SWR and TX power output questions.

[WRCC711]

I have a question or two for people who are way more knowledgeable than me about GMRS base radio set ups. I have a Midland MXT 400 40w GMRS radio paired with a Pyramid ps15k.5 power supply hooked up to a Retevis GMRS base antenna 7.2 dbi uhf repeater antenna mounted on a telescopic 30ft flag pole (because of terrain) , that's my base station set up. I've measured my SWR on lower channels 1-5 at 1.1 the upper channels including repeater channels are measuring 1.81 . Is that an acceptable range for SWR readings? Second question my radio is supposed to have a maximum tx of 40w my meter was showing a maximum of 38 to 37w on the high side.  My radio is a few years old so not new. Is that an acceptable reading? I am using a surecom gam3gear SWR meeter.  

[SteveShannon]

Yes, that’s an acceptable SWR range.

Yes, that’s an acceptable power output. 

[Socalgmrs]

7 minutes ago, WRCC711 said:

I have a question or two for people who are way more knowledgeable than me about GMRS base radio set ups. I have a Midland MXT 400 40w GMRS radio paired with a Pyramid ps15k.5 power supply hooked up to a Retevis GMRS base antenna 7.2 dbi uhf repeater antenna mounted on a telescopic 30ft flag pole (because of terrain) , that's my base station set up. I've measured my SWR on lower channels 1-5 at 1.1 the upper channels including repeater channels are measuring 1.81 . Is that an acceptable range for SWR readings? Second question my radio is supposed to have a maximum tx of 40w my meter was showing a maximum of 38 to 37w on the high side.  My radio is a few years old so not new. Is that an acceptable reading? I am using a surecom gam3gear SWR meeter.  

Swr below 2 is fine.  Sorry to here about the midland but yes on most radios the actuall wattage is less buy 10% or more then advertised 

[WRCC711]

27 minutes ago, Socalgmrs said:

Swr below 2 is fine.  Sorry to here about the midland but yes on most radios the actuall wattage is less buy 10% or more then advertised 

Thanks for answering my questions. I've been wondering if im getting out when I do a radio check . Yeah I would like to upgrade from the Midland. 

[nokones]

2-3 watts is nothing to worry about. How did you check your RF power output? With a meter in-line with an Antenna connected or a Power Terminator connected? If you're using a Power Terminator make sure it measures out at 50 ohms for an accurate reading. Having an antenna connected is not the most accurate method because of the reflected power.

[WRCC711]

2 hours ago, nokones said:

2-3 watts is nothing to worry about. How did you check your RF power output? With a meter in-line with an Antenna connected or a Power Terminator connected? If you're using a Power Terminator make sure it measures out at 50 ohms for an accurate reading. Having an antenna connected is not the most accurate method because of the reflected power.

I did use a meter with a 50 ohm termination load on the end. I wanted to make sure all my readings were OK on my setup.  I wasn't too sure my signal was getting out. Thanks for replying, the missing wattage did have me woried a bit. 

[WRYZ926]

As others have said, getting 37-38 watts out with a 40 watt radio is perfectly fine. A 50 watt radio only putting out 35 watts would be enough to contact the manufacturer and ask questions.

I also would not worry much about having an SWR of 1.8. You will be fine as long as the SWR is 2.0 or below.

[WSEZ864]

3 hours ago, WRYZ926 said:

As others have said, getting 37-38 watts out with a 40 watt radio is perfectly fine. A 50 watt radio only putting out 35 watts would be enough to contact the manufacturer and ask questions.

I also would not worry much about having an SWR of 1.8. You will be fine as long as the SWR is 2.0 or below.

Agreed.

One thing to take notice of is that most GMRS radio marketing statements specify power as "up to x watts", or "as much as x watts" and do not actually state your 40 watt radio will deliver 40 watts.

[Davichko5650]

1 hour ago, WSEZ864 said:

"up to x watts", or "as much as x watts" 

Made me think of the old Mad Magazine quote, "remember that the phrase 'up to' also includes the number zero."

