NetNews Usenet Archive 1992 #18

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Path: sparky!uunet!netronix!mycal From: mycal@netronix.com (Mycal Johnson) Newsgroups: sci.electronics Subject: Updated FM-10 Info File Distribution: world Message-ID: <713724711snx@netronix.com> Date: Thu, 13 Aug 92 16:51:51 GMT Organization: Netronix, Inc. Lines: 440 Ramsey FM-10 Info by mycal@netronix.com 2nd Edition ----------- Here is a rough compilation of information about the Ramsey FM-10, and BA1404 Stereo FM broadcasters. It is in no way complete, nor do I take any responsibilty for its accuracy. I know you haven't seen this statement but a 1000 times but here it is : For informational purposes only. I have been swamped with requests for information about amps, antennas and other mods for the FM-10, so I decided to dig through my mailbox and notes and compile this file. I hope It helps, and if anyone has more information about the FM-10 or FM transmitters, please send it to mycal@netronix.com -or- gallaghe@sonoma.vax.edu. I will try to update this file as new information arrives or is found out. A Postscript version with schematics and board layouts is also not out of the question. I would like to acknowledge the following people for the contibutions and support: John Brewer -- brewer@anarky.enet.dec.com Alan Bryant -- uunet!csn.org!adb Greg Thornwall <uunet!wam.umd.edu!thorn> If I missed anyone, sorry, please drop me a note and remind me. FM-10 Mailing List ------------------ First Things First. There is now a mailing list that deals with the topic of the Ramsey FM-10 and other BA1404 based FM Stereo Transmitters. Feel free to join up and contribute. To send a message to the mailing list, send your question, reply, comment, or contribution to : fm-10@dg-rtp.dg.com To add or delete yourself from the list, send a short message with the function (add/delete/change address) along with the revelent e-mail address to: fm-10-request@dg-rtp.dg.com If you have any questions I can be reached at myca@netronix.com. Once again I want to thank Ed Savage and the guys at Data General, NC for making this list possible. Recommended Test Equipment -------------------------- An SWR/Power meter is a giant help, a CB to 2 meter one will suffice. Power readings will not be accurate, but can be usefull for peaking. The most important part is the SWR meter, this is very important when making an antenna. Ramsey FM-10 70mw output amplifier ---------------------------------- Provides 9db gain to bring the output power of the Ramsey FM-10 Stereo transmitter from 8mw to 70mw. All parts can be found at Radio Shack. +12v | / \ R1 *220 ohms(1/2 watt) / \ R2 9k | C2 -/\/\/\/-----------||-----> output | / | / | | / C1 | |/ <----------mps2222a (276-2009) in --||------|\ -or- 2n4401 ^ | -> -- | | | gnd currently on board * you can also use 2 440 ohm 1/4 watt resistors run in parallel I built this thing right on the underside of the FM-10 kit, C1 is the cap that currently goes to the RCA ant jack, the 9k and the 220 ohm resistor have to be bought, note that if you cannot find 220 ohms you can make one by using 2 440 ohm resistors in parallel, and that a 10k will work in place of the 9k but yealds poorer preformance (-5%). Note that you can lower the resistance of the 220 ohm resistor to about 200 ohms for more power, but do not do this unless you can check to see if the transistor has gone into ocillation. The mps2222a is from Radio Shack part number 276-2009, use this part! if you substitute it for a 2n2222a you will get only half the gain. Be very carefull to get the leads in the correct orentation! I have found that a 2n4401 can be used in place of the mps2222a with a little better preformance, about 5mw more. I think the 2n4401 can be found at Radio Shack too. C2 is of the same value of C1, I took the one that goes to the on board antenna pad. Important! the value for R2 that seems to be optimal is 205 ohms, but it is very close to the sat point, If the amp seems noisy (interfears with the TV etc) back this value off to 220 ohms. If you lower this value below 200 ohms the power meter may read higher power but this will not be true, the transistor will be