NetNews Usenet Archive 1993 #3

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Internet Message Format | 1993-01-28 | 23.6 KB

Path: sparky!uunet!netronix!mycal From: mycal@netronix.com (Mycal) Newsgroups: sci.electronics Subject: FM-10 FAQ (Repost/Update) Distribution: world Message-ID: <728086198snx@netronix.com> Date: Tue, 26 Jan 93 22:09:58 GMT Organization: Netronix, Inc. Lines: 620 --------------------- cut ------------------------------------------------ Ramsey FM-10 Info by mycal@netronix.com 6th Edition ----------- Here is a rough compilation of information about the Ramsey FM-10, and other BA1404 Stereo FM broadcasters. Some of the modifications may make your BA1404 based broadcaster illegal to use on the open airwaves in the US and Canada. Also it has been brought up that the stock Ramsey FM-10 kit may exceed FCC power limits when used with a proper antenna. The infomation contained in the file is in no way complete, nor do I take any responsibility for its accuracy. With that in mind, along with the above paragraph I must say : "This file for informational purposes only." About This File --------------- When I first started hacking on my FM-10, a few of us on alt.radio.pirate were exchanging information on mods to improve the range, stability and audio quality of the FM-10. After a couple of posts about filters and amps, my mailbox was swamped with requests for copies of previously posted infomation and other questions about the FM-10. So rather than drive myself crazy with sending a piece of info here and there, I decided to dig through my mailbox an notes and compile this file. I hope it helps. Also if anyone has more infomation about the FM-10 or FM transmitters, antennas, mixing equiptment, programming information, stories about pirates, or anything else that falls into this realm, please send it to mycal@netronix.com. I will try to update this file as new information becomes availible. Also I am working on a some Postscript files that will contain instructions on how to build some equiptment that is to complex for ASCII art. You might want to check the FTP'able archives every month or so. I would like to say thanx to all the people that contributed to the information in this file. The list has grown quite long, and some of the contributers would like to remain anonymous. So for now I am going to forgo all the names, if this is not up to your liking please let me know. 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 relevant e-mail address to: fm-10-request@dg-rtp.dg.com If you have any questions I can be reached at myca@netronix.com. FM-10 Archives -------------- Yes it is finally here, message archives of the fm10 mailing list and a place to put/find schematics, reviews, stories, etc. related to the FM-10 and other BA1404 based FM transmitters. People can FTP into dg-rtp.dg.com with user "anonymous" and password "<your EMail address>". In the fm10 directory you'll currently find two sub-directories: incoming This is writeable by everyone and this is where people should upload new stuff. msg-archives This directory will have files named according to the date they were last "sealed". The file "Current" is a running log of all EMail messages from the last "seal" date of the archives. I want to thank Ed Savage and the guys at Data General, NC for making the list and the archive possible. Snail Mail Info Packet ---------------------- For $3 in the US, $6 overseas, I will send you an info packet I have put togeather. It includes plans for 4 amps (light years ahead of the 70mw one shown here) with outputs from 200mw to 5watts, instructions for modifing the Ramsey PA-1 for fm radio band operation, a little blurb on antennas, and the preliminary design of my new synth transmitter. The content may change as I get new info. Address to send the $$ to is: mycal - FM info pobox 750381 Petaluma, CA 94975-0381 You can also use this address to send me any info that would be hard to send by email. Note : in the last FAQ I had the price at $1 and $4 bucks. The packet cost me $2.73 to produce and mail (in the US), so I lost my butt on that one. In the future, after I post this version of the FAQ, people sending me only a buck will get an abbreviated version of this packet. Sorry for the inconvenince. Other Places to Look -------------------- alt.radio.pirate is another good forum to find or post information on FM radio transmitter. Although you may not have pirate aspirations, many of the things talked about can benefit everyone. Other places to scan, sci.electronics and the amateur radio groups. 