This is where you post messages about those odd pieces you need and can't
seem to get.

34 responses total.

I need a mobile mount bracket for a Kenwood TR-7850.  The Kenwood dealers
can't help me because the radio was made in about 1982.  Anyone know where I
might get one?

I make my own out of .090 aluminum.  You can get .125 thick aluminum at
most hardware stores.

I made a GPS receiver bracket/holder out of a plastic wiring box, with a
little cutting and folding over of its edges (aided by heat from a torch). 
Bending 0.125 aluminum is not particularly easy without a brake. You might
also look at other plastic boxes that could be adapted. 

Re #2: The problem is that Kenwood radios don't have screw holes or any such
mounting attachments; what they have as a channel on each side that mates
with the bracket.  The radio slides in, then locks.  It'd be hard to
duplicate that, I think.

For a while I kept my ICOM HT in a cup holder, made for cars, that clipped
into the space between the window and its frame. Very convenient, in fact.

Yes, but his Kenwood is not a HT.  I have a Kenwood mobile 2M radio that I
inherited.  It has the slide mount you mention.  If it were me, I'd just
make a bracket and attach it to whatever screws are already on the radio.
You might even be able to use the screws that mount the rails to the radio?
(I don't even recall the model No.  nor do I recall where all the screws
are.  I just know that it works but the deviation is low.)

I'm supposed to know what a TR-7850 is? 8^} I put my mobile in a
cubby-hole in the dash - presumably made to keep keys, gum, who-knows... -
. It just sits in there, though propped to better expose the speaker. I
brought the power and transmission line to it via the hole where the
ashtray was, so there are no wires trailing around the front seat. In
another car, I cut a hole in the dash and made a simple bracket to support
a mobile in that. I have noticed, however, that new cars don't have holes
for "miscellaneous", and it looks difficult to get behind the dash to find
spaces to install things. 

Sorry, I guess I should have specified. :>  The TR-7850 is a 40-45 watt
mobile 2m radio made in the early 80's.  Your basic 2 meter FM mobile.  It's
about 7x1.5x9 inches, not quite as miniaturized as modern mobiles.  It's
also about five pounds, so I want it anchored well so it doesn't off me in
an accident. ;>  I will, indeed, probably have to fabricate something using
the existing screws.

There's the classic (damn this qwerty keyboard, I've forgotten how to use
them) 'velcro platd' method, where you mount a sheet metal plate that matches
the bottom of the radio, then cover it and the bottom of the radio (or the
top...) with velcro.  Very strong, has the secondary use of reducing
trasmission of vibrations to the radio.

Could also bend up a clamping strap to hold the radio against a surface
with screws. By the way, consider mounting the radio 'on edge' rather than
flat. Just as easy to use, but increases options for mounting.

Re #9:  Didn't think of that!  What I ended up doing is fastening the radio
to the top of the dashboard (there aren't many good locations to stick one,
in a Ford Club Wagon) with hangar strap, using existing screws in both the
radio and the dash.  Some 1/2" self-stick foam weatherstripping I had lying
around serves as a cushion between the dash and radio.  So far, I'm happy
with the results; the radio is staying put, and doesn't rattle.  It's also
at a good location and angle for me to see the display without taking my
eyes too far off the road.  The power and antenna wiring go across the dash
to the edge, then are tucked between the dash and door post.  The coax then
goes under the carpet, and the power wiring goes to the fuse panel.

Other ideas that I ultimately rejected: Fastening the radio to the metal top
of the dash (behind the padded part) or to the metal seat pedestal using a
Ridiculously Strong Magnet.  I also pondered attaching it to the inside
engine cowling between the seats, but the engine cowling on the Club Wagon
XLT has a really nifty fold-out table, and I didn't want to lose use of
that.

It is a *very* good idea to wire your radio directly to your battery,
to keep noise down. You should also put fuses in *both* wires to the
battery (or your negative return might try to conduct starter current
if your battery ground strap fails). 

I'm aware that wiring the radio to the battery would be better, but so far
noone's reported alternator whine on my signal.  If I discover it's a
problem, I'll change that later.  The circuit it's on currently is the cigar
lighter circuit, which has a 20 amp fuse and has nothing else on it except
the radio and cigar lighter.  The radio is supposed to draw 9 amps at full
power, when transmitting.  This is enough to pull the ammeter on the dash
into the 'discharge' range if the engine's idling and the van's just been
started, but at higher speeds it stays in the 'charge' range.

I "discovered" an unexpected source of less-than-common components -
radioshack.com (formerly TechAmerica = Tandy). I looked for a DC
power plug, 4.8/1.6 mm. Mouser, DigiKey and even Newark came up
blank - but radioshack.com carries them. They carry many things that
are not in the Radio Shack catalog, and the web site actually works
well. Amazing. They even had a 2m/70cm HT collapsing antenna on
sale for 50% off. 

I check their site quite frequently.  They have good internet only sales too.
I ordered one item from them so far and I was very happy with the price,
delivery and reasonable shipping charge.

Hey all...

Been a long time, anyhow, I'm looking for some parts for a 
vibroplex vibrokeyer... the knobs and a spring, if you can help,
please e-mail me at k8cpa@arrl.net




thanks

-chuck K8CPA 

Anyone have a copy of one of QST's "Hints and Kinks" collections?  I 
need a circuit that I'm reasonably sure appeared in one of them.

