[Repeater-Builder] Re: Any Repeaters Taken Off Air Permanently?
Hi Tony, I'm curious to know why you are asking (but admittedly I haven't read the entire thread yet, maybe I just missed the reason...)? But to answer your question, I/we have one that isn't quite off the air (yet); but as the primary Trustee, I am considering doing so, if I cannot retarget it and/or the site. As a little bit of background, quite a while ago a bunch of us got together and put a 70cm box up on a local mountain. At the time, there was a need for an open box serving the area. Without going into all the painful details, we ran into a lot of problems getting it coordinated; and before it ever happened, a local repeater club put one up (too close to ours to make ours necessary anymore). For the past several months I've been pondering what to do with the site, equipment, and all that goes into having such an asset; and while I/we haven't decided completely, retargeting seems the most viable option (if I can find a better band or application for the terrific high-level site). I'm open to suggestions, if you have any that still serve the intended goal of in some way helping the local Amateur Radio and/or Emergency Services community. vern --- In Repeater-Builder@yahoogroups.com, railtrailbiker railtrailbi...@... wrote: Are there any current or former repeater owners/operators out there who have recently taken a repeater off the air on a permanent basis? If so, what were your reasons? Tony
[Repeater-Builder] Re: Duplexer tuning with an Oscilloscope
Hi Darrell, I've done it with an oscilloscope (slower than yours) and a Sweep-Marker generator; but not with just the oscilloscope, signal generator and frequency counter. If I recall, the HP 8640B is also an RF Signal Generator; so if combined with an RF-detector and your oscilloscope and frequency counter, you could theoretically do it. I have tuned simple filters with a signal-generator, frequency counter and an oscilloscope; but haven't had any luck with tuning full duplexers this way. The problem with this approach is that it is like trying to understand what's happening in the forest by only looking at one tree at a time. What I mean by this is that you will see the apparent changes at one frequency, without seeing what's happening to the spectrum around it. If you were only looking to tune a single notch band-pass circuit, then it might be Ok to just use the equipment you listed; but today's duplexers are made up of several band-pass and several notch stages, all working on a common signal. You can easily tweak one piece and completely destroy your ability to meet the overall goal (because you aren't also looking at the spectrum around the one frequency). The other (not-so-intuitive) part to this is that it is often difficult to do the tuning of a duplexer piece-meal; not impossible, just difficult. What I mean by this is trying to tune one stage (cavity), then another, then another; and combining it all together into the overall duplexer system. The problem is that the interconnecting pieces of coax become part of the tuned circuit. Once combined together, one cavity's tuning can impact the adjacent cavities. When I pre-cut the interconnecting cables to the specific resonant lengths, I could get much closer to having the combined system pretty close; but I've always had to adjust things just a little after it was all connected together as a duplexer system. I am also told that a service monitor or spectrum analyzer with a tracking generator built-in is also a preferred method; but I have never been able to afford either. A Sweep Generator effectively turns the oscilloscope into a spectrum analyzer (so that you can see the forest); and a Sweep-Marker Generator also provides you references to use to easily make your adjustments (letting you see which trees are important to you). To my perception, a decent Sweep-Marker Generator and even a home-made RF-detector can promote even a relatively low bandwidth oscilloscope into something nearly equivalent to an expensive spectrum analyzer with a tracking generator. By the way, you can often find used Sweep Generators around that will work on Amateur Radio frequencies (especially VHF/UHF); many that were made to help align TVs are even applicable. If it doesn't have the Marker Generator built-in, you could substitute the signal generator and frequency counter to inject a reference marker at a known frequency; but it will take you a bit longer to continually adjust the setup. Anyway, that was my 2-cents; hopefully it was useful. de W6NCT (Vern) --- In Repeater-Builder@yahoogroups.com, jistabout [EMAIL PROTECTED] wrote: Just curious if anyone here has used a wide-band oscilloscope (along with a signal source, of course) for duplexer and/or filter tuning? I use an older Tektronix 7904 500mhz scope along with an HP 8640B Signal Generator and it works great. ... - Darrell/KA7BTV
[Repeater-Builder] Re: Phelps Dodge Duplexer
