Its all math and luckily power is power. So, 100w out means 100w in (+a few for display and whatever else your radio draws). So 100w out = 100w/13.8v dc gives 7.3 amps dc in. If input is 12v then it is 8.3 amps in. Now add an amp or two for the rest of the radio and you should be looking at about 8.3 or 9.3 amps. But, there's a bit more to it. You also need to keep your voltage up and having larger current input (and appropriately sized wires to maintain it) helps with that so think double what your calculations are. That means 18.6 amps input and if you want a little headroom throw in a couple more to make it 20.6 then round that to 21. Magically you now have what the book says. Honestly you could key down two radios at once off one of these 25-30 amp supplies and be ok, but why? Can you say two things at once...

@stuc9910

Жыл бұрын

Wrong. You're not considering the efficiency losses of the radio which are dissipated as heat. Radios are maybe 50% efficient so you need to account for that.

@W6EL

Жыл бұрын

It's a bit more complicated. In order for a radio to have a 50 ohm output impedance, which drives a 50 ohm load, there must be equal power dissipated inside the radio's own 50-ohm source impedance as there is at the antenna. For this reason, to dissipate 100 watts into a load, the radio must also dissipate 100 watts of heat inside the radio, and thus, 200 watts input MINIMUM. Now add an amp for the digital stuff, reference oscillators, audio circuits, house keeping, lights, etc. That'll be about 15.5 amps input current.

Thanks, guys. I have always been to scared that if I keyed two radios (other than FRS) too close to each other I would blow something up.

@CoffeeandHamRadios

Жыл бұрын

Hey Don, thanks for stopping by!

@gfodale

11 ай бұрын

You still can 'blow things up'. Do not key up a radio, when it's on the same frequency as another with antennas in proximity. We had a goofball (lazy) Air Traffic Controller that set all 10 UHF radios to the same frequency for testing 'radio checks' at the air field, just before we went live to cover the base ATC for maintenance. In an instant 9 receivers were blown. He got the 10th when he went to the next radio to try it, then couldn't understand why he couldn't hear anyone. Easy fix, but time consuming. 2 days later we were back up after scrambling for transistors from other units. Definitely exceeded our 6 month on hand order limit. As long as there is adequate frequency separation, you're ok. (all 10 could be addressed from any of the 7 positions in the shelters.)

The 21 amps in the owners manual is apparently an engineering safety factor number. The rig doesn't actual draw that much current. Just keyed down my IC7300 at 100 watts output and my Astron RS-35M power supply says about 15 amps draw which is about right according to calculations.

@CoffeeandHamRadios

Жыл бұрын

Thanks Daniel!

Good discussion, but Molex is the OEM power pole, and it is smarter to use them, and less expensive too.

@CoffeeandHamRadios

Жыл бұрын

Power Poles are a racquet I tell you, it's how they get you!

@W6EL

Жыл бұрын

I cut all my radio cables down to short pigtails with power pole SB-50 connectors long ago. It is by far the best connector for these power levels. Even at 5 amps continuous the smaller power pole connectors will noticeably heat up. You can get SB-50 connectors and contacts for a few bucks a pair, and it's well worth it for the convenience it provides when you're hooking up equipment.

Merry Christmas to the Coffee And Ham Radio Gang. KO4HPC 73

@CoffeeandHamRadios

Жыл бұрын

Thanks Adam!

My Icom 7300 on RTTY on 80m with active internal tuner claims to draw 17A which is in line with what the current meter on my PSU says. It also depends on the voltage of the PSU. If the voltage drops, the current will drop as well, resulting in a lower power consumption and as a consequence a lower RF power output. I guess a 20A PSU is enough, but running a PSU at 100% load is probably also not a great idea, especially if it's a switch mode PSU.

@CoffeeandHamRadios

Жыл бұрын

Agree, I prefer to not run anything at full load.

I got an RM Italy 500 watt amp that I run on ham. And it works great.

@CoffeeandHamRadios

Жыл бұрын

Sweet, I just got the 200W

@benhawke7231

Жыл бұрын

@@CoffeeandHamRadios I'd really like to build a 10k multi-band like what BBI builds, but I'm a truck driver and barely have a minute when I'm home.