Basically, I want a circuit that'll switch on when a transmitter keys 
up.  I'd like to do this without tapping into the PTT line.  I recall 
seeing a circuit that did exactly that by sensing leakage from the coax 
line.  It was intended to switch on a cooling fan, and used several 
turns of wire around the coax to pick up RF leakage.  I think it used a 
MOSFET.  It was really simple, but I don't remember much about it other 
than that.  Can anyone help me out?  I've tried doing the same thing 
with a Darlington pair (I'm more comfortable with bipolar transistors 
than with MOSFETs) but I can't get it to work.

You need to mismatch your feed line - there isn't any RF on the outside
if you have a perfect match. (joke)

I could *imagine* just putting a capacitor/dioide detector in series with
that coil, and connected to the gate of the MOSFET (with all polarities
and biases correctly chosen). This is the circuit of the simple RF voltage
probe in the ARRL Handbook.

you may also find a section of the radio where there is some RF to tap into.
Rectify it and use it to turn on a FET.  You may not have enough current to
turn on a current device like a transistor, darlington or otherwise.  A
voltage device, like a FET, would be better.  You may also want to tune your
pick-up loop to the 2M band so that it will be more effective.

I want to mount a perfboard circuit in a metal chassis/box. Are there
available guides with adhesive that can be fastened to the box into
which the board can slide? Or, does anyone have suggestions for doing
this (so far, I have only thought of hot-gluing the board into the
box, but it would be nice to be able to slide it out again).

The box should be fairly small, you could clamp it to the coax, near a
support point for the cable.

Another option for doing all this would have been to use small reed relay
to switch a bias for a transistor.  Sorry I couldn't offer this before,
but this just popped up as new to me.  :)

Re #20: The classic method is to use stand-offs, screws, and nuts.

True - lots of those are available, but the other half of the chassis
slides into the one in which the board will go, and I want to mount the
board parallel to the open sides of the half-chassis. There is no place to
fix standoffs and they would interfer with the other half of the box. (It
would take too long, or require pictures, to explain why I need to mount
the board as indicated.)

I would think that others would want edge guides for board - after all,
some plastic boxes are made with guides for inserting boards. 

I guess I can cut some strips and glue them into the sides of the box to
make guides, but it would sure be nice if guides came preformed and
attachable. Just another construction convenience. 

Yeah.  Some boxes come with those already installed, but I don't know of
anywhere you can purchase them seperately.  You'll probably have to
fabricate something.

I fabricated an attachment for the perfboard. The board is 2x4 inches and
was to be fastened along the opposite 2 inch sides. I have used four
1/8"x1/4" split rivets put through the box sides and clasping the board in
the splits. I had to widen and deepen the splits slightly with a needle
fire, drill the holes, and put small notches in the sides of the board to
accept a bit the solid part of the rivet. The rivets are tight fits, and
the board is very secure. I don't think any adhesive will be necessary. 

I did find board guides in a catalog, but they are large and clumsy, for
bigger boards.

I'm looking for a commercial grade VHF antenna, preferably one from Decibel
Products DB-224 family.  As many businesses and public safety organizations
move from VHF to UHF, trunked, digital, or cellular systems, these antennas
often appear on the used market (or worse, are just thrown out).  These run
about $650-$750 new so I'm hoping to find something used at a reasonable
price.

Is this a base antenna?  Colinear array?

Yeah, a 4-bay folded dipole design.  Omnidirectional with 6 dBd gain, or if
you move all of the elements to one side you can shift the radiation pattern
a bit to get 9 dBd gain in the preferred direction.  It's about 22 feet long
with a heavy-duty all metal construction (no fiberglass).

Sounds like a nice antenna.  Is this for the digi?

Yeah.  I received an offer to move it to a commercial site.  No charge for
rent or electricity.  In return, I'd help maintain the site (i.e. stop by
every couple of months and pick up trash that's blown into the area, help keep
the weeds under control, etc.)  The offer was from a guy who works for a
company who owns a lot of tower sites.  He and the ham club he's in has a lot
of equipment (repeaters & digis) at various sites.  The site he's offered is
about four miles down the road from the current site.  The tower is higher
(80 feet as opposed to the top of a 28-foot barn) and is on top of a ridge.
Moving there will definitely help increase the coverage along I-35 which is
lacking right now.  Under the right conditions the digi covers part of it but
it's not 100% reliable.  He recommended a commercial grade antenna over a
Diamond or Comet fiberglass type since it'd be nice to only install it once.

The bad news is that I'd have to come up with more equipment since everything
at the current site belongs to the land owner, except for the TNC.  The good
news is that I have a spare FT-1500M so I'm set for a radio, and the rest of
the components are relatively inexpensive (compared the the antenna, anyway).
The only parts I'm missing right now are the antenna (and mounting bracket)
and a lightning arrester.  Actually, I have a lightning arrester that I could
use (It's destined for a Comet GP-15 at my house, which I plan to put up this
spring) so that's an expense that I could put off for a couple more months.

How about approacing a club in the area for it?  Or multiple clubs, since
it would link a larger area, that might benefit multiple clubs.

That's a possibility.  A couple of the clubs know I'm looking for one, but
I haven't asked any of them if the'd support this project financially.

The search is over.  I found one within driving distance.  The price was
reasonable, and it included the mounting brackets.  In a related story, the
equipment for the new digi has been mounted in a 1U 19" rack mount chassis
and is undergoing bench testing.

Sounds like you'll have a good setup for this in no time flat.  :)

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