Brad, I'm not familiar with that model number. Is it a can-type; or perhaps a smaller one to go inside a portable-type repeater? I have a manual for the Phelps-Dodge can-type (pass/reject) duplexer; but it's discussion is pretty simplistic. There are several in this group that are better experts on duplexers than I am; but if you don't hear back, and if it is the can-type (pass/reject) duplexer, let me know and I'll post it in the Files area. vern ([EMAIL PROTECTED]) --- In Repeater-Builder@yahoogroups.com, n3nrn [EMAIL PROTECTED] wrote: ... Phelps Dodge 440 Duplexer Cat# 522-509 ... Brad (N3NRN)
[Repeater-Builder] VXR-1000
Does anyone know if the VXR-1000U be easily converted for use on Amateur frequencies? If so, is the method documented somewhere? Does anyone have any experience using either the VXR-1000V or VXR-1000U for an Amateur Band repeater? I'm looking to setup a small portable Amateur band repeater with a UHF/VHF link; and I was considering these units. Thank-you. Vern (W6NCT)
[Repeater-Builder] Re: Duplexer tuning - sanity check
Thank-you for all the prompt responses, both on and off the group thread. As always, I apprecitate the input and guidance. Vern (W6NCT)
[Repeater-Builder] Duplexer tuning - sanity check
I'm tuning up a cavity-type duplexer for a 70cm repeater, and in the process, I showed my results to a fellow ham. He asked a couple questions that cause me to think; so I decided to ask the experts... FIRST QUESTION TOPIC: For reference, my primary cavities were made by Tx-Rx Systems, and have both bandpass and band-reject tuning controls on each cavity. When tuning them (either singularly or as pairs in-series), I see and can adjust the band-pass and notch for the desired Tx and Rx frequencies. However, in the broad-band sweep, I can also see a bunch of other signals passing through the cavities; all of which are well away from my Tx/Rx frequencies. I suspect that these are normal, and are a side effect of how the can-type resonant cavities work. Am I correct in this assumption? As a sanity check, I combined this set of cavities with another (Phelps-Dodge) set I have, and tuned these supplemental cavities for band-pass only (one cavity for my Tx frequency, and one cavity for my Rx frequency). Sure enough when I put these in series with my primary set, I can eliminate nearly all of the other signals from the broad-band sweep. This observation seems to reinforce my initial assumption about the Tx-Rx cavities. Do you agree? SECOND QUESTION TOPIC: The other ham thought that I should end up with a band-pass that is narrow enough to eliminate adjacent repeaters (at 16kHz spacing, as per the current SCRRBA band-plan separation). I tried but I cannot get either set of cavities to have that narrow of a band-pass; at least not without sacraficing most of the signal in the process. I suspect that the receiver and transmitter need to actually inforce these much narrower bandwidth requirements within the broader protection provided by the cavity-duplexer. I suspect that I should focus my duplexer tuning on passing the desired frequency, notching the alternate repeater frequency, and trying to do so with the least amount of signal attenuation. Am I correct in these understandings? For both of these question topics, feel free to point out anything that I might be missing or misunderstanding. I'm by no means sensative about this stuff, and still consider myself on the learning curve about duplexers and repeaters in general. Thank-you (in advance) for your time, thought, and opinions. vern
[Repeater-Builder] Re: Manuals FS
Jim, Let's try this again. Apparently the group automation truncates email addresses (for privacy?). I am still very interested in the indicated manuals (see below). Please send me an Email directly (using the address W6NCT @ ARRL . net, omitting the spaces). Please tell me if they are still available. Once we connect, we can discuss any specific payment or mailing instructions. Thank-you. vern --- In Repeater-Builder@yahoogroups.com, w6nct [EMAIL PROTECTED] wrote: Jim, I am very interested in the following manuals. Please contact me directly ([EMAIL PROTECTED]) if they are still available. Your message posting clipped your email address, so I couldn't respond directly. Standard RPTS-LMR-1 90 watt ?UHF/FM Repeater System Owner's Operating and Maintenance Manual Standard DPX-1B/3B UHF Duplexers Instruction Manual Standard MTP-4B Multiple Tone Panel Inst. Manual Standard RPT-20 UHF/FM Repeater Owner's Operating and Maintenance Manual Thank-you. vern --- In Repeater-Builder@yahoogroups.com, Jim, K8COP jimk8cop@ wrote: I have the following used manuals for sale: snip As far as I can tell they are complete. All manuals are $10.00 each. Shipping via USPS flat-rate shipping. e-mail me at: k8cop@ (...address was truncated ...) Thanks, Jim, K8COP
[Repeater-Builder] Re: Manuals FS
Jim, I am very interested in the following manuals. Please contact me directly ([EMAIL PROTECTED]) if they are still available. Your message posting clipped your email address, so I couldn't respond directly. Standard RPTS-LMR-1 90 watt ?UHF/FM Repeater System Owner's Operating and Maintenance Manual Standard DPX-1B/3B UHF Duplexers Instruction Manual Standard MTP-4B Multiple Tone Panel Inst. Manual Standard RPT-20 UHF/FM Repeater Owner's Operating and Maintenance Manual Thank-you. vern --- In Repeater-Builder@yahoogroups.com, Jim, K8COP [EMAIL PROTECTED] wrote: I have the following used manuals for sale: snip As far as I can tell they are complete. All manuals are $10.00 each. Shipping via USPS flat-rate shipping. e-mail me at: [EMAIL PROTECTED] Thanks, Jim, K8COP
