Subject: Ramsey FM100 report From: xxxxx@sweden.hp.com (John) Date: 1997/01/22 Message-ID: <5c5bue$fcs@hplvejl.lvld.hp.com> Newsgroups: alt.radio.pirate A REPORT ON A RAMSEY FM100 KIT Jan 22 1997 ************************************************************************* ***DISCLAIMER**** The following report is my observation and opinion and is neither supported by or representative of my employer. I'm nor a Ransey Employee Your results and observations may vary from my own. Let's just say, "In my opinion.... " PS, I did have a few moments that I was smiling while writing this, I hope you have a few while reading it. ;-) ************************************************************************* ***The Report Stuff***** This is my kit builders report on the Ramsey FM100 "Professional FM Stereo Transmitter" kit. Assembled in December 1996. ************************************************************************* To qualify myself: I have had ~25 years of experience designing, building, testing, repairing and generally fooling around varying degrees of quality audio and RF stuff. I have built many kits in the past; Heathkit, when they were still around, PAIA, and Ramsey kits for example. ************************************************************************* Buying the KIT: I purchased the FM100 from Ramsey mid year of 1996. The fact that I'm also building a house (the hard way) has kept me too busy to put the kit together until now. To contact Ramsey Electronics for current prices, availability and catalog info you can punch them up on the web at [16]http://www.ramseyelectronics.com/ or by other conventional means: TELEPHONE 716-924-4560 FAX 716-924-4555 POSTAL ADDRESS Ramsey Electronics, Inc. 793 Canning Parkway Victor, NY 14564 USA The FM100 arrived in the mail and the packaging was very good, the kit arrived within 2 days of when Ramsey said it would. ************************************************************************* What about the quality?: Upon unpacking, my first impression of the kit is that the quality of the components and case is possibly the best I have seen in the kit category and defiantly better that a lot of consumer products that are being marketed. The overall quality of the FM 100 hardware is top notch. For me, I was very impressed with the quality that Ramsey put into the PC boards. . . a good quality fiberglass PC board with component locations clearly silk screened on. The quality of the ground plane is exceptional. The board is coated with solder resist where needed. The mounting holes and vias were pretined and have barrels to make connection to both sides of the PCB. The plating is heavy so that lifted solder pads shouldn't be a problem if assembled with reasonable care and a low wattage soldiering iron. NO MISSING PARTS! All the parts were in the kit. At assembly time, the parts all looked and were marked as described in the instructions. This is a big plus when assembling the kit. None of the parts broke during assembly. Perhaps the most difficult part of the assembly was getting the case on... how hard could that be? The assembly time in the book is somewhat accurate. It does take a lot of time to put together the kit. It might be worth the extra money to get the assembled version if your time is limited or if the kit building experience isn't what you want.... just to get something on the air. I found the assembly instructions are 99.9% accurate and it will be easy for any one to follow the well thought out step by step instructions. ************************************************************************* *HOWEVER* One thing in the assembly manual that did bother me (Perhaps just 'cause I'm a grumpy ol' fart?) was that it tended to include the use of that all time classy catch phrase "cool" a little too often in combination with the word "professional" . To me, it appears that the FM100 is geared for and the the marketing ploy for the FM100 to be more appealing to folks that just want to get on the air with some tunes and aren't quite as critical of the quality of the transmitted signal. (Or a simi anal retentive internet consumer junkies like myself.) ************************************************************************* Build the Kit by following the instructions. ************************************************************************* After assembly, here are basic observations of my particular kit: As far a the specs are concerned, the FM100 is 'ok' for the price ,however, in my opinion it isn't a "PROFESSIONAL FM Transmitter" as is emblazoned on the front panel and printed within the manual. My freshly built FM100 works in that it will go to the desired frequency and has an OK kind of stereo like signal.... all the buttons and knobs do what they say. But for me, the FM100 has a way to go to really be a 'PROFESSIONAL' FM stereo exciter/transmitter. Since Ramsey chose not to publish specs on separation, signal to noise ratio and frequency response, I won't either. ************************************************************************* *Boo Boos, Mods, SPECs AND CAVEATS* I have to clarify that, yes I did assemble the FM100 correctly and yes I did use high quality HP test equipment and a top of the line Pioneer tuner to check things out. 1) I opted to wire the AC main as shown on the schematic diagram.... The AC hot side now goes through the fuse and then to the power switch. Unfortunately, the PC trace that handles the the hot side of the AC power runs next to the edge of the PC board and is too close to one of the power transformer mounting bracket's hold down nuts. When this trace is wired to the "hot" side of the line I had the following problem. The nut shorted to the trace and POP! there went the fuse and a small piece of the PC trace. This is no big deal. But I do strongly recommend that owners install a nylon washer under this nut to keep it from shorting out whether wired as per the written instructions (in this case the trace *should* be wired to the neutral side of the line and shorting the neutral to ground usually doesn't cause a problem.... unless something goes wrong.) or wired as per the schematic. 1A) I'd also recommend covering the fuse holder with heat shrink tubing or several layers of electrical tape.... this is a shock hazard. 