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Digital Voice for Amateur Use - Discuss use of digital voice technologies on the amateur radio bands. This is to include technologies such as VoIP, P25, DMR/TRBO, NXDN, D-STAR, etc.

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Old 03-17-2016, 6:30 PM
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Question UHF amp for Tytera MD -380 DMR HT ?

I want to use my Tytera MD-380 for mobile use. Is there a UHF amp that will work with digital?
Thank you.
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Old 03-17-2016, 6:58 PM
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Merlin, the short answer is no. None of the amps can turn on and off fast enough to accommodate the time slot spacing. Unlike analog, the subscriber radio only transmits of one-half the time. The other half of the time is spent "receiving" the signal sent back from the repeater. Even if one used a fast RF detector, and fast PIN diode switches instead of a relay, the performance would be very poor.

You may have noticed that sometimes when a cheaply shielded speaker mic is being used, you'll hear what sounds like a "motorboat" while they are talking. What you are actually hearing is the result of the transmitter switching on and off continuously!

I wont get into the DMR standard that governs the guard band timing but over large distances this can be come an issue too because of propagation delay invoking a time-synch issue. In a severe enough case it can actually provoke a bleed through into the adjacent slot.
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Old 03-17-2016, 6:59 PM
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Not really. Due to the nature of how TDMA and other digital modes work there are no amps. I'd suggest a mobile rig.


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Old 03-17-2016, 7:53 PM
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Darn.
Thanks for the replies.
Merlin K3MEJ
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Old 03-17-2016, 8:11 PM
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Quote:
Originally Posted by djs13pa View Post
Not really. Due to the nature of how TDMA and other digital modes work there are no amps.
Yes there are, but seeing as the OP has a MD-380, he probably won't want this amp.
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Old 03-17-2016, 8:41 PM
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Originally Posted by MOONBOOTS View Post
Yes there are, but seeing as the OP has a MD-380, he probably won't want this amp.
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Isn't that more for use as a repeater's final? Although as I recall, the repeater doesn't actually do any switching, fast or otherwise, since it's always running in full-duplex mode.
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Old 03-17-2016, 8:57 PM
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A repeater can use a normal amp. I'm just showing there are DMR amps, but they're not $129.
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Old 05-06-2016, 11:37 PM
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Hi from Adam Kb2jpd in NYC

You might want to look at this from the other end.

The most important part of the ham radio station is you, the operator. The antenna is the 2nd most important thing. So invest in a window mount or a mobile mount and see how things improve from there. the improvement from 5 watts to 45 watts is mininal.

Focus on the antenna and you will see the performance right away. Your gear will love you too since it will be working to a healthy antenna system.
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Old 10-24-2016, 7:06 PM
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So... sounds like this might just work on simplex? If I manually key the amplifier and am operating simplex then (in theory) it should not matter that the amp is taking up both time slots... right? de KL1IF
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Old 10-24-2016, 8:02 PM
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Quote:
Originally Posted by N4GIX View Post
Isn't that more for use as a repeater's final? Although as I recall, the repeater doesn't actually do any switching, fast or otherwise, since it's always running in full-duplex mode.


A DMR repeater can use a normal amplifier, because it transmits on both time slots all the time. Only the subscriber radios rapidly key and unkey.
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Old 10-24-2016, 8:04 PM
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So... sounds like this might just work on simplex? If I manually key the amplifier and am operating simplex then (in theory) it should not matter that the amp is taking up both time slots... right? de KL1IF


No. Does not work that way. The transmitter power output rises and falls extremely fast. I doubt a normal FM amplifier would be happy, manually keyed or not.
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Old 10-24-2016, 8:16 PM
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Originally Posted by kayn1n32008 View Post
No. Does not work that way. The transmitter power output rises and falls extremely fast. I doubt a normal FM amplifier would be happy, manually keyed or not.
Ok. Well, there are other ways to get more range... switching to horizontal and stacking some UHF loops on the car... These are part of my "bug-out" plan and I just want to keep with the same radios so the encryption function works transparently. Higher power would be nice but not needed I guess.
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Old 10-24-2016, 8:18 PM
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If you were to run a 15dB gain antenna, using your portable with 4w output, with 3dB feed line loss, you would have an ERP greater than a 45w mobile into a 1/2wave or 1/4wave with zero feedline loss.

