GMRS Daytime Performance

[Talkinggoat]

Is it normal for GMRS to have significantly decreased range during the day? Normally, I can hit repeaters 30+ miles away, after the sun goes down and I come in loud and clear. As soon as the sun comes up, though, I can't hear them and they can't hear me.

 

[N4SRN]

I’ve never once made a post saying “Following”. So, I won’t…

 

[KevinC]

I’ve never once made a post saying “Following”. So, I won’t…

Much easier to click the "Watch" button.

 

[Hans13]

Is it normal for GMRS to have significantly decreased range during the day? Normally, I can hit repeaters 30+ miles away, after the sun goes down and I come in loud and clear. As soon as the sun comes up, though, I can't hear them and they can't hear me.

I have noticed decreased range in the daytime. I don't pretend to know why but I always chalked it up to possibly more particulate in the air, greater RF noise floor, moisture levels, etc.

I would also be interested in reading if there is a difference and what factors might cause it.

 

[Hans13]

This link has some good information regarding VHF and UHF propagation. I noticed it discusses air density.

CHAPTER 2 VHF/ UHF RADIO PROPAGATION

 

[Talkinggoat]

I would think it would impact 70cm, too, since they are pretty close.

 

[Hans13]

As with other times I have tried to research this; it isn't appearing to me that there is a significant daily difference between day and evening and GMRS propagation. Perhaps it is simply an elevated RF noise floor in the daytime?

VHF/UHF & Free Space propagation


"- 2m band – This band falls in the middle of the VHF spectrum and is ideally suited for frequent DX using almost all the modes available to the 6m band plus the manifestation of trans-equatorial propagation mode across the equator that might cover DX distances in the order of 6000-8000 Km.

- 70cm band – Most of the propagation methods cited above are also applicable to this band, however, the probability of robust and reliable Sporadic-E as well as Trans-equatorial openings get significantly reduced due to the lack of sufficient ionization density required at these frequencies. On the other hand, the tropospheric scatter mode becomes more frequently available due to the reduction in wavelength."

70cm is what we are looking at so for day/night propagation influences, I looked at the VHF entry below...

Atmospheric impact on VHF Radio Propagation

 

[Talkinggoat]

This link has some good information regarding VHF and UHF propagation. I noticed it discusses air density.

CHAPTER 2 VHF/ UHF RADIO PROPAGATION

Sounds like it's ducting the radio waves, which would make sense. It is passing over the largest swamp in the US, causing increased humidity and reflection off all the mosquitos. When the sun comes out, the humidity drops to around 30% and the waves travel straight out of the atmosphere, but when the sun goes down, humidity goes up around 100% and the waves get bent to the repeater.

 

[Talkinggoat]

As with other times I have tried to research this; it isn't appearing to me that there is a significant daily difference between day and evening and GMRS propagation. Perhaps it is simply an elevated RF noise floor in the daytime?

VHF/UHF & Free Space propagation


"- 2m band – This band falls in the middle of the VHF spectrum and is ideally suited for frequent DX using almost all the modes available to the 6m band plus the manifestation of trans-equatorial propagation mode across the equator that might cover DX distances in the order of 6000-8000 Km.

- 70cm band – Most of the propagation methods cited above are also applicable to this band, however, the probability of robust and reliable Sporadic-E as well as Trans-equatorial openings get significantly reduced due to the lack of sufficient ionization density required at these frequencies. On the other hand, the tropospheric scatter mode becomes more frequently available due to the reduction in wavelength."

70cm is what we are looking at so for day/night propagation influences, I looked at the VHF entry below...

Atmospheric impact on VHF Radio Propagation

Can you check that link, it tells me the site can't be found.

 

[Hans13]

Sounds like it's ducting the radio waves, which would make sense. It is passing over the largest swamp in the US, causing increased humidity and reflection off all the mosquitos. When the sun comes out, the humidity drops to around 30% and the waves travel straight out of the atmosphere, but when the sun goes down, humidity goes up around 100% and the waves get bent to the repeater.

