repeater, but one of the problem sites is already really close to the base-station. THIS is the transmitter we use...and we are sort of locked down with this type (contract with the company). We have about 30 sites and the problem ones are close to the base-station/have all new equipment inside. My guess was something not related to the system (atmospheric sounds likely). We can try to add a bigger amp, but it seems strange with theses sites so close.

 

[SamTaylor]

All the Creeks and Rivers in Canada are monitored by a government agency and these graphs are Readily available.

Yeah, their info is great. We're a bit farther south but all our info is public as well. Feel free the check it out.
https://rain-flow.slco.org/home.php

 

[chemelec]

This is the Creek beside my house, But you can search others.

 

[JimB]

We have a couple gauges... ... that are acting really strange

What is the total number of gauges, and how many of them are failing during the night time?

We have done quite a bit of work to improve the site with amplifiers and we can try to add a repeater, but one of the problem sites is already really close to the base-station.

Increasing transmitter power is not a universal cure all and can be counter productive sometimes.
How close is "really close" for the problem site?

Does the base station receiver have facilities to listen to the incoming signals, ie a loudspeaker?
If not, can you beg/borrow/hire/buy a suitable receiver so that you can listen to the signals?
That way you can compare the sound when it is working to when it is failing.

Where is the base station receiver located?
You say that the system works during daylight, but that also corresponds to the normal working day.
Could it be that something is switched off when someone goes home?
or
Something is switched on when someone goes home, such as a "burglar alarm" type system?

JimB

 

[Les Jones]

Another possibility is interference from lighting that comes on after dark. Some idea of the frequency of the radio liinks would be helpful. Also what sort of distance is there between the sensors and the base station. Does the sensor only transmit or does it also receive requests from the base to send data.

Les.

 

[Nigel Goodwin]

Some idea of the frequency of the radio liinks would be helpful.

He's already said:

Our frequency is 170.275

 

[dr pepper]

Thats well into Vhf, atmospherics are less likely at that frequency.
And if the problem is on a transmitter close to you then upping tx power probably wont fix it either.
I didnt read all the blurb but just looking at that gizmo it looks well made and capable.
Interesting all the problem childs are close to base, there is probably a connection.
Do you have good space around the transmit antenna, you need I guess about 10 metres, also if the transmitter is in a dip compared to the receiver that wont help. Is your antenna directional or just a whip?
Have you tried talking to the manufacturer, their engineers probably know what they are doing.
Jim had a good idea, if you have access to a scanner try several points along the path and see if you can hear where the signal degrades, and what is in the vicinity at that location.

 

[ronsimpson]

Something is switched on when someone goes home, such as a "burglar alarm" type system?

If I was there I would connect a Spectrum Analyzer to a antenna. And see who is transmitting near 170mhz. I would look at 1/2 to 2x frequency. It could be someone is transmitting at 85mhz or 340mhz. More likely some one is also having problems with their 170mhz radio when your are transmitting.

RF is something to share.

Can you find a radio receiver that will operate in the 170mhz range? Maybe battery powered. It will be easy to carry around looking for trouble.

 

[SamTaylor]

What is the total number of gauges, and how many of them are failing during the night time?

We have 18 stream gauges and 19 precipitation gauges that all run on the same transmitter. Two of them are giving us trouble. They are both pretty close to the base station but they are also located in a much more urban area when compared to the other locations.

 

[SamTaylor]

If I was there I would connect a Spectrum Analyzer to a antenna. And see who is transmitting near 170mhz. I would look at 1/2 to 2x frequency. It could be someone is transmitting at 85mhz or 340mhz. More likely some one is also having problems with their 170mhz radio when your are transmitting.

RF is something to share.

Can you find a radio receiver that will operate in the 170mhz range? Maybe battery powered. It will be easy to carry around looking for trouble.

This is a great idea. I'll see what I can find. Thanks!

 

[SamTaylor]

Thats well into Vhf, atmospherics are less likely at that frequency.
And if the problem is on a transmitter close to you then upping tx power probably wont fix it either.
I didnt read all the blurb but just looking at that gizmo it looks well made and capable.
Interesting all the problem childs are close to base, there is probably a connection.
Do you have good space around the transmit antenna, you need I guess about 10 metres, also if the transmitter is in a dip compared to the receiver that wont help. Is your antenna directional or just a whip?
Have you tried talking to the manufacturer, their engineers probably know what they are doing.
Jim had a good idea, if you have access to a scanner try several points along the path and see if you can hear where the signal degrades, and what is in the vicinity at that location.

Our antenna is omnidirectional. As far as space from the transmitter, there are a couple small trees around, but they aren't very tall.
We spoke with the manufacturer and they are scratching their heads as well.
I'll work on getting a scanner to see where the signal fades.

 

[SamTaylor]

Another possibility is interference from lighting that comes on after dark. Some idea of the frequency of the radio liinks would be helpful. Also what sort of distance is there between the sensors and the base station. Does the sensor only transmit or does it also receive requests from the base to send data.

Les.

The distance for the problematic sites is between 3 and 5 kilometers. Our transmitters are only setup to send signals. As for the frequency of the radio links, is that the same as the signal frequency? If so it's 170.275

 

[Nigel Goodwin]

Our antenna is omnidirectional.

As the slave sites are fixed, replacing their omni-directional aerials with yagi's would greatly increase your signal strength, a ten element yagi gives 10dB gain, so a 1W transmitter becomes a 10W one.

 

[SamTaylor]

As the slave sites are fixed, replacing their omni-directional aerials with yagi's would greatly increase your signal strength, a ten element yagi gives 10dB gain, so a 1W transmitter becomes a 10W one.

With the problem sites there isn't a great line of sight to the base station. Both problem sites are in a constrained valley (+-50m below the elevation of surrounding ground) and there are quite a few big buildings in the way. Would this create problems for a yagi?