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
see embedded responses (w/VERN prefix) below --- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: A quick reply... w6nct w6nct@ wrote: I am setting up my duplexer using four Phelps-Dodge cavities (all in series for Rx), and two Cell-wave cavities (in series for Tx). All of these are individual, cylindrical, PASS-REJECT cavities. Are the 5 or 8 inch... or some other size diameter cavities? VERN: All are approximately 4 diameter by 8 long. At this point, I have a setup and test methodology to tune the PASS and REJECT adjustments; and have done so for the individual Phelps-Dodge cavities (mostly as a pre-tune and confidence building exercise). Nothing wrong with taking the time to learn... I do it all the time and it really pays off. Undestand a single cavity adjusted location will be different from a dual series cavity setup... and different from a triple cavity setup. Broadly speaking you might see how additional cavities change the final adjustments. So starting from scratch you'll get single cavities in the ballpark and the final assembly will require a second or third final adjustment. VERN: What I've noticed already is that if I use bad interconecting cables (i.e., lossy, or ones not near odd 1/4 wave in electrical length); then the combination of multiple cavities in series changes a lot. But the closer the interconnecting cables are to good ones, the less I need to re-tune once I connect the cavities in series. I've also noticed that I can work to tune up a duplexer system with less than ideal cables; but it's much more difficult and touchy, and doesn't seem to provide as good of an end-result. I expect that the duplexer system will work much better (i.e., more stable and and more efficient) if I invest the time into setting up the best interconnecting cables I can. I'm expecting that I may have a bit more of adjustment when I connect the Tx string to the Rx string, using the T-connector; since the two strings are tuned for different frequencies. We'll see... I have not re-tuned them in the full duplexer system configuration as I am still trying to make up the proper length cables (see other related topic thread, measuring coax for duplexer). I'm still a little stuck in making these cables, due to the unknown length and velocity factor for the loop inside the cavities. If you have any thoughts on this topic, please add them to the associated thread. You didn't mention the type of coax you are using...? Consider the physical loop/probe length to be added to the coax length. The coax will have a velocity factor of say... .66 to .93 typical and the internal loop/probe length is most often considered free space, which is also known as vel= 1.0 I don't march with the crowd on this one... every time I try to follow the various posted cable length text the results never seem to work out. So I use my own methods and test gear, which gives me the nearly exact performance of the specific network I'm working with. If you want some rules of thumb I like to consider... I'd need to know more about the cavity loops/probe assemblies. Email me direct if you like. VERN: I'm using RG-400 (Vf=0.695), using N-connectors on Phelps-Dodge and BNC on Cell-wave cavities. Several from this repeater group have indicated that the loops (one per port) inside adds to the length; even though Hams local to me aren't convinced. I've already decided to believe the group's experts; but I am having a bit of problem determining how much length it adds. I suspect that if I had a TDR I could tell; but I haven't found a way to get my MFJ to tell me. I hand-calculated a starting length for the cable alone; and using that as a test/reference cable, I have been trying to measure the internal loops of the cavities. The measurements I have taken (in trying to figure it out experimentally) have shown that the apparent/combined electrical length (i.e., reference cable plus single cavity loop) change dramatically if I change the cavities bandpass adjustment; and it is also dramatically different depending on what I do with the other port (e.g., open, 50-ohm termination, or 0-ohm termination). Thus far, I haven't figured it out; or decides what termination is appropriate. Perhaps I should buy an extra cavity and cut it open to see what's really inside (?). Beyond that, I have the Tx/Rx sections of the repeater operational; and am trying to figure out how to best interface my (NHRC-5) controller and (ComSpec TS32) PL decoder/encoder (see other related topic thread, Controller connection to RPT-21). This portion is still in progress, trying to figure things out. If you have any thoughts on this topic, please add them to the associated thread. An original Standard RPT-21 ..? VERN: Yes, it was still virgin when I got it; still tuned to a commercial frequency
[Repeater-Builder] Re: Poor Mans Repeater Project anyone?
