Thoughts on BTECH U25 AMP?

[WRVG593]

So I attached my GMRS Radio to the BTECH-U25 AMP (2-6W Input = 20-40W Output) as well as a Nagoya Magnetically Mounted UT-72 on top of my car. I Don't understand why, but I get more power when i'm using a stubby antennae than when I Use my Amp!!! Can't Figure out why! Any help would be wonderful. 

The Radio cannot be the issue as itself is extremely useful and has great receiving as well as output. I've Returned the original U25 Because it was Broken (Grr!) and the Nagoya UT72 was... less than expected. Any help would be great!

[SteveShannon]

1 minute ago, WRVG593 said:

So I attached my GMRS Radio to the BTECH-U25 AMP (2-6W Input = 20-40W Output) as well as a Nagoya Magnetically Mounted UT-72 on top of my car. I Don't understand why, but I get more power when i'm using a stubby antennae than when I Use my Amp!!! Can't Figure out why! Any help would be wonderful. 

The Radio cannot be the issue as itself is extremely useful and has great receiving as well as output. I've Returned the original U25 Because it was Broken (Grr!) and the Nagoya UT72 was... less than expected. Any help would be great!

What do you mean by "I get more power?"  How are you measuring the "power" you're getting?

Or do you simply mean that others receive you better?  Clearer? Louder? Or are you actually measuring the power output where it feeds into the antenna?  

So: GMRS Radio -> U25 -> UT-72 gives you less power than GMRS Radio -> UT-72?

Or GMRS Radio -> U25 -> UT-72 gives you less power than GMRS Radio -> Unknown stubby antenna

Have you tried using GMRS Radio -> U25 -> Unknown stubby antenna?  How does that compare?

What's the SWR of the UT-72 at the frequency you're transmitting?

What does the amp's SWR look like to the radio?

If you're truly measuring power (watts) using the U25 and UT-72 combination, and it's less than measured power going into the stubby antenna, where are you measuring?  

Assuming they're both the same measurement point (right at the antenna) then it could be bad feedline, bad amp, or bad antenna: high SWR on antenna (reflected power subtracts from forward power).

 

[WRVG593]

31 minutes ago, Sshannon said:

What do you mean by "I get more power?"  How are you measuring the "power" you're getting?

Or do you simply mean that others receive you better?  Clearer? Louder? Or are you actually measuring the power output where it feeds into the antenna?  

So: GMRS Radio -> U25 -> UT-72 gives you less power than GMRS Radio -> UT-72?

Or GMRS Radio -> U25 -> UT-72 gives you less power than GMRS Radio -> Unknown stubby antenna

Have you tried using GMRS Radio -> U25 -> Unknown stubby antenna?  How does that compare?

What's the SWR of the UT-72 at the frequency you're transmitting?

What does the amp's SWR look like to the radio?

If you're truly measuring power (watts) using the U25 and UT-72 combination, and it's less than measured power going into the stubby antenna, where are you measuring?  

Assuming they're both the same measurement point (right at the antenna) then it could be bad feedline, bad amp, or bad antenna: high SWR on antenna (reflected power subtracts from forward power).

 

So I'm Brand New to GMRS, but let me clarify a few things. 

I Unfortunately do not yet own an SWR Meter, Working on that, so when i say power I didn't mean Wattage or even a measured amount of anything. I realistically meant the ability to hit other repeaters, reach people in the area, etc. 

The Antennae in question was one of 3 that work roughly as good as each-other. I Have a stock 5(?) inch Antennae, a 48 Inch Antennae, and A 15 inch Whip Antennae, all of which work about as well as each-other. I receive and transmit better when I'm not using the AMP/UT72 Combo. I have yet to place another Antennae up to the U25. I am going to hook up the UT72 to the radio later today and see what happens. Maybe then I can diagnose it as being an antennae issue rather than an amp issue. 

There was a while the microphone i was using was causing bad transmission, but I ended up using the radio itself instead, and that cleared up part of the issue. But even when I found the repeater, for Test purposes I used the radio right underneath and to no surprise got great results and got a repeater tail as well as a human copy. But when I plugged up to the U25 Amp, it almost seemed as a threshold more than an Amp, dimming the power instead of increasing.  

TLDR; I don't yet have a way to measure power, but after testing the radio in the field, the radio by itself transmits and receives better without the U25/UT72 Combo. 

[Bande1]

one of the things is the UT-72 is a dual band ham antenna. its going to be less good on UHF than a dedicated UHF antenna. I have that antenna and Ive ditched it for a used diamond MR-77 I found for $10.

