Re: [Repeater-Builder] Re: Repeater receiver testing
Kevin, I'm sorry to have to tell you this but I think your calculator batteries need to be changed. 0 dBM = 0.2236 volts in a 50 Ohm circuit. +20 dBM is indeed 100 mW and P=EI and inserting 100 mW into the Eq. for Volts in a 50 Ohm system, E= the sq. rt. of the quantity (.100 x 50) = sq. rt. of 5 = .707 V. or 707 mV. not the 2.24 V. you indicated. Even if the rcvr had an input Z of 50 Ohms (without any X component at the operating freq. which I doubt but let's accept that as so) , the rcvr input Z at a freq. removed by 6 MHz can hardly be assummed to be any thing close to 50 Ohms and is more likely to be highly + or -X therefor not absorbing or accepting any input signal and your analysis lacks merit. Allan Crites WA9ZZU From: Kevin Custer kug...@kuggie.com To: Repeater-Builder@yahoogroups.com Sent: Mon, July 26, 2010 3:47:08 PM Subject: Re: [Repeater-Builder] Re: Repeater receiver testing yes I know -55db is I think around 399 microvolts which will flatten any receiver, I sure hope not; there are many signals coming down my antenna that are that strong. In fact, my 440 repeater 13 miles away is at about that level at my antenna connector. Reminds me of a test I did with a GE MASTR Pro VHF receiver (stock - no preamp - ER-41C) and a GE MASTR II PLL exciter (stock - 200 mW output) and a tee connector. Receiver and exciter on each end of the tee (with short cables) and antenna/service monitor on the center. As I remember, the frequencies were about 6 MHz apart and the 'repeater' would duplex reasonably well considering no filtering was used between the units. Of course, I'm not saying there wasn't desense, but it worked - pretty well. Obviously, the 200 mW was split into two paths and who knows how much was hitting the input port of the receiver, but lets say half of it was - 100 mW. That power level is +20 dBm. I can almost guarantee you that transmitter side band noise is what created the desense - not the shear power of the transmitter. +20 dBm is 2,240,000 μV or 2.24 volts of RF. My receive antenna for the UHF remote receivers is top mounted across the tower face beside the VHF stick. The VHF repeater runs 250 watts. 4 watts of VHF power appears at the splitter (in the shelter - including feedline loss) which feeds the 4 UHF receivers. The splitter (old CATV type) gets warm - you figure out how much VHF power is getting to each UHF receiver grin. Kevin Custer
RE: [Repeater-Builder] Re: Repeater receiver testing
Kevin, I'm sorry to have to tell you this but I think your calculator batteries need to be changed. 0 dBM = 0.2236 volts in a 50 Ohm circuit. +20 dBM is indeed 100 mW and P=EI and inserting 100 mW into the Eq. for Volts in a 50 Ohm system, E= the sq. rt. of the quantity (.100 x 50) = sq. rt. of 5 = .707 V. or 707 mV. not the 2.24 V. you indicated. I think you blew that one OM. Too much tequila down in XE land perhaps? The square root of 5 is 2.2236 volts, not sure where you got 0.707, that would be square root of 0.5. Kevin was right. Or, to make it even simpler without having to do any real math, +20 dBm is 20 db greater than 0 dBm. 20 dB more than 0.2236 volts is, obviously, 2.236 volts. --- Jeff WN3A
Re: [Repeater-Builder] Re: Repeater receiver testing
I sure did. Thanks to you Jeff for your response and my sincerest apology to Kevin. I did the calculation four times and got the same wrong answer four times before I hit the send button. Only after I sent did I redo the calculation on another calculator and was I horrified to learn of my mistake. It's time for a new calculator for me. And then the computer crashed. Time for a new computer too. AC From: Jeff DePolo j...@broadsci.com To: Repeater-Builder@yahoogroups.com Sent: Tue, July 27, 2010 11:09:55 AM Subject: RE: [Repeater-Builder] Re: Repeater receiver testing Kevin, I'm sorry to have to tell you this but I think your calculator batteries need to be changed. 0 dBM = 0.2236 volts in a 50 Ohm circuit. +20 dBM is indeed 100 mW and P=EI and inserting 100 mW into the Eq. for Volts in a 50 Ohm system, E= the sq. rt. of the quantity (.100 x 50) = sq. rt. of 5 = .707 V. or 707 mV. not the 2.24 V. you indicated. I think you blew that one OM. Too much tequila down in XE land perhaps? The square root of 5 is 2.2236 volts, not sure where you got 0.707, that would be square root of 0.5. Kevin was right. Or, to make it even simpler without having to do any real math, +20 dBm is 20 db greater than 0 dBm. 20 dB more than 0.2236 volts is, obviously, 2.236 volts. --- Jeff WN3A
