Saber Service cable and external antenna switching?

[oh2lak]

Hi.

I build a service cable for Saber radio, and I'm having trouble switching on the external antenna.

Also I built the RTX-4005B service box, and according to the schematic of the both previous, the Opt Selection pin on saber radio (pin 7) is connected to the PTT pin of the service box, and grounded according to the PTT switch on RTX4005. This does not make the external antenna switch on, or what?

Erik

[kd6kml]

I thought tere was a zener diode in therer somewhere that set a voltage so the radios knew what accessory was plugged in? A different value for speaker mic, Convertacom, and public safety mic.

The test cable needs to make the radio think it's connected to a public safety mic. That way, the antenna is routed to the test cable for both TX and RX.

I think I am remembering things right. It's been a few years since I played with those radios.

Josh

[Monty]

Hi:

I am always impressed when one
will take the time and effort to build
one from scratch.

However, I suspect you may have missed
the Mode Control lines which are part of the
D connector.

Please review the wiring and 2 resistors
located on pINS 10,1, AND 14.

In order to take advantage of all the
neat service options, everything MUST
be exactly like the diagrams in the service
box as well as the connector.

Also, double check your work ! Sometimes
you might cause irreversable damage to the
radio if the wiring is inncorrect !

I do have the Factory Cables and Box if you
should ever elect to go the full route.

Monty

[oh2lak]

Hi.

After studying the service manual, the Opt Selection pin recognizes three different modes, and switch microphone, loudspeaker and antenna accordingly to the accessory connector.

I have now everything working, but I might want to notify that the schematics of the Saber service cable and the schematic of the RTX4005B service box lack some details, for example the mode control resistors are not shown in the svc box schematic.

I'll try to sketch a new schematic of the service box with full details.

Thanks for revealing the missing spot :)

Erik

[Tom in D.C.]

Erik,

Just for the record, I once owned a Saber I on which the
antenna sensing and switching module was bad. It's
clearly shown on the schematic of the Saber. If you
plugged in a public safety speaker mic the radio still
put its RF out via the connector on top of the radio.

Tom in D.C.
W2NJS

[Will]

Our Saber cable does not have the RF contacts or RF cable on it. It does have the connections and plug for the test box. Seems that it is for the later Saber that has the coax connector in the antenna connection.

[eleet]

I just got a sys saber VHF and it always wants to use the accessory connector for the antenna. Verified that OPT SEL is still 5v and mike and speaker still work. Looked inside the machine and some clown was in here before - the gold finger coming to the rf board from the top of the radio housing was not aligned properly and touching who knows what with the back cover attached.

Looks to me like both the accessory connector and the stud are connected during rx operation and all power is sent to the accessory connector during tx operation.

Since it will take a couple of days for big M to get the manual here, can someone point me to the antenna switch module?

[AEC]

For some reason, I recall that both the internal antenna post and external antenna were connected to the same point, the pin that routes to the rear jack is at the same R.F potential as the supplied whip(see the "M" shaped wire on the controller board) this connects directly to both ports(external & internal) antenna connections, the PIN diodes are on the controller board before the connection point of these two items.as the screw-in antenna is the point where the pin supplies R.F to the accy. jack on the rear of the radio.
There's no switching of R.F between the internal antenna and the external since they are a common point and "should" be at a nominal 50 ohm level.

Take the top housing off and take a peek, there are no physical differences, and the yellow tab that connects to the ground of the controller board is just that, ground, which is also the common ground for the ring on the accy. connector and is held in place with the top screw for the rear cover(also retains synth. module as well) All screws MUST be tight or the nasties will pop up and spoil the day(hums, squeals and the like).

My .02 cents on the subject.........

This response in no way is to be construed as a comment about the service cable, only the common antenna connection points.