Guest nodoze Posted February 26, 2023 Report Share Posted February 26, 2023 Between the BTECH AMP-U25 & AMP-U25D amplifiers which is better for the For GMRS-PRO? In reading this reddit thread it sounds like the data is APRS compatible: Does using APRS mean you need the AMP-U25D (digital version)? If price isn't a consideration, any thoughts as to which is better to go with (AMP-U25 or AMP-U25D)? I do like that AMP-U25 has "Out-of-Band Transmit (Pass-through the HT's power to the external antenna while amp is powered off)" but to get that it sounds like you have to give up "DMR and P25 Phase 2 modes" which I don't know if the GRMS-PRO needs those... Quote Link to comment Share on other sites More sharing options...
Lscott Posted February 27, 2023 Report Share Posted February 27, 2023 14 hours ago, Guest nodoze said: Does using APRS mean you need the AMP-U25D (digital version)? That depends on the transmitting radio and the mode in use. The main difference between the two models is the AMP-U25D will work with digital transmitting modes like DMR, P25 Phase 2, TETRA, etc. All of those use a form of TDMA, time division multiple access, which means the radio's transmitter is switching between transmit and receive many times per second and the amplifier has to keep up. The other digital modes don't do this thus the AMP-U25 will work fine. For the small difference in cost I would get the AMP-D25U. At some time in the future you get your Ham license, if not already, and want to try out some of the digital voice modes the amplifier will work. In Ham radio most of the digital voice mode activity seems to be on the UHF 70cm band anyway. One big caveat, the amplifier IS NOT FCC Part 95 certified. AMP-U25D Users-Manual.pdf Internal-Photos AMP-U25D.pdf Review BTech AMP-U25D.pdf Test-Report AMP-U25D.pdf Quote Link to comment Share on other sites More sharing options...
Guest nodoze Posted February 27, 2023 Report Share Posted February 27, 2023 Thanks Lscott! Do you think that the regular non-digital AMP-U25 will allow an amplified GMRS-PRO communicate GPS/messages/etc with other GMRS-PROs? It sounds like you think the AMP-25D should work fine. I wasn't sure from your response if you were thinking both the AMP-U25 & AMP-U25D should work for the regular interoperability/usage of multiple GMRS-PROs. Unfortunately I can't yet access the PDFs you posted... I submitted my request & paid for my GMRS license but am waiting for FCC to process so only have guest access for now... Quote Link to comment Share on other sites More sharing options...
Lscott Posted February 27, 2023 Report Share Posted February 27, 2023 6 hours ago, Guest nodoze said: Thanks Lscott! Do you think that the regular non-digital AMP-U25 will allow an amplified GMRS-PRO communicate GPS/messages/etc with other GMRS-PROs? It sounds like you think the AMP-25D should work fine. I wasn't sure from your response if you were thinking both the AMP-U25 & AMP-U25D should work for the regular interoperability/usage of multiple GMRS-PROs. Unfortunately I can't yet access the PDFs you posted... I submitted my request & paid for my GMRS license but am waiting for FCC to process so only have guest access for now... For your application I think it would work just fine on transmit. The radio does have a GPS receiver. I don't know if it will pass the GPS satellite signal from the antenna to the radio. There is a filter network internal to the amplifier that would likely block this. In that case your GPS would be non-functional. This would not prevent you from getting APRS packets from another radio however. If the radio has it's own internal GPS antenna then the amplifier won't be an issue. You should be able to get good position data for sending APRS packet info. Quote Link to comment Share on other sites More sharing options...
Guest nodoze Posted February 28, 2023 Report Share Posted February 28, 2023 15 hours ago, Lscott said: For your application I think it would work just fine on transmit. The radio does have a GPS receiver. I don't know if it will pass the GPS satellite signal from the antenna to the radio. There is a filter network internal to the amplifier that would likely block this. In that case your GPS would be non-functional. This would not prevent you from getting APRS packets from another radio however. If the radio has it's own internal GPS antenna then the amplifier won't be an issue. You should be able to get good position data for sending APRS packet info. Thanks again Lscott ! Good considerations regarding the GPS as I had not thought of that and will have to do some testing. I went ahead and ordered an AMP-U25 to do some testing as the costs for either amplifier are not that significant and I want to test what out of band transmission allows when the amplifier is off. One use case I am considering this for is making GMRS-PROs with AMP-U25s as the mobile base stations for the RVs in a convoy of friends/family which are going into areas with sparse mobile phone coverage. It would be great if when the RVs are parked/off if an RV's GMRS-PRO can still function at/in a base camp with the RV on battery power without the extra power draw of the amplifier. On a related note I am thinking of also recommending a GMRS-PRO for each occupant (in addition to mounting one with the RV) so that when they go out on ebikes or the trails they can exchange GPS with the RV itself which would help if they get lost/hurt. I may also recommend one SHTF multi-band scanner for the entire convoy but think the GMRS-PROs make the most sense for the convoy itself. Quote Link to comment Share on other sites More sharing options...
Guest nodoze Posted March 1, 2023 Report Share Posted March 1, 2023 Tested the AMP-U25 and could both send & receive messages between the GRMS-PROs with the amplifier on AND off. Very pleased. Quote Link to comment Share on other sites More sharing options...
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