spewing all kinds of junk and the power meter will mistake this for higher output (in reality the signal we want will drop considerably.) Well thats it, effective range with a good antenna should be a little over double. ------- On Wed, 1 Jul 1992 13:16:47 -0600, "Alan D. Bryant" <adb@csn.org> wrote: > The second stage idea didn't appear to do anything here, but I don't have any > measuring equipment, so it may have been a small enough improvement that I > couldn't detect it. > Hmm, very interesting, I havn't tested it in the real world, just with a HP power meter and spectrum analizer. Also note that using a 2n2222a I could only get 30mw, but when using the mps2222a I got 75mw. This was all into a 50 ohm load, with a mismatched antenna it could actually degrade preformance. I was kind of amazed when I calculated the optimal Rl and found it to be 52 ohms for that circut. > I've been playing around with antennas a little myself. Made up a weird > concoction I'll have to describe to you at some point. No real test results > from it yet. I would like to hear about the details of what you have come up with when you get it all up and running. The $19 RS CB power meter would probibly come in handy for doing antenna and power tests, It would be alot better than nothing. ANTENNAS -------- Also Do you have a good antenna? I think that is the most important thing that you can do for extended range. I built a 1/4 wave ground plane using a uhf connector and 4 lengths of copper plated brazing rod (found at the local welding shop). Works great and only cost $3 dollars to make. use the formulas out of your FM-10 manual 234/freq=length of rod. insert the 4 ground plane rods in the 4 holes of the UHF connector, stick them through about 1/4 inch and solder. Solder the radiator in the top of the UHF connector (you may have to grind it a bit to fit.) Then bend the ground plane rods to a 45 degree angle to the radiator. There you have it a very effective antenna, just connect with a 50 ohm cb cable to your amplified ramsey, stick the antenna in a tree or in another high place and you should have 1.5 miles of solid coverage (when using the above amp). Also If you have an SWR meter you can cut the rods a little longer and start clipping the ends off a little until you get the best SWR reading. | | | | = brazing rod | | | | | ----- ----- ----- = uhf connector | - | / - \ - | | / \ | | / \ be carful when you bend the brazing rod, don't break the connector. Grab the rod right below the connector with a pair of vice-grips (or the likes) and bend the brazing rod at that point. I have been told that you can shorten the radiator and make the ground radials longer to lower your radiaton angle, but I havn't tried this, nor do I know what this would do to the antenna impedence. On The Road ----------- Old magnet mount CB antennas can make great moble antennas, just take all of the base load out of them and cut the radiator to 1/4 wave length. If you need a longer radiator than the one that comes with the antenna use the above mentioned brazing rod. I've tried this antenna and it works great! It rivals my di-pole at home and you can drive to a high, optimal location for your broadcasts. You could also try a 5/8 wave length antenna, this would give you 2+db gain, or almost 2x power gain on transmit. Filter design for FM Radio Transmitters. ---------------------------------------- It is very important to have a clean signal, the way 99% of all people who get busted for illegal transmitting is that the people that live around them complain about interfearance. Do not do this, keep everyone happy, including yourself, be clean. When you amplify a signal, you get unwanted byproducts these are called harmonics. The show up at multiples of your starting frequency. For example if you amplify a 50mhz signal you may get echos on 100mhz, 150mhz 200mhz, 250mhz... If you walk on your neighbors tv, the local fire depart- ment, or anyone else, you are going to get nailed. If you are only on the FM Band, you will hardly be noticed. ... I have looked into the filter design more, I have come up with these two: (basically scailed from the charts in the ARRL handbook). Filter Design: 7 element Chebyshev I run @ 88.1 so my 1st harmonic is 176.2 This filter seems ideal. Fc 3db 20db 40db 85.8mhz 95.9mhz 116mhz 148mhz .132uh .152uh .132uh -----()()()-----()()()-----()()()----- | | | | <-50ohm - 33pf - 68pf - 68pf - 33pf 50ohm-> - - - - | | | | -------------------------------------- Filter Design: 5 element Chebyshev Not as good as above, but thrown in anyway. Fc 3db 20db 40db 81.8mhz 105mhz 147mhz 222mhz .128uh .128uh -----()()()-----()()()----- | | | <-50ohm - 30pf - 62pf - 30pf 50ohm-> - - - | | | --------------------------- The tuff part in the above is winding the coils. 