My SSTran and cold weather

I recall reading an interesting article years back about laptops.. While I don't remember the details, I do remember it saying how very cold weather can do permanent damage to your laptop hard drive, and the lcd, and how you shouldn't have it out in the cold.. but the same article also said that extreme cold would do little damage the laptop circuitry itself...
I don't know how that might relate, but just mentioning it since your question brought it to memory.

By the way... I used to go see the window seals at Sea-World. Amazing creatures... but why would you put your transmitter on one? 😉

Very likely certain capacitors and resistors in the transmitter are changing values in the cold. Unless they are "NPO" quality and 1 percent or less tolerance, the cold will change the values enough to change the sound of the transmitter. These components can also cause the transmitters master oscillator to drift off frequency which can cause the signal to change in a modern day digital style receiver.

The best way to test a transmitter for these affects is to spray specific components on the circuit board with "cold spray". This substance is usually in a spray can and is used for TV repair. After warming the transmitter to operating temperature, open the case and spray components one at a time. Listen for signal changes. You will find the culprit.

First question ... How cold?

All circuits, especially solid state types, have a temperature operating range. Looks like you're exceeding the lower limits.

I'd close the window ... or maybe put it in a PVC weather-sealed box.

"Commercial" grade ICs are spec'd down to 0 C which is 32 F. This doesn't mean they quit working rather the specifications are not guaranteed outside of thieir temperature range. It could be the semiconductors are causing what you experience but it is more likely something in the tuning circuit is drifting as Marshall said.

It is also possible that there is a bad connection in the transmitter that is changing with temperature.

Neil

Yes, Neil just put the finger on a possibility.. a bad connection could be in the form of a "cold solder," that is, a solder point that is cracked or not properly made which makes contact when warm but looses contact in the cold due to expansion/contraction of the metals. You should look over the entire circuit board on both sides under a good light with a magnifier. But also, if a contact is bad, just poking at the contacts with a non-conductive stick or plastic tool while its operating could locate the connection.

Otherwise, if it is merely a temperature related circuit failure, has anyone tried the heating tape that is used on water pipes to keep them from freezing? That would heat up the transmitter, but maybe it would introduce hum.

The proximity effect of the heating tape could further monkey with the tuning inside the transmitter. Until you find the cause through testing, I would suggest not using heat tape. Without first finding the cause, you could experience catastrophic transmitter failure eventually. Just my humble opinion based on years of baling wire and bubble gum fixes.

Also keep in mind the transmitter also distorts when first turned on.
But not like it did last night

The audio started cracking, until the point where it was unlistenable.
It sounded like listening to an AM station off frequency, but no matter how I tuned the radio, the audio stayed the same.
it was about 1.2 C outside when this happened. 34.8 F

I fiddled with the modulation control, compression and gain. Not one of them did a darned thing.
After a last attempt I carefully smacked the SSTran on the window seal (or whatever you call it), and poof the audio returned to normal.

This could be a cold solder, but the SSTran didn't always do this.
It didn't start hating cold until lightening zapped it a year ago
(its since been fixed)

"This could be a cold solder, but the SSTran didn't always do this.
It didn't start hating cold until lightening zapped it a year ago
(its since been fixed)"

This is a significant clue which points to a problem with the repair. The symptoms are more indicative of a bad connection than a component drift effect.

The most efficient way I have found to repair a bad solder joint on a board the size of the SSTRAN is to retouch all the connections with a bit of new solder. It seems like a lot of work but compared to trying to find the bad joint it actually saves time in most cases.

Edit to add: Check the RCA Phono jacks and your cables. The cutting out or distortion of audio is exactly what I have experienced with these connectors.

Neil

It started doing it again tonight, so I checked the RCA connectors, they were fine.
So I tried smacking it back into regular audio,
this did not work.

So I cranked up all the controls on the AM to max and left it there for a minute or so, upon restoring the controls to their original settings the audio was fine.

Why would "blasting" the transmitter fix this issue?

Not sure what you meant by blasting the AM but if you meant increasing the audio voltage by turning the pots on the SSTRAN a couple of things could be happening.

With age, pots can develop a dead spot where the wiper contacts the resistance element. Turning the shaft can wipe the spot clean or result in parking on a good spot in a different location.

Another thing which happens with bad connections is increasing the voltage sometimes "fixes" the problem (or so it would appear though it is not a fix). Most metals develop a layer of very thin oxide or corrosion when exposed to the air. This can take a long time and the layer is very thin but it is thick enough to form an insulating barrier to current. Raising the voltage breaks down this insulating layer as the voltage "punches through" and burns the layer away. The voltages involved are low, on the order of tens or hundreds of millivolts, but can be sufficient to burn through.

Designers of switches and connectors which do not use gold plating deal with this problem by providing a wiping action when the devices are operated or mated which scrapes the oxide away. This is why unplugging and replugging a connector or operating a switch many times will fix the problem.

Now, back to a bad solder joint. This same effect could operate with the joint and increasing the voltage could be a temporary fix. The permanent fix would be to resolder the connection.

Neil

You Know upon a little discovery I found it might just be the VC for the tuning is moving with the cold weather. Upon getting a death grip on the wire antenna the distortion stopped. I adjusted the antenna a bit (I Couldnt find my meter).
and at the moment it looks like the distortion has stopped.
Time will tell

From the sound of things, I'd venture a guess that your SSTRAN is exhibiting instability when the output tuning is just a little off. I had the same experience with mine.

To solve this problem, I swamped the output by installing a 5.6K resistor at R18 and a 560 pF capacitor at C23. This does waste a tiny bit of power, but it helps stabilize the output. My operating frequency is in the 1600-1700 kHz range. If your frequency is lower, you might have to tinker with the value of C23 a bit.

Simply use a 5 watt cement resistor mounted on a small heat sink inside the thing and let that keep things warm. Also put a layer of thin foam packing used in shipping on the inside of the case.

Run a seperate power source to the heat resistor, you can even use a diode and op amp to control the temperature and when the heat resistor kicks in by adjusting it to turn on when the inside reaches a certain temperature and turn off when it warms up at a certain point.

Or use a thermo chip in place of the resistor..but the thermo chips draw a lot of current..but is just another way to take care of the problem. Both methods will work without doing modifications to the transmitter itself which may alter its specifications.

Or go with Marshall's suggestion and install NPO components with wider tolerances. But caps and resistors wont be the only thing you want to swap out....you would also want to go with military rated IC chips in place of the standard chips. I can guarantee that caps and resistors are not the only things being affected by the cold temperatures...the board itself, the foil patterns, switches, pots, practically everything can shift with temperature in that unit with the stock components...so perhaps using a heat resistor on a small heat sink is the better method and you wont alter the unit's design and specifications. After all....those things MUST use the components supplied with the kit..otherwise they will be considered outside of compliance ability. FCC rules ya know. 😛

RFB