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 useful for peaking. The most important part is the SWR meter, this is very important when making an antenna. A note on power meters. I recommeded the above powermeters because they are inexpensive and most people that are interested in hacking a FM-10 have very limited funds. These are by no means accurate, but they will give you some idea what is going on. If you can spend the money you can get an accurate power meter that is designed for this band, but the cost is 10-15 times more. A 50ohm non inductive load is also very helpfull, for low power applications a 50ohm 1/4 or 1/2 watt carbon resistor works well. This can be used to tune up your kit and amp without interfearing with anyone. Also note that you can run as much power you want, legally, as long is it doesn't radiate. A VOM with amps is very helpfull. I would put out the extra bucks and buy one with a freq counter (if you shop around, about $60-$70). If you are serious about electronics you need one of these! Ramsey's Address ---------------- If your looking to purchase a FM-10 kit and can't find one locally try : Ramsey Electronics, Inc. 793 Canning Parkway Victor, New York 14564 Phone (716) 924-4560 Fax (716) 924-4555 Ramsey FM-10 70mw output amplifier ---------------------------------- Provides almost 9db gain to bring the output power of the Ramsey FM-10 Stereo transmitter from 8mw to 70mw. Not the best design, but all parts can be found at Radio Shack! Much better designes are soon to be available at the archive site. +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 performance (-5%). 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 careful to get the leads in the correct orientation! I have found that a 2n4401 can be used in place of the mps2222a with a little better performance, 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 220 ohms, but it is very close to the sat point, If the amp. seems noisy (interferes with the TV etc.) back this value off to 240 ohms. If you lower this value below 205 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 that's it, effective range with a good antenna should be a little over double. ANTENNAS -- read, read, read, read, most important! -------- 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 5 lengths of copper plated brazing rod (found at the local welding shop). Works great and only cost $3 dollars to make. Remember good antenna will improve you range much further than a good amp into a bad antenna. So this should be your 1st project to increase your range. 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 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 | - | / - \ - | | / \ | | / \ The final antenna should look like this: | ^ | | // \\ sky ground --horizon-- | v That is 1 radiator pointing strait up and 4 ground plane radials. (sorry for this extream description, but there has been some confusion.) Be careful 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. Try not to have anything metal near the radiator, this will effect the radiation pattern. The radiation pattern should look alot like a donut surrounding the radiator, though deformed a bit. I have been told that you can shorten the radiator and make the ground radials longer to lower your radiation angle, but I haven't tried this, nor do I know what this would do to the antenna impedance. On The Road ----------- Old magnet mount CB antennas can make great mobile 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 (and you can see the vans comming for miles ;'). 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 interference. Most of this interference is caused by harmonics. Filters cut down these nasties. So don't draw attention to yourself, keep everyone happy, including yourself, be clean, use a filter. 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 echo's on 100mhz, 150mhz 200mhz, 250mhz... If you interfear with your neighbors TV, the local fire department, or anyone else, you are just asking for trouble. If you are only on the FM Band, you will hardly be noticed. ... Filter Designs -------------- (basically scaled 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 .150uh .132uh -----()()()-----()()()-----()()()----- | | | | <-50ohm - 33pf - 68pf - 68pf - 33pf 50ohm-> - - - - | | | | -------------------------------------- | --- - lowering the 33pf caps to 30pf and the 68pf caps to 62pf would make this filter sutable for higher frequencies like 100mhz. 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). You could just use molded inductors, I have found these work well. Try to use fixed value caps, or fixed value with small 5pf trimmers. The latter works well when you have a spectrum analizer to tune there babies. I just pulled a program of a BBS that tells you how to wind inductors. Give it the value and wire size you have and it will tell you how many turns. Way cool. More on this later. Very simple Chebyshev filter. ------------------------------ .15uH from fm10 >------()()()------> to antenna | | - c1 - c2 - - | | --- --- - - 88mhz 102mhz 107mhz c1 62pf 54pf 50pf c2 62pf 54pf 50pf It won't knock the harmonics down as much as the other two designs but the good thing about this one is that it uses standard off the shelf parts. The inductor is one of those molded jobbies that looks like a resistor so you can make this very small. You may stack these things to make a better filter. Each stage will knock the 1st harmonic down about 16db. Use the above cap values depending on which freq range you want to operate at. ie. if you run 87-90 use the 88mhz vals, 90-103 use 102mhz vals, and above that use 107mhz vals. Try to use fixed value parts! [Also of interest is that the FM-10 puts out about 8-9mw and the 1nd harmonic is -25db off the fundamental (frequency we are broadcasting on). The FM-4 Kit by ramsey puts out 130mw and the 1nd harmonic is only -12db off the fundamental, which means the 1nd harmonic of the FM-4 is about as powerful as the FM-10. db is log10, ie 3db is 2 times 6db is 4 times...] FM-10 Myths ----------- There have been several myths about the FM-10 kit, the most prevelent are : 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 12mw when driven with a 12volt supply. (note: there has been several revisions of the FM-10, it is possible that the original version put out more power, but I find even that highly unlikly since it would require another amplifier stage.) Also the FM-10 is the only low cost kit, that I have seen, with an amplifier stage. Most others have power outputs in the fraction of a MW area. 