RE: [Repeater-Builder] Help needed with TX combiner problem
Alex, You have a nice list of frequencies but I wished they were not so evenly spaced with both the TX and RX frequencies separated by exact equal amounts. This way if any IM exists, it will be right on an RX frequency. I did an IM analysis with the good news that there is only one 9th order IM but 69 11th order IM's. If I include 13th order IM's there are as many as 639. The bad news is that every IM falls exactly on an RX frequency of one of the six channels. However, 13th, and higher order, IM products are usually not causing too much trouble. But if they are right on frequency as in your case they may show up depending on antenna selection and antenna combination. We have had special antennas made with all the Aluminium junctions welded as much as was possible. In other words, as few clamps and bolt/nut type hardware that mechanical integrity allowed. ANY loose hardware on the tower/antenna structure is a candidate for creating IM problems. All cables should be new and of the double shielded variety. Proper connectors, specifically designed for the cable to be used, are a must. All connectors should be as tight as possible without creating mechanical stress on them. We have trunking systems with as many as 7 channels combined with 3 or four other conventional VHF repeaters and no IM and/or desensing. TX RX spacing is usually 4.02 MHz and TX/TX spacing is as little as 190 kHz. They are all multi coupled with Sinclair C2027 and C2037 multi coupling units over two or three antennas and where TX/TX spacing is less than 200 kHz Isolators are used. Great care is taken to have TX frequencies that may create IM products separated on different antennas. Generally two antennas such as the Sinclair 210C4 on one mast above each other should have an isolation of at least 25 dB. This will be different if one is on the top and the other one is side mounted on the tower. Greater vertical separation will help. I have attached a file that shows the relationship of the 9th and all 11th order IM products with the TX frequencies that are involved. For example (161.125 X 5)-(160.125 X 4) creates a 9th order IM on exactly 165.125 MHz. It does not take a strong IM signal to be heard this way. And there is no way to filter that out other than preventing the IM from being created. I wish you good luck and hope that you will be able to solve this annoying issue. 73, Tony Lelieveld VE3DWI -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo WN3A Sent: August 3, 2005 11:21 To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Help needed with TX combiner problem Not knowing what the Telewave and Sinclair part numbers translate into in terms of the actual hardware in use, you'll need to provide some details. First of all, what kind of filtering is done on the tx combiner and rx multicoupler? Is the tx combiner hybrid-ferrite or cavity-ferrite? What is the measured isolation between antennas (if known)? Since all of the tx's are spaced at 200 kHz and all of the rx's are also spaced at 200 kHz, if there is any nonlinearity in the receive portion of the system (due to preamp overload, front end overload, etc.), there is a good chance that the desired signal is mixing with the transmitters, yielding new products that fall onto the other receive channels. Not knowing any other details, that would be my best-guess as to what's happening. If this is, in fact, the case, then there needs to be additional isolation between transmitters and receivers, either by increasing the antenna-to-antenna isolation, or adding additional filtering ahead of the preamp/power divider in the rx multicoupler to further attenuate the tx carriers. The less-likely cause would be a passive (external) mix such as in a rusty tower joint or guy wire hardware, but that type of mix is usually of the variety of only the transmitter carriers mixing, i.e. the much weaker receive signal transmitted by a user in the far field wouldn't contribute an appreciable level to the mix. --- Jeff Jeff DePolo WN3A - [EMAIL PROTECTED] Broadcast and Communications Consultant > -Original Message- > From: Repeater-Builder@yahoogroups.com > [mailto:[EMAIL PROTECTED] On Behalf Of > vintageaudio2004 > Sent: Wednesday, August 03, 2005 10:52 AM > To: Repeater-Builder@yahoogroups.com > Subject: [Repeater-Builder] Help needed with TX combiner problem > > > Hello, > > I just installed a new 6-ch VHF MPT1327 system using MTR2000 Motorola > repeaters (100W) with optional preselectors installed, a Telewave > M101-150-6TRM combiner, and Sinclair RM201-112S1B RX multicoupler. > Antenna system is two DB228, one RX, one TX. RX antenna in on top of > tower, RX is a bit lower from about half the t
RE: [Repeater-Builder] Help needed with TX combiner problem
On Wed, 3 Aug 2005, Jeff DePolo WN3A wrote: > Not knowing what the Telewave and Sinclair part numbers translate into > in terms of the actual hardware in use, you'll need to provide some > details. First of all, what kind of filtering is done on the tx combiner > and rx multicoupler? Is the tx combiner hybrid-ferrite or > cavity-ferrite? What is the measured isolation between antennas (if > known)? Yeah, get a ton of circulators on that system, stat. You may find that the mixing product is coming from the repeater down the road's TXR. -- Kris Kirby <[EMAIL PROTECTED]> "BIG BROTHER IS WATCHING YOU!" This message brought to you by the US Department of Homeland Security and the now-permanent PATRIOT Act 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/
RE: [Repeater-Builder] Help needed with TX combiner problem
Not knowing what the Telewave and Sinclair part numbers translate into in terms of the actual hardware in use, you'll need to provide some details. First of all, what kind of filtering is done on the tx combiner and rx multicoupler? Is the tx combiner hybrid-ferrite or cavity-ferrite? What is the measured isolation between antennas (if known)? Since all of the tx's are spaced at 200 kHz and all of the rx's are also spaced at 200 kHz, if there is any nonlinearity in the receive portion of the system (due to preamp overload, front end overload, etc.), there is a good chance that the desired signal is mixing with the transmitters, yielding new products that fall onto the other receive channels. Not knowing any other details, that would be my best-guess as to what's happening. If this is, in fact, the case, then there needs to be additional isolation between transmitters and receivers, either by increasing the antenna-to-antenna isolation, or adding additional filtering ahead of the preamp/power