For my AO, my conclusion always has come down to noise floor when I've tried to figure it out. When we experience noticeable ducting here, it is obvious as to the cause. We can also pull up the 70cm propagation maps and see what's happening.

 

[Hans13]

Can you check that link, it tells me the site can't be found.

VHF/UHF & Free Space propagation | VU2NSB.com - Amazing Amateur Radio

Radio wave propagation across the entire spectrum including VHF, UHF, and microwave primarily works on the principles of Free Space propagation. As the radio waves propagate, they are subsequently acted upon by several other physical phenomena like reflection, refraction, diffraction...

vu2nsb.com

Atmospheric impact on VHF Radio Propagation | VU2NSB.com - Amazing Amateur Radio

The overall influence and impact of atmospheric conditions on VHF radio propagation quite significant. In this article when I say VHF, it would usually mean VHF and UHF bands. Although the magnitudes of various effects would vary, the behavior and performance of both these bands follow a similar...

vu2nsb.com

 

[Talkinggoat]

VHF/UHF & Free Space propagation | VU2NSB.com - Amazing Amateur Radio

Radio wave propagation across the entire spectrum including VHF, UHF, and microwave primarily works on the principles of Free Space propagation. As the radio waves propagate, they are subsequently acted upon by several other physical phenomena like reflection, refraction, diffraction...

vu2nsb.com

Atmospheric impact on VHF Radio Propagation | VU2NSB.com - Amazing Amateur Radio

The overall influence and impact of atmospheric conditions on VHF radio propagation quite significant. In this article when I say VHF, it would usually mean VHF and UHF bands. Although the magnitudes of various effects would vary, the behavior and performance of both these bands follow a similar...

vu2nsb.com

 

[Hans13]

View attachment 171184

Hmm. That's odd. I tried it on a different network and it came right up. I tried it on mobile data on a different device (android phone with Firefox) and it came right up. The previews on this site seem to come up for the link. The issue might be on your end?

 

[tomk62]

Is it normal for GMRS to have significantly decreased range during the day? Normally, I can hit repeaters 30+ miles away, after the sun goes down and I come in loud and clear. As soon as the sun comes up, though, I can't hear them and they can't hear me.

ChatGPT says ...

Yes, it is common for GMRS (General Mobile Radio Service) and other UHF communications to experience reduced range during the day due to several factors:

1. Atmospheric Conditions: UHF frequencies (like those used in GMRS) are affected by temperature and weather conditions. During the day, the sun heats the ground and air, causing thermal turbulence, which can increase signal attenuation. This means that the range can decrease during peak daylight hours due to atmospheric instability.
2. Temperature Inversions: At night, the ground cools faster than the air, sometimes creating a temperature inversion where a layer of cooler air gets trapped under a warmer layer. This can actually enhance radio signals by reflecting them over longer distances, often extending the range. During the day, these inversions break down, reducing the range.
3. RF Noise and Interference: During the day, there may be increased man-made interference (from devices like power lines, machinery, etc.), which can degrade UHF signal quality and reduce range.
4. Foliage and Terrain Changes: If you're in an area with trees, buildings, or other obstacles, the effects of foliage and structures can be more pronounced during the day due to changing environmental factors such as increased moisture in the air, which can further absorb and scatter UHF signals.

In short, the reduced range you're noticing during the day is likely due to a combination of these factors. UHF frequencies typically perform better at night or during cooler, more stable atmospheric conditions.

 

[prcguy]

I've run GMRS, UHF commercial business band and UHF amateur since the 70s and have never noticed any reduction in rage day to night. I have experienced tropo ducting where stations 100-150mi away suddenly come in great during the summer then disappear and of course when their on the air your range would be reduced, but otherwise no changes.

I also think ChatGPT is full of sh*t and should not be taken seriously.

 

[Talkinggoat]

I've run GMRS, UHF commercial business band and UHF amateur since the 70s and have never noticed any reduction in rage day to night. I have experienced tropo ducting where stations 100-150mi away suddenly come in great during the summer then disappear and of course when their on the air your range would be reduced, but otherwise no changes.

