View Full Version : How do I check my 1 watt module
06-04-2002, 12:59 PM
I bought a 1 watt fm 100 from ramsey (fully assembled) but it seems that my 1 watt module is not working is there any way in which I can check this using a volt meter. My setup is a fm 100 with RG-6 cable to the FMBA1 to the FMA200 Antenna but I am only broadcasting about an 1/8th of a mile. Any help would be appreciated.
New Tec Country Radio 104.9FM
06-04-2002, 01:52 PM
There is a dc current sent up the coax to power the fmba1. If you are running through a component that doesn't pass this current, the unit will now be powered. Are you grounding the coax with a splitter that has emi filtering built in? Are you using metal right angle adapters? Here is a simple test: Hook the output of a camcorder to a whip antenna and try to recieve channel 3(or 4) on your tv. The rf signal will travel through the air, but not far. Then insert the fmba between them and try again. You should be able to see a change in the power of your signal. If this shows you that your unit is functioning, then begin adding your coax and adapters and right angles, etc, one piece at a time to find out which part isn't passing the dc signal. I know this isn't what the unit was designed for, but it's easier than getting in your car and driving around all day. Hope this helps. Happy radiating!
The best way to check your power is to get an RF power meter calibrated for 88-108MHz, or coverage up to 150MHz.
If you are running 1 watt or more, a Power/SWR meter is essential.
I have no experience, with the FMBA1, but you might be putting too much power into it, especially if your coax is short, and of good quality. The FMBA1 is designed to boost flea power TXs such as the FM25B. I'd be concerned about burning out the FMBA1's input. Also, there is a setting in the FMBA1 for use as a receive pre-amp, check to be sure you have it set for use as a transmit amp.
Another area to check is your antenna system: cable, connectors, antenna construction/tuning. How high up is the antenna. Power and range have a funny relationship. That is an antenna 30feet in the air being fed with 20mW may have just as good range, if not better, than an antenna 7feet off the ground being fed with 2 watts.
For example, my CB radio with 4 watts out to an A99 36feet from ground to the coax input gets out 20 miles or more on a regular basis. That same CB connected to a back of set antenna barely gets me a mile down the road.
Ooops! As Insider notes, the FMBA1 is designed to boost very low power transmitters up to a full 1 watt. Feeding the 1 watt version of the FM100 into the input of the FMBA1 will not accomplish anything good! What may have happened is that you may have fried the front end of the FMBA1 and the fried circuitry is acting to whittle down the power output of your FM100! Let's hope your FM100 is still OK. Get the FMBA1 out of there, try feeding your FM100 direct to your antenna - you may need to get something to act as a jumper to replace the FMBA1 - I'm sure Radio Shack would have something to connect the two male ends of coax together. Or, if your main length of coax is long enough - just put an appropriate connector on it for your antenna. One watt into a one watt booster will not give you anything more than 1 watt - and may give a lot of splatter or harmonics even if you didn't fry the FMBA1. Give this a try and let us know how things turned out!
Just to add - the easiest way around this might be to replace the FMBA1 with the FMLP1 low pass filter. The "LP" will not only serve as a coax jumper but provide better harmonic filtering than the FM100EX is capable of. Running 1 watt may be illegal in Canada, and definitely is in the USA. - although there are situations where this is allowed by Industry Canada. Regardless, the FMLP1 will give you the pro quality harmonic filtering which you will need if you are cranking out 1 watt!
Make sure you read the Regs and don't break them!
06-05-2002, 11:28 AM
Ramsey claims the fmba1 to be "virtually overload proof". Insider is correct that the fmba1 is designed as a pre-amp to RECIEVE weak fm signals. There are two places on the unit to install one 1.2 uH inductor. One position (next to J2, the antenna side) makes it fuction as a preamp. If the inductor is in the preamp position it will have to be moved to the empty, unmarked position next to J1 (the transmitter side) to make it function as a transmitter booster (not legal in the United States!). It is true that putting one watt into a one watt booster will accomplish little. I would say that having the fmba1 right under the antenna makes long coax runs less problematic (long coax equals signal loss). The one-watt module in the FM100ex can even be disabled so that only 25mW goes out and the fmba1 will still work fine.
One other thing, maybe. The fmba1 consists of two units: the little board that does the boosting, and a power insertion box that puts the dc signal into the coax. If this box is not between the transmitter and the fmba1, and turned on, the fmba1 will not be powered. Let us know what you find out. Happy radiating!
06-19-2002, 12:00 PM
BTW We have a couple power meters coming out; the PM50, which will allow you to test very small powers up to 50 watts into a dummy load (it measures forward power only), and another PM10DC which will allow you to read both forward and reverse via a directional coupler which gives you VSWR readings which are useful for tuning antennas. These auto-ranging meters have the amazing capability to measure down to picowatts, AM percent and more!
These power meters are coming in LATE July-August so stay tuned! (Perfect for FM transmitter adjustments!) BTW please don't Email anybody at Ramsey about this or I will get in big trouble for even mentioning it, consider this a little "Insider" secret for our friends supporting the BBS. I got in trouble because you guys started asking questions about the FM100B before it came out ;)
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