3t of #12 wire 1/2" diam should be about .12 uh. 4t is .17 uh. (but ugh, #12 wire is big stuff). I may just make all the coils 3t, and bend them around a little while watching the analizer. Maybe use var-caps too. Well I will build this weekend and try tuesday. I will let you know how it goes. mycal .... I built the 7 element Chebyshev, I substituted .12 uh inducters for the .132 and .15 uh for the .152. Also I put 10-50pf var caps in place of the 33pf's and 10-90pf varcaps for the 68pf's. After a bit of tweeking I got -45db on the 2nd harmonic -55db on the 3rd -65 on the 4th, every thing else was off the scale. That is much better than -25db,-27db,-30db,-40db... -40db off the fundamental is required by FCC. [Actually the fcc says no more than .7mw out on any harmonic when dealing with VHF equiptment, thats on top of the -40db requirement. But if you are running 1 watt out -40db is .1mw] I have found that peeking (buy tuning the var-caps) for maximum power output into a 50ohm load will give you close to maximum attenuation on the harmonics. Also the Fc can be raised or lowered quite a bit, I tried +-10Mhz (of 88Mhz) and could tune the Fc there. I am going to stick with the .12uh and .15uh inductors because I can get them for $.25 apiece at HSC, But I may try winding my own later on, especially if I use it on a high power output device. These molded inductors don't look like they can handle much power, but I have run 2 watts through them without problem.. On a side note, I don't think the Q of these inductors is that high, I think that if you wound the above mentioned #12 coils you would have a higher Q, hence, greater preformance on the filter. On a second try I built another filter useing variable inductor cans, and used fixed caps, this one seemed to have better preformance than the last one, it was also much more stable. Var caps are not very stable, so I would reccommend using fixed caps. [Also of intrest is that the FM-10 puts out about 8-9mw and the 2nd harmonic is -25db off. The FM-4 Kit by ramsey puts out 130mw and the 2nd harmonic is only -12db off, which means the 2nd harmonic of the FM-4 is about as powerfull as the FM-10.] FM-10 Myths ----------- 1) The fm-10 puts out 100mw of power. This is not true, or at least not true for the Ramsey FM-10's that I have tested. They put out between 8 and 15mw when driven with a 12volt supply. 2) The fm-10's output can be cranked up by reducing the value of R9. This like the above is not true. R9 and R10 are optimized for maximum output and greatest harmonic suppression at 12volts. There are much better ways of getting more output power than to mess with this output stage. FM-10 Improvements - -------------------- (Most from ACE magazine.) 1) One of the first problems experienced with the FM-10 is difficulty in getting the stereo pilot to operate correctly. One solution is to replace C7 and C8 with a 38khz crystal, this works the best and is recommended. If you cannot find a 38khz crystal, you can make your life a whole lot easyer with a couple part changes. As indicated on the Ramsey schematic, about 110pf is necessary to tune the oscillator. The components supplied to achieve this are a small fixed value capacitor (C7) abd a slightly larger value trimmer (C8). Since proper setting of the trimmer occurs within a very small 'window' (about 5% of the trimmers range), it can bet difficult or impossible to adjust the pilot to 19khz and have it stay put. This can be cured by increasing the value of c7 to 100pf and replacing c8 with a 6-50pf trimmer (Radio Shack #272-1340); a 5-30pf trimmer will do the trick. The RS trimer will not fit the holes in the pc board; one needs to cut the leads off a spare resistor and solder them to the legs of the trimmer (just use bits of wire) to mount it on the component side of the board. 