Your antenna system (antenna and feedline) will make or break your whole system. If you have a high quality(no fibreglass ham-craptastic stuff) antenna and high quality feed line(LMR-400 at a minimum, preferable 1/2" hardline) using minimal amount adapters, will make a bigger impact on your talk out range than even a 1000w amplifier.
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Old 10-24-2016, 8:22 PM
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Quote:
Originally Posted by bradrnstyle View Post
Ok. Well, there are other ways to get more range... switching to horizontal and stacking some UHF loops on the car... These are part of my "bug-out" plan and I just want to keep with the same radios so the encryption function works transparently. Higher power would be nice but not needed I guess.


If you want to improve range with or with out using an amplifier, going to SSB will be the real range improver, or using a low SNR digital mode like WISPER or JT65. Simply going horizontal polarization will not improve your range much while staying with a FM transmission.
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Old 10-24-2016, 8:41 PM
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Quote:
Originally Posted by kayn1n32008 View Post
If you want to improve range with or with out using an amplifier, going to SSB will be the real range improver, or using a low SNR digital mode like WISPER or JT65. Simply going horizontal polarization will not improve your range much while staying with a FM transmission.
All good ideas. But this specific project involves SHTF use of the DMR encryption algorithm, so other modes are apples to oranges. I do like the HF sound-card digi modes and it seems something encrypted would be easy to come up with... if I knew anything about writing programs. It is possible to transfer encrypted files (Word; PDF; etc) with the DIGITRX Digital SSTV software... you just load a "file" that's not a "picture." Works really well.
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Old 12-07-2016, 5:05 AM
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Originally Posted by bradrnstyle View Post
So... sounds like this might just work on simplex? If I manually key the amplifier and am operating simplex then (in theory) it should not matter that the amp is taking up both time slots... right? de KL1IF
To add an update. This is for simplex use because it's horizontal not vertically polarized like most repeaters. I stacked 4 of the VHF M2 antennas with their phasing harness as high as I could. And put one M2 loop on my vehicles. Horizontal is NOT just for SSB work. You can get and extra 2.5 db "ground effect" (google it) gain just by switching polarities. For me. I can get about 15-20 mile coverage from base to car reliable without a repeater with md380s (VHF). Sure, their a little harder to mount on a car but I just use an MFJ 5inch three magnet array with home brew 3/8x24 threat rod from lowes. The key is to get it exactly 1/4 wavelength above your vehicle. Paint it black and it's nearly visible. That's my two cents from 23 years in radio experimentation. KL1IF.
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Old 12-30-2016, 4:21 PM
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Quote:
Originally Posted by N4KVE View Post
Yes there are, but seeing as the OP has a MD-380, he probably won't want this amp.
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I don't think that "Digital Modular Radio" is the same "DMR" that the OP was asking about. Note that DMR is not on the list of modes for that amp, either.
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Old 12-30-2016, 8:17 PM
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Quote:
Originally Posted by troffasky View Post
I don't think that "Digital Modular Radio" is the same "DMR" that the OP was asking about. Note that DMR is not on the list of modes for that amp, either.
See reply #6 above where I stated the same thing. The answer to the OP's question remains "no..."
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Old 04-07-2017, 5:05 AM
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Default DMR linear amps for 70cm handhelds

The Chinese bg7sgm amp from taobao works with DMR. 2-5W in for a measured output of around 35W. The amp uses an Mitsubishi 3 stage RF module RA 30H4047M and high speed diode switching to cope with the pulse nature of DMR.

The bg7sgm build quality is fair, the SM circuit board is quite good and fitted to a generous heatsink with fan cooling but the aluminium case is flimsy. For about $120 delivered you cant have everything.

The amp is designed for mobile use and when checked with a Rhode and Schartz analyser had an unacceptably high 900mHz harmonic. Fortunately there is space within the case to fit an lpf, I used an Minikits LPF7. This cut the 1st harmonic from -25dBc to -54dBc, The output was rechecked and found to be acceptably clean.

My QTH is on the fringe of the local DMR repeater (about 18km and just below a ridge line so I don't have los. The bg7sgm provides enough boost to get in and DMR sig reports have been good. It also works well on FM, I haven't yet tried it on ssb but have some doubts whether it would work in this mode (due to the swicthing detection circuit).It should be fine for AM and breakin CW.

Overall the bg7sgm works well as a DMR amp but you need to be prepared to make modifications out of the box (actually mine came wrapped in bubble wrap and newspapers).

Jim VK2JHG
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Old 04-07-2017, 3:15 PM
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That sounds like a great deal for a linear amp, but not reading Chinese nor facile in French, I cannot seem to learn much from the taobao website...
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