[Repeater-Builder] Re: Measuring duplexer insertion loss
This did help! Now I found the missing 40 dB... I posted some pics: Duplexer pics http://conturafm.mine.nu/photo/photo_thumb.php?dir=68616d726164696f2f72\ 657065617465722f6475706c657865722f41464c In the folder pass-reject readjusted there's a picture of the view with the 40 dB hidden and how it looked after lowering the ref level. Many thanks for this tip. This is the duplexer leg that I have already readjusted for our freq. Concerning the insertion loss I'm still confused. The procedure is clear to me now, but the result is so far off of what it should be that something must still be wrong. In the folder insertion loss factory condition there are pics to show what I mean. The measured leg is the one that is still in factory condition and has a passband of 425-430 MHz at an insertion loss of 1 dB, according to the factory, and it has not been worked on previously. As suggested I did first connect the cables together with a double female and got 2 dB. This is quite a lot but you see that the resulting insertion loss is still far off 1 dB. What the heck? In the third folder there's a picture of how that duplexer looks from the inside. On the right side you see the removed cover of the cavity flipped over. You see on the far left the adjustment studs, there are big ones to adjust the frequency and in between there are small ones. Does somebody know duplexers of this kind and can tell me what the small ones are for? I could not see any effect in any way when moving these. 73 Martin
[Repeater-Builder] Re: Measuring duplexer insertion loss
Can somebody please explain how the insertion loss of a Duplexer is properly measured using a HP 8920A (with Spectrum-Analyzer). Jeff DePolo j...@... wrote: 1. Connect duplexer Tx port to duplex port on 8920. 2. Connect antenna port on duplexer to antenna port on 8920. I have to think if where you apply the source and sample matters in this example and why. One should be able to apply the Duplex Output Source Signal to the antenna port and sample each outer leg (back to the antenna port). The unconnected leg/port should probably have a termination (load) on it. Might matter more or less maybe depending on where the other half of the Duplexer is tuned. Hm...? For example, if you're generating 0 dBm, and the amplitude at the marker is -2.10 dBm, and you have 0.5 dB of patch cable loss, the insertion loss through that leg of the duplexer is 1.6 dB. Another relative comparison is to insert a barrel connector in lieu of the duplexer to get a relative idea of the cable loss (with the barrel in line). s.
[Repeater-Builder] Re: Measuring duplexer insertion loss
Thanks guys I'll have another go tomorrow (it's 0.30 a.m. in my place now). Concerning the isolation question I was obviously wrong, I came up with the idea because the duplexer is a commercial tetra duplexer of which I had the factory test certificate filed and only remembered something like 80 dB. So I hooked it up (in factory condition) and only got 40 dB difference between the high point of the curve to the low when I looked at it in the spectrum analyzer with the tracking generator on (same value on both legs). My first calculation was 40 + 40... In the meantime I dug out that spec sheet and indeed there are values of Rejection (Ant - RX Port) : -80 dB Rejection (Ant - TX Port) : -80 dB Now what am I doing wrong in this case? Somewhere there are missing 40 dB each... I have to admit that I don't have double-shielded cables available at the moment, first need to get some, but that can't make such a difference can it? 73 Martin
Re: [Repeater-Builder] Re: Measuring duplexer insertion loss
Martin, The other 40dB is hiding in the lower regions of the sweep. I'll try to describe what to do from memory but I may be a bit off target. The bottom of the sweep should look a bit wide and ragged, not a smooth line. Drop the Reference level down to -40 or -50. You should now see the bottom of the sweep and see a smooth, well defined line on the trace. Milt N3LTQ Quoting cruizzer77 atlant...@gmx.ch: Thanks guys I'll have another go tomorrow (it's 0.30 a.m. in my place now). Concerning the isolation question I was obviously wrong, I came up with the idea because the duplexer is a commercial tetra duplexer of which I had the factory test certificate filed and only remembered something like 80 dB. So I hooked it up (in factory condition) and only got 40 dB difference between the high point of the curve to the low when I looked at it in the spectrum analyzer with the tracking generator on (same value on both legs). My first calculation was 40 + 40... In the meantime I dug out that spec sheet and indeed there are values of Rejection (Ant - RX Port) : -80 dB Rejection (Ant - TX Port) : -80 dB Now what am I doing wrong in this case? Somewhere there are missing 40 dB each... I have to admit that I don't have double-shielded cables available at the moment, first need to get some, but that can't make such a difference can it? 73 Martin Yahoo! Groups Links
