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Power supply for the transceiver

[email protected]
 

I thought about how to power the transceiver and found a nice solution that probably others have seen but perhaps not pointed out. ?There is a cable for sale on eBay that contains the electronics to go from usb to 12 volts and I picked one up for $1.68. ?It is rated at 750 ma and the current drawn by mine in the receive mode is 142 ma. ?I have not tested the draw when transmitting but if it does 3 watts like the construction article states, that would take the draw up by 250 ma for what would be a total of about 300 ma., well under the rated power. ?With this, my battery problem is simple. ?


If you want to look at the cord, search for


?USB DC 5V to DC 12V Step-up Module Converter 2.1x5.5mm Male Connector


?WB6TOU
 

I decided to check the current draw of my 49er in the Xmit position. With a steady 3 watt out and key down, current drain from my old Heath DC bench supply was 860mA.

Conditions: ?
Power out: 3w
Vcc: 13.85V?
VSWR: 1:1 into 50 ohm, non-reactive load?
1-3/4(L) x 3/8(H) x 1/8(D) Alum. heat sink
2.5 ohm?emitter?resistor (reported earlier)

D882 data sheet lists maximum DC collector current as 3 Amps! ... you better have a massive heat sink on that collector if you intend to leave key down for any length of time with that load. ?

Jim, ?AB1BR
 

Addendum: the 49er RCVR draws ~115mA, so minus the total Xmit current would be?
860mA - 115mA or ...? ?;)
 

Add-addendum: ...of course the DDS takes its share of power too...
[email protected]
 

So I decided to check the actual current draw to be sure I had a decent choice. ?I prepared a 50 ohm resistive load for the antenna, plugged in my ear buds and set the supply voltage to 12.0 volts with my bench supply. ?I put my Harbor Freight ?vom in as an ammeter and observed the current to be .14 amps on receive and .54 amps during transmit.?

Noticing that my fat fingers had put in .3 amps when the math really was .39 amps (I had intended to round it to 400 ma and didn't notice the typo), and that I thought that would be safe, I needed to correct that. ?My actual draw was bigger and probably since different parts of the circuit are involved and there must be efficiency stuff to consider, I should have expected something higher. ?.54 amps is higher but not as high as was obtained with the 13,85 volts and below the specified limit of 750 ma on the cord.

I think the cheap cable sold on eBay is not a bad choice. ?I am waiting for it's delivery so I can see the actual voltage but it lets me use a bunch of battery backups that I have for phones, etc ?and they can be charged from the usb outlet on my car, my generator,my charging station, etc. It may be a better idea to use higher voltage for the power but it is not a bad choice for emergency use.??My thermoelectric stove lamp can run the transceiver so I can run my system if I just have firewood. ?Not bad but probably a bit extreme for an idea.

WB6TOU
 

I picked up a small wall mount supply 12VDC 860ma, is this sufficient to drive the 49er and the VFO circuits. I am pretty sure I will be fine on the 49er, but don't know what the VFO boards will draw. Thanks.
 

I've never actually sat down and calculated the power consumed by the 49er in transmit mode, but I would think that supply would work fine. If anyone has the actual current draw, I think all of us would be interested in your findings.


Jack, W8TEE


From: "rzwork@... [SoftwareControlledHamRadio]"
To: SoftwareControlledHamRadio@...
Sent: Tuesday, August 23, 2016 9:56 AM
Subject: [SoftwareControlledHamRadio] Re: Power supply for the transceiver

?
I picked up a small wall mount supply 12VDC 860ma, is this sufficient to drive the 49er and the VFO circuits. I am pretty sure I will be fine on the 49er, but don't know what the VFO boards will draw. Thanks.

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