Re: [Repeater-Builder] Re: Repeater receiver testing
allan crites wrote: Kevin, I'm sorry to have to tell you this but I think your calculator batteries need to be changed. 0 dBM = 0.2236 volts in a 50 Ohm circuit. +20 dBM is indeed 100 mW and P=EI and inserting 100 mW into the Eq. for Volts in a 50 Ohm system, E= the sq. rt. of the quantity (.100 x 50) = sq. rt. of 5 = .707 V. or 707 mV. not the 2.24 V. you indicated. Not sure what planet you are from Allan, but since you admit that 0 dBm is .2236 Volts, and everyone knows that an increase in power by 10 dB is the same as multiplying that figure by 10, I'm correct - you are way off. Even if the rcvr had an input Z of 50 Ohms (without any X component at the operating freq. which I doubt but let's accept that as so) , the rcvr input Z at a freq. removed by 6 MHz can hardly be assummed to be any thing close to 50 Ohms and is more likely to be highly + or -X therefor not absorbing or accepting any input signal and your analysis lacks merit. My statement said power hitting the input port, I said nothing about power being accepted or absorbed into the receiver, therefore again - I'm correct - you are way off. Let me remind you that, on this particular email list, I (we) strive for accuracy. I don't just come up with some crap to make things interesting - I've been 'doing' duplex radio systems since I was 14 - I'm now 46, so you do the math, correctly this time. You state my analysis lacks merit. Unless you have tried the the experiment I refer to - and have found something different to report, why don't you try keeping your off base thoughts and inaccurate calculations/information to yourself. If this seems to come off as a hot headed warning - you have read this post correctly. (I'm the list owner (in case you haven't figured that out)). By the way, the GE PLL exciter has 22 dB less phase noise at 600 kHz from its primary carrier than does its multiplier counterpart, you can bet it's way more than that at 6 MHz. End of thread - everyone please more forward. Kevin Custer
Re: [Repeater-Builder] Re: Repeater receiver testing
Get a Mac. Much more efficient and crash free.. Keep your PC for programming if its old enough. :) John Hymes La Rue Communications 10 S. Aurora Street Stockton, CA 95202 http://tinyurl.com/2dtngmn - Original Message - From: allan crites To: Repeater-Builder@yahoogroups.com Sent: Tuesday, July 27, 2010 10:05 AM Subject: Re: [Repeater-Builder] Re: Repeater receiver testing I sure did. Thanks to you Jeff for your response and my sincerest apology to Kevin. I did the calculation four times and got the same wrong answer four times before I hit the send button. Only after I sent did I redo the calculation on another calculator and was I horrified to learn of my mistake. It's time for a new calculator for me. And then the computer crashed. Time for a new computer too. AC -- From: Jeff DePolo j...@broadsci.com To: Repeater-Builder@yahoogroups.com Sent: Tue, July 27, 2010 11:09:55 AM Subject: RE: [Repeater-Builder] Re: Repeater receiver testing Kevin, I'm sorry to have to tell you this but I think your calculator batteries need to be changed. 0 dBM = 0.2236 volts in a 50 Ohm circuit. +20 dBM is indeed 100 mW and P=EI and inserting 100 mW into the Eq. for Volts in a 50 Ohm system, E= the sq. rt. of the quantity (.100 x 50) = sq. rt. of 5 = .707 V. or 707 mV. not the 2.24 V. you indicated. I think you blew that one OM. Too much tequila down in XE land perhaps? The square root of 5 is 2.2236 volts, not sure where you got 0.707, that would be square root of 0.5. Kevin was right. Or, to make it even simpler without having to do any real math, +20 dBm is 20 db greater than 0 dBm. 20 dB more than 0.2236 volts is, obviously, 2.236 volts. --- Jeff WN3A
Re: [Repeater-Builder] Re: Repeater receiver testing
