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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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  #21 (permalink)  
Old 04-07-2017, 2:54 PM
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NEW 50w 400-470MHZ DRM hand handset power amplifier RF power amplifier | eBay
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Old 04-07-2017, 3:24 PM
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Thanks for the link. I see that the same seller has at least three eBay ads for this same amp, at three wildly different prices, and each claiming different "wattages" (50, 70, and 80 respectively).

If you scroll to the bottom and check the specs, it's funny that the 80watt cites
Output power: real standard 40W (measured 40-48W)

Where the 50watt link states
Output Power: 50W real standard

NEW 50w 400-470MHZ DRM hand handset power amplifier RF power amplifier | eBay
NEW 70W UHF 410-470MHZ Ham Radio Power amplifier Interphone | eBay
NEW 80W UHF 410-470MHZ Ham Radio Power amplifier Interphone
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N4GIX - Ham / WQWU626 - GMRS
VV-898, TK-840(N), 2xTYT-7800, 2xUV5R v2+, HP1, BCD436HP, TMV7A, Ritron RRX-450 Repeater, MD-380, XPR7550, 2xCS800, Bridgecom BCR-40U Repeater, Elecraft KX3 + PX3

Last edited by N4GIX; 04-07-2017 at 3:28 PM..
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Old 04-07-2017, 3:57 PM
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The charitable interpretation would be that he is grading the amps by output, such that the cherry ones are in a higher price tier. But I'm skeptical...
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Old 04-08-2017, 12:52 AM
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Default taobao bg7sgm DMR linear

Hi Bill

The text on the taobao website (Chinese equiv to eBay) can be translated using Google translate. After crunching the Chinese text I found most of it is marketing hype rather than technical detail. Some technical information is available re the Mitsubishi RF module from Mitsubishi's tech data sheets.

The bg7sgm is not aimed at amateur use, the sales pitch in Chinese is to travelling salesmen who rely on 400mHz DMR handhelds for sales. In short it says why miss a sale if you are out of range, when the bg7sgm can give you 20% more coverage!

Below are some performance figures logged by our local DMR repeater when using this amp with an Anytone 858. Results at line 1 are for barefoot Anytone and at line 2, with the bg7sgm DMR amp operating in line (fitted with the Minikits 450mHz lpf across the amp output):


06:35:48.303 Feb 3 4.3 VK1RBM VK2JHG Jim VK 505 -102.3 VK-TRBO 0.0%
06:34:13.503 Feb 3 4.3 VK1RBM VK2JHG Jim VK 505 -93.5 VK-TRBO 0.0%

The 6th column shows the signal strength received at the repeater. The bg7sgm gives approx 9dB improvement (suggesting approx =32W output). However, I am running it at only 12V using a LiPo 3S battery so power out would likely be higher with higher voltage psu.

Note the bg7sgm includes a RX low noise receive pre-amp so is probably best installed as close to the antenna as possible.
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Old 04-08-2017, 7:44 AM
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Quote:
Originally Posted by merlin3rd View Post
I want to use my Tytera MD-380 for mobile use. Is there a UHF amp that will work with digital?
Thank you.
Merlin K3MEJ
I never tried it with my MD-380, but the Mirage BD-35 is designed for HT's and it has worked just fine on D-Star for several years.

Hank - KI4UMX
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Old 04-08-2017, 8:08 AM
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Quote:
Originally Posted by hankv View Post
I never tried it with my MD-380, but the Mirage BD-35 is designed for HT's and it has worked just fine on D-Star for several years.

Hank - KI4UMX
Unlike DStar, that transmits a constant carrier, DMR rapidly switches between transmit and receive every 30ms. The Mirage amplifier will NOT work with a DMR radio.
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Old 04-08-2017, 10:30 AM
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Quote:
Originally Posted by JimVK2JHG View Post
The 6th column shows the signal strength received at the repeater. The bg7sgm gives approx 9dB improvement (suggesting approx =32W output). However, I am running it at only 12V using a LiPo 3S battery so power out would likely be higher with higher voltage psu.

Note the bg7sgm includes a RX low noise receive pre-amp so is probably best installed as close to the antenna as possible.
Thanks for the detailed reply, Jim. I will be sharing this information at our next club meeting on 04/14/17. A bunch of club members have only MD-380 or CS750 HTs and have been asking about external amplifiers for improved mobile use. That is particularly relevant to us here in Indiana since we are blessed with 36 UHF DMR repeaters that provide ~97% state-wide coverage for mobile radios.

Would it be possible to take a screenshot of the assembled/modified amp, with particular attention to the LPF installation?
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Old 04-08-2017, 4:25 PM
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Quote:
Originally Posted by N4GIX View Post
for improved mobile use.
Work on getting a much better mobile antenna and installation.
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Old 04-10-2017, 2:33 AM
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Hi Bill

LPF7 installation notes for the bg7sgm are below. Noting in your higher density environment a BPF centred on the selected repeater or even an in line cavity filter maybe more appropriate (400mHz cavity filters are on taobao for around $40).

1. Build up the minikits LPF7 per instructions, fit an sma socket to the input end per the **ver illustration attached.

2. Open up the bg7sgm and drill two holes through the heatsink aligned with two of the LPF7 mounting holes (see **hor illustration attached).

