SWR of 1.75, can i do better or leave it as is?

[TxHunter777]

Hello All!

New to GMRS and having a blast learning and getting gear together. I recently did a install on Gen 3 Tacoma and I am getting a SWR of 1.75. Below is my build. Looking for some suggestions on how to get the SWR a bit lower, or being what it is, maybe just accept the 1.75 and call it good. Appreciate all suggestions!

 

Equipment Utilized:

Btech GMRS50-Pro - https://baofengtech.com/product/gmrs-50pro/

Midland MXTA24 NMO - https://www.amazon.com/dp/B0842B1WFS

MIdland MXTA26 Antenna - https://www.amazon.com/dp/B084BPXNC5

Ditch Light Bracket - https://www.amazon.com/dp/B0FG7P4DWY With a 3/8" Stainless Steel washer for fitment. 

Surcom Sw-102S - https://www.amazon.com/dp/B01M7QPXEY

 

NMO Mount to Ditch bracket. Recognize the antenna is not perfectly straight up and is at an angle, I'll try to figure out how to get this mount more straight up, but the way my ditch light bracket is, this may not be easily achievable. 

 

 

 

 

I then ran it across the engine bay and then into the cabin through a gromet. 

 

Both the power and NMO cable were tucked under panels.

 

I then created a mount for the BTECH GMRS50-PRO and connected everything behind the drivers side backseat storage. 

 

 

 

Current readings on meter.

 

Once BTECH releases their Mic extension, i will run the mic extension wire from the back panel to the front drivers seat, so i can control the whole radio via the BTECH mic remote. 

 

Thanks!

[TxHunter777]

Ah i see now. No it is a LED ditch light which is on the truck. can't see the entire light in this photo, but you can see how the bracket shares the mount. 

[TxHunter777]

Just noticed as well, in my original post i did have a photo showing the setup.

 

[WSHH887]

I also have a Gen 3 Tacoma.  I should take photos.  I mounted the mxta26 on an nmo mount attached to a bracket that mounts to the rear of the bed.  I ran the  coax under the lip of the bed and then through the drivers side pressure vent on the rear of the cab.  Then down and under the panels on the door frame to the front of the cab, across under the drivers seat and to the radio.  No holes were drilled, and the SWR is 1.01.  My bed cover is a multiple section accordion folding type made of aluminum.  I've seen a few other installations, but all required drilling holes.  While I've done that with my Jeep I'm avoiding it on my other vehicles.

[jwilkers]

I also have a Gen 3 Tacoma.  I should take photos.  I mounted the mxta26 on an nmo mount attached to a bracket that mounts to the rear of the bed.  I ran the  coax under the lip of the bed and then through the drivers side pressure vent on the rear of the cab.  Then down and under the panels on the door frame to the front of the cab, across under the drivers seat and to the radio.  No holes were drilled, and the SWR is 1.01.  My bed cover is a multiple section accordion folding type made of aluminum.  I've seen a few other installations, but all required drilling holes.  While I've done that with my Jeep I'm avoiding it on my other vehicles.

Leave it as is. You'll be fine.

Sent from my SM-S911U1 using Tapatalk

[WRKC935]

I see this question so often that this almost needs to be a direct post about it so it can be referenced.

I came up from CB radio many years ago where guys would think that if they had a 1:1 match that they had somehow accomplished something almost magical and akin to hitting the lottery.  Or they would brag about how they had a 1 to 1 match and how great their radio system worked and nothing could come close to it's performance. 

The truth is far less dramatic than that.  And when you really start to understand signal levels, delta of signal levels, meaning how much difference in signal level A from signal level B actually is and what the perceived and actual effects of that level difference is, you quickly find out that it ain't much.

Now you meter actually SHOWS the percentage of signal forward VS reflected which is SWR.

SWR is the RATIO of forward vs reflected power.  Of course reflected power is power that is NOT being radiated by the antenna.  Some same it backs up to the radio and is burnt off as heat, others will tell you it reflects from the radio back to the antenna and is then radiated (which is BS and due to phase changes would really DECREASE your signal) and there are a few other stories out there of what becomes of the reflected power..  but the crux of it is, it's not going out the antenna as signal.

