I would not want any part of a transmitter that is going to fry that easily. Just to carry it from Home to a trip? Well looks like Ramsey would be a poor choice then. I guess there is only a few good ones.
Didn't have when I had mine but there's a mini surge protector you can now get that goes across the conductor and ground at the antenna to protect the GAL-5.
Mark
wdcx, why would anyone in their right mind have an issue with ensuring that a transmitter is Part 15 compliant?
Ditto Neil.
The schematic for the old Ramsey FM25A transmitter shows a 2SC2498 transistor as the RF output, a seemingly simple circuit with apparantly no filtering. Memory says Neil might have a 25A transmitter, so we can ask how pure the output might be.
Having experienced two Ramsey FM25B transmitters I was unaware of the perishabilty of the GAL5 output chip and luckily had no failures.
Now looking at the diagram for FM30B, we note that the circuit is almost the same as the FM25B except for two parts that I'm guessing might have been added to reduce the tendency of GAL5 to expire due to static discharge...
L8, 2.2uH, an inductor coil, shunts RF output to ground right at the BNC out, probably able to sink any voltage caused by touching the telescoping antenna. No such part exists in the 25B.
The other new part is also a 2.2uH inductor between the +12V and R34, 120_Ohm 1W resistor, supplying DC to GAL5.
My good luck in the past might be owing to the floor.
Back in 1990 when my late wife and I set up to operate an AV business from here we decided to dispense with static-causing carpeting to protect our delicate audio/video equipment. As a result, there's no static electricity unless we crinkle a trash bag.
The new copper solder tips now have a tracking number so construction of the FM30B is not far off.
When the soldering begins I intend to do a marathon session to get the transmitter built in one continuous stretch, with a dinner break before testing.
While waiting I've read the manual about four times, noting one informative thing and one un-informed thing.
In the circuit description section it says, "L6 (inductor) is simply to provide a DC path to ground in case of any static electricity or low frequency interference."
Aha! That's what I guessed. L6 is 2.2 uH from RF output to ground and helps protect GAL5, the output chip. Those with FM25B transmitters might benefit by adding such a part.
The un-informed thing is the distinct presence of a loudspeaker symbol in the circuit diagram which is not mentioned anywhere in the manual except during the building steps, where it tells to install the mini-speaker. What I cannot imagine is what purpose the speaker serves.
My guess is that a speaker might be used to "beep" when the buttons are pressed.
I recall that there was many a discussion about the GAL5 static problem on the defunct Ramsey user's forum. Their solution was the addition of the inductor as you have deduced. This probably helps but the inductor is only going to shunt energy at low frequencies. It is probably a good practice to avoid touching the antenna but if you need to then ground yourself to the case first. My solution would have been to shunt the output with a couple hundred ohms of resistance to dissipate the static. This would be frequency independent.
Yes, I have a FM 25 first model but I have no way to measure the spectral purity of the signal. We used one for demonstration in the lab at the college and I did connect it to a spectrum analyzer and don't recall seeing anything unusual in the spectrum, but don't take this to the bank.
Neil
On the question of the spectral purity of the FM25 original transmitter I gather from your answer Neil that no out of band emissions were happening.
If the new FM30B has a beeper for acknowledging pressed buttons that seems like a friendly thing and I may be doing a lot of beeping.
I used the FM 25 and the analyzer to demonstrate the occupied bandwidth of a FM signal. When a sine wave audio signal is applied there is a predictable spectrum found by using the modulation index, the audio frequency, and Bessel Functions. The calculated and measured components were very close to agreement and I don't recall seeing anything near the displayed spectrum.
All transmitters produce harmonics and it is a matter of keeping them below legal limits so I would expect to see harmonics unless they are below the analyzer noise floor. Unfortunately, I do not recall measuring harmonics but I also do not recall seeing any and I wish I could be more certain of this.
Neil
I know you'll get some harmonics at close range, but greater than 40 feet would be a concern for harmonics. I've heard Ramsey Transmitters are quite clean. It will be interesting to see just how true this is.
Gearing up for marathon kit building session.
The new copper soldering tips for the 25-Watt iron departed from the west coast on Wednesday, October 28.
There is no tracking information posted yet for Thursday October 29th.
I hope it's on a train. Trains make better deliveries than planes.
In 10-minutes I'll start clearing the working surface and getting the Ramsey FM30B parts all lined up and ready to go.
We'll charge the camera batteries for before, during, and after pictures.
Hobbies are good when building a project you don't need becomes such fun.
Here on the east coast of the U.S.
it's 11:19 PM local EDT. The clocks go
back in a couple of hours.
I bet Carl is hard at work.
Carl, don't give bags of electronic parts
to the Halloween goers by mistake.
You need all of the parts to get this done.
Brooce, WLP and all other goofy radio set-ups
including
Hi Bruce!
That's funny, bags of resistors would make great halloween handouts.
On Friday the tracking department said the solder parts were moving closer and should be delivered on Tuesday, November 3rd.
Tonight is halloween and I am 20,000 fathoms below the floor hiding from street creepers who drool around looking for free resistors.
Somewhere I heard about a book by Plato so I'm airing it tonight on "Radio Books" starting at midnight from librivox.org. No matter how hard I try to listen, I know it will put me to sleep. I think Plato's first name was Ed, but I'm not sure.
UPS tracking says the solder tips have reached Lenexa, Kansas and now enroute across the state of Missouri. They are due to arrive here at the Internet Building Tuesday by end of day.
Meanwhile the corner work-surface is nearly cleared for the building of a Ramsey FM30B Transmitter Kit.
The main obstacle was an LPB AM-5 Carrier Current Transmitter which has filled the work area for about two years while I did little more than admire it. It is now set aside and waiting its turn to be re-outfitted for a different frequency. It's on 1510 kHz, not an open frequency here, and needs to be moved to 970 kHz.
Oh, I need to charge the camera batteries so we can share the experience. I'll go do that while you do other business here at part 15 dot u.s.
Keep us posted!
Brooce, WLP