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!

[WRKC935]

OK, you get more power??? not sure what you mean here.  Are you meaning that you have a power meter between the amp and antenna and the meter shows more power with the amp off or that you simply have more range with it?  Clarify this please.

If you are not getting power out of the amp it's probably also bad.  Hard to say with the description.

 

[WRVG593]

So to clarify, I receive and Transmit better with my rubber stock antennae while hooking up to my U25 Amp and Nagoya UT72. In fact, with the AMP and Magnetically mounted antennae, it is almost impossible to receive many signals, and it almost acts as a resistor for my wattage rather than an amp with my amplifier. For Example, I once drove to the repeater for a test, and using my rubber antennae got a positive tail on the repeater, as well as a human copy. Once plugged into the amp, even directly under the repeater, my transmission immediately dwindled and became scratchy, and even underneath the repeater became near impossible to pick up conversations over the repeater. 

[WRUU653]

The Nagoya UT72 is duel band, not sure what antenna your rubber stock is but if it's tuned to GMRS specifically it would likely be better.  Also and others here may elaborate more on this but my understanding is more isn't always better. If you drove as you say to the repeater and are putting out 40 watts I think you may be over shooting it. Don't use a 3 wood when a putter is what you need so to speak.  I don't have any experience with the amp so this is just my thinking. 

[WRUU653]

It looks like double threads with the same name here... one in equipment reviews 

[Sshannon]

34 minutes ago, WRUU653 said:

The Nagoya UT72 is duel band, not sure what antenna your rubber stock is but if it's tuned to GMRS specifically it would likely be better.  Also and others here may elaborate more on this but my understanding is more isn't always better. If you drove as you say to the repeater and are putting out 40 watts I think you may be over shooting it. Don't use a 3 wood when a putter is what you need so to speak.  I don't have any experience with the amp so this is just my thinking. 

There is also a UT72G that’s tuned for GMRS. 

[WRUU653]

22 minutes ago, Sshannon said:

There is also a UT72G that’s tuned for GMRS

My bad, thanks.

[Sshannon]

1 minute ago, WRUU653 said:

My bad, thanks.

I didn’t mean it as a correction. The amp is frequently sold as a package with a UT72 but I don’t know if it’s the GMRS tuned version. 

[WRUR505]

I have the exact same setup as you. I get great results. Have you checked the SMA to SMA cable that goes from the HT to the amp? Eliminate the Amp and try the UT72 straight to the HT. Something isn't right based on my experience with the same setup.

[WRUU653]

2 minutes ago, Sshannon said:

I didn’t mean it as a correction

No worries, I wasn’t bothered. My thanks was sincere. I may have been wrong about the antenna. I would have just given you a “like” but I guess I was heavy handed with those today and mygmrs has said my cup is empty  

[WRVG593]

42 minutes ago, WRUR505 said:

I have the exact same setup as you. I get great results. Have you checked the SMA to SMA cable that goes from the HT to the amp? Eliminate the Amp and try the UT72 straight to the HT. Something isn't right based on my experience with the same setup.

I want to try. but i don't have the right adapter yet. Definitely going to try. if my HT dosen't work properly with the antennae, we'll know its the antennae because the HT runs great. 

[Lscott]

Hum... Just for grins I looked at a photo of the UT72 antenna. I'm rather suspicious of it's claim to be a "dual band" or tuned for GMRS. You would normally expect to see a loading coil part way up the vertical element, which I don't see, for a simple antenna like this. What I think is going on it's really a 5/8 wave VHF antenna, I read it has a base loading coil which a 5/8 wave will have, but tweaked to run on the third harmonic to get it resonate on UHF.

I ran a simple EZNEC model, didn't extensively test it, but it does work with the major caveat the radiation pattern's main lobe is at a very high angle. That results in greatly reduced power in a nearly horizontal direction. This tends to suggest any gains in power from the amplifier are offset by most of it being shot up in the air due to the antenna's poor radiation pattern when use at the third harmonic of the VHF frequency.

I could be way wrong on this but it's something to think about.

[Borage257]

1 minute ago, Lscott said:

Hum... Just for grins I looked at a photo of the UT72 antenna. I'm rather suspicious of it's claim to be a "dual band" or tuned for GMRS. You would normally expect to see a loading coil part way up the vertical element, which I don't see, for a simple antenna like this. What I think is going on it's really a 5/8 wave VHF antenna, I read it has a base loading coil which a 5/8 wave will have, but tweaked to run on the third harmonic to get it resonate on UHF.

I ran a simple EZNEC model, didn't extensively test it, but it does work with the major caveat the radiation pattern's main lobe is at a very high angle. That results in greatly reduced power in a nearly horizontal direction. This tends to suggest any gains in power from the amplifier are offset by most of it being shot up in the air due to the antenna's poor radiation pattern when use at the third harmonic of the VHF frequency.

I could be way wrong on this but it's something to think about.

I have one (UT-72G) I can sweep with my nanoVNA when I get home if y'all want.

[Lscott]

42 minutes ago, Borage257 said:

I have one (UT-72G) I can sweep with my nanoVNA when I get home if y'all want.

All the sweep will tell you is how well the match is. The model I ran also showed a reasonably good match but the radiation pattern was poor. What is really useful is making some "far field" signal strength tests. Remember a dummy load can show a nearly perfect match, but that doesn't imply it's a good antenna to use on a radio to communicate with other people.

[Borage257]

Ok. I run the antenna on my van and haven't had any issues with it hitting my local repeaters. I feed the UT72G from a 5w Uv5G and battery eliminator. 

 

Any other data I could provide to improve you model? Im trying to learn EZENC.

[Sshannon]

38 minutes ago, Lscott said:

All the sweep will tell you is how well the match is. The model I ran also showed a reasonably good match but the radiation pattern was poor. What is really useful is making some "far field" signal strength tests. Remember a dummy load can show a nearly perfect match, but that doesn't imply it's a good antenna to use on a radio to communicate with other people.

Don’t let this bleak response convince you that an SWR sweep is of little value. Dummy loads look completely different to a VNA than antennas 

He’s right that there’s more to measuring the effectiveness of an antenna than just SWR, but if an antenna has a very high SWR, that must be addressed. 

[Lscott]

5 hours ago, Sshannon said:

Don’t let this bleak response convince you that an SWR sweep is of little value. Dummy loads look completely different to a VNA than antennas 

He’s right that there’s more to measuring the effectiveness of an antenna than just SWR, but if an antenna has a very high SWR, that must be addressed. 

Yes the antenna has to match, of course. One gentleman did a number of field strength tests on HT antennas since trying to get good SWR sweeps was really difficult. That was a far better indicator of which HT antenna(s) performed the best.