This sounds very interesting; I don't know how much I could contribute, but I'd like to at least read along, and perhaps toss in a comment or question every once in a while. In a way it goes along with a similar project I have been working on, that being a portable Emergency Repeater. In my case, I specifically want/need to avoid using duplexers; since the base equipment requirements includes spur-of-the-moment cross-banding (even to/from commercial band, police and fire band frequencies). In our area I/we already have an application/need for this sort of setup as part of our Emergency Response equipment. I have been looking into using vertical separation in place of duplexers; but I haven't tried it much yet. I've also been looking at passive repeaters, using two beam antennas and a piece of low-loss coax. Both of these have caught my interest, since I already have a portable tower platform to work from. In any case, I'm interested; but I am concerned that your project will become too big of a discussion for a single message thread. You may want to setup some message title infrastructure upfrount, so that sub-topics can work from similar related threads and still work with searches and filters. vern
[Repeater-Builder] Re: Poor Mans Repeater Project anyone?
Wesley; I'm interested in your work with the UHF Mitrek setup. I already have one that was built up by another local Ham; but it seems a little deaf. I'm pretty sure that he used some of the reference information from the main (Repeater-builder.com) site; and thus far, I haven't ruled out its problems being more site related than equipment related. In my case, I'm building up a replacement; and plan to use the Mitrek configuration for my backup as well. ... mind if I tag along? vern --- In Repeater-Builder@yahoogroups.com, Richard W W Bazell Jr [EMAIL PROTECTED] wrote: Sound good to me. Would certainly like to observe learn. Have a project going of converting an Motorola Mitrek UHF as an Backup for an Repeater that I have in operation. Wesley AB8KD
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Hi skipp025; Thanks for the input and comment. You are actually coming in mid-thread; but I'll try to catch you up. Unfortunately, some of the information exchange has been off-list; so I appologize for the loose-ends it left in the group's message thread(s). I do have some of the other support items you mentioned (e.g., dummy load, attenuator/pad, RF detector, oscilloscope, watt-meter, MFJ-269,...); I was only mentioning the items I was most concerned about. I am setting up my duplexer using four Phelps-Dodge cavities (all in series for Rx), and two Cell-wave cavities (in series for Tx). All of these are individual, cylindrical, PASS-REJECT cavities. At this point, I have a setup and test methodology to tune the PASS and REJECT adjustments; and have doneso for the individual Phelps-Dodge cavities (mostly as a pre-tune and confidence building exercise). I have not re-tuned them in the full duplexer system configuration as I am still trying to make up the proper length cables (see other related topic thread, measuring coax for duplexer). I'm still a little stuck in making these cables, due to the unknown length and velocity factor for the loop inside the cavities. If you have any thoughts on this topic, please add them to the associated thread. Beyond that, I have the Tx/Rx sections of the repeater operational; and am trying to figure out how to best interface my (NHRC-5) controller and (ComSpec TS32) PL decoder/encoder (see other related topic thread, Controller connection to RPT-21). This portion is still in progress, trying to figure things out. If you have any thoughts on this topic, please add them to the associated thread. I've figured out a lot about using the Wavetek 1080. It's a pretty amazing piece of equipment; but I still haven't gotten the manual(s) for it. QUESTION 1: Do you have the same model Wavetek (i.e., 1080)? If so, do you have the manual(s) for it? QUESTION 2: I'm curious about the Marker input on the front. Do you know what it is for, and how it is used? QUESTION 3: Do you know how to read the display in terms of the calibrated signal amplitude, given a specific setting of the Output (in dBm)? More specifically, a friend was saying something like in order to read the actual bandwidth of the PASS and NOTCH, I needed to measure it a the 6 dB point. Does that make sense? Do you know how I would do it using the Wavetek 1080's display on an oscilloscope? I suspect that it's just a calibration/visualization thing that I am missing. I appreciate any wisdom and experience you can offer; especially relating to the Wavetek 1080. vern
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
I haven't received it yet. You might want to double check the TO-address you used (S/B: [EMAIL PROTECTED]). Occasionally, my eMail bounces; but I haven't figured any reason for it. If it does, please try again. Thx. vern --- In Repeater-Builder@yahoogroups.com, Mike Morris WA6ILQ [EMAIL PROTECTED] wrote: I've responded to this message off-list.