So then we get into the discussion of decibel or dB.  And here's where the rubber really hits the road.  Because while the radio is rated in WATTS for transmit, the receiver is rated in dBm for receive.  And the whole idea of GMRS radio is talking to others.  The other guys receiver is what you are trying to effect a response from. And NO amount of power matters if there is no one listening on the other end.  That is referred to HAM radio at this point... no one listening.

So a cool little tidbit of radio is that wattage can also be expressed as dBm.  Now, some might know something of decibels from school and that it's a logarithmic number that is a delta or difference from some other value.  That's where the little 'm' comes in on dBm.  The 'm' in this case is 1 milliwatt and it equals 0 dBm.  so the 'm' sets the reference point of the delta.  Positive numbers are values above 1 milliwatt and negative numbers are values BELOW 1 milliwatt. So then we can start looking at something recogniziable.

0dBm = 1 milliwatt  0.001 watt

30dBm = 1 watt

33dBm = 2 watts

36dBm = 4 watts

39dBm = 8 watts

42dBm = 16 watts

50dBm=100 watts

60dBm = 1000 watts

Couple things to see here.   A change of 3dB is double / half the original power.  10dB adds or removes a zero from the value and 30dB of change is 1000 times or 3 zeros  So for every 10 dB of change, you add or subtract a zero or move the decimal place up or down.

Now we have that established.  We can get into receivers and receiver sensitivity.

Most GMRS radios are going to hear down to -115 to -120dBm range.  Now that's pretty wide, but that range covers from the crappiest radio to the best UHF receivers you will find.  Then we get to the 12dB Sinad which is a 12dB signal to noise ratio receiver test.  This is the intelligible signal (receive audio) being 12dB above the background noise in the sound coming out the speaker.  Still has some noise but is fully understandable.  This falls around -108 to -105.  Then there is full quieting at -100 to -90.  That is a dead silent signal where only the intelligence (spoken word) is heard in the receiver.  These are in 10dB hops.  Remember the 10 dB rule right.  It's a signal level change factor of 10, one decimal place.  Obviously smaller changes can be measured with test equipment.  But your NOT going to HEAR a difference in the speaker with less change than the 10 dB hop. 

So NOW we get to SWR.  And we start looking at signal change based on SWR or 1.5 , 1.75, 2, and 3.  Anything over 3 is bad.  And it's not really effecting the signal levels mean as much as it's creating a problem for the radio that's transmitting.

All numbers are based on 100 watts transmit power.

1.50 : 1 SWR is 4 watts reflect and 96 watts radiated  or a 0.1773dB difference from  a 1 : 1 match

1.75 : 1 SWR is 6.7 watts reflect and 93 watts radiated or a 0.3152dB difference from a 1 : 1 match

2.00 : 1 SWR is 11 watts reflect and 89 watts radiated or a 0.5061dB difference from a 1 : 1 match

3.00 : 1 SWR is 25 watts reflect and 75 watts radiated or a 1.25dB difference from a 1 : 1 match

SO... it takes a signal change of 10dB to HEAR it, and these changes are less than 1dB change until you get out in dangerous territory.  So from a perfect match to a 2 : 1 match makes basically NO difference in the signal the other guy hears.

These are the numbers.  All this is on the web, and yes I use a calculator for it because math SUCKS.  But it doesn't lie. 

But this is how I can sit down and figure out if you give me distance, antenna gain at both ends, cable loss at both ends and receive signal strength, I can tell you how much power you are running.  There are some other things not mentioned like path loss that are taken into account (that's the distance portion) but it's all numbers once you have a good understanding of it.

 

[AdmiralCochrane]

2 hours ago, WRKC935 said:

I see this question so often that this almost needs to be a direct post about it so it can be referenced.

I came up from CB radio many years ago where guys would think that if they had a 1:1 match that they had somehow accomplished something almost magical and akin to hitting the lottery.  Or they would brag about how they had a 1 to 1 match and how great their radio system worked and nothing could come close to it's performance. 

The truth is far less dramatic than that.  And when you really start to understand signal levels, delta of signal levels, meaning how much difference in signal level A from signal level B actually is and what the perceived and actual effects of that level difference is, you quickly find out that it ain't much.

