Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Sep Tue 02, 2014 7:58 pm


All times are UTC [ DST ]



Post New Topic Post Reply  [ 126 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7  Next
Author Message
 Post subject: do you use an AM transmitter?
PostPosted: Oct Mon 25, 2004 6:22 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 15974
Location: Utica, NY 13502 (USA)
The trick to getting good sound out of any AM transmitter, either with flea-power devices or with high power broadcast transmitters, is to have a good impedance match between the transmitter and antenna. Unless the transmitter and antenna system are "happy" with each other, not only will the coverage be poor but significant distortion usually results as well. I understand that at least one of the commercially available flea-power transmitters goes to considerable length to achieve a good match with an output tuning network designed for this purpose.<P>Dave<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Tue 26, 2004 7:12 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6420
Location: Beaver Falls, PA. USA
I built my own little transmitter from plans in the MAARC newsletter, and have been using it since the first of this year. It works well, but it doesn't have enough range to cover the whole house. I'm going to move up to an old LPB TX2-20 carrier-current transmitter, which came from a drive-in theatre. Initial tests show that I can get adequate coverage with this unit; with the power turned down to less than two watts it just covers the house and a little bit of the yard. The antenna is a 30 foot piece of zip cord, terminated in an 8 ohm 25 watt resistor. I found that I had to ground the antenna coupling unit to eliminate hum on the carrier. <P>I emailed LPB to question the legality of running this beast in my home, and they assured me that it was OK.<P>Tim<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Thu 28, 2004 6:14 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 778
Location: Tucson AZ
woohoo, i just found a 6bm8 tube in a box of tubes a friend gave me......figure the luck.....<P>: )<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Thu 28, 2004 6:28 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 7668
Location: Minnesota
easyrider8 wrote:
<font>quote:</font><HR>Originally posted by xwarp:<BR><B>woohoo, i just found a 6bm8 tube in a box of tubes a friend gave me......figure the luck.....<P>: )<P></B><HR>
<P>And your project box is on the way!! Let us know how this project turns out.<P>Dave<P><P>------------------<BR>Intelligence is the ability to use your knowledge


