FM02 Power Supply Confision

[corytcline]

I bought an enercell ac to dc power adapter from radio shack cost just under 20 bucks it will run from 1.5v 3v 4.5v 6v 7.5v 9v and 12v at 300ma. I coiled the cord about six times just before it goes into the fmo2 power in that got rid of all hum that was present. Also never hook power to the transmitter without your antenna connected first. that info is in the link ukewarrior sent you as well.

[RFBurns]

Most wall wart power adapters have very simple rectifier and filtering. Usually just one rectifier diode and a small value filter capacitor. They are not well filtered for RF either. Modifications are simple, but usually not required if the device being powered has adequate on-board filtering.

Interesting that coiling the cord six times prior to the connection point into the transmitter got rid of hum. That indicates that you have RF traveling along the ground path, probably due to RF traveling down your coax ground shield. The hum is residual AC energy from the 120v AC power getting back into the RF final by way of RF leakage onto the ground of the feed line and power supply. You can use a Radio Shack 100uF choke in series with the B+ to eliminate much of that AC residual hum.

But this brings up some concern regarding the FM02 on board B+ filtering. From what I can tell by the images on the Vast website, the FM02 really doesn't have much on-board filtering, thus typical wall wart's will cause issues such as the hum.

If inadequate filtering is on the transmitter B+ rails, RF energy can and will travel right down the B+ rail and into the power supply as well as going out the antenna connector. Another cause for this is if the antenna and coax are not properly matched and a high VSWR is present, forcing some of that returned RF energy from the coax and antenna to feed back into the power supply..again causing hum.

I really enjoy reading all the neat fixes everyone has developed to resolve issues. It is creativity at it's finest!

Happy Holidays!!

RFB

[ukewarrior]

Ask and you shall receive.

The FM02 Schematic and PCB layout are now available in the FM02 wiki !

Wiki link:
http://www.doityourselfchristmas.com...=Vastelec_FM02

[RFBurns]

Ask and you shall receive.

The FM02 Schematic and PCB layout are now available in the FM02 wiki !

Wiki link:
http://www.doityourselfchristmas.com...=Vastelec_FM02

Thanks! As we can see now in the schematic, Pin 19, the pilot level adjustment point, has absolutely nothing connected to it!!!

A 220pf to 5nanofarad cap will tame that pilot level down. Off to study this thing a bit.

Happy Holidays!!

RFB

[RFBurns]

I hope everyone realizes that this thing has no low pass filtering on its output. No wonder so many are having antenna problems. This thing could cause an improperly tuned antenna to resonate at a harmonic more than the fundamental and burn up the final and all kinds of other things.

Well...the road map points the way to all kinds of issues that can pop up with this unit. Is it any wonder why?

Happy Holidays!!

RFB

[ags0000]

I hope everyone realizes that this thing has no low pass filtering on its output. No wonder so many are having antenna problems. This thing could cause an improperly tuned antenna to resonate at a harmonic more than the fundamental and burn up the final and all kinds of other things.

Well...the road map points the way to all kinds of issues that can pop up with this unit. Is it any wonder why?

Happy Holidays!!

RFB

Given all the potential shortcomings of this design that you have pointed out, can you recommend a transmitter with similar low power output in the same (<$100) price range that you feel is a more robust design?

[RFBurns]

Given all the potential shortcomings of this design that you have pointed out, can you recommend a transmitter with similar low power output in the same (<$100) price range that you feel is a more robust design?

The C-Crane is probably the best and it carries FCC certification. C-Crane FM Transmitter

If your into building kits, Q-Kits has several to choose from. Q-Kits

If your budget can handle a few more bucks, there are of course the Ramsey units. Even the basic FM transmitter can be modified for frequency lock by adding an external PLL module.

If you want plug and play, here is a PC TX from PCS Electronics PCIMAX 3000

Happy Holidays!!

RFB

[RFBurns]

Here is another PCS FM transmitter that is Part 15 compliant, and has the on-board RDS capability by the addition of the RDS module.

Part 15 FM Package

The FM02 is a good unit..it just has a few things that could be improved to help its performance and could have a few preventive measures added to help keep them gremlins and bugs away.

I go by a certain rule when it comes to making purchases of transmitters. Their life cycle expectancy and serviceability vs replacement price range. Clearly the FM02 is not intended to be field servicable, it is comprised of 99.99 percent surface mount components cluttered together, so field repair is pretty much a file 13 and replacing the unit is a better option.

The FM transmitter my station uses is the infamous Ramsey FM 100 (first model). I bought that as a kit and had it put together and running within 6 hours of opening its box. That was in 1997. It has ran 24/7/365 since and not once has it glitched or gripped. It still serves my station well and is built like a tank. It is also field serviceable with IC's sitting in sockets as is all the transistors (my modification) so that its a quick fix to simply pull out the bad part, insert the new part and your back on the air in under 5 minutes or less.

Try that with the FM02 next to swapping out the whole thing, which is about the only thing that can be done in the field with the FM02 is swap the defective one with a new one.

I don't knock "module swapper" or swapping, but I prefer equipment I can dive into myself and repair that equipment at component level. I realize some do not have that level of expertise and swapping modules is their only choice. For those of us who can do component level repair, its a lot easier to work with standard components than these rice sized parts!

Ahh its just the old tymer in me..me eyes are fading and steady soldering iron hand is a wee wobbly..but hey at least I got the blob of solder on my pants and not the new carpet!

Happy Holidays!!

RFB

[ags0000]

Wow, I love that PCIMAX card. Maybe next year. Probably not the best for a year-round radio enthusiast (but then again, this time last year I hadn't ever thought of Christmas lighting either...) but that looks perfect for driving seasonal "shows" coupled with PC light control.

As an alternative, are there any (<1watt) Ramsey units to be had for under $100.

Thanks.

[RFBurns]

Wow, I love that PCIMAX card. Maybe next year. Probably not the best for a year-round radio enthusiast (but then again, this time last year I hadn't ever thought of Christmas lighting either...) but that looks perfect for driving seasonal "shows" coupled with PC light control.

Those PC slot transmitters should be the perfect unit to work with considering what the application is here. I have one and it works flawlessly. It serves as my backup FM transmitter in the backup Maestro automation computer.

As an alternative, are there any (<1watt) Ramsey units to be had for under $100.
Thanks.

Hmm..not that I am aware of. Their least expensive PLL FM kit is around 150 bucks or so, sometimes you might find one on ebay for 50 or so.

I have a CSI FM-20 FM exciter, a Panaxis FM-10 FM transmitter and 4 of the CZH series FM transmitters, all work perfectly..but my Ramsey FM 100 unit still serves as the primary FM transmitter, and has done so since 97 when I first put it together and fired it up. Its just been one solid steady working unit and have had no reason to replace it or use one of the others.

The Vast FM02 unit seems like a really good transmitter. I like its modular design and size. But there is room for some improvements no doubt about that.

Happy Holidays!!

RFB