Now you meter actually SHOWS the percentage of signal forward VS reflected which is SWR.

SWR is the RATIO of forward vs reflected power.  Of course reflected power is power that is NOT being radiated by the antenna.  Some same it backs up to the radio and is burnt off as heat, others will tell you it reflects from the radio back to the antenna and is then radiated (which is BS and due to phase changes would really DECREASE your signal) and there are a few other stories out there of what becomes of the reflected power..  but the crux of it is, it's not going out the antenna as signal.

So then we get into the discussion of decibel or dB.  And here's where the rubber really hits the road.  Because while the radio is rated in WATTS for transmit, the receiver is rated in dBm for receive.  And the whole idea of GMRS radio is talking to others.  The other guys receiver is what you are trying to effect a response from. And NO amount of power matters if there is no one listening on the other end.  That is referred to HAM radio at this point... no one listening.

So a cool little tidbit of radio is that wattage can also be expressed as dBm.  Now, some might know something of decibels from school and that it's a logarithmic number that is a delta or difference from some other value.  That's where the little 'm' comes in on dBm.  The 'm' in this case is 1 milliwatt and it equals 0 dBm.  so the 'm' sets the reference point of the delta.  Positive numbers are values above 1 milliwatt and negative numbers are values BELOW 1 milliwatt. So then we can start looking at something recogniziable.

0dBm = 1 milliwatt  0.001 watt

30dBm = 1 watt

33dBm = 2 watts

36dBm = 4 watts

39dBm = 8 watts

42dBm = 16 watts

50dBm=100 watts

60dBm = 1000 watts

Couple things to see here.   A change of 3dB is double / half the original power.  10dB adds or removes a zero from the value and 30dB of change is 1000 times or 3 zeros  So for every 10 dB of change, you add or subtract a zero or move the decimal place up or down.

Now we have that established.  We can get into receivers and receiver sensitivity.

Most GMRS radios are going to hear down to -115 to -120dBm range.  Now that's pretty wide, but that range covers from the crappiest radio to the best UHF receivers you will find.  Then we get to the 12dB Sinad which is a 12dB signal to noise ratio receiver test.  This is the intelligible signal (receive audio) being 12dB above the background noise in the sound coming out the speaker.  Still has some noise but is fully understandable.  This falls around -108 to -105.  Then there is full quieting at -100 to -90.  That is a dead silent signal where only the intelligence (spoken word) is heard in the receiver.  These are in 10dB hops.  Remember the 10 dB rule right.  It's a signal level change factor of 10, one decimal place.  Obviously smaller changes can be measured with test equipment.  But your NOT going to HEAR a difference in the speaker with less change than the 10 dB hop. 

So NOW we get to SWR.  And we start looking at signal change based on SWR or 1.5 , 1.75, 2, and 3.  Anything over 3 is bad.  And it's not really effecting the signal levels mean as much as it's creating a problem for the radio that's transmitting.

All numbers are based on 100 watts transmit power.

1.50 : 1 SWR is 4 watts reflect and 96 watts radiated  or a 0.1773dB difference from  a 1 : 1 match

1.75 : 1 SWR is 6.7 watts reflect and 93 watts radiated or a 0.3152dB difference from a 1 : 1 match

2.00 : 1 SWR is 11 watts reflect and 89 watts radiated or a 0.5061dB difference from a 1 : 1 match

3.00 : 1 SWR is 25 watts reflect and 75 watts radiated or a 1.25dB difference from a 1 : 1 match

SO... it takes a signal change of 10dB to HEAR it, and these changes are less than 1dB change until you get out in dangerous territory.  So from a perfect match to a 2 : 1 match makes basically NO difference in the signal the other guy hears.

These are the numbers.  All this is on the web, and yes I use a calculator for it because math SUCKS.  But it doesn't lie. 

But this is how I can sit down and figure out if you give me distance, antenna gain at both ends, cable loss at both ends and receive signal strength, I can tell you how much power you are running.  There are some other things not mentioned like path loss that are taken into account (that's the distance portion) but it's all numbers once you have a good understanding of it.

 

Excellent