At 7/27/2010 10:29 AM, you wrote:  Get a Mac. Much more efficient and crash free.. At the last coordinators' meeting I attended there was one laptop crash... Yup, it was a Mac ;) Bob NO6B
Re: [Repeater-Builder] Re: Repeater receiver testing
At 7/27/2010 10:15 AM, you wrote: case you haven't figured that out)). By the way, the GE PLL exciter has 22 dB less phase noise at 600 kHz from its primary carrier than does its multiplier counterpart, you can bet it's way more than that at 6 MHz. That 22 dB is an interesting figure: the amount of increased phase noise contribution as a result of multiplication is 20*log(N), where N is the multiplication factor. The multiplied-crystal G.E VHFHB exciter's multiplication factor is 12, which gives 20*log(12)=21.58 dB! My theoretical guess as to what would happen @ 6 MHz out is that the difference in phase noise between the 2 exciters would greatly diminish due to the Q of the tuned stages in the multiplied exciter kicking in. Bob NO6B
Re: [Repeater-Builder] Re: Repeater receiver testing
Yep, Mac's crash all the time. They get virus' too. Chuck WB2EDV - Original Message - From: n...@no6b.com To: Repeater-Builder@yahoogroups.com Sent: Tuesday, July 27, 2010 9:38 PM Subject: Re: [Repeater-Builder] Re: Repeater receiver testing At 7/27/2010 10:29 AM, you wrote:  Get a Mac. Much more efficient and crash free.. At the last coordinators' meeting I attended there was one laptop crash... Yup, it was a Mac ;) Bob NO6B
Re: [Repeater-Builder] Re: Repeater receiver testing
Hi yes sort of, getting a bit confused my end. What I usualy do is using a sig gen on the tx port put in the tx freq, terminate the ant port at 50 ohms put my analyser on the rx port and see what level of tx freq iam getting ie -80,-90 or whatever. Steve - Original Message - From: Tim tahr...@swtexas.net To: Repeater-Builder@yahoogroups.com Sent: Monday, July 26, 2010 12:06 AM Subject: Re: [Repeater-Builder] Re: Repeater receiver testing Hi Steve, I measured each way to the common point... RX to antenna Tx to antenna, and each one had a notch of about 102dB at the opposite frequency. With the 50 watts at the antenna port is where I see the -55dBm on the receiver port. (into the spectrum analyzer). Are these the measurements you mean? (you are up late tonite!) tim Yahoo! Groups Links
RE: [Repeater-Builder] Re: Repeater receiver testing
Good thoughts Milt, and I'll add a few While not an easy thing to find I would suggest that you most likely need some sort of a bandpass cavity on the receiver to protect from the noise that gets past the heliax notches. Remember that a notch duplexer only removes the notched portion of the TX signal on the RX side and the RX signal on the TX side, all other noise is passed directly to the load. Thus you only have two small notches, one at the RX frequency and one at the TX frequency. Everything else is passed. A duplexer specification that often goes overlooked is mid-band isolation; that is, how much isolation there is between Tx and Rx ports mid-way between the Tx and Rx frequencies. For notch-only duplexers, this value is often very low, often less than 10 dB. The effect of low mid-band isolation is that wideband noise or spurs from the transmitter can result in receiver desense, even if there is enough isolation at the operating frequencies. In other words, the wideband noise passes right across the duplexer at frequencies far enough removed from the notches to cause problems. For pass/reject or bandpass duplexers, the mid-band isolation will be substantially higher, may be somewhere in the range of 30 to 60 dB depending on band, offset, number of cavities, etc. Mid-band isolation is often quoted in manufacturer's specs as a simple scalar value, if it's given at all. Quite often they just give you isolation, and that's just at the Tx and Rx frequencies proper; it doesn't tell you anything about what's happening at other frequencies. A swept transmission response across a broad range from Tx to Rx port with the antenna port terminated will show the true isolation you're getting. As far as adding a pass cavity to attenuate desense caused by noise or spurs coming from the transmitter, it would most likely be more effective if you put it on the