I also think ChatGPT is full of sh*t and should not be taken seriousl

I've tested for two nights, now. They start to come in at about 9pm at 1x9. By 6am, I am getting 8x9 on the signal meter. Just like a switch, when the sun comes up, the atmosphere starts warming and the humidity drops, I lose contact.

ChatGPT says ...

Yes, it is common for GMRS (General Mobile Radio Service) and other UHF communications to experience reduced range during the day due to several factors:

1. Atmospheric Conditions: UHF frequencies (like those used in GMRS) are affected by temperature and weather conditions. During the day, the sun heats the ground and air, causing thermal turbulence, which can increase signal attenuation. This means that the range can decrease during peak daylight hours due to atmospheric instability.
2. Temperature Inversions: At night, the ground cools faster than the air, sometimes creating a temperature inversion where a layer of cooler air gets trapped under a warmer layer. This can actually enhance radio signals by reflecting them over longer distances, often extending the range. During the day, these inversions break down, reducing the range.
3. RF Noise and Interference: During the day, there may be increased man-made interference (from devices like power lines, machinery, etc.), which can degrade UHF signal quality and reduce range.
4. Foliage and Terrain Changes: If you're in an area with trees, buildings, or other obstacles, the effects of foliage and structures can be more pronounced during the day due to changing environmental factors such as increased moisture in the air, which can further absorb and scatter UHF signals.

In short, the reduced range you're noticing during the day is likely due to a combination of these factors. UHF frequencies typically perform better at night or during cooler, more stable atmospheric conditions.

Thanks for the additional info.

 

[mmckenna]

I also think ChatGPT is full of sh*t and should not be taken seriously.

I agree. That ChatGPT was crap from different bands. AI doesn't negate the need for a good internet B.S. filter.

I've tested for two nights, now. They start to come in at about 9pm at 1x9. By 6am, I am getting 8x9 on the signal meter. Just like a switch, when the sun comes up, the atmosphere starts warming and the humidity drops, I lose contact.

So, when the sun comes up, you lose contact. That sounds more like someone near you has solar panels that are either creating noise themselves, or a cheap @$$ inverter connected to them that's spewing out trash that wipes out the signal. Or, since it's a hobby type radio service, I'd look at deficiencies in the installation. Not all hobbyists have the skills/money to properly install a repeater.

I've run a number of VHF, UHF and 800MHz system for 30 years now, and I've never had atmospheric conditions impact performance like that.

 

[ladn]

Makes me wonder if it's temperature related. Possibly a marginal contact that loses continuity when it warms up and expands. The OP should check his station's cabling/connectors.

 

[KC3ECJ]

Higher noise floor due to more UHF business band users during the day?

 

[prcguy]

I agree. That ChatGPT was crap from different bands. AI doesn't negate the need for a good internet B.S. filter.



So, when the sun comes up, you lose contact. That sounds more like someone near you has solar panels that are either creating noise themselves, or a cheap @$$ inverter connected to them that's spewing out trash that wipes out the signal. Or, since it's a hobby type radio service, I'd look at deficiencies in the installation. Not all hobbyists have the skills/money to properly install a repeater.

I've run a number of VHF, UHF and 800MHz system for 30 years now, and I've never had atmospheric conditions impact performance like that.

Yup, there is no perceivable loss through humidity like fog or even rain at UHF or 800MHz. When you get past about 2GHz rain fade starts to be measurable, at 6GHz rain is a slight concern and at 14GHz and above it’s a big problem. I spent 18yrs working on satellite uplinks and downlinks monitoring 4GHz, 12GHz and 20GHz satellite beacons passing through the atmosphere in clear sky, fog and rain. I’ve never measured even the slightest change from clear sky to dense fog through 12GHz, none. My equipment logged various satellite beacon levels 24/7 and I had many years of data to review.

Now if the OP is seeing day/night changes in a non line of sight system with moisture on foliage that both passes signals through it or foliage on a hillside that is bouncing the non LOS signal to him, then yes you may see day/night or dry/wet changes in signal strengths. That is a real problem. And no ChatGPT was used for this post.