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Fri 29, 2004 7:49 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3008
Location: Québec!
C3 and C5 are 0.05uF not 0.5uF<P>D1 can be a 1N4007. <BR>I prefer using the 53xx series but that's me...;o)<P>Rest is fine so far.<P>If you have a higher voltage transformer, use it (as long as it is within tube's limit) you will gain on the output RF...<P>Syl<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Fri 29, 2004 4:46 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1421
Location: Portland, TX, US
I'm using a nondescript RCA radio (1X521 or something like that) for my project...a small AM looking radio acting as a transmitter. My transformer is a little hot (190-0-190 vac) so I'm using a 6X4 full wave recifier for a little voltage drop. This set has the loop antenna mounted on the back cover...I'm wondering if that will be an acceptable transmitter antenna or whether I need just a straight wire. When my 6BM8 arrives, I guess I will find out.<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Fri 29, 2004 8:17 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 15974
Location: Utica, NY 13502 (USA)
Tim...I'm surprised the people at LPB told you that running a couple of watts into a 30 foot antenna would be legally OK when the rules clearly state no more than 100 milliwatts into 9.84 foot (3 meter) antenna can be used. Nonetheless, you probably won't get into trouble if the signal does not leave your property. While the main signal might not cause interference, people often forget to check to see how far the harmonically related frequencies are being radiated. <P>Here is a link to another company selling "Part 15" transmitters: <A HREF="http://www.am1000rangemaster.com/index.html" TARGET=_blank>http://www.am1000rangemaster.com/index.html</A> <P>Dave<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Fri 29, 2004 9:25 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6176
Location: Burbank CA
tubbytwo wrote:
<font>quote:</font><HR>Originally posted by Dave Doughty:<BR><B>Tim...I'm surprised the people at LPB told you that running a couple of watts into a 30 foot antenna would be legally OK when the rules clearly state no more than 100 milliwatts into 9.84 foot (3 meter) antenna can be used. Nonetheless, you probably won't get into trouble if the signal does not leave your property. While the main signal might not cause interference, people often forget to check to see how far the harmonically related frequencies are being radiated. <P>Here is a link to another company selling "Part 15" transmitters: <A HREF="http://www.am1000rangemaster.com/index.html" TARGET=_blank>http://www.am1000rangemaster.com/index.html</A> <P>Dave<P></B><HR>
<P>...ah, little expensive! <A HREF="http://www.ebsradio.com/part15.htm" TARGET=_blank>http://www.ebsradio.com/part15.htm</A> <P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sat 30, 2004 5:30 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1153
Location: Cambridge MN USA
Syl- is there an error on that schematic? I noticed the cathode cap on the triode is .1u and the one on the pentode is 4.7- shouldn't it be the other way around? After all, the triode is handling audio and the pentode primarily RF.<P>Scott Todd<BR><P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sat 30, 2004 5:51 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1421
Location: Portland, TX, US
I wondered about those two caps myself but built it as indicated anyway. I haven't fired up my transmitter yet so it's not too late to change it.<P>What would the antenna look like for a transmitter like this? Just a piece of wire? How long?<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sat 30, 2004 7:41 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6176
Location: Burbank CA
tubbytwo wrote:
<font>quote:</font><HR>Originally posted by Rene:<BR><B>I wondered about those two caps myself but built it as indicated anyway. I haven't fired up my transmitter yet so it's not too late to change it.<P>What would the antenna look like for a transmitter like this? Just a piece of wire? How long?<P></B><HR>
<P> I used a piece of magnet wire strung tight with push-pins, under an 8' wall shelf above a double window that worked really good. I also have a 31' antenna in the attic thats works better.<P><BR><P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sat 30, 2004 9:12 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4294
Location: USA
"Legal" antenna length is 3 meters maximum. This is nowhere near the actual resonant length for an AM BCB antenna. For a 1/4 wavelength longwire, it's 240 divided by the frequency in MHz, this gives you the length in feet. <P>For example, 1000KHz (1MHz) would be 240 feet. 240/1=240<P>To broadcast at 1600, 240/1.6=150 feet.<P>Just a smidgen longer than legal, LOL!<P>-Ed<BR><P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sat 30, 2004 10:41 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 13246
Location: Tennessee,USA
For M82alpa,<BR>Maybe a little late, but here's a link to the pinouts of the 6BM8 tube: <A HREF="http://www.nj7p.org/cgi-bin/tube?tube=6bm8" TARGET=_blank>http://www.nj7p.org/cgi-bin/tube?tube=6bm8</A> <BR> Nice database also for tube data.<BR> Gary<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sat 30, 2004 11:55 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6420
Location: Beaver Falls, PA. USA
My original queston to LPB concerned using the AC line as a "carrier-current" system, which would cover a lot more area. I tried this method, but I found that the AC was feeding back into the transmitter and causing hum. <P> I'm still using the original LPB TCU-30 RF coupling box, which matches the SWR and converts the 50 ohm output of the transmitter into an adjustable very low impedance. This equipment has been used legally in drive-in theatres for many years, with the coupling box feeding the speaker lines. Actually, the amount of RF radiated is quite low; with a portable, I can't pick up the transmitter very far from the house. I'm losing a lot of the power in the termination resistor (it gets hot!) , but that's not a problem.<P>Tim<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sun 31, 2004 12:40 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6176
Location: Burbank CA
tubbytwo wrote:
<font>quote:</font><HR>Originally posted by Tim Tress:<BR><B>My original queston to LPB concerned using the AC line as a "carrier-current" system, which would cover a lot more area. I tried this method, but I found that the AC was feeding back into the transmitter and causing hum. <P> I'm still using the original LPB TCU-30 RF coupling box, which matches the SWR and converts the 50 ohm output of the transmitter into an adjustable very low impedance. This equipment has been used legally in drive-in theatres for many years, with the coupling box feeding the speaker lines. Actually, the amount of RF radiated is quite low; with a portable, I can't pick up the transmitter very far from the house. I'm losing a lot of the power in the termination resistor (it gets hot!) , but that's not a problem.<P>Tim<P></B><HR>
<P>Has anyone tried this carrier-current transmitter?<BR> <A HREF="http://home.att.net/~weatheradio/carrier.htm" TARGET=_blank>http://home.att.net/~weatheradio/carrier.htm</A> <BR><P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sun 31, 2004 3:19 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
I am going to ask a question that probably I should already know the answer to, but I really don't.<BR>What if a person was to take a couple hundred feet of wire and coil it up, say a half inch or three quarters of an inch in diameter and maybe fifteen turns per inch. It would look like a long coil spring. It could be stretched to the legal maximum length and still be legal that way. However, it would act like a big loading coil and probably could be made to resonate quite well, with greatly increased radiation.<P>I have experimented along these lines with helically wound mobile HF antennas for 80 and 40 meters. I got fantastic results out of a couple of them, especially with capacitive hat top loading. Bandwidth was quite narrow, but for BCB you are only looking at a fixed frequency, so that should be no problem.<P>Back several years ago when I was very active in ham radio, I had a mobile setup with a 100 watt output transceiver. I made several mobile antennas with capacity hats on them. My maximum height was 13 foot, six inches, as anything higher kept hitting bridge overpasses and such. But I managed to work a total of 186 countries with that mobile setup that most hams looked down at. So try it, I am sure the performance can be increased considerably.<BR>Curt<P>------------------<BR>Curt, N7AH


