When connecting an R-390A balanced antenna to an AN/URM-25 Signal Generator for testing, most of the documentation says to use the DA-121 impedance adapter. But, only very little documentation says that you can find it in the MK–288/URM Electronic Equipment Maintenance Kit, or where the documentation can be found for the kit. Well, a few years ago, David Hallam asked about the documentation and Manfred Antar provided it through the R-390 List forum. Thank you Manfred.
Then, a few weeks ago, I realized that it would be beneficial to have a link to the online version of it on our website for easy access to it. Since the documentation is an Army document, the link to it (TB SIG 319) is at the bottom of the Army section of our 'Reference' page. The MK–288/URM (TB SIG 319) doc is on 'radionerds.com' at: nfe82b2.tmp (radionerds.com) <https://radionerds.com/images/b/bd/TB_SIG_319.pdf>. Because the DA-121 impedance adapter is a resistance 'L' pad and as such the output voltage is a percentage of the input voltage (45% of input, 9.1 db loss, or 4/9 of the input) for this adapter (each adapter is different). EG: if the sig gen reads 1 uv out, the voltage seen at the rx will be .45 uv. Of course, this is only true when the actual input impedance of the R-390A Balanced antenna connection is 125 ohms. Well, as you probably know, the impedance varies from about 50 ohms to about 200 ohms, depending on the received frequency. Although I have not calculated it, I believe the variance is small enough to not make much difference. Regards, Larry ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
