Effect of Nearby Cell Tower?

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WeldGuy

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I've been helping a friend (retired dispatcher) improve the reception on her Uniden 436. She lives in Fairfield County, Ohio and is trying to receive the MARCS digital system. The problem is her location is about ten miles from a MARCS tower to the north and fourteen miles from another MARCS tower to the south. Up until now she has been using an 800 MHz rubber duck on the scanner. Reception is poor.
I installed a Tram 1411 discone with a chimney mount and ran about 65 feet of RG-6 Quad cable. Reception is still disappointing.
Here's my concern: Her house is located about 1500 feet from a cell tower. Could the rf from the cell tower in the 800 MHz range be desensitizing or overpowering the weak MARCS signal?
 

iMONITOR

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A discone is not the best choice for the 800 MHz band. Discones usually do better in the 100-500MHz spectrum. A yagi might do better providing the target site it not in the same direction as the cellular tower and preferable in the opposite direction. This will boost the signal of her target while attenuating the cellular tower interference.

Numerous choices:
 

nd5y

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It possible that the cell site is causing it but more likely that the antenna is no good on 800 MHz.
A VHF discone like that has a high radiation angle at 800 MHz. It's looking for signals almost straight up instead of at the horizon where the signals from 10 - 14 mile distant towers would be.
 

AJorge1219

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I've been helping a friend (retired dispatcher) improve the reception on her Uniden 436. She lives in Fairfield County, Ohio and is trying to receive the MARCS digital system. The problem is her location is about ten miles from a MARCS tower to the north and fourteen miles from another MARCS tower to the south. Up until now she has been using an 800 MHz rubber duck on the scanner. Reception is poor.
I installed a Tram 1411 discone with a chimney mount and ran about 65 feet of RG-6 Quad cable. Reception is still disappointing.
Here's my concern: Her house is located about 1500 feet from a cell tower. Could the rf from the cell tower in the 800 MHz range be desensitizing or overpowering the weak MARCS signal?
Yes. I am in Franklin County and in about the same situation, although my closest simulcast site is only a couple of miles away. The cell tower is about 600' away.

I have had success with doing two things. One, HVAC Tape on cardboard between the Unication and the cell tower. Secondly, I loosen the antenna about 3-4 turns to attenuate the interference from the tower. With this, it works like a charm.

Once I leave the house, and travel a few hundred yards in any direction, crystal clear reception. Ive had success with picking up sites greater than 20 miles away without the cell tower issue.

Good luck!
 

WeldGuy

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Yes. I am in Franklin County and in about the same situation, although my closest simulcast site is only a couple of miles away. The cell tower is about 600' away.

I have had success with doing two things. One, HVAC Tape on cardboard between the Unication and the cell tower. Secondly, I loosen the antenna about 3-4 turns to attenuate the interference from the tower. With this, it works like a charm.

Once I leave the house, and travel a few hundred yards in any direction, crystal clear reception. Ive had success with picking up sites greater than 20 miles away without the cell tower issue.

Good luck!
Sounds like the Unication doesn't have attenuation options.
 

KOK5CY

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Get rid of rg6 qual comm junk . I'm using rg8x and I'm also using the tram 1410 and it's receiving the 800 trunked okwin system fine . I have 3 towers that are within 20 miles and our system is fine .

Grecom psr-600
 

iMONITOR

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Get rid of rg6 qual comm junk . I'm using rg8x and I'm also using the tram 1410 and it's receiving the 800 trunked okwin system fine . I have 3 towers that are within 20 miles and our system is fine .

From what I'm seeing on the charts at 900 MHz loss with RG8X is double of what RG6 is.

86363
 

cmdrwill

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From what I'm seeing on the charts at 900 MHz loss with RG8X is double of what RG6 is.
According to the chart you posted, but there is a missmatch as the RG6 is for 75 ohm antenna systems.
And who knows what the 'discone' antenna impedance is at 800 band.

And you may need a filter to reduce cell tower RF over loading your poor scanner.
 

JoshuaHufford

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You are loosing most of your signal in the coax.

Are you wanting to monitor anything besides stuff in the 800MHz range?

As others have mentioned a discone is not the best antenna for anything above 500MHz unless the signal is strong, and your current coax is a poor choice for that high of a frequency.
 

iMONITOR

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According to the chart you posted, but there is a missmatch as the RG6 is for 75 ohm antenna systems.
And who knows what the 'discone' antenna impedance is at 800 band.
It's been generally accepted over the years that 75 vs 50 ohm impedance with RG6 does not negatively impact scanner recption. Bob Grove of Monitoring Times wrote about this on numerous occasions. Many RR members have been using it for years.
 

Ubbe

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It'a 0,2dB loss due to the mismatch between 50 and 75 ohm. But antennas and scanners usually has a wider impedance spread than that so impedance matching are a non issue in wide frequency range receivers and antennas.

RG6 are used for sat dishes with up to 2GHz frequencies. It's for sure the most cost effective solution for scannerists.

For monitoring a single simulcast system, and nothing else, a $20 yagi antenna from Amazon or Ebay are the best solution. Try different directions until the best one are found. Connect the scanner directly to the antenna and listen while changing directions, or use a remote streaming app, connecting the audio from the scanner to a PC that runs ProScans free streaming app.

/Ubbe
 

KO4IPV

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I've been helping a friend (retired dispatcher) improve the reception on her Uniden 436. She lives in Fairfield County, Ohio and is trying to receive the MARCS digital system. The problem is her location is about ten miles from a MARCS tower to the north and fourteen miles from another MARCS tower to the south. Up until now she has been using an 800 MHz rubber duck on the scanner. Reception is poor.
I installed a Tram 1411 discone with a chimney mount and ran about 65 feet of RG-6 Quad cable. Reception is still disappointing.
Here's my concern: Her house is located about 1500 feet from a cell tower. Could the rf from the cell tower in the 800 MHz range be desensitizing or overpowering the weak MARCS signal?
You might want to try RG- 8 coax my manual for the 436 days that the RG- 8 is a must.
 

iMONITOR

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You might want to try RG- 8 coax my manual for the 436 days that the RG- 8 is a must.
The manual is misleading. RG8 is not a great choice for 800MHz, especially for a long run. Check the chart in post #10. It shows the loss as twice as much than RG6.
 

KO4IPV

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The manual is misleading. RG8 is not a great choice for 800MHz, especially for a long run. Check the chart in post #10. It shows the loss as twice as much than RG6.
Someone out to inform Uniden they’re putting out miss leading information
 
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