R39 is correct (10k pot) as is R10 (100k) and all the measurements confirm this. The adjustment range, measured at pin 2 of the amplifier module, is 2.5-4.7V, also what is expected from the circuit. The maximum voltage is limited to 4.7V because of the 5mA flowing through R28 which swamps the 1mA bias current.
What I would like to know is what the bias voltage should be on a correctly set up XV50. The datasheet seems to indicate it must be at least greater than 4.5V. It seems my amp needs more than 4.7V to get the correct bias, and judging from previous posts on this subject I don't think I am alone. 73 Dave G3YMC On 24 Oct 2014 at 7:46, Don Wilhelm wrote: > Dave, > > The PA bias control usually has much greater range than is needed, and > the PA bias input should draw very little current. Check the resistance > of R39. Is there a chance that you swapped R39 and R10 during the > assembly? > > 73, > Don W3FPR > > On 10/24/2014 6:46 AM, Dave Sergeant wrote: > > I am aligning my new XV50, latest build using the RA30H0608M module > > and having issues with setting the quiescent bias of the pa as per the > > manual. I see others have had this same problem but I can find no > > answers. > > > > The manaul calls for R39 to be adjusted for 20mV on the DMM across > > TP3/4 (across the 20mohm current sense resistor R17). With R39 at its > > maximum I get 16mV corresponding to a total current of 800mA as > > against the required 1A. This is confirmed by the digital current > > meter on the 12V psu powering it and my K2, which increases from 0.5A > > to 1.3A when I enable transmit on the XV50. > > > > Before anybody asks, I DO have link W1 fitted, and in fact I have the > > correct bias voltage on pin 2 of the output module. However there is > > where I suspect the problem as the maximum voltage achievable there is > > 4.7V. > > > > I found a datasheet of the RA30H0608M, albeit a preliminary one which > > has a few sheets 'in preparation'. It does not give any figures for > > standing bias versus the bias volts but suggests it must be somewhere > > between 4.5 and 5V (there is no power output below 4.5V). The voltage > > at the R29/R39 junction is limited by the current flowing through R28 > > and the module bias current (typically 1mA). So I am wondering whether > > some rf modules need a bit more than 4.7V to get the correct bias > > current of around 1A. Maybe reducing the value of R39 (56 ohms) is the > > answer. Or is mine near enough for good linearity? > > > > > http://davesergeant.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
