Maybe I miscalculated

[ROBV60schwifty]

Im afraid I may have misunderstood the transmit power restrictions and could use some clarification. My setup:

Radioddity db25-G @25W used as a base station , probably more like 18W in reality, but I do not know for sure as I do not have the tools to test.

18' run of LMR400 to the attic, which effectively places the antenna roughly 20 'from the ground in my house.

Antenna is the Slim Jim from https://www.jpole-antenna.com/shop/uhf-440-470-mhz-slim-jim-antenna/ tuned to 465MHz, with a claimed gain of 6dBi, which to my understanding equates to ~3.85 dBd (?)

Using the calculator below, using an SWR of 1.5, I do not know the actual SWR just yet, I used this as a middle-ground, doesn't make a notable difference on the calculator

https://kv5r.com/ham-radio/coax-loss-calculator/

These numbers given above result in an ERP of just under 50W when using 20W as the transmitter output, again probably figuring high. I was calculating off of the 50W transmit power limitation, but saw a couple write-ups a few minutes ago that have me confused about the power limitations for TX with this set up, as it relates to ERP.  Its a wording issue Im having trouble with, essentially. Is there any difference between the radio's power and the "ERP" out of the ANT?  Am I able to transmit and receive on channels 15-22, and equivalent repeater channels when my ERP is <50W, after cable loss and ANT gain are taken into account?  Or does my power need to be no more than 50W at the radio? Does that make any sense?

 

[SteveShannon]

9 minutes ago, ROBV60schwifty said:

Or does my power need to be no more than 50W at the radio?

This ^

But it depends on the channels.  Some channels don't allow that much and some channels require ERP calculations.

§ 95.1767 GMRS transmitting power limits.

This section contains transmitting power limits for GMRS stations. The maximum transmitting power depends on which channels are being used and the type of station.

(a) 462/467 MHz main channels. The limits in this paragraph apply to stations transmitting on any of the 462 MHz main channels or any of the 467 MHz main channels. Each GMRS transmitter type must be capable of operating within the allowable power range. GMRS licensees are responsible for ensuring that their GMRS stations operate in compliance with these limits.

   (1) The transmitter output power of mobile, repeater and base stations must not exceed 50 Watts.

   (2) The transmitter output power of fixed stations must not exceed 15 Watts. (You'll probably never need to know this)

(b) 462 MHz interstitial channels. The effective radiated power (ERP) of mobile, hand-held portable and base stations transmitting on the 462 MHz interstitial channels must not exceed 5 Watts.

(c) 467 MHz interstitial channels. The effective radiated power (ERP) of hand-held portable units transmitting on the 467 MHz interstitial channels must not exceed 0.5 Watt. Each GMRS transmitter type capable of transmitting on these channels must be designed such that the ERP does not exceed 0.5 Watt.

[WRXP381]

50w at the radio.  That is why it’s totally ok for guys to run 50w radios and 12db gain yaggis. 

[ROBV60schwifty]

1 hour ago, WRXP381 said:

50w at the radio.  That is why it’s totally ok for guys to run 50w radios and 12db gain yaggis. 

So Im OK with my ERP at just below 50 on the repeater channels? I was trying to find a combo that between cable loss, antenna gain and the wattage at the radio would net me as close to 50W as possible without going over 50 because I thought that was THE limit after ANT gain. Are you saying people are running WAY more then 50W TX ERP, because all that matters is that the radio itself isn't putting out ore than 50W? In other words, I could have a 50W radio, the maximum allowed, and boost it with a 12dbi ANT to WAY over 50W, and be fine because the RADIO is only rated for 50W? Am I over thinking this?

[ROBV60schwifty]

1 hour ago, Sshannon said:

This ^

But it depends on the channels.  Some channels don't allow that much and some channels require ERP calculations.

Im only really interested in repeater channels when using this setup as a base station, so I should be more than fine at the ERP ~43W output? Any other time Ill either be using a hand-held, or the DB25G will be mobile in the car. Which in that case I'd probably still be using RPT or 15-22, standard channels.

[WRXP381]

1 hour ago, ROBV60schwifty said:

So Im OK with my ERP at just below 50 on the repeater channels? I was trying to find a combo that between cable loss, antenna gain and the wattage at the radio would net me as close to 50W as possible without going over 50 because I thought that was THE limit after ANT gain. Are you saying people are running WAY more then 50W TX ERP, because all that matters is that the radio itself isn't putting out ore than 50W? In other words, I could have a 50W radio, the maximum allowed, and boost it with a 12dbi ANT to WAY over 50W, and be fine because the RADIO is only rated for 50W? Am I over thinking this?

Yes on the proper channels as already stated and you’re not running an amp.   Just 50w out of the radio to the antenna and you’re good.   Heck you can even run a 5w radio with a 50w amp.   Then the antenna can be what ever you want.  I run a 20w base with a 9db antenna and get over 200miles.  A friend runs a 50w radio and a 12db gain yagi directional antenna and does VERY well for distance but only in one direction.