# Airwire T9000 Antenna fallen off



## Pete Thornton (Jan 2, 2008)

Hi guys. I have a T9000 on my bench being repaired. I found the main problems (bad battery and the center pin of the antenna socket had been pulled through so it didn't contact the antenna.)

I'm left with one puzzle. The antenna socket is soldered to the top of the PCB and this is also the mechanical support for the antenna. (See image I copied from cvp's website.) However, this one on my bench has no solder pads for the two outer tabs. (Photo attached.)

I imagine the outer tabs are ground plane, so there should be something to tie them to the PCB ground? Any idea where it is?

(I have no problem with the mechanical support - I'll drill a couple of small holes and thread some copper wire or small bolts through as solder pads.)

I did attempt to email [email protected] and it bounced. Any idea how to contact them?


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## Totalwrecker (Feb 26, 2009)

Pete in my limited knowledge base, all antennas are a single wire. I'd connect the one you can see detached and see if that works before worrying about a 'missing' anchor.
dos centavos


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## Greg Elmassian (Jan 3, 2008)

Pete, you are right, you would expect the outer pins of the socket to be soldered to pads on the circuit board.

It's a crappy design, but electrically, it is as John says, just the center conductor is important. (was there solder on the 2 outer legs of the socket?)

Possibly any pads on the circuit board were ripped up, since you stated the center pin in the socket was pulled down, I'm guessing the antenna was pulled away from the unit, pulling the outer shell up, and leaving the center pin still attached to the circuit board.

A better picture would help.

Greg


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## Pete Thornton (Jan 2, 2008)

> A better picture would help.


Too late! When I got it to my bench, the antenna was connected to the socket that was 1/4" away from the PCB, and only the center wire was soldered. (As the socket was pulled away, the center, soldered lead was pulled out of the socket and thus wasn't touching the antenna core.) There's no sign of pads to solder the outer pins of the socket, and I can believe they were ripped off as the antenna got loose.

So thanks, guys, for the suggestion that the antenna doesn't need grounding. I'll drill some tiny holes and give the antenna a decent mechanical mount so it doesn't get ripped out again!


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## Totalwrecker (Feb 26, 2009)

Pete Thornton said:


> Too late!
> 
> 
> The better picture part; Hold your camera farther away and zoom in a little, will help focus the pic.
> It was fuzzy. Mine does that when I get too close.


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## Pete Thornton (Jan 2, 2008)

Totalwrecker said:


> Pete Thornton said:
> 
> 
> > Too late!
> ...


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## Pete Thornton (Jan 2, 2008)

*More antenna stuff*

Very interesting. I drilled the PCB for some mechanical support and found 2 solder pads on the underside of the board. (see photo - hope it's clear enough for you.)

I put some 00-90 bolts in and resoldered the antenna socket. Didn't make a big effort to connect the pads underneath to the socket ground - maybe I should.


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## Greg Elmassian (Jan 3, 2008)

OK, so just to understand, the "legs" on the socket are on the side opposite the solder. 

Is the center pin trace on the side of the board shown, or the other side?

Looks like the traces shown, that the hex bolts are going through are connected to the ground plane in the circuit board.

If those bolts go into the socket "legs" then you have it connected to the ground. That's good, for a 1/4 wave antenna, basically more ground plane the better.

Funny, there's no way to solder the legs of the socket to those 2 pads?

Often an SMA socket has 4 legs for edge mount:


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## Pete Thornton (Jan 2, 2008)

> the "legs" on the socket are on the side opposite the solder.
> 
> Is the center pin trace on the side of the board shown, or the other side?


The center pin had a big blob of solder left after I unsoldered the socket. I didn't touch it - assume it is still connected somehow to the PCB circuitry. We'll find out on Monday when I take it back to the owner for testing.



> Looks like the traces shown, that the hex bolts are going through are connected to the ground plane in the circuit board.


Not explicitly. I think the bolts probably make a connection to the metal pads, but I made no attempt to solder them. The comments that the antenna doesn't need grounding may be right.


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## Greg Elmassian (Jan 3, 2008)

this is a 1/4 wave antenna, you can verify that by calculating the 900 MHz wavelength with any rf calculator on the web.

(here's a calculator, be sure you set the 1/4 wavelength, you will get about 3.28 inches)

you can then validate that 1/4 wave antennas work best (most people will tell you require) a ground plane

(here's a reasonable article: http://www.radio-electronics.com/info/antennas/vertical-antennas/quarter-wavelength.php)

You can also see the ground plane in the circuit board, and also your hand helps a bit. (RF is like horseshoes, close counts too, besides touching)

All this stuff is on the Internet or if you talk to an RF engineer or most people with a EE degree.

There are no special laws of physics for model railroading. 

(Oh you could also ask a Ham Radio operator, my callsign is N6RGZ)

Anyway, you don't need solder to make an electrical connection.

Back to the subject:

1. are there only 2 legs on the socket as opposed to the picture I posted?
2. can you see if the solder pads are indeed connected to the rest of the ground area? I'm pretty sure they are just from your pictures.

I had one here, doing the same repair, and remember it was a poor mechanical connection, and subject to easy damage.

Greg


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## Pete Thornton (Jan 2, 2008)

> There are no special laws of physics for model railroading.


No, but you do have to study them to understand RF antennas.



> are there only 2 legs on the socket as opposed to the picture I posted?


Did you post a picture? I don't see it. Anyway, this pic from CVP's website shows the socket with a center, insulated pin and 2 outer ground pins - or presumably they are grounded.












> can you see if the solder pads are indeed connected to the rest of the ground area? I'm pretty sure they are just from your pictures.


Nope, though I suspect the bolt is in contact with one ground pad. I'm reluctant to pop the knob and take the PCB out, as it seemed there was just a simple mechanical problem.

Incidentally, what's with CVP's lack of email? I tried twice and it bounced.


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## Greg Elmassian (Jan 3, 2008)

Drat, forgot to double check the picture:

Most edge mount SMA's have 4 legs, and you never posted a picture of the connector alone... did yours have 4 legs or just 2... if just 2 that is a clear reason they come apart.


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## Pete Thornton (Jan 2, 2008)

Only 2 legs. And yes, it seems like a terrible way to make the mechanical attachment. One bang and the pads rip off, as these did.


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## Greg Elmassian (Jan 3, 2008)

Wait, that picture shows 4 legs, 2 in the air and 2 on the other side it appears.

The idea is to have legs on both sides of the board, and then the center pin "lies" on the top of the circuit board.

Looks like 2 of the legs have been cut short.

Greg


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## Pete Thornton (Jan 2, 2008)

> Wait, that picture shows 4 legs, 2 in the air and 2 on the other side it appears.


Naw, that's the bolt head and under it the pcb that I soldered the single leg to. You can see the other side is just 1 leg out on it's own. (It's supposed to be soldered the a bolt piece that is screwed in the board - maybe time to reapply some solder.


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## Greg Elmassian (Jan 3, 2008)

In the picture below, the legs are against the pads on the board and the solder acts more like glue.

I think your repair might still flex the solder too much... so it's hard to see but you have a bolt from this side going through the leg and then the circuit board?


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## Pete Thornton (Jan 2, 2008)

Well, it's Monday, and whaddya know. We have a defective socket. Jack had another (bad) T9000 so I popped the PCB out and noted a 4-pin socket (+center conductor) soldered to the board. See photos of the other T9000.

The one I worked on, with the strange colored pads, obviously had the pads ripped off the PCB at some time. (And my attempts to fix it are not robust enough - it was bent by the time I drove to his place!!)


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