how test PA without Ant?
How we can test that it gives 10W into 50 ohm ant. without using Anttena?
Get an swr meter that works at 200 mHz, then either
1. Buy a 50 Ohm dummy load - check amateur radio stores
2. Use a bunch of power resistors that are not wirewound in parallel to get 50 Ohms. (eg, 20 1000 Ohm, 1 watt resistors in parallel)
3. Use an ordinary light bulb.
When testing make sure the swr is better than 3:1 otherwise you're not matching your load.
You can tune the load if you need to.
Be carefull making the dummy load , remember that latest carbon film resistors are a film with some turns arround the support and could introduced inductions.
The best resistors to be used are Morganite type that are carbon compost no film.
I think its better to attenuate the PA output signal to the range where a common power-meter can measure.
How can you attenuate the power without a load?
Doesn't make sense.
Uhh, guys, I know hams like to do things with chicken wire and bubble gum, but there is such a thing known as a "directional coupler" that you would place between the output and a 50 ohm medium power load. A 20 or 30 dB coupler would be in order.
How does a coupler help? He's asking how to load the PA so he can test it. He still needs a dummy load, which is what we're trying to answer.
Added after 16 minutes:
Just looked up "directional couplers" and found out that they are simply power dividers. You still have to have to load the PA. There's no magic in them. They help determine power levels.
If your reference to chicken wire and bubble gum was meant to diminish the use of an SWR meter, I suggest you read the replies again. The use of the SWR meter was simply to check the matching of the load not measure the power.
If fact it looks like a directional coupler is only accurate when the load impedance is correct. So in testing various loading devices, it's probably not very useful.
Hi 7rots51,
There are two reasonably cheap solutions.
Construct a dummy load using two 100 Ω or three 150 Ω thick film
resistors of 20 or 50 watts and bolt them to a suitable heatsink
and measure the power with a thruline wattmeter like a Bird 43.
http://www.vishay.com/resistors-disc...product-50005/
Construct an attenuator with standard E 12 series resistors and measure
the output power with a sampling voltmeter or a milliwatt meter.
The first 39 Ω resistor will have to dissipate about 80 % of the
applied power, the 12 Ω resistor about 20 %. The 12 Ω resistor can
be a 3 w type but the 39 Ω resistor has to be split up in to
different resistors e.g. 12 + 12 + 15 or 10 * 390 in parallel.
Remember that the dissipation of a resistor is specified in still
air and not surrounded by a dozen other resistors dissipating the
same amount of energy. So measure intermittent and allow time to
cool down. The circuit is a standard 50 Ω type with 40 dB attenuation.
( OK, put the calculators back, it's 49,990 Ω and 39,998 dB.)
Construction is straightforward, connect the resistors using
chicken wire and glue them to a PCB with bubble gum.
on1aag.
Hallo
I SUGGEST:
1-use a directional coupler to attenuate power by 20 to 30 db and use the low sensor power meter to measure the power.(tack into consideration to add 20 or 30dB attenuation)
2- use a second hand cheap 50Watts dummy load (10S up to 500MHz) to load your PA
best rergards