Upping the power on the AM 25

LaMartiniere · #1 10-29-2002, 05:11 PM

As the old saying goes, don't fix what ain't broke... right?

The AM station here on Day Street has been faithful to the max 24-7 since July. Even during a hurricane where we ran Radio Free Day Street on a car battery!

I am tempted to bypass the resistors that limit the power output and "OOMPH"it just a bit.

How citical is the antenna matching in this case?

I don't want to blow the finals. I'm getting a consistant 1.5KM during the day.

Any AM guys out there in FM land?

By the way... is Ramsey planning to release a stereo AM kit anytime soon?

Phil · #2 10-30-2002, 10:53 AM

Cal, as an AM Stereo enthusiast and relatively new convert to the joys of AM broadcasting myself [though I like FM too!]I would be a bit cautious of upping the power as I suspect that at high power the AM25 would become much pickier when it comes to antenna matching. However, the quest for experimentation is an integral part of the electronics hobby - if none ever experimented, nothing would never have been invented! So, you might wish to consider cautiously upping the power. For example, lets say the AM25 uses resistors to throttle back how much power goes into the final output, and lets say the high power mode involves jumpers which short accross these resistors. You might want to try replacing the resistors with a lower value - so instead of 100mw at low, 1 watt at high, you were producing say 200mw. You could monitor how hot the output transistors were getting to keep tabs on things. I suspect you'll find that say doubling your power output will result in a very minimal increase in coverage - and you'll end up going back to the 100 mw level. It sounds like your getting great coverage as is! Tell us about your antenna etc!

Currently, I'm running about 10 mw on my AM Stereo transmitter and find that experimenting with antenna and ground ideas make an enormous difference. Based on your coverage, I'd say you've got a rather effient antenna going!

e92fm · #3 11-03-2002, 02:05 AM

before upping power, remember that putting a million watts into a inefeicient antenna will get you nowhere, try building a simple outside antenna system, consisting of a main radiator and some ground radials, a ground system is a important part of AM broadcasting. make some ground radials.at least 1/4 the length of the main radiator (if space allows), and lay them out on the ground in a circular pattern around the radiator, you could try 4 to 6 to maybe even 24 radials, just going to the hardware store and buying a ground rod and putting it into the ground will improve signals..remember to keep the soil around the rod wet for best conductivity..which will improve coverage!

maverick390 · #4 11-20-2002, 06:09 PM

Cal ,
I don't know if this helps or not, but on Ebay there is a guy selling (or auctioning off)some home brewed A.m. stereo transmitters. I saw these posted two nights ago and they look really good. Not sure of the power output but with a little work, and the coverage you have now you couldnt go wrong with one of those transmitters.

I would love to see Ramsey produce one of these gems as well. I would buy one in a heartbeat. Hope this helps. [img]smile.gif[/img]

Phil · #5 11-21-2002, 11:02 AM

The guy is Chris Cuff, he is a really nice guy who makes wonderful little AM Stereo transmitters, along with decoder boards for converting boomboxes and other such rigs to AM stereo. I have one of his transmitters, and I love it. I have one of his decoders too - its great as well. The transmitter is very legal - adjustable from 2 to 10 mw. Spend your time and money on a good antenna - not an rf amp, unless the rf amp is no more than a maximum of 100 mw [1/10 of a watt]. With the right antenna, you'd be surprised how far 10 mw can go! The sound is really good on his transmitter - it shows how AM Stereo can sound better than FM stereo - with much nicer stereo! CQUAM AM Stereo is newer, better technology than FM Stereo, and when coupled with an AMAX compatible receiver, sounds awesome. Although its mono, a GE SR III radio on wide will show off how good AM radio can sound, especial on the now famous Alfredo Lite transmitter Chris builds.

I look forward to giving rave reviews to a Ramsey AM Stereo transmitter in the hopefully near future!

ryan_ctXhc · #6 11-21-2002, 05:42 PM

http://www.vcomp.co.uk/gizmo/amtx.htm

theres a tunable part 15 antenna coming out in Dec at the bottom of that page. im suprised ramsey isnt hookin up an AM antenna kit yet

LaMartiniere · #7 11-22-2002, 07:25 AM

Hey, Thanks for that British Gizmo URL! I think I'm going to get that capacitance loaded tophat AM antenna! Now if we could get Ramsey to build us an SWR bridge that's insertable between the antenna and the AM transmitter, huh? I mean hell! How hard can that be? Can't one of those old CB jobs be modified? Another thing for the Ramsey folks, how about a place on the web site where folks can post pictures of their equipment in use? I'd like to see that truck with the transmitter in the glove box! Of course it'd have to be a monitored site, I'm not sure you'd want to see someone doing a DJ show in their Calvin Klines!
Kindest Regards from Louisiana!

Phil · #8 11-22-2002, 11:11 AM

Hmmmm, I'm getting ideas as to how to make my own top hat antenna. copper pipe is one ingrediant, or in the alternative, aluminum pipe - say from an old roof rake. a large old pizza pan would make a dandy top hat, and a base loading coil - with a plate type tuning cap accross it - this could work! Thanks for the tip!

LaMartiniere · #9 11-22-2002, 02:19 PM

Wait! Don't just drop that tidbit and quit on me! How about some dimensions? I have a 4' x 4' sheet of 1/3 inch thick copper, 10' of 1/2 inch copper pipe, a torch, solder and a hack saw. Now what?

Cal

Phil · #10 11-22-2002, 04:00 PM

not sure of any precise dimensions myself - may just have to experiment!