divider in the rx multicoupler to further attenuate the tx carriers. The less-likely cause would be a passive (external) mix such as in a rusty tower joint or guy wire hardware, but that type of mix is usually of the variety of only the transmitter carriers mixing, i.e. the much weaker receive signal transmitted by a user in the far field wouldn't contribute an appreciable level to the mix. --- Jeff Jeff DePolo WN3A - [EMAIL PROTECTED] Broadcast and Communications Consultant > -Original Message- > From: Repeater-Builder@yahoogroups.com > [mailto:[EMAIL PROTECTED] On Behalf Of > vintageaudio2004 > Sent: Wednesday, August 03, 2005 10:52 AM > To: Repeater-Builder@yahoogroups.com > Subject: [Repeater-Builder] Help needed with TX combiner problem > > > Hello, > > I just installed a new 6-ch VHF MPT1327 system using MTR2000 Motorola > repeaters (100W) with optional preselectors installed, a Telewave > M101-150-6TRM combiner, and Sinclair RM201-112S1B RX multicoupler. > Antenna system is two DB228, one RX, one TX. RX antenna in on top of > tower, RX is a bit lower from about half the tower down. Tower is > 90FT. > > Frequencies used are: > > CH1 - T160.125 R165.125 > CH2 - T160.325 R165.325 > CH3 - T160.525 R165.525 > CH4 - T160.725 R165.725 > CH5 - T160.925 R165.925 > CH6 - T161.125 R166.125 > > Yesterday we finished putting together the system, and coverage is > currently more than was expected. But we are having a big problem (I > suspect) with IM products, as when I for example have the control > channel on CH1 (160.125) and key repeater CH6 (161.125) my carrier > indicator on CH1 opens up, and this also happens when doing other > combinations by keying the other channels in different combinations > and see other carrier indicators opening up on other channels. The > interfering signals are very weak in most cases, barely opening the > squelch of the receivers, but even so they are a problem. When I look > at the spectrum analyzer with a small antenna I see all kinds of > spikes left and right of the main carriers (most of them 40 or 50db, > or more, bellow carrier), but if I hook up the combiner output into a > dummy load and sample it into the analyzer display it looks much > cleaner, and of course the interference problem disapears. I don't > want to jump into conclusions, but it seems the IM (if it is) is being > generated somewhere outside the equipment. Furthermore, if I scan the > 160-170MHz segment (with a Icom IC-2GAT) while transmitting with more > than one repeater channel, I can pick up a lot of signals, so it seems > to be all over the place. I know they come from the system as I can > hear the control channel signaling. > > BTW, this is a very remote location, and the only other system that > operates anywhere near ours is anothe VHF conventional repeater (a > plain GR300) at 157.700 and 162.700. The other tower is located about > half a mile away. > > I'm really a bit concerned about this problem, as it disrupts > communications between channels when for example two groups are using > separate channels at the same time, as audio from one group will show > up on the others, and so forth. > > Please if you have any suggestions as to where to start looking for > solutions, they would be very appreciated. So far as a test I tried to > lower the TX power of the repeaters, but even at 25W I still see some > interference as described above. Much less but still it is there, > besides there are still numerous combinations of TX that I even have > tried so I'm sure the solution is not there. Since the interfering > signals are weak, as another test I
[Repeater-Builder] Help needed with TX combiner problem
Hello, I just installed a new 6-ch VHF MPT1327 system using MTR2000 Motorola repeaters (100W) with optional preselectors installed, a Telewave M101-150-6TRM combiner, and Sinclair RM201-112S1B RX multicoupler. Antenna system is two DB228, one RX, one TX. RX antenna in on top of tower, RX is a bit lower from about half the tower down. Tower is 90FT. Frequencies used are: CH1 - T160.125 R165.125 CH2 - T160.325 R165.325 CH3 - T160.525 R165.525 CH4 - T160.725 R165.725 CH5 - T160.925 R165.925 CH6 - T161.125 R166.125 Yesterday we finished putting together the system, and coverage is currently more than was expected. But we are having a big problem (I suspect) with IM products, as when I for example have the control channel on CH1 (160.125) and key repeater CH6 (161.125) my carrier indicator on CH1 opens up, and this also happens when doing other combinations by keying the other channels in different combinations and see other carrier indicators opening up on other channels. The interfering signals are very weak in most cases, barely opening the squelch of the receivers, but even so they are a problem. When I look at the spectrum analyzer with a small antenna I see all kinds of spikes left and right of the main carriers (most of them 40 or 50db, or more, bellow carrier), but if I hook up the combiner output into a dummy load and sample it into the analyzer display it looks much cleaner, and of course the interference problem disapears. I don't want to jump into conclusions, but it seems the IM (if it is) is being generated somewhere outside the equipment. Furthermore, if I scan the 160-170MHz segment (with a Icom IC-2GAT) while transmitting with more than one repeater channel, I can pick up a lot of signals, so it seems to be all over the place. I know they come from the system as I can hear the control channel signaling. BTW, this is a very remote location, and the only other system that operates anywhere near ours is anothe VHF conventional repeater (a plain GR300) at 157.700 and 162.700. The other tower is located about half a mile away. I'm really a bit concerned about this problem, as it disrupts communications between channels when for example two groups are using separate channels at the same time, as audio from one group will show up on the others, and so forth. Please if you have any suggestions as to where to start looking for solutions, they would be very appreciated. So far as a test I tried to lower the TX power of the repeaters, but even at 25W I still see some interference as described above. Much less but still it is there, besides there are still numerous combinations of TX that I even have tried so I'm sure the solution is not there. Since the interfering signals are weak, as another test I tried to raise the squelch setting of the repeater receivers to the maximum, but still some interference gets trough. Thanks very much in advance for any help. Alex 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/