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Ron; Thank-you for your comments and suggestions. I didn't get around to trying to tune then with just the audio of a receiver to go on; fortunately I got the Sweep/Marker Generator and Oscilloscope setup to work. I really like how the display output is linear (vs log.); I think that it makes it easier to read/adjust. I didn't have the problem you described with the narrow notch. I'm not sure if it is because of the linear (vs. Log.) display, or perhaps the cavities I was using. It might also be because I tuned each cavity individually first, before looking at them in series. Either way, it seemed to dial right in. I haven't done the final tune (of the entire duplexer system) yet; as I am still trying to get the interconnecting cables cut just right. Perhaps the situation you describe might show up more notably during the final tune when the pass and reject behavior is more pronounced (e.g., narrower BW,...). Either way, I'll keep my eye out for it. Another Ham here asked me about reading the actual bandwidth of the cavities (referring to a 3db or 6db point, or something like that). To be honest, I wasn't quite sure what he meant or how I might do it; but I suspected that it is just the width at a certain number of DB from the peak (of the pass or notch). The Sweep/marker generator does seem to have data to indicate the signal strength (in db); so I am guessing that I can actually do it if I was more familiar with the Wavetek 1080 and how to read the vertical display it generates (I'm still looking for the manual). vern
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Ok Mike, I can probably do that. I certainly qualify as a first-time repeater builder, and all of the pieces that it has required. I'll start collecting some of the pieces and images I need. I'd prefer to hold off publishing it until I actually get the repeater up and running; as proof that I really did learn what I thought I learned. ;-) Is there someone that I could/should submit a draft copy to? I'd prefer to run it by one or more knowledgable and experienced repeater-builders before it becomes visible to the world (sorta as preemptive damage control,...). vern --- In Repeater-Builder@yahoogroups.com, Mike Morris WA6ILQ [EMAIL PROTECTED] wrote: Why not do an entire article for repeater-builder? Something like A first-timer's experience at tuning a duplexer ??? snip Mike WA6ILQ
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Thank-you; it has been an interesting learning exercise for me. For the detector, I actually used a little gadget box circuit that my Dad had made up years ago. When I first found it (unlabeled) in his electronics stuff, I didn't know quite what it was. Like so many other little boxes he had, he used to toss a handfull of components into a small box and use it when he was testing something out. When I was young, they always seemed like magic and mystery. It was only after several years at college that I could even start to figure out the mysterious little circuits inside. The particular setup I used was much like N5ESE's QRP Dummy Load with it's built-in RF Detector (http://www.io.com/~n5fc/dummy3.htm); but in my case, I used a standard T connector to combine my Dad's detector and a separate 50 ohm dummy load (also in a gadget box). I stumbled on N5ESE's version when I was trying to convince myself of what my Dad's actually did; especially since Dad's was wired a bit different from the others that I had seen. At Gary Schafer's (K4FMX) recommendation, I also put a 6db pad between the sweep/marker generator and the cavity's input. If you like, I can sketch out the whole test setup; just let me know with an off-group message ([EMAIL PROTECTED]). Enjoy. vern
[Repeater-Builder] Re: Controller connection to RPT-21
Terrific. Thank-you. vern
[Repeater-Builder] Re: Controller connection to RPT-21
This is great. I like that it also includes the information on the other parts of the controller(s); even the older ones. Thank-you. vern
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
UPDATE: I have an operational test setup working using the Wavetek 1080 (sweep/marker generator), oscilloscope, RF detector, and a couple 50 ohm terminators. With them I was able to successfully reset the band-pass on the individual cavities I am using for the duplexer. All I have left to do with the duplexer is make up the associated interconnecting cables and re-adjust things a bit as a complete duplexer system. I am still a little hung up on making these interconnecting cables; but I am making a little progress there as well (see other message chain in the group). Thank-you all for helping me figure out how to setup this tuning configuration. vern (W6NCT)
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Hi Larry; I have two sets of 70cm cavities. Each set is comprised of four independent cavities (approx. 