Monday, December 28, 2009

Daves Power Meter

Yesterday, Dave - W7AGJ came by my Shop. He had been to RPC (PC Recycling) in Seattle to buy a heat sink for a Home Brew Power Meter that he is building,

The large (about 6x5 inch) heat sink needed some of it's fins milled off of one side to provide a flat surface to mount to a the side of an enclosure he was planing to use. A lot of mill chips later, the heat sink was ready to mount. But, the aluminium enclosure was painted which prevents direct contact - after taping a mask (or shield) a paint patch, the size of the heat sink, was removed with the sand blaster.

Before leaving we discussed the frequency response of capacitors, Dave will need several for his voltage divider and detector circuit of the power meter. His goal is to provide reliable response from HF to 70cm (450mHz).

Using my AIM-4170B it was easy to see the effects of lead length and the different types of capacitors - it was not looking good for my best and available junk box capacitors above 150mHz. Dave is hoping to select the diode, capacitor type, lead length and construction methods to minimise the need for radical calibration chart - we will see. One idea, is to use several; Parallel, Surface Mount or Mica Capacitors.

Dave will no doubt want to scan his new project with an analyser with a greater frequency range than that which is possible with an AIM-4170B (1-181mHz).

I will continue to follow this project.

NOTE: RPC as mentioned above is a great place to find parts for Home Brew QRP project,  re-purposed PC boards/equipment/parts are abundant for only very few dollars.


No comments:

Post a Comment