Oak Hills Reseach 100A 40 meter QRP CW Transceiver - Page 1
Forum section: electronics / projects

author: Rgreen50
author_rank: Newbie
timestamp: November 15, 2015, 08:21:02 pm
content: I have a problem with the OHR 100A radio kit that will not transmit and have posted details below. In and effort not to load down the web with repeat data here is the link.https://forums.qrz.com/index.php?threads/ohr-100a-not-transmitting.500802/Thanks for your helpRickHi All, I just built the Oak Hills Research 100a 40 meter qrp radio. I used a DVM, frequency counter, Lambda power supply, and A function generator to do the receiver alignment.Warmed up everything applied 13.6 V and checked idle current at about 80 mA.choose to align at 7 MHz.. set controls to the proper locations as per the manual.adjusted L114 for 16.0001 MHz measured with Heathkit IM2400 and adjust C172&C191 to get maximum voltage which was measure on my Rigol ds1102e at 208mVpp at TP1. leveled the voltage accross the band 15.9986-140 mVpp 16.030 MHz-148 mVpp and 16.0763-141 mVppinjected signal into SO-239 at 7.030 MHz at 10mVpp using Siglent SDG1025 thru a 30 Db Trilithic RA54-1 attenuator and tuned radio to frequency. Adjusted C146 for tone 700Hz. Checked zero beat behaves as expected. Bandwidth control functions as expected. Adjusted C116 'maxium effect', C132 'no effect', C144 'some effect' to achieve maximum receive signal.transmitterAttached QRP Wattmeter and terminated into 15W 50Ohm dummy loadset Output power potentiometer to mid way point.connected DVM to TP2 and keyed transmitter by shorting the cw key input**** this is where i found my first issue.. there was no voltage at TP2 and no power out and only a very slight increase in current draw maybe 10 mA if anything not totally sure if it did increase. Adjusting trim caps C120 and C122 did nothing. I made some measurements at the IF SA602AN pins 1,4,6,8 and have include the images from my scope.I have checked my coils and added 2 turns to L114 and found it wouldnt tune so I dropped back 1 turn and it tunes it is set with 26 turns as indicated in the instructions however the schematic calls for 27 which didnt work and 25turns did also. I include the schematic below for the transmitter section.Any help would be wonderfulThanks Rick, N3KCA 73

author: AF6LJ
author_rank: Unknown
timestamp: November 15, 2015, 08:32:26 pm
content: Manual link?That could be over the head of most (but not all) folks over there.

author: kg4arn
author_rank: Unknown
timestamp: November 15, 2015, 11:31:04 pm
content: I would prefer you repeat the info here. Don't want to log into another site to see the schematics and scope tracings.

author: Rgreen50
author_rank: Newbie
timestamp: November 16, 2015, 12:24:57 am
content: ok here ya go!

author: AF6LJ
author_rank: Unknown
timestamp: November 16, 2015, 02:51:56 am
content: There are a couple of good tips given on that other forum.I don't post there because of sexual harassment and other crap I endured there.Besides for being banned for no reason, nobody will admit to.It is generally a place for appliance operators with a few exceptions who actually know what they are talking about.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: November 16, 2015, 08:44:44 am
content: While the supplier provides a block diagram athttp://www.ohr.com/100block.jpgit's a bit hard to figure it out without a circuit.

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 16, 2015, 09:47:33 am
content: Looks like the 9MHz oscillator in the transmit mixer is not oscillating. You could start by swapping the SA602 and the crystal from the receive side and see if anything changes.Unfortunately I have no idea what TP2 is and what a missing voltage there indicates, we would need some detailed pictures for that.

author: Rgreen50
author_rank: Newbie
timestamp: November 16, 2015, 11:47:23 pm
content: the alignment procedure says adjust for maximum voltage at tp 2.. I did find the voltage was the same 13.6 V at the base and collector of the 2n5179 transistor so its bad, but I might have done that testingneed to replace and recheck

author: Rgreen50
author_rank: Newbie
timestamp: November 17, 2015, 07:14:07 pm
content: Problem has been solved!! i had a bad transistor new out of the box. 2n5179 @ Q103Just need to align the radio now and it appears to be putting out about 5Watts.Thanks for the helpRick, N3KCA 73

author: AF6LJ
author_rank: Unknown
timestamp: November 19, 2015, 03:00:45 am
content: Good to hear you found the problem.