4 diam. x 7.5 high). I don't see a model number on any of them. One set is made by Phelps-Dodge; and I am told that the other (Vari-notch) set was made by Cell-wave. The Phelps-Dodge cavities have built-in type N connectors; but the Cell-wave cavities have BNC connectors on a block on the top, near what I believe is the notch adjustment (?). Because of the high-noise environment that the repeater will be in, I am planning to use the four Phelps-Dodge cavities (in series) for the Rx side of my duplexer; and two (of the four) Cell-wave cavities for the Tx side of the duplexer. I'm told that when I make up the cables for these, I need to include the length of a loop inside; but I am still trying to determine how to do that. That aside, I'm not sure if these loops that are being referred to for the length measurement are the same ones that you are referring to as well. I was only aware of bandwidth and notch adjustments on these cavities (i.e., not a specific impedance adjustments as well). Once I make up the cables, then I get back to the task of trying to tune them up. I guess that I could throw money at the problem or try to get someone else to do it for me; but I'd like to be able to do it myself. I could also rent a tracking generator or network analyser (as you suggested); but I suspect that renting a technician to run it is illegal in this state ;-) . Kidding aside,... as I said, I'd like to get to where I can tune these things myself. So if it can be done with what I have access to, I'd prefer to do so; even if it takes me a bit longer. I was under the impression that I could, if I get the test setup and procedure correct. Alternatively, I guess that I could try to sell my Wavetek 1080, and use the money to go toward a tracking generator, network analyzer, or whatever else is usable; but I haven't looked into that option much yet. In the mean-time, I was trying to get it done with what I have. Which post (from Gary) are you referring to; and what specifically should I be paying special attention to? His post dated 4/1/07 at 9:21 pm. He starts out Duplexer and cavities have been tuned for many years... Excellent post - one of the best I've ever read. Now that I know what to look for, I'll go read the message you indicated. Albeit, I am reluctant to throw money at the problem or have someone else do it for me, I do appreciate all your advice. Thank-you. vern (W6NCT)
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Hello again larry, Now that you pointed it out, I already know about the message you indicated. In fact, it turns out to be one of the responses to one of my postings. Subsequent to this particular posting, he and I have been communicating a bit more one-on-on (off-list) with even more QA on the topic. So as a result of his kind assistance and patience, I am now aware of even more than what is in the group's copy of the message. And now that I understand even more of what he was saying, I agree with you that it is a good starting description. Thanks again, vern (W6NCT)
[Repeater-Builder] Re: Controller connection to RPT-21
Thank-you Bob, for pointing that out. As it turns out, someone else had mentioned that to me as well. In this instance, the analog delay module came out of an S-Com 5000 controller; and the contributor told me what the pinouts were supposed to be. Although I would prefer to confirm things with proper schematics, I have made the connecting cable according to the information he provided. By chance would you happen to have a schematic and documentation for this module? At this point, I do not know what the pots are for; although I would suspect that one (of the three) is the delay time. The PCB has S-COM Audio Delay Module in the silkscreen on the componend-side; and J703021 in the etch on the solder-side. Thanks again. vern (W6NCT)
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
responses/questions embedded below --- In Repeater-Builder@yahoogroups.com, nj902 [EMAIL PROTECTED] wrote: You can use a sweep generator and scope for swept alignment of filters and duplexers. The manual for your sweeper should show the setup procedure. If you don't have the manual, try BAMA or other internet sites. W6NCT: This sounds encouraging; unfortunately I do not have the manuals for the (Wavetek 1080) sweep generator; nor does BAMA as near as I can tell. I have started making enquiries around; but was hoping that someone might be able to tell me how to set it up in the near term. You will need an RF detector probe or preferably a detector such as the HP 423A or 423B crystal detectors. These have a 50 ohm interface to the device you are tuning and provide a rectified output to drive the vertical deflection of your scope. W6NCT: My dad's equipment included a simple (full-wave) diode detector (i.e., RF in, DC out); would this be ok? The scope horizontal is driven by a ramp voltage from the sweeper. Using the scope in X-Y display mode thereby provides a display of device response versus frequency. W6NCT: I also have an oscilloscope. If it is being driven by the sweep generator, do you know how fast a scope it needs to be? The one I have with an X input is an older storage scope (20 MHz?). Might this be ok; or will I need a much faster one? As I recall, my dad used an old (5MHz?) Heathkit back when he used the sweep generator to align the Tx cavities on the UHF-TV transmitters, so I was guessing that a slower one might be ok. I tried connecting my oscilloscope (X and Y) to the sweep generator; but I can't get something to display on the screen that looks anything like a spectral waveform. Do you if or know how I need to connect the other IOs of the 1080 (RF out, demod in, and marker in)? Be aware that your display will be linear whereas a spectrum analyzer + tracking generator display - or a network analyzer display - will look like the duplexer manufacturer's spec sheet with a logarithmic vertical axis. W6NCT: understood. You can also tune the duplexer using the generator in the IFR along with a receiver that has a receive signal level indication - even your repeater's receiver and a test meter showing the limiter. W6NCT: If I use the IFR to generate an FM signal at my Tx and Rx frequencies, and feed it into one side of the cavities; then how do I setup the output? Thank-you.
