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.......dummy load at testing!?!

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Willen

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I have seen maximum time, When testing RF circuit at first time they were using Dummy Load instead of antenna. Basically, grounding the RF line through a resistor is called dummy load, isn't it? 75 ohm resistor connected between RF out and ground mean it is as a 75 ohm dipole antenna, isn't it? What is the purpose of dummy load?
Tell me other essential also in basic way plz!
 
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A good antenna will behave as a 75Ω resistance at its design frequency. Putting a 75Ω resistance to ground is a "dummy load" and is used to test a transmitter without actually transmitting much power. There will always be some leakage so there will be some signal transmitted.
 
Here is a class C amplifier page: https://hem.passagen.se/communication/clc.html

Most of RF loads are 75 ohm. The biggest issue, is that mose RF amps are class C. Without the load, the voltage gets too high and damages the final amplifier. I typical problem from the CB days.

When I worked on 1000 W tube RF amps, I had to do the same too. I didn't have a 1000 W load. Only a 200 W one, so I could only use it for a short time.
 
Um...I am going to test my 5 watt RF FM Tx, then should I have to use ''5 watt resistor'' of 75 ohm as a dummy load?
 
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Basically yes. Resistors don't necessarily have the same Z at all frequencies. Take this one for example, **broken link removed**

So their 200W load is only good for 5 seconds.

But you risk blowing the final amplifier if there is no load connected.
 
For testing a 5 watt transmitter I used to use a #47 light bulb.
For testing Hi Fi amps I used a ten watt resistor in a jar of water.
 
For testing a 5 watt transmitter I used to use a #47 light bulb.
For testing Hi Fi amps I used a ten watt resistor in a jar of water.

distilled water i would think... i have a bank of 40 ohm 200W resistors mounted on a metal plate and wired in parallel for an 8 ohm 1000 watt load (and yes, i have used it at or above 1kw once or twice).

i used to have one of those 50 ohm "cantenna" loads. my kenwood radio is only 200W, so i never got that one hot. when i was at the Army Signal school at Ft Gordon, the place where we did our comms training had 20 or so comms shelters each with a "cantenna" on the transmitter, and a whip antenna on the receiver; there was enough signal leakage from the coax to the dummy loads that we could communicate and send rtty messages to each other easily. judging from that setup, i would say that 400 watts into a dummy load leaks enough RF to transmit a few hundred yards, and that depends on the type of cable and especially the shield effectiveness. some cables are lossy (shield effectiveness of 60-70%) and some are not (S.E above 90%). i have a friend who got caught running a 5 watt FM station. the FCC gave him a warning. so now he runs it in a dummy load with lossy cable, and he can pick it up anywhere in his house, but can't get it at all more than about 50ft away from his house.
 
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I use this RF ammeter & 25 Watt 50 ohm dummy load for checking out small transmitters & there power output. Picked up the RF ammeter many years ago from a Disposals store.
 
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