Phase 6 ~ Power On Testing


So Ok you can hardly contain yourself. But you must as the old adage so well states: HASTE MAKES WASTE. The last thing you want to do is to smoke your board. Using the pictorial supplied on the web site recheck your wiring to assure that you have everything connected properly.

For this test you will need to have a proper power supply. VU2ESE recommends a linear type 12 VDC supply rated at 2 amps. This is not a place to use that bargain walwart! You will also need an 8 ohm speaker or headphones. I have used an external powered speaker system (Staples ~ $13) and this greatly helps me to sort things out. I am an OT and my hearing is not so good. You will need to have the microphone built and available. Finally a proper SWR bridge and a resonant antenna on 40 Meters. This is not the time to hook a clip lead to a rain gutter and hope it works.

A particular area of concern since the kit as supplied for the two pin headers uses brown and black wire with the black being to identify which pin is ground. The problem is in the upper right hand corner with the board facing you and the IRF510 toward the back of the board. There are two sets of two pin contacts. One set is power to the main board and the second is the Push To Talk control. Mixing those two up is problematic in that if you connect the main power to the PTT header you will smoke a whole bunch of components. I suggested to VU2ESE that he include two cable/header combinations using red and black for the power wiring. This would highlight the colors and make less of a problem mixing up the cables.

Initial testing should be done with the varactor tuning pot. Yeah the tuning is finicky and the varactor diode tuning drifts but it will give you a quick go no go that the board is working. I strongly advise the purchase of the digital VFO board as that then becomes a simple plug-in to the main transceiver board. For those new to homebrewing you will be chasing your tail trying to get the varactor tuning to settle down.

VU2ESE has modified his "get it up and running page". Make a copy of that page and follow along the various steps. An SWR bridge is a handy indicator tool of RF output. I am often surprised how many hams lack this basic device in their ham shack. Get one! It is also important that a low SWR be presented to the radio. Many of the expensive transceivers have built in SWR protection such that when the SWR exceeds 3:1 there is an automatic power reduction or even a complete shutdown. The Bitx40 does not have that sort of protection and having a high SWR will smoke your rig!