transmitter leg of the duplexer rather than the receiver leg. You probably should also look at the TX signal to check for spurs. Micors are generally pretty clean machines, but keep in mind that lowband repeaters were fairly rare back in the day; I don't know if duplex isolation curves were ever published for lowband Micors (ZZU, you QRV?). For the Mastr II you only needed about 50 dB of carrier supression and a little over 60 dB of noise supression for 100 watts at 1 MHz split. I also have had duplexers that look good with a tracking generator but fail under TX power. And we've all had antenna systems that did the same. And I've had dummy loads that did the same as well; point being, don't rule out a problem in your test equipment... --- Jeff WN3A
Re: [Repeater-Builder] Re: Repeater receiver testing
At 7/25/2010 15:54, you wrote: Hi Jeff yes I know -55db is I think around 399 microvolts which will flatten any receiver, I sure hope not; there are many signals coming down my antenna that are that strong. In fact, my 440 repeater 13 miles away is at about that level at my antenna connector. Bob NO6B
[Repeater-Builder] Re: Repeater receiver testing
Hi Jeff, Thanks for the info. any idea about the complexity of the 'summing' device? Can I do with a resistor combo, then perhaps sub some from the actual generators' output? Tim --- In Repeater-Builder@yahoogroups.com, Jeff DePolo j...@... wrote: The holy grail for FM performance testing, which includes adjacent channel rejection measurements, is EIA/TIA-603. I believe revision C is the latest. Unfortunately, you'll have to pay to get a copy of that document unless you can scrounge one up. To summarize how the test is done (and I'm doing this from memory, so someone please verify/correct me). 1. You need a way to sum the output of the two sig gens together such that they are properly isolated from each other, and done in such a way that the amplitudes can be calculated accurately at the output of the summing device. 2. You start out by measuring the 12 dB SINAD of the receiver with only the on-channel signal generator active (standard SINAD test, 3 kHz deviation, 1 kHz tone, typically measured at the speaker terminals after deemphasis/filtering/etc.). Simple enough. 3. Increase the RF level of the on-channel generator 3 dB higher than the 12 dB SINAD sensitivity value you found in step 2. This will push the measured SINAD up higher than 12 dB obviously, that's what's supposed to happen. 4. While still generating the on-channel signal, now also generate a signal on the adjacent channel, modulated by a 400 Hz tone at 3 kHz deviation. 5. Increase the level of the adjacent-channel signal until you degrade the SINAD reading of the on-channel signal back down to 12 dB (remember, it was something greater than 12 dB, because you had increased the RF level by +3 dB before you started introducing adjacent-channel dinterference). 6. The difference (in dB) between the offending signal and the 12 dB SINAD sensitivity measured in step 2 is the adjacent channel rejection ratio. So, for example, if the 12 dB SINAD sensitivity was measured at -117 dBm in step 2 without any interference, and you were back down to 12 dB SINAD in step 5 when you had the interfering signal cranked up to -30 dBm, the adjacent channel selectivity would be 87 dB. --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Saturday, July 24, 2010 10:27 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Repeater receiver testing I have this lowband Micor receiver that I want to test for adjacent channel rejection. I have two calibrated signal generators and a calibrated spectrum analyzer if I need it. How can i measure the rejection of the off channel signal? Thanks, Tim
Re: [Repeater-Builder] Re: Repeater receiver testing
