Discussion in 'Amateur Radio Amplifiers' started by KI4RVX, Jul 9, 2011.

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  1. KI4RVX

    KI4RVX Ham Member QRZ Page

    This amp is 136-175 MHZ and 15-40w input and 80-120w output. I want to have it hooked up on my boat marine VHF for emergency use. I plan on having it POWERED OFF untill / if in an emergency when I could power it on. Will this AMP pass thru my routine VHF power of 25W without being on? I looked inside and it has some type of relay in a clear case. I don't want to test a transmit without the amp on for fear of blowing my VHF outputs. I can't routinely transmit legally above 25w in the marine bands. 80 - 100 W in the marine band would make the USCG very upset! I would risk it in an emergency however. Over the legal limit in the marine band in an emergency may be legal like it is in the Amateur bands in an emergency...?
  2. WB0LSR

    WB0LSR Ham Member QRZ Page

    I have that exact amp. They do pass your signal through when not powered, yes. Even a 25W signal.

    Also, it's not entirely on topic, but those are always factory tuned to a specific section of the 136-174MHz band, so while they do work across the whole bandwidth, they don't always work well. Typically they're tuned for the commercial/public service portions of the band. Very often you'll experience low output and relay chatter outside the tuned band. I've uploaded a service manual for TPLs VHF line to my Dropbox here:
    Inside you'll find very simple tuning instructions to tune the amp for the ham band if it isn't already. There is a variable capacitor on the input, right where the coax from the input SO-239 connects to the PCB. You just adjust this cap for the lowest input SWR at the center of the desired frequency range, so 146MHz for 2m ham. That's it! The amp should be good to go

    I should add that I only supplied the above because I needed that info when I got my amp.. It doesn't pertain to the amp when powered off. The amp doesn't draw any current when not transmitting though, so in commercial installs they are just left powered all the time.
    Last edited: Jul 9, 2011
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I doubt the Coast Guard or anyone else would know if you were running 25W or 120W, since the difference is only 6.8 dB. That could be less than the difference between a really good antenna and an average one. In terms of "range," having an antenna up on a higher mast will blow the doors off one that's down lower to the deck on VHF...and that difference could be well more than 6.8 dB, when you're over the horizon for the lower antenna.

    How much power do the marina stations use? If they're only running 25W, it would be senseless to run more than that, since you'd be getting out farther than you could hear. But I really don't know how much power they use.

    I wouldn't "re-tune" (peak up) an amp like this for marine/maritime or commercial use. For amateur use, within our bands, we can do whatever we want and "peak away."

    For me, as an ex-small time mariner (owner of small craft over the years), I'd be more concerned with having auxilliary power and a backup transceiver, and possibly even a backup antenna connected to that backup transceiver, than I would be about running more power. Most of the bad stories I used to hear were about radios that died (no backup) or batteries that went dead (no backup), or antennas that broke -- all of which rendered radio communications impossible. Then, I never had a big seaworthy craft and probably never ventured more than thirteen miles from shore (Santa Monica to Catalina). A handie-talkie can cover that.:p
  4. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    It has been my experience, sailing a 43 foot cat, that output power higher than 25 watts or so is not needed. When a 2006 hurricane damaged just about everything on the boat, the sealed (?) 1/4 wave marine VHF antenna was replaced with a run-of-the-mill Larsen NMO150 using their ground plane base adapter. It was relocated about 3 foot higher, and somewhat clearer of the mast. The difference was night, and day. However, I'd say that 99.9% of the time, a handheld is all that's needed to get the attention of the drawbridge operator, or any nearby boat (< a mile).

    What you really need for emergencies, is a channelized SSB marine HF radio. That is now an Icom IC-M802. It is loaded into the port mast stay using an AT-140. The starboard stay supports the IC706MkIIg, and AH-4. Best of both worlds!
  5. WB0LSR

    WB0LSR Ham Member QRZ Page

    The suggestion to tune in accordance with the factory service manual isn't strictly about peaking. I've seen the input swr outside of the factory tuned frequency range run as high as 3:1. In those cases it's about impedance matching.
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Of course it is, but it's still unlawful for unauthorized parties to tune commercial equipment. As hams, using stuff in the ham band, we can do whatever we want.
  7. WB0LSR

    WB0LSR Ham Member QRZ Page

    Ahh.. I see what you're saying. Very true, and that's something I wasn't taking into account.
  8. KI4RVX

    KI4RVX Ham Member QRZ Page

    Thanks all for the thoughtfull input. The manual from WB0LSR was extremely helpfull. The antenna mounting issues from WB2WIK are very valid. The suggestion of a second radio or a marine HF from K0BG makes sense also. I presently keep 2 marine HT's on board and also a portable VHF antenna should my fixed mount become inoperable. In an emergency, the stations I would want to call would be the shore stations like the USCG or the Tow Boat operators all of who have tall tower mounted equipment that could hear me outside of my normal range. If I routinely transmitted, at an unlawful power, on the marine band, the Coast Guard would eventually wonder why they routinely hear me from such a great distance and surely would investigate. Yes, as in our amateur radios, a quality instalation is the most important factor, as even the best equipment installed poorly will be ineffective. My present SWR is 1.5 so I think my antenna is good. It ia s shakespeare galaxy 5225XP 8' 6db gain with RG 8x coax mounted on top of the fly bridge enclosure. However, I have no experience with external power amplifiers, so all the input was sincerely appreciated!
    I will check back for any more replies.
    Thanks, Mike
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Hi Mike,

    I know that 5225XP antenna pretty well. It's actually 3 dB gain (or "6 dB marine gain," which is kind of a marketing thing).

    The Coast Guard may wonder about signal strength, but frankly if you just used a better antenna or a higher one, you could easily be 6 dB stronger without an amplifier and they couldn't possibly tell if the change in signal strength was a better antenna or an amplifier. That's impossible.:)

    Shakespeare is a "big name" in marine antennas, although the products are just average. I always stuck with Celwave Marine stuff. Their "3 dB" marine antenna has more gain than the 5225XP, although it is heavier and more expensive. I liked the Celwave stuff because it uses a weatherproof N connector which screws off the antenna, in lieu of the RG8X "pigtail" like the Shakespeare, which is attached inside the antenna. It's a better design, but as I said, more expensive.:(

    Happy sailing!
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