On Thu, 27 Mar 2025, 20:07 Bob D., <ajamas.rn@gmail.com> wrote:
> I've been looking at some of the Q5 transverters. They have a 70cm amp.
>
>
> 100mw to 25W for $US215
> http://q5signal.com/index.php?route=product/category&path=63
>
> It might provide some ideas.
>
Thanks. $215 is not a bad price (although at the lowest drive level of
100mW I'd still need a preamp - one of these "20dB 0 to 5GHz" boards). If
it was just that I probably would've ordered it by now. Unfortunately
shipping and taxes will make it into at least $350. With me not being sure
about vhf long term (I'm just checking it out) I think I'll leave this
option a bit further down the list.
> There are plenty of inexpensive, broken, 70cm FM transceivers floating
> around if you don't need linear amplification or want to re-bias and run at
> lower power.
>
I do need linear amplification. One of main things that interest me is
running other modes like ssb, ft8, wspr and so on. Good that you mentioned
the linearity because I arrived at a similar idea and I was eyeing used
baofeng uv5r's that are available locally for $10-$20. The schematic is
online and looking at it, it would be very easy to plug into the rf path.
But as you said. These are not linear, because they are FM only. I didn't
think of it at the time. There are all mode trx like tr-851 (I own one, but
I'm not looking to mod it.). These have linear amplification, but are hard
to find at a good price.
As for linearity. I wonder how linear bigger amps - like ones based on
mrf186 (a 100w device) are? Supposedly if you feed 1W in you get up to 20W
out(not sure how it gets 20x from 11dB. So, let's say I feed it 100mW. I'm
hoping that means I get 2W out. It is a bit of a waste to use 100w amp to
bump 100mW to 2W, but hopefully at least it will allow me to use the thing
long enough to figure out if I want to spend more money on the uhf side of
the hobby.
I have a DIY kit "pallet" with mrf186. I've assembled it yesterday. It
still needs tuning, (trimming quarter wave lengths, squeezing/pulling
coils), drilling and tapping the radiator before I can start it.
Also, hopefully today I get 3 spare transistors for these Chinese
mini-amplifiers(seems only 3 are available locally) so I can fix all but
the one with a chip. I'm not sure how do I prevent them from burning up
again. Perhaps I need to tweak the bias and or output matching. Remembering
the one that burned up with only few(+3dBm if I remember correctly ) input.
It was about 1.2W when it smoked. Had I known back then they are actually
rated at 1W output (and not 2W, 3W or even 4W) I may have backed off marked
the highest dBm when it reaches 1W and use it like that. Perhaps that will
be sufficient not to burn up more of them.
73, Lukasz
>
>>>>>
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