I bought one of those amps and the first one just quit working. sent it back got and the second one worked but I could barely tell a difference in performance. next to my 50w mobile radio the amp and handheld combined was a FAR cry. I sent the amp back. 

I have also gone back to only running my stock rubber ducky on my radio. frankly it outperforms every aftermarket I ever bought BESIDES a motorola someone gave me. That thing is phenominal. I hear comet makes a 9" antenna thats good.

another thing Ive realized is all these amazon brands are like cheap toys. look at real ham brands. comet, hustler, diamond, larson, etc. except for the abbree on VHF those are actually pretty good.

my advice is to send the amp back and get a 25w mobile radio. better yet get a crossband radio that will link your handheld in U-U like a TYT TH-9800, Alinco DR-735T, Wouxon KG-UV920, etc and you can go into stores and whatnot, transmit out to your vehicle, and then to a repeater. 

[WRVG593]

My First U25 pooped out too! Then my second one makes strange noises when plugged up to a 12V that isnt a full 13.8V power supply which didn't happen on the first one. Strange, crazy, and annoying. Maybe i'll just keep the U25 in my Garage and hopefully it will be okay and hook up to my House Antennae okay.

[wrtq652]

I can see from the post above a Standing Wave Ratio (SWR) meter wasn't available at the time and checking the SWR was suggested. It would be worth taking a look at the SWR when a meter becomes available.

I'm curious to know if anyone is checking the Standing Wave Ratio (SWR) between the BTECH-U25 AMP and the antenna after swapping the feed line from the handheld to the BTECH-U25?

Having an antenna with a low SWR would allow the most output power to be sent through the antenna.  I'm curious as to what reflected power the BTECH-U25 is able to handle and if it has any protection circuitry built into it, for example to reduce the output power if the reflected power at the transmitter is too high.

It's reasonable to say a high reflected power for a handheld is going to be under 5 watts, as we go up in power closer to 40W, the reflected power of a poor SWR match may be enough to damage the amplifier.  A properly matched antenna/feed line is going to be important as the wattage increases so the reflected power will not damage the finals of the amplifier.  (Also be sure the SWR meter in use is rated for the GMRS band (~462MHz - ~468MHz) / (UHF)).

 

A good description of safe ranges for radios SWRs is posted on the CB World website.  The article describes best practices for SWR common to antennas.

SWR 1.0-1.5: The ideal range!

SWR 1.5 - 1.9: There's room for improvement, but SWR in this range should still provide adequate performance.

SWR 2.0 - 2.4: While not good, this likely won't damage your radio with casual use.

SWR 2.5 - 2.9: Performance in this range will be noticeably decreased, and you might even damage your radio if you transmit frequently and for extended periods.

SWR 3.0+: Performance will be severely affected, and you're likely to damage your radio with extended transmission use.

 

The second item worth mentioning is having a stable input voltage and power delivery for the amplifier power supply.  The BTECH website lists the power draw at "13.8 VDC (±15%), 5.5 A maximum" (BTECH, 2022), another test indicates 13.6V 30A power supply was just under 6A (Miklor, 2022).  Two of the most common problems with installing radios and amplifiers are SWR and proper power supply voltage (Shannon, 2022).  Testing the voltage at the power supply to the amplifier to be sure it's receiving the proper voltage at 13.8 volts would allow the amplifier to deliver the most power to the transmitted signal. 

There's a good discussion of the input voltage to the radio, related to a different transmitter, and how a 3.5volt to 4 volt drop was seen when transmitting at the radio/amplifier side of the connection contributing to undesirable transmitting results (Spatz, 2022).

A direct to battery connection would make it more likely the amplifier is operating at the correct voltage, at least the power connection would be isolated to power draw from the amplifier.  A fused power connection directly to the battery and into the passenger compartment or to where the BTECH-U25 amplifier is located would be ideal.  The connection to the battery could have a cigarette lighter input adapter attached to it, to make the install of the BTECH-U25 easier to plug in or move to another location.

 

Thanks @WRVG593 for sharing your install story and I wish you the best in getting the BTECH-U25 installed. Keep us updated if you decide to move the amplifier again and how it all works out for you! I'm curious to know how the 2nd choice for the install location works out if you decide to go that route?