yes I know -55db is I think around 399 microvolts which will flatten any receiver, I sure hope not; there are many signals coming down my antenna that are that strong. In fact, my 440 repeater 13 miles away is at about that level at my antenna connector. Reminds me of a test I did with a GE MASTR Pro VHF receiver (stock - no preamp - ER-41C) and a GE MASTR II PLL exciter (stock - 200 mW output) and a tee connector. Receiver and exciter on each end of the tee (with short cables) and antenna/service monitor on the center. As I remember, the frequencies were about 6 MHz apart and the 'repeater' would duplex reasonably well considering no filtering was used between the units. Of course, I'm not saying there wasn't desense, but it worked - pretty well. Obviously, the 200 mW was split into two paths and who knows how much was hitting the input port of the receiver, but lets say half of it was - 100 mW. That power level is +20 dBm. I can almost guarantee you that transmitter side band noise is what created the desense - not the shear power of the transmitter. +20 dBm is 2,240,000 ?V or 2.24 volts of RF. My receive antenna for the UHF remote receivers is top mounted across the tower face beside the VHF stick. The VHF repeater runs 250 watts. 4 watts of VHF power appears at the splitter (in the shelter - including feedline loss) which feeds the 4 UHF receivers. The splitter (old CATV type) gets warm - you figure out how much VHF power is getting to each UHF receiver grin. Kevin Custer
[Repeater-Builder] Re: Repeater receiver testing
If you are attempting to verify a manufacturer's specification, the TIA-603 procedure should be used. If you are serious about that, you should probably acquire TSB-88 in addition to TIA-603. Here is a link to a presentation that discusses adjacent channel testing and explains the roles of the various standards documents: http://www.apcointl.org/frequency/documents/W09-olson.ppt Jeff has summarized the procedure correctly with the exception that the current procedure utilizes a two-tone modulation for the interefering signal. This test requires that the signal generator ustilized for the interefering signal have exceptional phase noise performance or the test results will be inaccurate. There are a number of suitable high-end generators such as the Aeroflex 2041. I doubt if the signal generation function of any service monitor is suitable. If you are simply wanting to compare various recever models for a particular application such as a repeater receiver, an alternative would be to use the actual repeater transmitter as the interferer. Connect it to a suitable load with a signal tap and attenuator configured to sample the signal and feed into the receiver test in place of the second signal generator. Here is another summary of a process similar to the TIA-603: ADJACENT CHANNEL REJECTION Method of Measurement Terminate the audio output of the receiver in a load specified by the manufacturer, and make measurements using a C-message weighted filter. (a) Connect two RF signal generators equally coupled to the receiver antenna input terminals through a suitable matching network. Set the first RF signal generator to the assigned channel frequency and modulate it with a 1004 Hz tone at 60% of the maximum permissible peak frequency deviation. Switch the second generator off. Adjust the first RF signal generator level to produce a 12 dB SINAD measurement at the audio-output terminals of the receive path. Record the RF signal level and increase this first RF signal generator output by 3 dB. (b) Set the frequency of the second RF signal generator to the adjacent channel above the frequency of the first RF signal generator and modulate it simultaneously with two tones, one at 650 Hz at a deviation of 50% of the maximum permissible frequency deviation and another at 2200 Hz at a deviation of 50% of the maximum permissible frequency deviation. The level of each of the two tones should be set to 50% of the generator's modulator input level specification. The deviation of the RF signal generator should be set to 100% of the maximum permissible frequency deviation. Adjust the level of the second RF signal generator to reduce the SINAD measurement back to 12 dB. Record the RF signal level. (c) Repeat step (b) with the frequency of the second RF signal generator set to the adjacent channel below the frequency of the first RF signal generator. (d) Calculate the ratios, in decibels (dB), of the undesired signal levels measured in steps (b) and (c) to the reference level obtained in step (a). The smaller of these ratios for the above and below channel undesired signals is the adjacent channel rejection. -- --- In Repeater-Builder@yahoogroups.com, tahrens301 tahr...@... wrote: I have this lowband Micor receiver that I want to test for adjacent channel rejection. I have two calibrated signal generators and a calibrated spectrum analyzer if I need it. How can i measure the rejection of the off channel signal? Thanks, Tim
