S

stevied925

I'm New Here
I can't figure out why I can't transmit from my kx170b.

I do not know much about radios so I apologies for terminology and my description.

I'll start by telling you what I need to do. I'm trying to put together a transmitter to receive and transmit communication from the gound (on the air field) to 4 jets flying around the airfield performing an airshow. I have been giving a kx170b.
Now since it's being used on the ground not in a plane we used a converter so we can plug into a 110V AC outlet.

I have a wiring diagram from this website,http://www.aeroelectric.com/Installation_Data/KX_170B_175B-Install_Manual.pdf, on page 25.

Now we only need the Comm and are doing nothing with the Nav. And I have a headset with a TRS type connection, along with a Push To Talk TRS connection.

So I hooked up my wiring simply by following the wiring diagram and I can power the unit up, I can tune to the weather channel and listen to the transmissions, and when using a handheld transmitter can receive the audio from someone on the handheld onto the kx170b, But I can not transmit from the kx170b to the handheld. If you blow into the microphone you can her a slight tone change in the static resembling the blowing in the mic.

A couple things I plan on trying to troubleshoot. For one I do not have a proper antenna on my kx170b unit yet, but most transmissions we test are done around 10-30ft away from the unit.

Another thing is the unit actually calls for 13.75VDC and we are providing it with 12VDC.

Now if anyone can make suggestions it would be greatly appreciated, but if anyone was an expert and could actually give a very detailed wiring detail it would be greatly appreciated.

The manuel at http://www.aeroelectric.com/Installation_Data/KX_170B_175B-Install_Manual.pdf has a wiring diagram on page 25, but all I know is what power and common are. I used the speaker terminal for my headset, but there are several audio terminals, and there is a mike audio, and mike key, also with a comm output 500 ohm terminal which, I'm not sure exactly what they do.

Please help.
 
stevied925 said:
...For one I do not have a proper antenna on my kx170b unit yet, but most transmissions we test are done around 10-30ft away from the unit.

Another thing is the unit actually calls for 13.75VDC and we are providing it with 12VDC...
Click to expand...

To transmit, you MUST have a proper antenna (using the proper 50 ohm coaxial cable) attached. Without going into too much detail, the antenna presents the correct load to the transmitter. Without the correct load (open or short, or anything too far away from the 50 ohms impedance that an antenna provides) you could actually damage the transmitter. Trying to receive without an antenna will not harm anything, just don't transmit!

Also, it should operate just fine on 12VDC.
 
A proper antenna is absolutely critical.

As for the specific wiring.. you have to read very, very carefully with these terse diagrams.

-Connect pin 33 to 12v or leave open
-Ground pin 38
-Make sure that pins 17 and 18 are jumpered with 16AWG or thicker
-Your headphones should be connected to pin 34 (COMM 500 Ohm output) and grounded to Power Ground (pin 21) but doing it this way without a speaker you would need to heed note #2: "2. IF SPEAKER IS NOT USED, INSTALL A 4OHM, 10W RESISTOR TO SIMULATE A SPEAKER LOAD BETWEEN PINS 41 AND 21"
It might just be easier to use your headphones on pin 34, but hook up a 4 Ohm radioshack speaker to pins 41 and 21 as well.
-It may or may not be necessary to connect pin 1 to 12v. If it works without it, then probably not.

Your power supply needs to provide at least 5 Amps. If the power supply is wimping out, it would do it during a transmit, so that could be the cause of your problems (that is, if the antenna is not the issue).

Hope that helps!
 
Thank you, Sparky and Daniel, I can't wait to get down to the hanger and make the changes.

I'm gonna purchase an antenna. Again forgive my ignorance but I assumed all antennas were the same. I wanted to purchase this antenna, http://www.frys.com/product/3063289?site=sr:SEARCH:MAIN_RSLT_PG, but now I'm questioning if it will work, as you can see it is a cb antenna for a car, but now I'm thinking I need an antenna that is specific for aircraft. Is there anything I specifically need for my antenna?
 
You need an antenna designed for the aircraft communications frequency range of 118 Mhz to 136 Mhz and 50 ohms impedance. The CB antenna will not work. Also, connect the antenna with RG-58 or RG-400 coaxial cable and BNC connectors.
 
12 volts should...

stevied925 said:
....
Another thing is the unit actually calls for 13.75VDC and we are providing it with 12VDC.
......
Please help.
Click to expand...

...be OK - but make sure that your power supply is actually producing 12 volts when you transmit.

The current draw in the older radios is probably quite high in transmit mode and might be pulling down the output voltage of your power supply.
 
I didn't see anyone mention the microphone inputs. the mic key should go to ground when you PTT. this is also known as the tip on the mic plug. it should go to pin 40. the mic audio needs to go to pin 39. Someone mentioned the note about the 4 ohm load on the speaker, that is very important for this unit.

Also be very careful with the locking pawl. If you try to loosen it too far it will swing around and break the wafer switch which can also cause it not to xmit and may make the unit uneconomical to repair.

I used to repair these units if you need any more help.

Jay
 
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