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4-5w GMRS Certified Radio?


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#41 mbrun

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Posted 17 August 2020 - 07:59 AM

Lscott, I agree with you on the rubber duck having negative gain. However, I still think that because that antenna can be replaced with one that has substantially higher gain then it becomes possible for ERP limits to be exceeded. And since for channels 8-14 the spec is max ERP, that might be why TX power is set so low.

Oddly, I have yet to use channels 8-14 for any purpose on these radios yet. I can check them against a couple of different brands/models of FRS to see if there is any notable distance difference.


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#42 Lscott

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Posted 17 August 2020 - 10:52 AM

Lscott, I agree with you on the rubber duck having negative gain. However, I still think that because that antenna can be replaced with one that has substantially higher gain then it becomes possible for ERP limits to be exceeded. And since for channels 8-14 the spec is max ERP, that might be why TX power is set so low.
 

Logically I can't see how limiting the output power will prevent exceeding the FCC's ERP limit. Since they have no idea what antenna is going to be attached it's impossible to set a power level that will not violate the rules, unless it's set at zero.

 

You don't even need to attach a gain antenna. A few people have built a corner reflector and just stuck the radio at the right point which results in a higher ERP than what you get out of the radio, even with a fixed mount antenna. The radio is place at the position where the dipole element would go. Then ran a external headset with a conveniently long wire to the accessory input jack on the radio.

 

https://www.qsl.net/ve3rgw/corner.html

 

While not exactly portable its been done for point to point communications.

 

 
 



#43 berkinet

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Posted 17 August 2020 - 11:56 AM

Logically I can't see how limiting the output power will prevent exceeding the FCC's ERP limit. Since they have no idea what antenna is going to be attached it's impossible to set a power level that will not violate the rules, unless it's set at zero.

 

You don't even need to attach a gain antenna. A few people have built a corner reflector and just stuck the radio at the right point which results in a higher ERP than what you get out of the radio, ...

Not to be (too) picky. But, I am pretty sure ERP is measured at the antenna and would therefore not include any external reflectors, etc.

 

The FCC defines ERP as the product of the power supplied to the antenna and the antenna gain (when the power and gain are represented in linear terms).


Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.

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#44 mbrun

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Posted 17 August 2020 - 12:08 PM

Here is FCC Definition of ERP.


https://apps.fcc.gov...ng_number=47469


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#45 Lscott

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Posted 17 August 2020 - 12:20 PM

Not to be (too) picky. But, I am pretty sure ERP is measured at the antenna and would therefore not include any external reflectors, etc.

 

 

So by that definition even a high gain Yagi really wouldn't be violating the rules. There is only one driven element (antenna) everything else is either a director or reflector element.



#46 Lscott

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Posted 17 August 2020 - 12:53 PM

Here is FCC Definition of ERP.


https://apps.fcc.gov...ng_number=47469


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On closer inspection the ERP is based on the field strength of the signal. That's the point people seem to miss. A gain antenna increases the "E-Field", Volts per meter. When the tests are performed the location of the field strength meter has to be specified. 

 

When doing antenna testing on an antenna test range the "E-Field" is measured at various points around the antenna. There are relationships that you can use to calculate power (ERP) based on the "E-Field" strength.

 

  https://en.wikipedia...e_power_density

 

The references below gives a bit more info on how the "E-Field" in Volts/Meter works out to power. Note that a number for the antenna gain is part of the calculations.

 

http://www.bccdc.ca/...ents/Guidelines and Forms/Guidelines and Manuals/EH/EH/Section2Final06062013.pdf

 

http://www.parc.org....ications/=Field strength vs radiated power.pdf

 

https://en.wikipedia..._radiated_power

 

There are two ways of looking at this EIRP, effective isotropic radiated power, and ERP, effective radiated power. The two are not the same. For EIRP it's assume the power is spread uniformly over a sphere, which will only happen using a "theatrical" isotropic antenna.  The other, ERP,  acknowledges that real antennas have some directional properties, thus a higher "E-Field" in some directions verses others. When the "E-Field" is measured then power calculated you will most likely end up with a power higher than what you see at the transmitter's output. That's the antenna's gain.    



#47 Lscott

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Posted 17 August 2020 - 01:06 PM

Hummm. Firefox doesn't cut and past links very well at times. These should work I hope

 

http://www.bccdc.ca/...ents/Guidelines and Forms/Guidelines and Manuals/EH/EH/Section2Final06062013.pdf

 

 

http://www.parc.org....ications/=Field strength vs radiated power.pdf



#48 Lscott

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Posted 17 August 2020 - 01:10 PM

Dang!! This form's software keeps screwing with the URL's, they won't post right. They cut and past OK but when I post the message they get trashed. I'll try one more time.

 

"https://www.google.c...&start=10&sa=N"

 

"http://www.bccdc.ca/...ents/Guidelines and Forms/Guidelines and Manuals/EH/EH/Section2Final06062013.pdf"



#49 Lscott

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Posted 17 August 2020 - 01:28 PM

Well the only way to get this to work is copy the whole URL into the address window up to the ".pdf" part. Then substitute the following for the "...ents" part. Then it should work for the long one.

 

resource-gallery/Documents

 

For the shorter one copy the whole URL into the address window up to the ".pdf" part. Then substitute the following for the "....ications" part. Then it should work for the short one. Don't miss the leading period.

 

.za/publications



#50 mbrun

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Posted 17 August 2020 - 05:13 PM

I have experienced the URL pasting issues in the past too. When I do have such an issue I past the URL in text editor, add quotes around it and then just pasted the quoted text. Quoted text often times prevents the automatic hyper linking. A pain? Yes! But sometimes necessary.


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#51 Lscott

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Posted 17 August 2020 - 08:16 PM

I have experienced the URL pasting issues in the past too. When I do have such an issue I past the URL in text editor, add quotes around it and then just pasted the quoted text. Quoted text often times prevents the automatic hyper linking. A pain? Yes! But sometimes necessary.


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Thanks for the tip. I’ll have to try it the next time. Having the links get messed up sort of ruins things.





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