[Repeater-Builder] Re: Repeater receiver testing
Hi Nj902, Well, I'm not trying to be exacting in the measurement, I'm just trying to track down a desense issue in the system. I figured I'd look at how the receiver does with the adjacent (transmitter) signal injected directly into the rx input port. The spectrum analyzer hooked up to the RX port on the duplexer shows -55dBm, which should be down sufficiently enough not to be heard by the receiver. I'm running the duplexer into a dummy load, and all interconnecting cables are double shielded. However, the desense is so severe that I am beginning to think there may be something wrong in the RX. Hence, the question. Just trying to find that silver bullet. Got any spares? Thanks, Tim
Re: [Repeater-Builder] Re: Repeater receiver testing
Hi you beat me to it, I would suggest a duplexer problem as -55dB isn't a lot you should have ideally better than 80dB. It also could be the fact that you are running too much tx pwr, have you tried dropping it down. 73 Steve, M1SWB(UK) - Original Message - From: Tim tahr...@swtexas.net To: Repeater-Builder@yahoogroups.com Sent: Sunday, July 25, 2010 9:24 PM Subject: [Repeater-Builder] Re: Repeater receiver testing Hi Nj902, Well, I'm not trying to be exacting in the measurement, I'm just trying to track down a desense issue in the system. I figured I'd look at how the receiver does with the adjacent (transmitter) signal injected directly into the rx input port. The spectrum analyzer hooked up to the RX port on the duplexer shows -55dBm, which should be down sufficiently enough not to be heard by the receiver. I'm running the duplexer into a dummy load, and all interconnecting cables are double shielded. However, the desense is so severe that I am beginning to think there may be something wrong in the RX. Hence, the question. Just trying to find that silver bullet. Got any spares? Thanks, Tim Yahoo! Groups Links
[Repeater-Builder] Re: Repeater receiver testing
The issue for repeater receiver desense is the same basic issue that affects the bench test. For the bench test if the generator used for the adjacent channel signal has too much phase noise - that noise will degrade the receiver before the carrier level can be raised to the manufacturer's spec. With a repeater - if the transmitter sideband noise is too great - or the duplexer's attenuation of that noise is insufficient - then the receiver will be degraded. Measuring the transmit carrier level at the receiver input - not so hard. Measuring the transmit sideband noise at the receiver input - not so easy. Your issue is probably due to not enough TX sideband noise suppression. We're assuming you used all double-shielded coax, but look at everything - maybe there is a faulty coax or connector allowing leakage to cause the degradation. --- In Repeater-Builder@yahoogroups.com, Tim tahr...@... wrote: Hi Nj902, Well, I'm not trying to be exacting in the measurement, I'm just trying to track down a desense issue in the system. I figured I'd look at how the receiver does with the adjacent (transmitter) signal injected directly into the rx input port. The spectrum analyzer hooked up to the RX port on the duplexer shows -55dBm, which should be down sufficiently enough not to be heard by the receiver. I'm running the duplexer into a dummy load, and all interconnecting cables are double shielded. However, the desense is so severe that I am beginning to think there may be something wrong in the RX. Hence, the question. Just trying to find that silver bullet. Got any spares? Thanks, Tim
Re: [Repeater-Builder] Re: Repeater receiver testing