3. Referring to the attached illustrations, using suitable screws and nylon standoffs, mount the filter on the heatsink as illustrated ensuring there is just sufficient separation between the underside of the filter and the top of the thermal switch. Selective use of foam and glue can be applied to mechanically stabilise the LPF7 installation against vibration etc.

4. Desolder the bg7sgm antenna output lead, and resolder it to the output side of the filter.

5. Prepare a 21cm length of sma coax with right angle plug (21cm length of the outer shield - allow another 7mm of inner conductor), for use as the filter input cable.

6. Per the **ver illustration, solder the filter input cable to the now vacant amplifier board coax output.

7. Attach the plug of this cable to the input socket of the LPF7.

8. Adjust the routing of the LPF input cable to keep it as far as possible away from the output side of the filter (see illustrations for general arrangement).

Check the work and the job is done.

Note that we found it is important for the filter to operate efficiently, the input and output cables to the LPF need to be routed so they are as far apart as the layout of the case allows.

The two .jpgs should be attached.
Attached Images
  
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Old 04-10-2017, 11:14 AM
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Quote:
Originally Posted by JimVK2JHG View Post
Hi Bill

LPF7 installation notes for the bg7sgm are below. Noting in your higher density environment a BPF centred on the selected repeater or even an in line cavity filter maybe more appropriate (400mHz cavity filters are on taobao for around $40).
Thanks, Jim. I deeply appreciate the detailed instructions and the pictures. That was nicely done.

I am curious about two things though. Was there any particular reason for using an SMA for the input to the LPF? Or was it just that you happened to have a bit of cable with a connector already installed?

I'm not sure what you mean by "higher density environment" because all of the repeaters are very well separated physically, being spread across the entire state. Or is it that the LPF is too narrow to cover the entire .75 cm ham band?
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Old 04-10-2017, 7:06 PM
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Hi Bill

The minikits LPF7 has lands for sma sockets but you can also direct connect the coax.

The output arrangement is limited by the available coax already installed in the bg7sgm. We cut this off as close as possible to the circuit board and bared a new short section for attachment to the LPF7.

On the input side we initially tried a short section of coax directly soldered between the output of the bg7sgm and the input of the LPF7 but got disappointing results in terms of suppressing the 900mHz harmonic. My technical adviser attributed this to io couplng..

We then tried some different cable lengths and routing and installed the sma socket initially to make trying different cable lengths easier, but in fact the socket itself seems to help isolate the input from the output. In the end we settled on the illustrated arrangement as by experiment giving us acceptable results. Further experimentation could get further improvement.

The LPF7 is a low pass filter, it starts to cut in at 450mHz and is designed to provide -54dB at 900mHz, The unit we built was measured and pre-installation was found to meet this spec within a dB or so. In Aust 900mHz is a tdma mobile phone band so it is important to minimise potential interference at 900mHz..

In relation to higher density, a problem with DMR and the proliferation of cheap handsets is that the tdma pulsing paradigm has potential cause cross channel interference. We have examined the spectrum of a number of popular DMR handhelds and in some cases found significant spurs mostly immediately either side of the nominal channel frequency. I think tdma mobile phone networks can get away with this as the cell towers use power management to minimise interference but in an amateur setting it is a bit more of a free for all so cross channel interference potential could be greater. In such cases a bandpass filter rather than low pass filter might be more appropriate.

We have done some field testing comparing DMR, DSTAR and FM over similar long paths (about 20km) using an ID51 and Anytone 858 handset to handset.. We found FM is better than either of the digital modes in fringe situations (digital cliff problem). DMR and DSTAR are about on par. However, DMR appears to have a bit better punch through at the fringe but audio quality is compromised. It is a subjective judgement but most situations DSTAR audio quality generally seems to edge out DMR, possibly because it is a continuous carrier system using forward error correction and is less reliant on handshaking.

In making comparisons another consideration is that DSTAR is easier to amplify, standard 2 and 70cm linears give a good result. Using higher powers DSTAR has been demonstrated over DX length paths of hundreds of kms whereas DMR is hard limited to about 120km - the two systems in some respects don't directly compare, its horses for courses.

Jim VK2JHG
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Old 06-28-2017, 7:29 PM
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Yes they make them and here is one you can buy, I might get one for my openspot.

NEW DMR DPM RP25 C4FM 80W UHF 410-470MHZ Ham Radio Power amplifier Interphone | eBay
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  #33 (permalink)  
Old 06-28-2017, 8:30 PM
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I have one of these amps and its working just fine with my UHF MD-380 in DMR mode. Since its broad band 30 to 512MHz it will also work with the VHF version. Its also tiny and fits in the palm of your hand. They show up occasionally on Ebay for reasonable prices but I don't see any this week.
https://www.ultralifecorporation.com...DS_A-320V1.pdf
prcguy
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Old 06-30-2017, 10:46 AM
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Here is another DMR amp that I came across when a few club members were discussing using an amp with their OpenSpot devices. I've never seen or used one, just pointing out that they do exist (these aren't cheap either, 3x the cost of an MD-380).

DF2FQ's Homepage
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Old 07-03-2017, 3:28 AM
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sorry but i NOT try on internet this dmr ampli china dmr 35 Watt bg7sgm...the link to see ? 73
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