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
--- In Repeater-Builder@yahoogroups.com, kb5vjy [EMAIL PROTECTED] wrote: Greetings, I use a Signal generator (Wavetek 3007 signal generator) and a Spectrum Analyzer Tektronix 7613 O scope with the 7L12 Spectrum Analyzer module) Tune them up just fine here with that. W6NCT: I have a 564 storage scope; but I don't have the (L-series) spectrum analyzer module for it (yet). I also have a faster oscilloscope; but don't see an easy way to drive it's X-input from an external sewwp generator. I have a spare vertical module for the 564; which is how I am currently driving the X-input from the Wavetek 1080 sweep generator. It does seem to sweep the oscilloscope beam; but I'm not sure how to hook up the rest of the test-setup to get a pseudo-spectral display for the output of the cavity. Any thoughts? All a tracking generator is in a Spectrum Analyzer for what you are using it for is a signal generator. 73 de Joe KB5VJY
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
see embedded responses below --- In Repeater-Builder@yahoogroups.com, Eric Lemmon [EMAIL PROTECTED] wrote: Your informant is essentially correct. A sweep generator is an instrument that generates an AF or RF signal either linearly or logarithmically between a start and an end frequency. By itself, it is useless for tuning cavities. However, when its sweep voltage is coupled to an oscilloscope's horizontal input, then we have a tool to visually characterize a cavity. A spectrum analyzer is essentially an oscilloscope with its input filter being driven by a sweep generator. W6NCT: I thought that to be the case; and I have already tried to connect the X/Y outputs from the sweep generator to my oscilloscope. The scope's display does sweep; but it does nor look lik what I was expecting. I suspect that I don't have the rest of the test confifured correctly. Can you tell me how to connect the other inputs and outputs to stimulate the cavity and see the response on the oscilloscope? A tracking generator is not really a separate piece of equipment, but is simply an output of the spectrum analyzer that can be used to excite the unit under test. The tracking in the name means that this signal generator is synchronized exactly with the sweep of the spectrum analyzer. Thus, the display on the analyzer is a graphic representation of the frequency response of the unit under test. W6NCT: I would have expected that the Sweep Generator, when combined with a connected oscilloscope would essentially result in the same functionality as a tracking generator; since the Sweep generator seems to both drive the DUT and the oscilloscope output display. Am I wrong? A spectrum analyzer with a tracking generator, or better still, a vector network analyzer, are ideal for tuning duplexers, notch and bandpass filters, and ferrite isolators. W6NCT: This is nice information; but again, you are talking about equipment I cannot afford. Which is why I was asking my questions to begin with. 73, Eric Lemmon WB6FLY
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
see embedded responses below --- In Repeater-Builder@yahoogroups.com, Gary Schafer [EMAIL PROTECTED] wrote: Duplexers and cavities have been tuned for many years without a tracking generator or spectrum analyzer. It is a little easier with a tracking generator or even a spectrum analyzer and a signal generator. But you can do the job with a signal generator that you can keep on frequency and a receiver. W6NCT: This sounds encouraging. It helps to have some kind of signal level meter on the receiver but you can also just tune for quieting by riding the generator level so that the receiver is always noisy. That way you can hear if the level goes up or down. W6NCT: I think that understand the notion of using a receiver with a quantifiable indicator of receiver signal strength; but I don't understand what you are saying in your statement tune for quieting by riding the generator level so that the receiver is always noisy. Could you explain this a bit more? Using a sweep generator works fine for tuning pass band cavities or even the pass band part of a pass/notch type duplexer but you can't tune the notches with a sweep generator. The reason being is that the detector is not sensitive enough for the low signal levels that you need to work with. A typical diode detector will only work at about -20 to -30 dbm. Even if your sweep generator is able to put out +20 dbm that