TAD6073A, Motorola Base Antenna

Josh · Post by **Josh** » Sun Apr 08, 2007 1:03 pm

This may be a post for the "system infrastructure" section, but I think more people check this forum over that one, maybe someone has info.

I acquired a TAD6073 antenna the other day, tore it apart, cleaned it, and reassembled it.

It's a folded dipole over what otherwise looks like one of those firecracker railroad locomotive antennas.

These aren't made anymore and I can't find a pic online but I know these were popular with public safety as I still see them everywhere, maybe not the same band segment, but the style is still common.

I'm wondering a bit about the theory behind this design. It has no ground-plane, but ones made today do. It also has a lot of extra crap which I can't figure out. For instance, the 3' pipe that leads to the folded aluminum on top, inside of it runs a brass conductor of varying thickness. The pipe makes the antenna much longer than it could be, and the similar ground-plane model on Tessco.com is completely without it.

Apparently it has withstood the test of time but I'm curious as to people's thoughts and opinions about this style of 0db gain antenna. If it's not the best then maybe it's no surprise that Moto doesn't make them anymore.

-Josh

Will · Post by **Will** » Sun Apr 08, 2007 2:36 pm

Josh,

That is a 1/2 folded dipole over a coaxial sleeve antenna made by Phelps Dodge originally. Dammed good antenna.

The 17" sleeve is the 'ground plane' part or counterpoise of the antenna.
The upper 1/2 wave element is folded for lightning and static grounding. Just one half of a folded dipole or 1/4 wave radiator. There is some impedance matching going on in the support pipe.

When mounting this type of antenna, coaxial dipole, make sure that the mounting is clear of the bottom of the sleeve by at least 18".

wa2zdy · Post by **wa2zdy** » Mon Apr 09, 2007 2:30 pm

I got one of them on ebay a few years ago for $6. Will is right and it is as far as I can tell absolutely indestructible.

sigmtr · Post by **sigmtr** » Sun Apr 22, 2007 3:24 pm

The railroads used these types of antennas at defect detector locations. But nowadays, they seem to go for the cheapest thing possible. Below are some "then and now" images...

Doug

Old style, at Perrysville, IN on CSX (then Seaboard System, June 1987)

New style, on CSX at Danville, IL at detector new last year. This is just an NMO-mount quarter-wave on an L-bracket attached to the cabinet!

Will · Post by **Will** » Sun Apr 22, 2007 7:09 pm

What the heck is that thing on the plastic PVC pipe?

Looks like a bug zapper...

Josh · Post by **Josh** » Sun Apr 22, 2007 9:52 pm

That's the antenna all right, and I already knew how common they are with the railroads.

As for the second one, I've found that to be quite typical on the defect detectors made by "Southern Technologies" . Norfolk southern uses them religiously and are actively replacing older Servo ones on Conrail lines with those.

I think they're kinda crappy.... running keys over the transducers can make the device transmit the report. Older units and those made by Harmon/GE use track circuits to actviate the units.

-Josh

Will · Post by **Will** » Sun Apr 22, 2007 11:21 pm

So that "bugg Zapper" is a transducer? So it is a sound picking up device?

Josh · Post by **Josh** » Mon Apr 23, 2007 7:02 am

Will wrote:So that "bugg Zapper" is a transducer? So it is a sound picking up device?

No, idk what that thing is. My guess is perhaps GPS related somehow?

A transducer in my context is a little black bar attached to the rail that that detects the train wheels and can easily be tricked by using a key ring.

-Josh

Post by Pj » Mon Apr 23, 2007 8:23 am

Looks more like a weather instrument.

sigmtr · Post by **sigmtr** » Mon Apr 23, 2007 12:16 pm

Pj wrote:Looks more like a weather instrument.

Right, I think it's a temperature sensor. By isolating it on a section of PVC pipe, the mount won't act as a heatsink back to the mass of the cabinet. I guess that gives you more of a true air temperature reading. There again, the sun ought to warm it up no matter what!

I'll ask my maintainer buddy what it really is sometime...

Doug

k2hz · Post by **k2hz** » Mon Apr 23, 2007 12:29 pm

It is a humidity and temperature sensor.

http://www.rotronic-usa.com/v2/products ... m_over.htm

sigmtr · Post by **sigmtr** » Mon Apr 23, 2007 12:37 pm

Doh, I guess it could be also PVC to avoid making a bizarre kind of yagi or reflector with the quarter-wave omni...

If anyone wants to see what the rest of the detector looks like, follow these links:

http://sigmtr.cooketech.net/software/pi ... _mp119.jpg
http://sigmtr.cooketech.net/software/pi ... -close.jpg
http://sigmtr.cooketech.net/software/pi ... -ded-1.jpg
http://sigmtr.cooketech.net/software/pi ... -ded-2.jpg

The little gray boxes on the outside of the rails are the hotbox scanners, also known as bolometers. They have a shutter inside that opens when a wheel triggers the magnetic wheel sensors (the boxes on the inside of the same rail). These sensors can also be used to determine train speed. The big black things are the dragging equipment detector. Each plate is attached to a shaft that will rotate in either direction. Anything that strikes the plates during a train passing will move a contact off-normal to indicate dragging equipment.

Doug

Terry_Glover · Post by **Terry_Glover** » Tue Apr 24, 2007 1:38 am

I like this Choo-Choo stuff.

KitN1MCC · Post by **KitN1MCC** » Wed Apr 25, 2007 6:07 pm

i think they are also using a smaller antenna so the detector will not go that far so it will not interfer with other comms

Will · Post by **Will** » Wed Apr 25, 2007 10:06 pm

I will second the limited range of the detectors radio transmitter. I think there is a transmitter power limit on them also according to licenses on the UP in the Cajon Pass in So California.

Did you see all those spikes that have 'pulled' loose? In So Cal most of the wooden ties are gone, replaced by 660 pound concrete ties with metal rail clips., and continious welded rail.

Great photos..

sigmtr · Post by **sigmtr** » Thu Apr 26, 2007 5:55 pm

Will wrote:Did you see all those spikes that have 'pulled' loose? In So Cal most of the wooden ties are gone, replaced by 660 pound concrete ties with metal rail clips., and continious welded rail.

Great photos..

Thanks, Will. This is CSX, so a few loose spikes is requisite.

The reason I shot those points is that they are going to install a second main track for a bridge project that will let them take one track out of service at a time. By extending the existing double track, they can still meet trains and in the end have more capacity. But no one told the signal gang this was in the works when they installed the new detector last fall, and it's right in the path of the new track. Another CSX moment, and continued employment for the signal gang!

Doug