Fluctuation in modulator's power supply in wireless transmission

[Wql]

Hi,

Thanks for all the advice. I will try to use something to shield the modulator to see if the problems lies in there.

And there is someone who told me that if the load outputs power too, it will cause it to not work properly since power supply likes to supply power. Is this true? Thanks again.

 

[Wql]

Hi,

I have did the testing. So it was the shielding problem. But just would like to ask, what is the typical max input power for the transceiver? In this case, is the Alinco DJ-C7E transceiver. Thanks.

 

[davenn]

input power ? where to .... antenna, audio to mic input, DC voltage supply ?

cheers
Dave

 

[lurchman]

Wql,

I'm not sure what you mean by "the load outputs power" and "since power likes to supply power".

What some people mistakenly belive is that they can put power supplies in parallel to increase available power to the load (the thinking is = can get 5amps from that PSU and another 5amps from that PSU giving me 10amps).

For a number of reasons it does not work unless you take the propper precautions (some lab PSU's have four connectors +V/+s and -V/-s the two 's' connectors being 'sense').

If you look at the cct diag of power supplies with multiple output transistors you will see smal values of resistor in the power path, these generate 'stabalising' voltages that allow the power to be balanced (the exact method varies from supply to supply).

Also looking briefly at your photos I'm going to mention "power supply" decoupling. Most people know you should stick a capacitor across the power supply rail to reduce "noise" etc. However they general just think an "electrolitic" will do. Not so with RF you often need to use three capacitors, an electrolytic for low frequency decoupling and various values of ceramic capacitor, often the smallest can be just a few tens of picofarads surface mount mounted as close to any "power circuitry" as possible, to cut down PCB track inductance effects. You especialy need to do this with prototypes where there is insufficient "copper weight" for ground plains etc.

 

[Wql]

input power ? where to .... antenna, audio to mic input, DC voltage supply ?

cheers
Dave

I mean the max input power into the receiver's antenna.

 

[davenn]

I mean the max input power into the receiver's antenna.

OK preferably dont input any more than around -50 to -40 dBm ( 1,000 to 2,000 uV), to avoid damaging the receiver front end RF amplifier
remember any decent receiver will have a sensitivity of ~ 0.2 - 0.5 uV ( ~ -120 to -110dBm)

0dBm = 1mW (milliWatt)

cheers
Dave