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sun 31, 2004 5:11 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4294
Location: USA
The spiral wire would probably be measured in it's uncoiled state, so it'd still be 250 feet long, but if it was encapsulated within a larger tube so it appeared to be a 3 meter rod antenna, well...who knows?<P>I saw this technique in an old article on CB antennas, it was called continuously loaded. Having the wire as a more conventional coil makes it top, center or bottom loaded, depending on where you place the coil.<P>Isn't the feed wire considered to be part of the antenna, if so, this shoots us down again another way.<P>One thing you can do legally is raise both the antenna and transmitter as high as possible. With the transmitter very close to the antenna, you'll be allowed maximum radiator length and height.<P>It would probably take complaints from people or a commercial broadcaster before anybody actually got checked out for compliance. The closest FCC office from me is probably in Denver, 350 miles.<P>But if somebody in the right location ran one of the tube amps capable of several watts, had a good ground and a perfect antenna, the broadcast could conceivably be heard for miles around.<P>-Ed<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sun 31, 2004 6:33 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 15974
Location: Utica, NY 13502 (USA)
Here is a link to the SSTran base loaded 3-meter broadcast band antenna design: <A HREF="http://www.sstran.com/pages/sstran_buildant.html" TARGET=_blank>http://www.sstran.com/pages/sstran_buildant.html</A> <P>It depends on who you talk to, but, it is my understanding that the FCC wants all wire used as part of the antenna system (inculding the wire length used in the loading coil and the transmitter ground wire) figured into the total antenna length.<BR>I believe SStran is interpeting this differently adding just the physical length of the coil assembly (not the total wire length) and neglecting the length of the mounting mast which really becomes part of the antenna system in their recommended installation.<P>I think the FCC's main concern is interference with licensed stations either within the broadcast band itself or outside the band resulting from harmonics radiated by these unlicensed systems.<P>With regard to carrier current systems, the rules for permitted radiation from the transmission line are fairly stringent unless it involves the campus of a learning institution.<P>Here is the link to the FCC rules for unlicensed RF radiators: <A HREF="http://www.access.gpo.gov/nara/cfr/waisidx_03/47cfr15_03.html" TARGET=_blank>http://www.access.gpo.gov/nara/cfr/waisidx_03/47cfr15_03.html</A> <P>Rules 15.219 and 15.221 apply to the broadcast band in particular.<P>Dave<P><P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sun 31, 2004 7:11 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6420
Location: Beaver Falls, PA. USA
One nice thing about the LPB units is the fact that they are very well designed; for this model, they claim harmonic suppression is better than 40db below carrier. There is a two-section filter at the output of the transmitter, before the output to the coupling box. I'm running a vintage audio chain ahead of it (Altec amp and equalizer, CBS Audimax and Volumax limiters), and have no problems with overmodulation.<P>Dave, that's an interesting link; I know where I can get some of that "leaky coax" cable. That may be a better setup than the way that I'm doing it now. I just need a field strength meter!<P>Tim<P>------------------<BR>


Top
 Profile  
 
 Post subject: do you use an AM transmitter?
PostPosted: Oct Sun 31, 2004 3:45 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 520
Location: Stafford, Texas USA
Quote<BR>The antenna is a 30-foot piece of zip cord, terminated in an 8 ohm 25 watt resistor. I found that I had to ground the antenna-coupling unit to eliminate hum on the carrier<BR>My original question to LPB concerned using the AC line as a "carrier-current" system, which would cover a lot more area. I tried this method, but I found that the AC was feeding back into the transmitter and causing hum. <BR>I'm still using the original LPB TCU-30 RF coupling box, which matches the SWR and converts the 50-ohm output of the transmitter into adjustable very low impedance. This equipment has been used legally in drive-in theatres for many years, with the coupling box feeding the speaker lines. Actually, the amount of RF radiated is quite low; with a portable, I can't pick up the transmitter very far from the house. I'm losing a lot of the power in the termination resistor (it gets hot!), but that's not a problem.<P>Tim<P>Is the LPB TCU-30 a power line interface box? Most of the TX2-20 transmitter used the T-8 power line interface box. Do you have a manual for the TCU-30? The power line interface box has to be setup just right. LPB transmitter work best using the AC line as a "carrier-current" system. The Cases have be HARD Grounded most were conduit from Transmitter to power line interface box to breaker panel an 3 wires run in the conduit from a breaker to Transmitter power supply. Plus 2 wires from the power line interface box to the breaker panel. One wire goes to the neutral bar this wire comes bottom of the torroid transformer the other wire comes from one of fuses in the power line interface box to one of breaker panel hot bars.<P>Your 30-foot piece of zip cord, terminated in an 8 ohm 25 watt resistor is not what a drive-in theatre speaker line looks like. Most drive-in theatres used a constant voltage (25 to 70 volts) speaker installation.<BR>Replace the 8 ohm 25 watt resistor with the primary of a power transformer. Radio Shack sells constant voltage line transformers but I think that the primary of a power transformer will work.<P>Try this site it has it all but it is hard to fine. <A HREF="http://www.part15.us/modules.php?name=Content" TARGET=_blank>http://www.part15.us/modules.php?name=Content</A> <P>Jimmie<BR><P>------------------<BR>


Top
 Profile  
 
Post New Topic Post Reply  [ 126 posts ]  Moderators: sofaslug, Paul Go to page Previous  1, 2, 3, 4, 5, 6, 7  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Alan Voorhees, Dustnstuff, Harbourmaster, radioalfa, Tommgb, tubeAMP and 14 guests



Search for:
Jump to:  



















Privacy Policy :: Powered by phpBB