2) Treble boost (pre-emphasis) improvement. The FM-10 appears to have been designed by someone outside the United States since it operates at the European audio standard of 50 microseconds. Receivers in the US are set up for 75 microsecond de-emphasis. R3 and R6 determine the time constant for the pre-emphasis curve. Replacing them with 75K ohm resistors (standard value 68K ohm is close enough) will result in improved audio response. A much better pre-empasis/input circut is shown in the July 1992 issue of "Radio Electonics". Not only do they use 75K ohm resisters in there pre-empasis, but they filtering of stray RF signals by inserting a .001 cap between pin 1 (of the BA1404) and ground, and pin 18 and ground. It has been noted that the above mod may actually cause distortion on cheaper stereo receivers, since they were mass produced for the world market, they were designed for the European audio standard, which Japan and other Asian nations use too. Try it out, let me know what works for you. 3) The FM-10 can drift a bit, but there is a simple solution that can help minimize transmitter instability. The FM-10 was designed to be inexpensive and cost-saving measures with components are inevitable. Disc ceramic capacitors are less expensive than silver-mica caps, and also much less stable. Simply replace c16 with a silver-mica, tantalum or negative temerature compensated disc (say anywhere from N150 to N750) cap of the same value. ============== ============== ============== Other Raw Info ============== ============== ============== the 2sc2570 is supposedly replaceable with an ecg10. Also I have used an MRF901 for a replacement, but it yealds 2.5mw less output. The MRF239 can be used a a direct replacement for the Ramsey 2 meter PA kit. Cost is around $14 bucks. From: Greg Thornwall <uunet!wam.umd.edu!thorn> Mycal, I called the company that produces the BA-1404 chip. The company is the Rohm Corp. in TN. They sent me some interesting data on the chip: some electrical characteristic curves, list of distributors & representatives, application diagram and some similar block diagrams that comes with the FM-10. If you want any more info just write or call them up and they will send it free! Their address & number is: Rohm Corporation Rohm Electronics Division 3034 Owen DR Jackson Business Park Antioch, TN 37013 PH: (615)-641-2020 (ask for someone who deals with the BA-1404) FAX: (615)-641-2022 Also they have: PO Box 1399 Antioch, TN 37011-1399 --Greg (KD3SU) 38Khz Crystals.... > > Does anybody have any idea where to find 38KHz crystal (H-18). > > Don't know what a H-18 is, but you can use a C-2 type quartz crystal > for 38.000KHz by Epson America, Epson part number C-2 38.000KA-P, which can > be ordered, for example from Digi-Key Corporation (1-800-DIGI-KEY), Digi-Key > part No. is SE3314 Thanks Andrew, I've got the DK catalog H-18 is a solder welded case and C-2 is a cylinder type. I don't know if there is any difference in specs between them. Aaron B. ... From: Greg Thornwall <uunet!wam.umd.edu!thorn> I have some more stuff on another company that sells "pirate" electrical kits. Panaxis productions, PO Box 130, Paradise, CA 95967-0130 (916)-534-0417 ($1.00 for a catalog). They have a bunch of FM & AM transmitters from 20mW to 10W! They only sell PLANS for the high power transmitters here to the US and will sell kits for export elsewhere. They have a PLL FM oscillator (500mW) for sale in kit form for $129.00 (better stability!). ... ------------------ ------------------ Well I have more info, but it is not organized enough even for this rough sheet. Given time I will polish it an post it. Once more If you have any info, I stress "ANY", about this subject please drop me a byte or two. have fun, mycal@netronix.com Mycal Johnson _ mycal@netronix.com | |_ _ _ There is only one (707)769-3309 | | | | |__ nor-cal ----------------- | ___\ so-cal - - - - \ / mycal Ban all Bans | |