Hi Steve, Running 80 watts into the duplexer, getting 50 out. Getting about 102dB notch out of the duplexers. From a previous thread a couple of days ago, the consensus was that -50 was fine for this receiver. I hooked up my IC-706 to the TX port, and even at 5w, I was getting significant desense. Figured I'd try take one variable on at a time... RX first. The RX was given to me, already crystalled 'tuned' up... it was a voting receiver at a multi-site repeater. Not sure if had any 'special' modifications done to it! Thanks, Tim
[Repeater-Builder] Re: Repeater receiver testing
Hi 902, Understand about the sideband noise, but I figured at a MHz away, it probably wouldn't be an issue. Getting the same performance out of both sides of the duplexer ... about 102dB notch 1.5dB attenuation. Using RG142 for all interconnects, except from TX/RX to duplexer, and those are RG-214. Guess I could hookup a signal generator with a -50dBm signal into the RX, and measure it at the input with a high impedance probe hooked to the spectrum analyzer. Take that measurement, and then hook up the duplexer key it up. Check the measurement again see if it's the same, or more. Thanks, Tim
Re: [Repeater-Builder] Re: Repeater receiver testing
Been following this thread for a while, some thoughts in random order: If I remember correctly you said that you are using the 1 5/8 heliax notches as your duplexer. If I also remember correctly others have reported problems of many sorts with these homebrew devices. While not an easy thing to find I would suggest that you most likely need some sort of a bandpass cavity on the receiver to protect from the noise that gets past the heliax notches. Remember that a notch duplexer only removes the notched portion of the TX signal on the RX side and the RX signal on the TX side, all other noise is passed directly to the load. Thus you only have two small notches, one at the RX frequency and one at the TX frequency. Everything else is passed. You probably should also look at the TX signal to check for spurs. If the RX has the extender circuit installed, turn it off and rerun your test. It could be that the extender is tuned to a frequency near the TX or a low level output from the TX. I also have had duplexers that look good with a tracking generator but fail under TX power. Milt N3LTQ Quoting Tim tahr...@swtexas.net: Hi 902, Understand about the sideband noise, but I figured at a MHz away, it probably wouldn't be an issue. Getting the same performance out of both sides of the duplexer ... about 102dB notch 1.5dB attenuation. Using RG142 for all interconnects, except from TX/RX to duplexer, and those are RG-214. Guess I could hookup a signal generator with a -50dBm signal into the RX, and measure it at the input with a high impedance probe hooked to the spectrum analyzer. Take that measurement, and then hook up the duplexer key it up. Check the measurement again see if it's the same, or more. Thanks, Tim Yahoo! Groups Links
Re: [Repeater-Builder] Re: Repeater receiver testing
Hi again Tim what you could try is this, put a signal gen on the tx port and see what the isolation is on the rx port, don't forget to put a dummy 50ohm load on the ant port Steve - Original Message - From: Tim tahr...@swtexas.net To: Repeater-Builder@yahoogroups.com Sent: Sunday, July 25, 2010 10:28 PM Subject: [Repeater-Builder] Re: Repeater receiver testing Hi 902, Understand about the sideband noise, but I figured at a MHz away, it probably wouldn't be an issue. Getting the same performance out of both sides of the duplexer ... about 102dB notch 1.5dB attenuation. Using RG142 for all interconnects, except from TX/RX to duplexer, and those are RG-214. Guess I could hookup a signal generator with a -50dBm signal into the RX, and measure it at the input with a high impedance probe hooked to the spectrum analyzer. Take that measurement, and then hook up the duplexer key it up. Check the measurement again see if it's the same, or more. Thanks, Tim Yahoo! Groups Links
RE: [Repeater-Builder] Re: Repeater receiver testing
Hi you beat me to it, I would suggest a duplexer problem as -55dB isn't a lot you should have ideally better than 80dB. It also could be the fact that you are running too much tx pwr, have you tried dropping it down. 73 Steve, M1SWB(UK) He said he measured the Tx carrier at the Rx port of the duplexer at -55 dBm; he didn't say he had 55 dB of isolation...
