PRS Power legality questions

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pomtom44

128 posts

Master Geek

#319724 26-May-2025 14:20

Not sure if this is the best forum group to post on, so if not, please move to the correct location
Just couldn't find anything better

Im a recently (ish) licensed ham (amateur radio) and iv started looking into antennas and such.
During this, I came across two different high gain antennas for PRS, one at 6db gain and one at 10db gain

PRS as far as I am aware is limited to 5W output, and looking at the RSM documentation its listed at 9.2 eirp

the 10db antenna states in the listing "get 56w out from 5w in"

And while i know the 56 will be the "theoretical" output, it is still way over the 9w eirp listed in the GRUL
Am i missing something here?
Or is that legal to operate?

And yes, i understand unless im causing interference somewhere, likely no one will care as no one will complain, but im still interested in how this works in terns of what is and isn't allowed

mentalinc

3229 posts

Uber Geek

Trusted

#3376902 26-May-2025 14:24

@MuzaNZ based on the ham cram weekend posts prob best placed to answer?

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rp1790

738 posts

Ultimate Geek

Lifetime subscriber

#3376935 26-May-2025 15:33

Perhaps provide the links to the antennas you're referencing so we can have a look. I don't see how any antenna can amplify the actual power output of the PRS handheld, it's the radio itself that provides the power output. Sounds like an overly excessive claim from the antenna company to say "it's like a radio transmitting at xx watt's".

pomtom44

128 posts

Master Geek

#3377036 26-May-2025 16:18

rp1790:

Perhaps provide the links to the antennas you're referencing so we can have a look. I don't see how any antenna can amplify the actual power output of the PRS handheld, it's the radio itself that provides the power output. Sounds like an overly excessive claim from the antenna company to say "it's like a radio transmitting at xx watt's".

https://techoman.co.nz/products/techoman-uhf-prs-477-mhz-high-gain-6-5dbi-tuned-base-fibreglass-antenna?srsltid=AfmBOorCWxzwdgTJxWIRZIaaB9T1vZKC1RTvGGaYjZTeiLovG_C-98x4
and
https://techoman.co.nz/collections/uhf-prs-476-477-mhz/products/techoman-477mhz-base-fibreglass-10-5dbi-antenna-477mhz-uhf-prs-band

tweake

2391 posts

Uber Geek

#3377103 26-May-2025 20:16

pomtom44:

Not sure if this is the best forum group to post on, so if not, please move to the correct location
Just couldn't find anything better

Im a recently (ish) licensed ham (amateur radio) and iv started looking into antennas and such.
During this, I came across two different high gain antennas for PRS, one at 6db gain and one at 10db gain

PRS as far as I am aware is limited to 5W output, and looking at the RSM documentation its listed at 9.2 eirp

the 10db antenna states in the listing "get 56w out from 5w in"

And while i know the 56 will be the "theoretical" output, it is still way over the 9w eirp listed in the GRUL
Am i missing something here?
Or is that legal to operate?

And yes, i understand unless im causing interference somewhere, likely no one will care as no one will complain, but im still interested in how this works in terns of what is and isn't allowed

what does your license limit? the power out of the radio or the rf output of the antenna?

i did an install many many decades ago where the license limits the rf output of the aerial. so a higher gain aerial means you have to reduce your power input into it.

elpenguino

3423 posts

Uber Geek

#3377110 26-May-2025 22:01

rp1790:

Perhaps provide the links to the antennas you're referencing so we can have a look. I don't see how any antenna can amplify the actual power output of the PRS handheld, it's the radio itself that provides the power output. Sounds like an overly excessive claim from the antenna company to say "it's like a radio transmitting at xx watt's".

The quoted gain is usually compared to an omni directional antenna.

And because the gain is directional, you will get more signal than before , but only in the direction with gain. In other directions, you'll get less.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

pomtom44

128 posts

Master Geek

#3377121 27-May-2025 06:14

tweake:

what does your license limit? the power out of the radio or the rf output of the antenna?

i did an install many many decades ago where the license limits the rf output of the aerial. so a higher gain aerial means you have to reduce your power input into it.

In the GURL license, it states it is output of the antenna (EIRP) at the 9.6dbw , but all the public documentation, links, manufatureres etc, states 5W for the handhelds (which I cant find any reference to anywhere)

pomtom44

128 posts

Master Geek

#3377122 27-May-2025 06:15

elpenguino:

rp1790:

Perhaps provide the links to the antennas you're referencing so we can have a look. I don't see how any antenna can amplify the actual power output of the PRS handheld, it's the radio itself that provides the power output. Sounds like an overly excessive claim from the antenna company to say "it's like a radio transmitting at xx watt's".

The quoted gain is usually compared to an omni directional antenna.

And because the gain is directional, you will get more signal than before , but only in the direction with gain. In other directions, you'll get less.

However both the antennas I have linked are omni as well.
Makes sense if its going from omni to directional, but omni to omni is apples to apples, and again falls outside my understanding of the legal limits

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elpenguino

3423 posts

Uber Geek

#3377157 27-May-2025 10:19

pomtom44:

However both the antennas I have linked are omni as well.
Makes sense if its going from omni to directional, but omni to omni is apples to apples, and again falls outside my understanding of the legal limits

Hmm, could still be different radiation patterns such as doughnut vs very squashed doughnut. You'd have to have documented radiation patterns to compare.

An alternative is , yes, a little stretching of the truth.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

elpenguino

3423 posts

Uber Geek

#3377166 27-May-2025 10:45

pomtom44:

And while i know the 56 will be the "theoretical" output, it is still way over the 9w eirp listed in the GRUL
Am i missing something here?
Or is that legal to operate?

And yes, i understand unless im causing interference somewhere, likely no one will care as no one will complain, but im still interested in how this works in terns of what is and isn't allowed

I looked at a gazette notice (couldnt find the PRS one) and I see all bands licensed with the footnote.

The maximum power is the radiated power in dBW e.i.r.p.

The 'i' is for isotropic (all directions, equally ) which means ,yes, if you transmit full power and use an antenna with gain (gain is quoted as 'dBi') , you will exceed the permitted ERP.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21