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Meat Plow[_5_] Meat Plow[_5_] is offline
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Default OT--Actual elecytronics repair question

On Wed, 12 Jan 2011 13:11:41 -0800, Jeff Liebermann wrote:

On Wed, 12 Jan 2011 20:21:54 +0000 (UTC), Meat Plow
wrote:

I've also had grounding problems with this radio. Makes the audio howl
when you turn it up past 50% on 70 centimeters.


That's not grounding. It's microphonics. The 440 PLL is getting
mechanically modulated by the audio from the loudspeaker. Get the phase
right and you have a howling oscillation. I use bees wax, hot melt
glue, or if desperate, RTV, to reduce the mechanical sensitivity of the
VCO. You might also try a rubber foam pad between the PCB and the front
panel to acoustically decouple the PCB.


Those that suggested the fix called it grounding. That's all I know.

Other than this, the radio has worked well, the batter has held up
remarkably and the audio is robust. I also have a dual band FT-60. Rock
solid radio, very loud audio with little distortion. Bought it back in
2006 from AES. They had a special on the radio and drop charger that I
couldn't resist.


The local animal rescue volunteer group all got licenses and
standardized on the FT-60. It's a better radio than the VX-5 but is too
much for many of the users to operate. It also has the irritating WIRES
function which must be disarmed before it can be used. They would have
been better off with channelized commercial radios but the ham stuff was
cheaper.


Yeah the WIRES/ inet radio is crap. And the beacon function for other
hams radios to alert when your in range. Forget what that's called maybe
ARS? It's got a lot of good functions besides that. I'd like to see a
battery voltage display option that keeps it on the screen past power on
like the VX-5 has.

I bought a Diamond SRH320A antenna for it. I've worked repeaters 50
miles away outdoors on 2 meters with that HT.


About 2 years ago, I gave a demo on HT antennas. It didn't take much to
demonstrate that bigger is better, no matter how weird looking. I
placed a field strength meter at a fixed distance from the radio, and
tried various antennas. The best on 440 MHz was an AMOS/Franklin
monstrosity that I conjured for the occasion. It was about 1.5 meters
overall, with the HT in the middle, which had to be held horizontally.
On 2m, it was a flex PCB antenna I had etched into a sheet of mylar,
representing something like a 3 element Yagi. The usual base and center
loaded dual band rubber ducky antennas were horrible by comparison, but
were greatly improved by the addition of a counterpoise.
http://www.k6gph.org/index.php?

option=com_content&view=article&catid=1&id=10&Item id=7
Incidentally, I brought an inflatable UHF loop yagi antenna that used a
1 meter long rubber sausage shaped balloon for mechanical support and
insulation. I didn't have time to try it as I ran out of time. (Hint:
I use the stock rubber ducky as everything else is too big and clumsy).


Unless your repeater is a few miles in radius from you a small duck is
good enough. My closest repeater is 12 miles. I have a Cushcraft AR270
about 15 feet above the roof with Belden 8319 coax @ about 560 foot.
Does a great job. Also have at about the same height a Cush Ringo AR6.
I sometimes serve as our district's backbone liaison for Skywarn and talk
to the NWS on 6. Make me feel like a big shot.

--
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