Nice test results! Confirms my beliefs! Would be nice to have a list of the worst/best connectors for those not fortunate enough to have the proper test equipment. Would make a good pocket guide when hamfesting!!! 73,Lee
nj902 wrote: >--- In [email protected], "skipp025" <[EMAIL PROTECTED]> wrote: >"I lifted the below text from the yahoo rfamplifiers group page, >posted this last week by my friend Dave. It's right on the money. > >http://groups.yahoo.com/group/rfamplifiers/ > > [paste] >If you are able to measure the SWR of a coax connection at VHF, then >you've installed a connector wrong. I used an HP 8510C network >analyzer to measure a whole bunch of UHF to N, UHF to BNC and so >forth, adapters, all stacked on top of each other to a foot long, and >the lowest frequency where I measured anything of concern was at 2 >GIGAhertz, where the SWR rose to 1.1:1. Yes, I know, amateur radio >lore is full of the claim that UHF connectors are awful. They are, but >only if you compare then to BNC and N, which are suitable for 10GHz >and above. Assembled correctly, a UHF connector is invisible below 1GHz. > [end] >________________________________________________________________________ > >I hope nobody is buying into this BS. > >Connector and adapter mis-match and loss issues are hardly "amateur >radio lore" > >RF manufacturers and instrumentation companies have stressed this for >years - justifiably. > >It's easy to verify if you have access to instrumentation. Just out >of curiosity I decided to run a couple of tests. > >When you measure a device for SWR you are actually measuring return >loss. You can do this on a network analyzer or with a spectrum >analyzer and tracking generator plus a signal separation device such >as a return loss bridge or directional coupler. > >I decided to try both instruments and compare the results. You first >calibrate the measurement setup with precision components from your >cal kit [e.g. Agilent 85032B]. The critical component is a precision >50 ohm load. With a good bridge or coupler you should be able to >measure a return loss of 40 dB or greater [equivalent to an SWR or >1.02:1] > >Normally your instrument test ports will be type N although some >instruments have APC-7 test ports. Your cal kit should match the test >ports. > >I started with a full 2-port cal of the VNA and a normalization of the >Spectrum analyzer. My reference load did measure as expected. > >The next step is to "insert" the device under test. In this case we >are interested in looking at a UHF connector. Obviously, since the >instrument is type N, we have to use adapters. Just out of curiosity, >I decided to compare two pairs of adapters. First an NF-NF mated to >an NM-NM. [UG-57B/U and UG-29B/U] This created an "insertable" device. > These are "standard" adapters as opposed to "precision" components >and as expected, there was some degradation of the return loss >measurement. > >I then compared this to two other adapters, NM to UHF-F and UHF-M to >NF [UG-146/U and UG-83/U], again creating an "insertable device" This >pair has just a single UHF male to female junction and results in a >significant decrease in return loss [i.e. increase in SWR.] > >I also tried inserting an 90 degree UHF adapter [UG-646/U] in line >between the UG146/U and the UG83/U which resulted in further >[significant] return loss degradation. > >I measured several sets of these parts and the results were not only >consistent from part to part but generally match within a few tenths >of a dB between the VNA and the spectrum analyzer. I always like to >see comparable results from two significantly different instrument >setups - it confirms your thought process and results. > >Results at: 150 MHz, 450 MHz, 900 MHz > >NM-NF adapters: >[VNA]: 36 dB, 35 dB, 31 dB >[SA/TG] 37 dB, 35.7 dB, 30 dB > >N-UHF + UHF-N adapters: >[VNA]: 26 dB, 16.5 dB, 11.4 dB >[SA/TG]: 23.6 dB, 17.2 dB, 11.5 dB > >N-UHF + UHF 90 + UHF-N >[VNA]: 20.2 dB, 12.03 dB, 9.3 dB >[SA/TG]: 21.6 DB, 11.9 dB, 9.1 dB > >Now just for reference, a return loss of 11 dB would be equivalent to >an SWR of 1.785 : 1 [ONE UHF junction @ 900 MHz] and a return loss of >17 dB would be an SWR of 1.329 : 1 [@ 450 MHz] > >UHF connectors "invisible" below a gigahertz??? Hardly. > > >Also - someone asked about the 90 degree N fitting at 900 MHz so I >tested a few of those. That's easy because being M on one side and F >on the other, it is inherently "insertable" > >The round kind [UG-27A/U] averaged return loss of 22 dB. The square >ones[UG-27D/U] are better at 27 dB [1.094 : 1 SWR] > > > > > > > > > > > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
