Static on My PTT Phone

[LarryInMichigan]

I am having alot of trouble with static on my PTT phone.  When the PTT transmitter is connected, there is loud, almost continuous static.  If I connect any T1 transmitter in its place, there is static after I speak or blow into the transmitter.  If I connect an AE81 transmitter,  I hear no static.  I tried the PTT transmitter in an AE80 phone, and I heard the same static, so I am assuming that my PTT transmitter is bad.  Why do all three T1 transmitters produce static?  All three work well in WE/SC 500 phones.  Do I need to buy a new PTT transmitter?  I was hoping to get away with a T1 which will fit into the handset. 

Thank You


Larry

[Phonesrfun]

Perhaps its the contacts.  The AE transmitter has a very pronounced tip that comes in contact with its contact spring, so maybe it just has a more solid contact than the other transmitters.  I can think of no reason why a T1 would not work.  Even if the resistance is widely different from the PTT, they should work under a very wide degree of circumstances.

[LarryInMichigan]

I thoroughly cleaned all contacts inside the phone and handset, and I even tried different handset and line cords.  Also, because the T1 transmitter does not fit very well into the handset, I soldered wires to the transmitter and connected them to the screw contacts in handset.  As an experiment, I just added a 150 ohm resistor in series with the transmitter, and the static seems to be greatly reduced, but not completely gone.  If I blow into the transmitter, there is a sizzling static sound for several seconds.  The same transmitter worked well in a 500 phone.

Thank You

Larry

[Phonesrfun]

I have no clue.  I would be curious to know what the resistance of the PTT transmitter is.  Did you try the age-old routine of rapping the PTT transmitter element on the table to unpack the carbon granuals?

[LarryInMichigan]

The back of the PTT capsule has 100Ω printed on it.  I tried rapping, banging, and heating the capsule.  I managed to make it more sensitive, but it still causes loud static.  I think that my last rapping attempts broke it altogether.  I might just see if Phoneco has a replacement.  I just hate to pay $20 or so for a transmitter for a phone which was $10, especially when I am not certain that it will solve the problem.

Thank You

Larry

[Phonesrfun]

Larry:

I am so sorry to hear about the transmitter.  I feel bad because I suggested you bang it.

I also understand the reluctance to buy another, not knowing if the problem is the transmitter or something else in the phone.  100 Ohms should be right in there, although at the lower end of transmitter resistances.  A T1 measures in at about 500 ohms, and Ralph Meyer's book says anything from about 75 to 750 is within range.

Static issues are sometimes very difficult to track down, because some element within the phone has not absolutely failed.  Just kind of.

One thing you have done is to indicate that an AE transmitter is static free.  The AE is roughly equivalent to a T1, electrically.  If there is no static with that arrangement, the phone should function.  The only thing I can think of is that the PTT phone is looking for a lower resistance.  I know little about the European phones, so maybe they are not as tolerant of a wide range of resistances, but they should be because a transmitter by design should have a wide range. 

You sound like you have been around the block with electronics before.  If you have a couple of jumper wires with alligator clips like the one shown below, you might try hooking a 100 ohm resistor to the transmitter springs and see if it gets static with a solid fixed resistor.  Then try a 500 ohm resistor and see if there is static.  Either way, a solid resistor should produce an absolutely quiet result in the receiver.  If you can eliminate the rest of the circuit from being the problem, you could feel better about buying another transmitter element. 

If it is still noisy, then I would look for a bad connection within the switches or even a bad solder joint on one of the components.  I know this sounds like a shotgun approach, but you could also try substituting the receiver element.  It may be that even with the AE trransmitter in place that it would start in with static too.

In another thread, Jorge solved a ringer problem for Dan, just by suggesting that the line cord be swapped out.  Sometimes the solutions are not where we most expect them to be.

So, don't give up.

-Bill

[dsk]

As have discovered these telephones has bin made with different circuits.

By experience I have this conclusion. If the telephone disconnects when removing the transmitter capsule, it will probably be designed for a low impedance capsule, if not it will be best with a high impedance capsule (Witch are the most common worldwide).

The next is: If proper working is the issue, just use whatewer feels like working well.  This may affect the sidetone, and hearing yourselves well in your own receiver does not tell you whats working best.

If you have no test setup, you may use 2 telephones and a 9V battery. (all in series circuit) or just call your mobile phone.

dsk

[LarryInMichigan]

Bill,

I appreciate your suggestions.  I should have thought of the 100/500Ω resistor test.  I plan to look for some resistors later today (my current supply is very limited).  I have a degree in electrical engineering, but I have writing software for the past 20+ years, so my skills are somewhat rusty.

I think that I already eliminated the other likely culprits.  I swapped the line and handset cords, cleaned the hook switch contacts, and bypassed the dial.  I also wiggled various other wires, but nothing seemed to make a difference.

Don't feel bad about the transmitter.  It wasn't your advice that caused me to break it.  It was bad anyway.


dsk,

Thank you for the information.  I have been calling my voice mail and leaving test messages to hear how the transmitters sound.


Larry

[Phonesrfun]

Larry:

Great that you are getting back into the electrical engineering field with telephones!  A good place to be.

After looking at the diagram that was posted some time ago, I had another thought last night after I made my last post. 

There are two resistors in the circuit that are in the sidetone impedance balancing network of the phone.  If they are composition resistors, one of them may have become brittle and become bad too  If the resistor on the transmitter terminals fails, you might also look to one of those as a suspect.

-Bill

[LarryInMichigan]

Bill,

I see that the diagram shows a couple of resistors, but they must be buried somewhere inside the inductor assembly, because they are not visible in the phone.  I measured the DC resistances between the various terminals on the inductor, and they all match with the values printed on the label.  Here is the diagram for my phone.  I apologize that it is not entirely legible.



Here is the inside of the phone:




Larry

[dsk]

These resistors are bifilar(?) windings made on the same core as the transformer.

dsk

[Phonesrfun]

OK, per d_s_k's post, the resistors are an intergral part of the inductor winding.  Not uncommon, and really not susceptible to giving problems either.  Larry, your phone is very clean, I must say.  The part with the yellow and blue leads soldered to the inductor must be the varisistor or two back to back diodes that are in the receiver circuit.

-Bill