All my RX path questions

Bonkk083

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It would be a better signal than what I gave as an example above. A problem with terrestrial path loss calculations is they are not accurate due to signals bouncing of things making alternate paths between antennas. Signals can arrive from these multiple paths in phase and add more signal to your receiver or they can arrive out of phase and degrade reception. The amount of uncertainty can be 25dB or more. Most path loss calculations are based on free space and we don't live or operate our radios in space.
I'm getting some signal from a tower 30 miles with a 6 dbi Remtronix, would that indicate that a 11 dbi omni would work 30-36 miles
 

prcguy

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I'm getting some signal from a tower 30 miles with a 6 dbi Remtronix, would that indicate that a 11 dbi omni would work 30-36 miles
How big is that Remtronix antenna, about 7"? If so its nowhere near 6dBi gain, that would take about 3ft of antenna. A 7" long antenna for 700-800MHz would be a little over 1/2 wavelength long, probably a center fed coaxial dipole and that would give about 0dBd or 2dBi gain. One of the first things you must learn about antennas is many antenna companies are compulsive liars and they simply make up big gain numbers to sell more antennas.

So if your getting some signal at 30mi with a 0dBd gain antenna, especially on the radio in the house, I would expect an actual 11dBi antenna to pick things up at 35mi in the same direction, assuming there is not a huge mountain in the way at 33mi.

BTW for an antenna length example, I have a couple of A/S ASP-977J antennas that are real 8.5dBd gain across 872-960MHz and they are 14.4ft long. 8.5dBd gain would be the same as 10.64dBi gain. Compare that to whatever the length is on the 11dBi antenna you are looking at. If its at least 10ft long it might be believable. If its only 6ft long its a lie.
 

Bonkk083

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How big is that Remtronix antenna, about 7"? If so its nowhere near 6dBi gain, that would take about 3ft of antenna. A 7" long antenna for 700-800MHz would be a little over 1/2 wavelength long, probably a center fed coaxial dipole and that would give about 0dBd or 2dBi gain. One of the first things you must learn about antennas is many antenna companies are compulsive liars and they simply make up big gain numbers to sell more antennas.

So if your getting some signal at 30mi with a 0dBd gain antenna, especially on the radio in the house, I would expect an actual 11dBi antenna to pick things up at 35mi in the same direction, assuming there is not a huge mountain in the way at 33mi.

BTW for an antenna length example, I have a couple of A/S ASP-977J antennas that are real 8.5dBd gain across 872-960MHz and they are 14.4ft long. 8.5dBd gain would be the same as 10.64dBi gain. Compare that to whatever the length is on the 11dBi antenna you are looking at. If its at least 10ft long it might be believable. If its only 6ft long its a lie.
It's 8" but counting the bend more like 7.5" I checked the specs it's 6 dbd if that's true and the antenna I'm looking at I think it's 90"
 

Bonkk083

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Your 7.5" antenna is around zero dBd gain, they lied. If the 90" antenna is the one you mentioned with 11dBi gain that is also stretching the truth.
And I was looking at a 8.15 dbi omni was 65" also
 

prcguy

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I recently got two real nice 800/900MHz A/S-DB Products ASP-977J 8.5dBd gain with adjustable downtilt for $50 each. There are good deals out there. Heck, just before typing this I finished gel coating a nice VHF Shakespeare 476 (the original 21ft and not the current 18ft) which is their biggest VHF marine antenna covering 155-164MHz with an original cost around $1200. I got it locally last month for $25 in perfect electrical condition with a little wear on the fiberglass. One coat of resin then sanding then a finish of sky blue gel coat and this is a really nice antenna for a really cheap price. BTW it came with about 80ft of 1/2" Heliax with N connectors thrown in for that $25.

Just imagine how well this thing will work for VHF marine or railroad monitoring. Yum! So get out there and find those used antennas that need a good home. That will also help free up the load on my antenna orphanage here.