 

 

References:

BTECH AMP-U25 UHF analog amplifier. BaoFeng Radios. (2022, December 12). Retrieved December 19, 2022, from https://baofengtech.com/product/amp-u25/

CB World. (n.d.). What is SWR and why is it SO important? . CB World. Retrieved December 19, 2022, from https://www.wearecb.com/what-is-swr.html

Miklor, J. (n.d.). Review btech power amp. Miklor. Retrieved December 19, 2022, from https://www.miklor.com/COM/Review_DMR-Amps.php

Shannon, S. (2022, December 19). KG-XS20G Plus problem. myGMRS.com Forums. Retrieved December 20, 2022, from https://forums.mygmrs.com/topic/4932-kg-xs20g-plus-problem/#comment-48811

Spatz, M. (2022, December 19). KG-XS20G Plus problem. myGMRS.com Forums. Retrieved December 20, 2022, from https://forums.mygmrs.com/topic/4932-kg-xs20g-plus-problem/#comment-48819

 

[Bande1]

replying to wrtq652 my btech amp was in fact ran with an SWR meter. it generally drove the swr up from 1.01:1 to maybe 1.3:1 or there about.

I read my first post again let me clarify the amp vs mobile. the mobile heard a repeater when the handheld + amp did not on same antennas. I would key up a repeater with the amp and hear nothing. but the mobile would hear the repeater tone. I hit the repeater but heard absolutely nothing back through the radio. It was as if my handheld was deaf. but really easy and close repeaters would come through. like ones under 10 miles away.

I also tested the amp with a simplex and found some difference, very marginal. I would radio check with amp off, then radio check with amp on. It gave me maybe a 10-15% difference at the edge of range.

[WRUT935]

On 12/20/2022 at 1:40 AM, wrtq652 said:

I can see from the post above a Standing Wave Ratio (SWR) meter wasn't available at the time and checking the SWR was suggested. It would be worth taking a look at the SWR when a meter becomes available.

I'm curious to know if anyone is checking the Standing Wave Ratio (SWR) between the BTECH-U25 AMP and the antenna after swapping the feed line from the handheld to the BTECH-U25?

Having an antenna with a low SWR would allow the most output power to be sent through the antenna.  I'm curious as to what reflected power the BTECH-U25 is able to handle and if it has any protection circuitry built into it, for example to reduce the output power if the reflected power at the transmitter is too high.

It's reasonable to say a high reflected power for a handheld is going to be under 5 watts, as we go up in power closer to 40W, the reflected power of a poor SWR match may be enough to damage the amplifier.  A properly matched antenna/feed line is going to be important as the wattage increases so the reflected power will not damage the finals of the amplifier.  (Also be sure the SWR meter in use is rated for the GMRS band (~462MHz - ~468MHz) / (UHF)).

 

A good description of safe ranges for radios SWRs is posted on the CB World website.  The article describes best practices for SWR common to antennas.

SWR 1.0-1.5: The ideal range!

SWR 1.5 - 1.9: There's room for improvement, but SWR in this range should still provide adequate performance.

SWR 2.0 - 2.4: While not good, this likely won't damage your radio with casual use.

SWR 2.5 - 2.9: Performance in this range will be noticeably decreased, and you might even damage your radio if you transmit frequently and for extended periods.

SWR 3.0+: Performance will be severely affected, and you're likely to damage your radio with extended transmission use.

 

The second item worth mentioning is having a stable input voltage and power delivery for the amplifier power supply.  The BTECH website lists the power draw at "13.8 VDC (±15%), 5.5 A maximum" (BTECH, 2022), another test indicates 13.6V 30A power supply was just under 6A (Miklor, 2022).  Two of the most common problems with installing radios and amplifiers are SWR and proper power supply voltage (Shannon, 2022).  Testing the voltage at the power supply to the amplifier to be sure it's receiving the proper voltage at 13.8 volts would allow the amplifier to deliver the most power to the transmitted signal. 

There's a good discussion of the input voltage to the radio, related to a different transmitter, and how a 3.5volt to 4 volt drop was seen when transmitting at the radio/amplifier side of the connection contributing to undesirable transmitting results (Spatz, 2022).

A direct to battery connection would make it more likely the amplifier is operating at the correct voltage, at least the power connection would be isolated to power draw from the amplifier.  A fused power connection directly to the battery and into the passenger compartment or to where the BTECH-U25 amplifier is located would be ideal.  The connection to the battery could have a cigarette lighter input adapter attached to it, to make the install of the BTECH-U25 easier to plug in or move to another location.

 

Thanks @WRVG593 for sharing your install story and I wish you the best in getting the BTECH-U25 installed. Keep us updated if you decide to move the amplifier again and how it all works out for you! I'm curious to know how the 2nd choice for the install location works out if you decide to go that route?

