6m and Antenna stuff
ka2zev at yahoo.com
Fri Nov 23 09:47:05 CST 2007
While most people are out feeding on Thanksgiving, I was playing with NMO antennas.
Yes I admit it, I don't have a life.
Had a wild one with a Diamond NMO base 6m antenna.
It's a base load design with a small coil and a whip.
I forget the exact p/n.
Ran it on the antenna analyzer and it failed on all frequencies.
It would not tune.
In my world antenna failures don't happen often.
It's like finding a hammer that can't seem to drive in a nail.
Worthy of investigation.
Did the basic DC (Ohm Meter) checks, and that came up zero connections for the center conductor.
Most base loads show zero ohms (DC)
center to ground,
ground to whip
center to whip.
This one only had the ground to whip path.
Since it didn't work at all in RF, there was no internal cap or similar trickery.
Either way, if it was not going to work, it was junk.
Junk can still be of value by ripping it apart and learning why it failed.
After a little digging I found two flaws with it.
The wire going to the metal part that holds the whip, was broken.
This may have failed when I twisted the top off the plastic coil protector.
After I removed the plastic (press fit no way it was coming off w/o a fight) I could see how the coil was made.
But the antenna still had no dc connection to the center conductor.
The second and greater mystery was why the center conductor was not working into the base of the coil.
The whole system looked idiot proof.
The only way to get at it was using a cut off wheel on the dremel tool, and start hacking through the base.
After much cutting and brass dust this was the answer.
The pickup tab mounts to a plastic disk in the base of the coil.
The contact to the center of the antenna is a press fit, and that lost it's ability.
Either the plastic lost it's resiliency or the metal parts developed a bi metallic failure, that prevented the RF and the dc from going through.
Either way, the thing was toast.
It's now littering the bottom of my junk pail.
I gotta wonder how many other Diamond mobile antennas are made the same way.
So consider this a heads up if you start getting flaky performance from yours.
The Larson's are soldered together, kinda prevents this from happening.
In other news...
Is there anybody who still wants a 6m radio.
I can spend part of the night and knock together a couple of more units.
At that point I want to stop.
Mostly to have some spares should a client's unit fail, or someone needs a control head.
Been thinking of ordering a second batch of ten, is it worth the time?
Got into testing the antennas Frank G has for the band.
These are AS base loads, similar in style to some old CB antennas.
The price is right.
Seems they were set up for about 49.9 mhz.
They re tune well to 52.5 with the 1.5vswr points outside the ham 6m range.
Did two of them and a base to test them on.
If anybody is holding one and wants me to 'tweek' it up, I'm going to try like heck to be at the TACO's meeting this week with the base, the antenna analyzer and my favorite bolt cutter.
I may skip out of work early today and visit a cb dealer/customer and pick up some bases.
Figure 7 or 8 units should do the trick.
Will also check with Radio Shack and see if they sell something adaptable.
One of the best places to shop for this kind of stuff is a Pilot Truck Stop.
They have a whole wall of CB goods that can be adapted for 10 and 6m w/o too much work.
Sandy said something that struck my fancy. The Larson 2m 5/8's wave mobile is also a 1/4 wave on 6m. I think I have this right. Saw the same thing happen on K3CSA's car. So a radio and a diplexer might be the trick to dual band that antenna. Something to look into.
Software Load Outs.
Will need to update any body using the first batch of Midland 6m radios.
The all black STR's that Ive passed out, have this updated load out already.
The ones I want to update are the 320 channel Syntech II's.
There is a repeater on 53.13 that uses a 107hz PL, and the Ashburn unit will get it's PL back some day when fixed.
Is there anybody who knows who is using 53.67?
I hear it active once in a while, but I don't know who it is.
Might be a closed system.
Is there any interest in a 6m users net.
Was talking to Evan of the 53.61 pl 67.0 hz now in Ashburn.
Was also thinking of a 6m group that meets every so often at the Old Dominion Brewing.
Just a thought.
"You are, what you do, when it counts"
"Gravity, the quickest way down"
Mayor John Almafi
"You ever drop an egg, and on the floor you see it break?
You go and get a mop so you can clean up your mistake.
But did you ever stop to ponder why we know it's true?
If you drop a broken egg you will not get an egg that's new?"
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