Re: [Repeater-Builder] Re: Repeater receiver testing
Hi OH right 30w loss is not right. You maybe getting -102db notch but it is the isolation between the tx an rx ports that count, you need better than 80db. I know of some 6mtr repeaters in the UK that use the heliax duplexers and get better than -90db isolation with insertion losses a round 1.5dB. We are limited to 25w erp so usual tx in is about 25w and out of the duplexer around 20w 73 Steve - Original Message - From: Tim tahr...@swtexas.net To: Repeater-Builder@yahoogroups.com Sent: Sunday, July 25, 2010 10:23 PM Subject: Re: [Repeater-Builder] Re: Repeater receiver testing Hi Steve, Running 80 watts into the duplexer, getting 50 out. Getting about 102dB notch out of the duplexers. From a previous thread a couple of days ago, the consensus was that -50 was fine for this receiver. I hooked up my IC-706 to the TX port, and even at 5w, I was getting significant desense. Figured I'd try take one variable on at a time... RX first. The RX was given to me, already crystalled 'tuned' up... it was a voting receiver at a multi-site repeater. Not sure if had any 'special' modifications done to it! Thanks, Tim Yahoo! Groups Links
Re: [Repeater-Builder] Re: Repeater receiver testing
Hi Jeff yes I know -55db is I think around 399 microvolts which will flatten any receiver, he needs to know the actual isolation between the tx and rx ports. I assume that the notch figure Tim mentions is the actual notch of each filter, which is why in my later mail I suggested doing an isolation test with sig gen and analyser 73 Steve - Original Message - From: Jeff DePolo j...@broadsci.com To: Repeater-Builder@yahoogroups.com Sent: Sunday, July 25, 2010 11:43 PM Subject: RE: [Repeater-Builder] Re: Repeater receiver testing Hi you beat me to it, I would suggest a duplexer problem as -55dB isn't a lot you should have ideally better than 80dB. It also could be the fact that you are running too much tx pwr, have you tried dropping it down. 73 Steve, M1SWB(UK) He said he measured the Tx carrier at the Rx port of the duplexer at -55 dBm; he didn't say he had 55 dB of isolation... Yahoo! Groups Links
RE: [Repeater-Builder] Re: Repeater receiver testing
Hi Jeff yes I know -55db is I think around 399 microvolts No, you're still missing it. He said -55 dBm (m = milliwatts), not -55 dB. which will flatten any receiver -55 dBm at 1 MHz offset isn't going to bother any half-decent receiver. A decent receiver would have 100 dB of adjacent-channel selectivity (that would be 20 kHz away on lowband), so if we assume the sensitivity is -117 dBm (0.3 uV), it should tolerate a signal int the vicity of -17 dBm at only 20 kHz away with only slight degradation. At 1 MHz away, a good lowband receiver with a real front end will tolerate much, much more, probably on the order of 0 dBm (over 2/10ths of a volt). 80 watts TPO = +49 dBm. He's measuring -55 dBm at the receive port, so he has 104 dB of carrier supression, way way way more than is necessary for a Micor at 1 MHz split. --- Jeff WN3A
[Repeater-Builder] Re: Repeater receiver testing
Tim, It appears to me that your measurement procedure is correct - and that the results you have gotten would normally be sufficient isolation to allow desense-free duplex operation. If you have some attenuators available - or better yet - a switchable [in 1 dB increments] attenuator - there is a test you could try. Assuming you are running your desense test with the repeater terminated in a quality 50 ohm resistive power load and feeding your generator in through an iso-T, you establish a sensitivity reference [e.g. 12 dBS] then key the repeater transmitter and readjust the generator for the same reference. The difference in readings is the amount of desense. Insert an attenuator in the receiver line between the duplexer's receive port and the receiver's antenna port. Start with about 10 dB. You should then require 10 dB more signal from your generator to achieve your initial quieting reference. Now when you key the transmitter again measure the desense. The attenuator gives you the equivalent of that much additional isolation. Your desense should be correspondingly less. With a switchable attenuator you can determine just how much more isolation you need. The results you get - whether they 'track' or aren't linear may give some clue as to the nature of the issue. WB0EMU --- In Repeater-Builder@yahoogroups.com, Tim tahr...@... wrote: ...I measured each way to the common point... RX to antenna Tx to antenna, and each one had a notch of about 102dB at the opposite frequency. With the 50 watts at the antenna port is where I see the -55dBm on the receiver port. (into the spectrum analyzer)
[Repeater-Builder] Re: Repeater receiver testing
Hi Nj, Thanks for the info. That's one test I'll be trying tomorrow. I did a bit of snooping in the IF chain with a scope probe my spectrum analyzer, and found that at the back end of the xtal filter chain/amplifiers, I saw two signals, one a MHz above the desired receive frequency, and it was quite large. So, either I was introducing it into the receiver.. always possible, or there is something big time wrong with the RX. I have another receiver strip, and I will re-tune it tomorrow see if anything changes. I'll keep all posted on the outcome. Thanks, Tim