[SteveShannon]

Another thing to consider is the voltage input to the radio. Most mobile radios are rated with an input voltage of 13.8 vDC and the output RF power frequently varies with the voltage. Boost your voltage by a half volt (observing the tolerances listed in the manual) and you might see 41 watts. 
But a variation of one or two watts at that general power will not make a bit of difference in your ability to communicate. 

[WRYZ926]

2 hours ago, WSEZ864 said:

Agreed.

One thing to take notice of is that most GMRS radio marketing statements specify power as "up to x watts", or "as much as x watts" and do not actually state your 40 watt radio will deliver 40 watts.

This goes for amateur radios too. 

 

1 hour ago, SteveShannon said:

Another thing to consider is the voltage input to the radio. Most mobile radios are rated with an input voltage of 13.8 vDC and the output RF power frequently varies with the voltage. Boost your voltage by a half volt (observing the tolerances listed in the manual) and you might see 41 watts. 

This is very true. You will definitely see a different output power when running on a 12V battery versus a 13.8V power supply or when running the radio in a vehicle.. The voltage on newer vehicles can go up to 15.1 volts when charging the battery and are around 14.1 to 14.3 volts under normal driving conditions.

[WSHH887]

Hmm. I worked with power conditioners for control equipment. That was AC. I wonder if they have these for DC. 

[SteveShannon]

14 minutes ago, WSHH887 said:

Hmm. I worked with power conditioners for control equipment. That was AC. I wonder if they have these for DC. 

Look at the Samlex or Astron product lines. There are very tightly regulated and filtered DC power supplies. 

[WSGU500]

I don't mean to hijack the thread but I have a related question regarding SWR and output power. I was using a HYSHIKRA FB22-GMRS 8'6" antenna that lists the gain at 8.5dBi.  With that antenna I was getting SWR readings of 1.01 to 1.28 and over 50 watts (53-56) on the high GMRS channels. I now have a Comet GP-9NC (16'9") antenna that list the gain for GMRS frequencies at 11.9 dBi. With this antenna I am getting SWR readings of 1.41 to 1.58 and 10 watts less power (~43 watts). With just those numbers it seems that the shorter (lower gain antenna) is the better choice. However, according to an online Power Calculator (qsl.net) the longer (higher gain antenna) is the better choice. I realize that this is probably splitting hairs but I wanted to ask since I will be taking down the mast next week to replace the coax cable and redo the guy wires. In case it matters, I am using a 40' telescoping mast next to my house (well above the top of the chimney and highest roofline). Thanks in advance for any constructive input that you guys may have.

HYSHIKRA FB22-GMRS 8'6" antenna at 8.5dBi gain
Effective Radiated Power (ERP) = 23.80465151952302
dBW = 240.14036 Watts 
Effective Isotropic Radiated Power (EIRP) = 25.95309
dBW = 393.83019 Watts 
___________________________________________________

Comet GP-9NC 16'9" antenna at 11.9 dBi
Effective Radiated Power (ERP) = 26.070051519523023
dBW = 404.58069 Watts 
Effective Isotropic Radiated Power (EIRP) = 28.218490000000003
dBW = 663.51233 Watts 

[SteveShannon]

24 minutes ago, WSGU500 said:

I don't mean to hijack the thread but I have a related question regarding SWR and output power. I was using a HYSHIKRA FB22-GMRS 8'6" antenna that lists the gain at 8.5dBi.  With that antenna I was getting SWR readings of 1.01 to 1.28 and over 50 watts (53-56) on the high GMRS channels. I now have a Comet GP-9NC (16'9") antenna that list the gain for GMRS frequencies at 11.9 dBi. With this antenna I am getting SWR readings of 1.41 to 1.58 and 10 watts less power (~43 watts). With just those numbers it seems that the shorter (lower gain antenna) is the better choice. However, according to an online Power Calculator (qsl.net) the longer (higher gain antenna) is the better choice. I realize that this is probably splitting hairs but I wanted to ask since I will be taking down the mast next week to replace the coax cable and redo the guy wires. In case it matters, I am using a 40' telescoping mast next to my house (well above the top of the chimney and highest roofline). Thanks in advance for any constructive input that you guys may have.