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. Lowering the value of R9 will most likly degrade the FM-10's preformance and cause lots of interfearance. ============================================================================= FM-10 Improvements - -------------------- (Some from ACE magazine.) Stereo Pilot Mod ---------------- 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 easier 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 trimmer 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. On a 2nd note: I replaced c7 with a 68pf cap and found it much easyer to tune a rock solid 19khz at the test point. Crystal Mod ----------- old set up new setup c8 c1 xtl where c1=10pf and xtl=38khz |-||-| |-||-|\|-| | c7 | | | v8=var cap |-||-| | | c7=cap | | | | Remove C7 and C8, replace with 38khz crystal and 10pf cap. Note that the 10pf cap and the crystal are running series and the old cap setup is running in parallel. Note: there have been good and bad reports on using the Epson crystal from digi-key. From what I have heard the crystal is quite delicate, and in at least one case the experimenter destroyed the crystal. In one of the positive case c1's 10pf cap was replaced by 2 22pf caps run in parallel, this yealded a rock solid stereo. Treble Boost Mod ---------------- 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 Electronics". Not only do they use 75K ohm resisters in there pre-empasis, but they filter 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. Anti-Drift Mod -------------- There has been quite a bit of discussion on the FM-10's frequency stability. Complaints that digital receivers cannot lock onto the FM-10's signal for any great length of time. I have used the below mod with good results (I used an N750 negative temperature compensated disc), but I have been told that Mylar or Polystyrene caps are even better. 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 temperature compensated disc (say anywhere from N150 to N750) cap of the same value. ============================================================================ Sources ------- The following is a list of sources for items used for modifications, replacement parts, or other kits and equiptment used in FM radio transmitting: -- BA1404's and other FM Broadcaster kits can be found at : D.C. Electronics phone: 1-800-467-7736 & 1-800-423-0070 fax:1-602-994-1707 They sell BA1404's for $2 a piece, seems to be the best deal going. -- -- 38Khz Crystals can be obtained by calling : Digi-Key at 1-800-DIGI-KEY. 38.000 KHz by Epson America, Digi-Key part No. is SE3314 (see notes on crystal mod on using this crystal, also note that this is a cylinder type crystal and kinda delicate.) -- -- Panaxis Productions makes some very high quality FM transmitters. The last word in Transmitting, tons of kits. Panaxis Productions PO Box 130 (right next to my old place of study Paradise, CA 95967-0130. Chico State! ) (916)534-0417 Catalogs are $2, well worth it, a must have item. A little taste of there catalog : MMC1 Macromod Compander for 2:1 compression Plans $12, PCB $18, P+P 26.50, Full kit $87 SG High performance stereo generator Plans $15, PCB $13.5, P+P 26.50, Full kit $105 FME PLL FM exciter Plans $17.5, PCB $15, P+P 24.50, Full kit $129 More expensive than a FM-10 but much higher performance. -- -- You want to build your very own FM-10? Try: Ramsey Electronics, Inc. 793 Canning Parkway Victor, New York 14564 Phone (716) 924-4560 Fax (716) 924-4555 Should be $29 -- -- The makers of the infamous BA1404 : 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 ============================================================================= -- ============== ============== ============== Other Raw Info ============== ============== ============== the 2sc2570 is supposedly replaceable with an ecg10. Also I have used an MRF901 for a replacement, though tough to mount, try bottom of the pc board and connecting the whip anttenna pad to ground plane. The MRF239 can be used aas direct replacement for the Ramsey 2 meter PA kit. Cost is around $14 bucks. ------------------ ------------------ Well I have more info, but it is not organized enough even for this rough sheet. Given time I may 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 ------------------------------------------------------------------------- Your Pal Mycal -- mycal@netronix.com vidiot look, a commercial vidiot was written after watching watch em stair my sisters kids for a few hours programmed, hello hello one day. Do all kids stop what they is anyone in there? are doing and stair when a commicial now back to our show comes on? welcome back kid for a moment, I lost you to a commicial vid.