 

 

References:

BTECH AMP-U25 UHF analog amplifier. BaoFeng Radios. (2022, December 12). Retrieved December 19, 2022, from https://baofengtech.com/product/amp-u25/

CB World. (n.d.). What is SWR and why is it SO important? . CB World. Retrieved December 19, 2022, from https://www.wearecb.com/what-is-swr.html

Miklor, J. (n.d.). Review btech power amp. Miklor. Retrieved December 19, 2022, from https://www.miklor.com/COM/Review_DMR-Amps.php

Shannon, S. (2022, December 19). KG-XS20G Plus problem. myGMRS.com Forums. Retrieved December 20, 2022, from https://forums.mygmrs.com/topic/4932-kg-xs20g-plus-problem/#comment-48811

Spatz, M. (2022, December 19). KG-XS20G Plus problem. myGMRS.com Forums. Retrieved December 20, 2022, from https://forums.mygmrs.com/topic/4932-kg-xs20g-plus-problem/#comment-48819

 

I have been using my BTECH U25 with my Wouxun KG-UV9G Pro (5+ watts) for a few weeks now.  It is connected to an Ed Fong antenna on my roof with 45 feet of KMR400 (thick cable similar to LMR 400). 20A/30A peak  PS.   I have a Surecomm SWR/Power meter connected.  SWR without the AMP (direct connected not bypassed) is less than 1.1, as low as 1.01.

SImplex:

GMRS 19 = 1.2 SWR Watts = 48W

Repeater Channels:

1.3 SWR = 46 W

Highest reading I got was 49W.

I have a Wouxun KG-20G which I alternate with the BTech Amp setup using the same antenna.  Since I can only TX at 20W, some repeaters could barely hear me.  I am challenged with a quarry and a mountain range on my SW.  The extra wattage does help and the BTech mic seems tx much louder, I am told by those who I have done test with switching radios.

[WRVG593]

5 hours ago, WRUT935 said:

I have been using my BTECH U25 with my Wouxun KG-UV9G Pro (5+ watts) for a few weeks now.  It is connected to an Ed Fong antenna on my roof with 45 feet of KMR400 (thick cable similar to LMR 400). 20A/30A peak  PS.   I have a Surecomm SWR/Power meter connected.  SWR without the AMP (direct connected not bypassed) is less than 1.1, as low as 1.01.

SImplex:

GMRS 19 = 1.2 SWR Watts = 48W

Repeater Channels:

1.3 SWR = 46 W

Highest reading I got was 49W.

I have a Wouxun KG-20G which I alternate with the BTech Amp setup using the same antenna.  Since I can only TX at 20W, some repeaters could barely hear me.  I am challenged with a quarry and a mountain range on my SW.  The extra wattage does help and the BTech mic seems tx much louder, I am told by those who I have done test with switching radios.

I've had 2 break on me in 3 months! 

[WRUT935]

40 minutes ago, WRVG593 said:

I've had 2 break on me in 3 months! 

Sad, poor reliability.

[gortex2]

8 hours ago, WRVG593 said:

I've had 2 break on me in 3 months! 

Radio or antenna ? 

[WRVG593]

7 hours ago, gortex2 said:

Radio or antenna ? 

The first I chalked up to being a dud. The second we took apart and the RF Chip was fried. But both of them put out 0.1W. Not to mention someone else I know has one, and just yesterday it broke. So that's 3 in a row!!!

[WRVG593]

7 hours ago, gortex2 said:

Radio or antenna ? 

Amp

[Lscott]

There are two models of this amp. One is usable for TDMA type radios, DMR mode, whereas the other one isn't. Are people sure it's the AMP-U25 and not the AMP-U25D? Could the amp have been misused by any chance?

A high SWR between the amp output and the antenna is likely a good indication the amplifier is generating a high level of harmonics, and other garbage, that's being reflected back to the amplifier.

The amp may have been over driven too. Some radios are not well behaved when the power is turned down. I know the old Icom IC-706MKIIG had a nasty habit of spiking up to full power very briefly before dropping down to a lower set power.

I have a new AMP-U25D version, haven't used it yet, that is rated for ALL the common digital modes.

A comment was made by a poster that a "chip" failed in their amp. I've attached a PDF file, from the FCC, showing the internals of the -U25D version. I'm going to guess it's similar to the -U25. Does anything in the photos look like the part that failed?

Internal-Photos AMP-U25D.pdf

[WRVG593]

9 hours ago, Lscott said:

There are two models of this amp. One is usable for TDMA type radios, DMR mode, whereas the other one isn't. Are people sure it's the AMP-U25 and not the AMP-U25D? Could the amp have been misused by any chance?

