[hackpgh-ham] Re: Hamfest cheapo 70cm radios - too good to be true
- From: Ed Paradis <legomaniac@xxxxxxxxx>
- To: hackpgh-ham@xxxxxxxxxxxxx
- Date: Mon, 8 Nov 2010 11:47:45 -0500
TLDR; Maybe they'll work after all.
The power requirements might be steep to run these power amplifiers on
the balloon, but thats a good use case. I'm also not sure that we'd
need that much power to do ATV from a balloon. My gut feeling is that
you need more power because the signal is "spread out" over a large
bandwidth, but I'd have to go look up the math.
The power amplifiers take about 300mW input and produce up to 25 Watts
output. You get less power the less supply voltage you give them.
The sheet has a graph that says they'll run any where from 5-13.6
volts, but I suspect they may act weird down at 5V. So there might be
some design options for getting "more power" but not having to go for
"max power".
Another issues is that these amplifiers are probably biased for "Class
C" operation, meaning they won't work on modes like SSB or AM, only on
FM. I'm not sure what side of the fence that ATV fails on regarding
this issue. My gut feeling says it requires Class A (or "linear")
amplifiers.
As far as "gotchas" for the repurposed radios, that has always been my
experience as well, but these seemed like such an awesome deal and
"they could be reprogrammed" and we just had a guy visit the shop who
used to work reprogramming radios. I spoke with him at the ham fest
and he seemed confident that he had the software and cables to program
them, but this was before I knew the specifics.
I see a lot of people online saying to use the "Type 1" version of
these radios as parts of repeaters. It should be noted that the "Type
1" radios don't seem to fall inside the ham band either.
Type 1 - 450 - 488 MHz
Type 2 - 488 - 512
Type 3 - 403 - 430 <- what I've got
Toshiba makes three variants of the power amplifier module:
S-AU27AL - 400 - 430 MHz <-- what are inside my radios
S-AU27AM - 450 - 490 MHz
S-AU27AH - 490 - 512 MHz
Coincidence? Probably not. I imagine Toshiba made these modules
specifically for these Kenwood radios (and maybe other vendor radios
that fall into the same three categories).
Since I don't know what modules are in the other radios, I don't know
for sure, but notice that none of them fall neatly into the
traditional simplex or repeater portions of the 70cm band: ~430 - 450
MHz.
So perhaps all is not lost, and these radios will perform okay
assuming we can program them to the right frequencies. "Bending" a
Type 1 down below its designed frequency shouldn't be that much worse
than "bending" a Type 3 above its designed frequency.
Ed
On Mon, Nov 8, 2010 at 9:48 AM, Doug Philips <douglas.philips@xxxxxxxxx> wrote:
> I've been skeptical of these repurposed radios, apparently there are
> gotchas.
> That said, could they be harvested for ATV balloon use?
>
> Speaking of which, I talked to a guy at the WACOM Hamfest yesterday who
> had a fast scan TV kit that he was willing to donate to us. The story is
> that he's
> had it (unfinished) for "years". He couldn't get anyone else interested in
> using
> fast-scan, so his enthusiasm tanked and he never finished it. I don't have
> -any-
> other details until I get a reply on email. He thought the balloon launch
> was pretty
> cool, and it was as we were talking about the pictures that I mentioned
> wanting to
> do slow-scan for 'live' images that he asked about fast-scan and offered the
> kit.
> I don't know what needs to be finished or what specific parts are needed,
> but its
> an interested coincidence...
>
>>
>> Both power up, and have clearly labeled pins internally that look like
>> the programming headers. You can find the programming protocol here:
>> http://www.interceptradio.com/wiki/index.php/Kenwood_TK-840
>> Generic info and link to user manual here:
>> http://www.ehow.com/list_7297456_kenwood-tk-840-specifications.html
>>
>> If anyone is interested in messing around with them, let me know.
>
> Mosty I'm not EE enough to get the subtle details, so my 'messing around'
> ideas are related to balloon video possibilities...
>
> -D
>
>
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