HYSHIKRA FB22-GMRS 8'6" antenna at 8.5dBi gain
Effective Radiated Power (ERP) = 23.80465151952302
dBW = 240.14036 Watts 
Effective Isotropic Radiated Power (EIRP) = 25.95309
dBW = 393.83019 Watts 
___________________________________________________

Comet GP-9NC 16'9" antenna at 11.9 dBi
Effective Radiated Power (ERP) = 26.070051519523023
dBW = 404.58069 Watts 
Effective Isotropic Radiated Power (EIRP) = 28.218490000000003
dBW = 663.51233 Watts 

Is it because of the lower SWR that you assume the lower gain antenna would be better?

That little difference in SWR isn’t as likely to make a difference as the gain, assuming the gain is the right direction. 

[WSGU500]

4 minutes ago, SteveShannon said:

Is it because of the lower SWR that you assume the lower gain antenna would be better?

That little difference in SWR isn’t as likely to make a difference as the gain, assuming the gain is the right direction. 

A combination of the lower SWR and the 10 to 13 higher watts is why I was curious if the lower gain antenna would be the better choice.

[SteveShannon]

40 minutes ago, WSGU500 said:

A combination of the lower SWR and the 10 to 13 higher watts is why I was curious if the lower gain antenna would be the better choice.

Not necessarily. But in the bottom portion of your post the higher gain antenna obviously has 70 or 80% more EIRP, so I’m curious why you mention 10-13 higher watts from the lower gain antenna?

[SteveShannon]

3 hours ago, WSGU500 said:

A combination of the lower SWR and the 10 to 13 higher watts is why I was curious if the lower gain antenna would be the better choice.

A gain of 11.9 db is more than twice the gain of 8.5 db when measured in the direction of the gain. So even though 10 less watts enters the antenna, in the direction of the gain twice as much RF power is focused. 
However, if you need an antenna that is less focused, more wide in its propagation pattern, a lower gain antenna might help. 
I’m curious what kind of coax you used when you measured the two different antennas. 
Honestly I would try both antennas to see which one works better. The calculations give an indication but real world usage is better. 

[WSGU500]

4 hours ago, SteveShannon said:

Not necessarily. But in the bottom portion of your post the higher gain antenna obviously has 70 or 80% more EIRP, so I’m curious why you mention 10-13 higher watts from the lower gain antenna?

The 10-13 watt difference is what shows on my SWR/Power meter. I had never heard of ERP/EIRP before doing some research over the last few days. I entered the data from the SWR/Power meter into the online Power Calculator to get the numbers at the bottom of my post. I didn't know if the Power Calculator was what I should go by but sounds like that is the actual power being put out.

[WSGU500]

1 hour ago, SteveShannon said:

A gain of 11.9 db is more than twice the gain of 8.5 db when measured in the direction of the gain. So even though 10 less watts enters the antenna, in the direction of the gain twice as much RF power is focused. 
However, if you need an antenna that is less focused, more wide in its propagation pattern, a lower gain antenna might help. 
I’m curious what kind of coax you used when you measured the two different antennas. 
Honestly I would try both antennas to see which one works better. The calculations give an indication but real world usage is better. 

I am using 50' of LMR400 from the antenna down to the lightning protector and then a 12' RG58 from there to the radio. Monday I will be receiving a 41' and 12' LMR400 to replace those 2 cables. Both antennas seem to perform equally well (as far as I can tell). I can hit a repeater 23 miles away on medium power and reports are that it is strong and clear. I have also had the same report from a simplex contact over 24 miles away in the opposite direction.

Sounds like the numbers indicate the higher gain antenna should be the winner and it performs well so will probably stick with it.

Thank you for your responses - not only in this post but many other posts that I have learned quite a bit from.