A high SWR between the amp output and the antenna is likely a good indication the amplifier is generating a high level of harmonics, and other garbage, that's being reflected back to the amplifier.

The amp may have been over driven too. Some radios are not well behaved when the power is turned down. I know the old Icom IC-706MKIIG had a nasty habit of spiking up to full power very briefly before dropping down to a lower set power.

I have a new AMP-U25D version, haven't used it yet, that is rated for ALL the common digital modes.

A comment was made by a poster that a "chip" failed in their amp. I've attached a PDF file, from the FCC, showing the internals of the -U25D version. I'm going to guess it's similar to the -U25. Does anything in the photos look like the part that failed?

Internal-Photos AMP-U25D.pdf 470.05 kB · 1 download

The version was correct. And the radio should definitely have been okay. The UV5G definitely didn't overload it. Heck, it's made by practically the same company.

[wayoverthere]

25 minutes ago, WRVG593 said:

 Heck, it's made by practically the same company.

Who, lets be real, aren't exactly industry leaders in quality control, or reliability.

[WRVG593]

8 hours ago, wayoverthere said:

Who, lets be real, aren't exactly industry leaders in quality control, or reliability.

I've had nothing but great things from "baofeng". They have made radios that suit my needs for a while now. I have a couple motorola and a couple if baofengs... for my needs they work the same. The "BTECH" side of it, I've had horrible experienced with. I've had 4 baofeng radios and they're all great, I've had 3 baofeng amps and they're all horrible. And the motorolas are great too. Heck even the AnyTone was better than the btechs

[Lscott]

Any clue as to exactly what failed in the 3 amps you had? If it's the same failure and knowing what it was there might be a fix for it, or avoiding whatever it was that precipitated the failure.

[WRVG593]

Just now, Lscott said:

Any clue as to exactly what failed in the 3 amps you had? If it's the same failure and knowing what it was there might be a fix for it, or avoiding whatever it was that precipitated the failure.

2 if them were unknown but started immediately. 1 of them lasted for about 5 days and the RF Chip failed

[Lscott]

Just now, WRVG593 said:

2 if them were unknown but started immediately. 1 of them lasted for about 5 days and the RF Chip failed

What do you mean by "the RF chip"? I only see one small black IC chip on the board. You're not mistaking the large power transistor that's screwed to the heat sink are you?

[WRVG593]

1 minute ago, Lscott said:

What do you mean by "the RF chip"? I only see one small black IC chip on the board. You're not mistaking the large power transistor that's screwed to the heat sink are you?

I didn't personally look. I had a shop that deals specifically with amplifiers and radios that has been very trustworthy for a while now. 

[Lscott]

1 minute ago, WRVG593 said:

I didn't personally look. I had a shop that deals specifically with amplifiers and radios that has been very trustworthy for a while now. 

OK. My guess is it was the power transistor that failed. That can happen for several reasons. I listed a few below but it's not all inclusive.

1. It was improperly installed. The screws were not torqued down correctly. Too much, too little or no thermal compound used between the transistor's mounting flange and the heat sink.

2. High SWR on the amplifier output. May not have to exist for very long, monetary, to blow the transistor.

3. High voltage transients on the DC supply.

4. If any kind of "bias" is applied to the transistor it wasn't designed right, or the temperature sensor is not installed VERY close to the transistor. That can cause the transistor to go into thermal runaway which will destroy it in seconds. This applies to bipolar types. FET's are different.

5. The transistor is being used beyond it's published power ratings. One might get away with this so long as the duty cycle is kept low.

[wayoverthere]

2 hours ago, WRVG593 said:

I've had nothing but great things from "baofeng". They have made radios that suit my needs for a while now. I have a couple motorola and a couple if baofengs... for my needs they work the same. The "BTECH" side of it, I've had horrible experienced with. I've had 4 baofeng radios and they're all great, I've had 3 baofeng amps and they're all horrible. And the motorolas are great too. Heck even the AnyTone was better than the btechs

Apologies, I'm being a little salty

The quality control is kind of expected at the price point a lot of the baofeng stuff rings in at. The handhelds have been decent aside from the battery latch breaking off from a les than 12" drop, and another battery that expanded. They seem to do better with handhelds than mobiles, haven't heard much bad about the 50x3 but maybe more due to few willing to buy it at that price than them lasting well.

 My 50x1 is losing power, others have had both the 50x1 and 50x2 die with minimal use. Makes me wonder if they're giving btech the rejected products/parts.