Anyone good with selecting transistors?

[70cutlass442]

Okay, little project going on here. Using two NEXTELS and trying to bridge them using the direct talk to make a repeater or to successfully cross band them... Here is what I have so far:

Pin 14 and 17 are GROUND
Pin 13 is grounded when PTT is pressed
Pin 9 has a 3VDC when receiving.


I need a transistor (believe I need a NPN) to receive that 3vdc signal, and inturn pass the ground through it. This is all very low voltage. I would have around 2.7-3VDC at the base.. I know very little about electronic components so any input would be great!

 

[krokus]

What you are describing makes no sense.

1) What are you interfacing?
2) What are you trying to connect this transistor to?

 

[5kw]

We will call this circuit Rat Avenger, do you have a good digital multi meter? When you say pin whatever is ground, check the pin against the chassis to verify ground. 2N2222 are cheap and Rad Shack may have several. Now put this killer voltage on the base to see if you are close enough to ground on the high side of the transistor, meaning there will be a voltage drop across the transistor junction, small amount but it is acting like a switch like PTT but not like putting two pieces of metal together. 5KW

 

[70cutlass442]

thanks for the response guys... what i am trying to do is use two Nextels and make a direct talk repeater. Also wanted to try to interface it with a maxtrac to see if I can make a "crossband" repeter. In order to trip the PTT feature of the nextel, it is just like most other radios as in a lead needs to be "pulled to ground" That part is fine. However, when the Nextel receives, instead of one of the leads giving me a ground, its give me a 3VDC signal... so im trying to use the transistor as a switch to signal ground so i can pipe that into another Nextel/radio... 5KW, to answer your question... I did not verify that its chassis ground... the pinout just says ground on the diagram, and i used this pin to verify the negative side of the 3vdc... My questions for you... I see transistors are rated in voltages... are these MAX voltages? I see some where the base is rated for 6V... but would 3V be enough to trip it?

 

[KC4RAF]

Pins 9, 13, and 14; are they

terminals to what? PLL IC? And from what you indicate you're trying to do; no. You will need quite a bit of electronic knowledge to do such an operation. You'll have feed back and cross modulation.

 

[5kw]

As others have said, I am not sure of your equipment, skill level and if you have any amatuer radio people or groups around for hands on advice. If you are using db9 connetions with tx,rx, ptt type signals, these rs-232 connections can take some abuse but not lightning. PLCC IC'S are not directly connected to anything close to the outside world, I have seen some poor designs, because of static or chip failure I have replaced by hand 68 pin 0.050 pitch PLCC's directly soldered to the board (SMD) nut much phun.

I did a google search "Cross Banding Two Radios" or you can vary the search criteria, I didn't spend much time but read the first link carefully, the second link, encryption is one of their options but not on the Ham Bands!

For now, forget I got in the mix with a 2n2222 transistor for PTT and do some more research.
Schematics and Assembly drawings are gold to any technician, so are a few good tools.

https://dps.mn.gov/divisions/ecn/programs/armer/Documents/standard3250.pdf

EFJohnson Technologies | Portable Repeater

 

[70cutlass442]

I will try to explain my self a bit better... I know its hard to visualize what it is i am doing so i will try to link a pic! If you can picture the connector on the bottom of a nextel phone.. there are 17 pins on the bottom. Those pins consist of several ones that are useable. One of the pins will signal 3VDC when the phone receives a direct talk or direct connect conversation... it is momentary only for the duration of the receive. Unfortunately, I need that to be a momentary ground instead. the ground is then used to trigger the PTT of a mic input which will then signal transmit on the transmit radio. I do have two constant ground pins available for use too. Does this make anymore sense? my knowledge on electronic components is spotty. I can read a schematic and solder just fine... but the actual logistics of what those parts do is hit or miss! Thanks again.