2) C58 and C72 in the audio circuit are installed wrong if in accord with the written instructions and markings on the PCB! The (-) side of these capacitors are connected to a (+)2.5 volt bias circuit while the (+) sides of the capacitors are connected to virtual ground via the IC U8, pins 7 and 8. I don't know if this is really an awful thing but I do suspect that it might lead to the early demise of these parts. I reversed the parts on my PC board and hence the polarity markings on the PC board don't match the components. 3) My FM100 has poor or nonexsistant stereo separation and the 19 khz signal tends to react weirdly to the tuning of L1. Also the the signal to noise ration of the dead carrier is unacceptable (say 40 db s/n typically). The primary source for this problem is the PLL/Filter circuitry. First, the PLL IC and filter circuits are 'over coupled' back into the varacter tuning diode via C13. The hash from the PLL output is mixed and modulated into the transmitted signal. Depending on what frequency is selected how the main tuning coil has been adjusted, phase lock adjustment pulses from the PLL will interfere with not only the 19 khz pilot but the L+R mono audio and the 38 khz dsb (L-R) signal as well. Since a .01 uf capacitor is used to couple the FM modulator/tuned circuit, it can be figured that some of the 38 khz dsb signal will pass through C13 back into the PLL filter. This will cause the L+R vs the L-R levels to be unequal and separation to be lacking or strange. Also this path will allow the high frequency edges of the PLL to FM modulate the Varactor And L1 tuned circuit. One mod I made to my RF section is to remove the .01 UF capacitor C13 (which couples the PLL to the varactor) and install a 300pf silver mica capacitor. This cleared up problems big time but there were other little things that bothered me..... the signal is still just a bit noisy. Another mod to help make the dead carrier a little quieter is to replace C15 and C18, 5pf ceramic capacitors with 5pf silver mica caps. This will boost the signal a bit and also make the oscillator circuit run cleaner due to an improvement in the "Q" of the resonate circuit. For my needs I also installed a 5-25 pf rotary trimmer capacitor across L1. This will allow me to roughly tune the frequency a little above where I want to set up shop and keep the PLL from working so hard (and consequently kicking up as much noise). This mod does limit the amount of frequency agility but helps a lot if one is into classical music. (Or throwing a really clean dead carrier, as I have heard them say on the CB radidio). I added a 10uf tantalum bypass capacitor to the junction of R8 and R7 (across C9) to help keep out the bass rumbles and sub sonic trash. This will make the PLL rather slow to lock up but is worth it if clean bass is needed. There is some strangeness in the separation of the left and right signals. With one channel plugged in and the other dead, the dead channel can be heard to to have some amount of signal in it... even with the balance control tweeked to max separation (R15). This isn't really that noticeable in most cases when both the channels are going at a similar amplitude. This is still under investigation but I suspect some mods to the BA1404 decoupling section (pins 12, 13 &14) might fix this problem. 4) Preemphasis and the ability to specifically set the deviation level high enough to over deviate seem lacking. The signal just isn't as bright on the high end as are the commercial stations... Granted that the big stations use 'stuff' to make the signal seem loud and full of high end energy, the FM100 just isn't bright enough on the high end. With the audio level meters just maxed out (both channels driven with a 1khz tone) the BA1404 level input adjustment pots (R23 and R35) are wide open and the deviation is not quite enough. Placing a 10k ohm resistor in parallel with a .0022 uf capacitor connected to (in parallel with or replacing) R34 (and the same for R72) will brighten things up a lot. Two things will happen. One is that the deviation level controls (R23 and R25) need to be turned down to about 1/3rd open. The result is that at 0 on the level meter, about 80% deviation should be easily obtainable for the typical rock CD. This leaves a little head room for dynamics and such. If the levels are set to loud then the sound will quickly distort and sound like crap... or is that carp. Don't try to make the level any louder than a commercial station.... since limiters and compressors aren't a part of the design, a little softer is advisable. Another good thing that happened is that the apparent stereo presence is improved by having more high frequency present. Since the signal is being preemphasised after the 15KHZ cutoff filter, the signal doesn't have a tendency to distort by heterodyning with the 19khz pilot signal. ************************************************************************* *I'd like to see these improvements and will eventually make them myself* A) A power switch for the frequency display. Being on solar power means I need to limit the amount of power I use. I'm not that worried about impressing the babes. Once the frequency is set, the display is of little use. B) I am thinking of ways to install an audio compressor/limiter that is tied into the VU meter circuit and feeding back to the audio muting fets, Q5 and Q6. C) I installed a diode across R5 to give a little quicker reset action for power glitches but need to sit down and design a good POP circuit to give even faster response. D) I plan to cover up the "Professional FM Transmitter" logo on the front of my unit and just tell folks that it is a stereo adaptor. Not ashamed, just ain't nobody's business but my own! ************************************************************************* In conclusion, I hope this helps folks in making a decision about building this kit. If given the chance again I would be swayed to let Ramsey assemble the kit and I'd make the modifications I have mentioned above. I'd strongly recommend this kit as an excellent choice for those that want to learn and those of us who have fond memorys of Heath gear. (This beats Heath by a long shot IMHO.) Not having the desire or the extra money to compare this unit to other suppliers of FM gear, I will leave this to those who have the time and money. I am satisfied with my FM100 and with a little tweeking I am quite delighted with how well it works.... PLUS the fact that it doesn't drift like the FM10 does. All the componentry is in one box and the finished kit looks clean and well thought out. I give Ramsey 1 and 7/8ths thumbs up for this unit. ;-) John