1702769929507.jpeg
 

Bonkk083

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I recently got two real nice 800/900MHz A/S-DB Products ASP-977J 8.5dBd gain with adjustable downtilt for $50 each. There are good deals out there. Heck, just before typing this I finished gel coating a nice VHF Shakespeare 476 (the original 21ft and not the current 18ft) which is their biggest VHF marine antenna covering 155-164MHz with an original cost around $1200. I got it locally last month for $25 in perfect electrical condition with a little wear on the fiberglass. One coat of resin then sanding then a finish of sky blue gel coat and this is a really nice antenna for a really cheap price. BTW it came with about 80ft of 1/2" Heliax with N connectors thrown in for that $25.

Just imagine how well this thing will work for VHF marine or railroad monitoring. Yum! So get out there and find those used antennas that need a good home. That will also help free up the load on my antenna orphanage here.

View attachment 153133
I searched ebay and haven't found any 800 are they other websites
 
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buddrousa

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Local Government Surplus and Government Surplus Auctions. These things are not everywhere every day just have to be at the right place at the right time.
And just a follow up
I would trust a Government Surplus or Government Surplus Auction before I would trust EBAY for Used Commerical Antennas.
 
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prcguy

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Bonkk083

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The path loss is 109.4 and 105.6 with different antenna dbi how do I calculate it to dbm
 

RaleighGuy

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The path loss is 109.4 and 105.6 with different antenna dbi how do I calculate it to dbm
According to Google...

Using the Friis transmission formula: This formula takes into account the distance between the transmitter and receiver, the frequency of the signal, and the gains of the antennas. It is the most accurate method, but it can be a bit complex to use.
Here's the formula:
Path loss (dB) = Pt (dBm) - Pr (dBm) = 20 log10(d) + 20 log10(f) - G_t - G_r + 27.55

where:
  • Pt is the transmitted power in dBm
  • Pr is the received power in dBm
  • d is the distance between the transmitter and receiver in meters
  • f is the frequency of the signal in MHz
  • G_t is the gain of the transmitting antenna in dBi
  • G_r is the gain of the receiving antenna in dBi
  1. Using a path loss model: There are a number of path loss models available that can be used to estimate the path loss for different environments, such as urban, suburban, and rural. These models are typically simpler to use than the Friis transmission formula, but they may not be as accurate.
Here are a few examples of path loss models:
  • Hata model: This model is commonly used for cellular systems in urban and suburban environments.
  • Cost231-Hata model: This is a modified version of the Hata model that is more accurate for higher frequencies.
  • Okumura-Hata model: This model is similar to the Hata model, but it is more accurate for long distances.
Once you have calculated the path loss in dB, you can convert it to dBm by subtracting 27.55.

Here are some online tools that you can use to calculate path loss:
 
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Bonkk083

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According to Google...

Using the Friis transmission formula: This formula takes into account the distance between the transmitter and receiver, the frequency of the signal, and the gains of the antennas. It is the most accurate method, but it can be a bit complex to use.
Here's the formula:
Path loss (dB) = Pt (dBm) - Pr (dBm) = 20 log10(d) + 20 log10(f) - G_t - G_r + 27.55

where:
  • Pt is the transmitted power in dBm
  • Pr is the received power in dBm
  • d is the distance between the transmitter and receiver in meters
  • f is the frequency of the signal in MHz
  • G_t is the gain of the transmitting antenna in dBi
  • G_r is the gain of the receiving antenna in dBi
  1. Using a path loss model: There are a number of path loss models available that can be used to estimate the path loss for different environments, such as urban, suburban, and rural. These models are typically simpler to use than the Friis transmission formula, but they may not be as accurate.
Here are a few examples of path loss models:
  • Hata model: This model is commonly used for cellular systems in urban and suburban environments.
  • Cost231-Hata model: This is a modified version of the Hata model that is more accurate for higher frequencies.
  • Okumura-Hata model: This model is similar to the Hata model, but it is more accurate for long distances.
Once you have calculated the path loss in dB, you can convert it to dBm by subtracting 27.55.

Here are some online tools that you can use to calculate path loss:
This is what I ran
 

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