I discovered that the supply voltage readout on my TX-500 is not quite as accurate as I would like. I use a Bioenno BLF-1203AB battery and monitor the TX-500 supply voltage indication when it drops to around 12.7 Vdc to determine when to recharge the battery. However, I've noticed that the TX-500 supply voltage reads about 0.3 Vdc lower than the true value. So I decided to measure the accuracy and linearity of the voltage readout. I powered the TX-500 in receive mode with a bench DC supply and measured the DC voltage with a calibrated Fluke 87V DMM at each display readout of the TX-500, from 13.8 to 9.00 Vdc in 0.1 volt increments. Of note, the display showed "LOW POWER SOURCE" in reverse video when the DC supply was set to 9.0 Vdc. (BTW, the receive current draw over this range was 100 mA to 135 mA .) The attached Excel workbook contains the measurements and a chart (see below) that plots the Fluke measurements vs TX-500 supply voltage displayed. Also shown is a regression fit of the data, which is as follows:
Vtrue = 0.9964 * Vreadout+0.2709 (Vdc) with an R-squared value of 0.9998
So for my TX-500, the readout consistently reads 0.27 Vdc low.?
?
I think a nice feature that might be considered in a future firmware upgrade would be to add a user-set battery voltage offset correction for a more accurate readout. I'd be interested in hearing from other TX-500 owners on how your unit reads true.
73,
Steve
NQ1F
Steve C