only lets you look down -40 to -50 db and the duplexer notch is going to be (hopefully) in excess of -70 db. You will never find the peak of the notch. So just a signal generator preferably a synthesized unit so you know what frequency it is on. You could use a tunable generator and a frequency counter but lots of generators tend to shift frequency slightly when you crank up the output level (high enough for the counter to see) and you will be working with the signal attenuated down to -80 to -100 dbm most of the time while tuning the duplexer. You can not afford to have the signal shift around or drift while you are trying to tune things as it doesn't take much of a frequency shift to mess up your tuning. W6NCT: Can I use the sweep generator to tune the band-pass; then just the generator in the IFR-1100 to generate the driving signal into the cavities to tune the notch? The IFR is synthesized and I'm guesing that it might be able to put out more than the sweep generator without becoming unstable. With a good generator tune the pass bands at the proper frequencies first. Then tune the notches at the opposite frequencies. On the transmit cavities you would tune the pass to the transmit frequency and then tune their notches to the receive frequency (etc.). Then tune the pass tuning at the proper frequency again now that you have everything in the ball park. Then tune the notches again at the proper frequencies. ALWAYS tune the notches last. Do NOT touch the pass tuning again when you are done with the notch tuning. Tuning the pass just slightly will throw the notch way off. W6NCT: Understood. Tx cavities are to band-pass Tx freq and notch Rx freq; similarly, Rx cavities are to band-pass Rx freq and notch Tx freq. Right? Be sure and have a dummy load on the port of the duplexer you are not working with and preferably 6 to 10 db pads on each of the ports that you are working with or you may not have the same tuning when you hook it up to your radio. W6NCT: This confuses me a little. In addition to the X and Y outputs to the oscilloscope, the Wavetek 1080 has an RF output, demod In, and a marker In. Not having a manual to tell me the proper setup, I was guessing that the sweep generator's RF output would connect to the input port of the cavity, and that maybe I should connect the output of the cavity to the demod in (leaving the marker input on the sweep generator unconnected). I wasn't sure if I should use some sort of an external circuit between the cavity output and the 1080's demod in. Do you know? Alternatively, I thought that maybe I should put a T connector on the output of the cavity with one side connected to a (50 ohm) dummy load, and the other side connected to an RF-detector that feeds into a second channel of the oscilloscope (leaving both the demod and marker inputs on the sweep generator unconnected). I tried this setup, since I didn't know what the demod In expected. Am I off-track with these possible setups? Either way, I don't understand what the pads are for. Please explain? 73 Gary K4FMX
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
Actually a network analyzer works better than a combination sweep and marker generator. Remember that when you change isolation, you are also changing impedance so you need to measure swr as well. There are other ways. Read Gary's excellent post carefully. -- Larry W1HJF rapp at lmr dot com Unfortunately, I doubt that I can afford a network analyzer either; and I curently don't know how to use one if I happened to come across one to use. I don't understand what you mean when you say when you change isolation, you are also changing impedance so you need to measure swr as well. I expected that the complex impedance of the cavity might be changing as we are changing its tuning stubs; but I thought that a resonance (with a low SWR) was essentially what we are getting when we were adjusting the stubs in the cavity to peak the bandpass at the desired frequency. Am I wrong in this assumption? Either way, how do I set this up, and where would it fit in a test procedure? Which post (from Gary) are you referring to; and what specifically should I be paying special attention to? Thx, Vern (W6NCT)
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
--- In Repeater-Builder@yahoogroups.com, Steven Samuel Bosshard \(NU5D\) [EMAIL PROTECTED] wrote: I can remember using a bearcat scanner on a HP608? (hope that is the right model number) signal generator to tune pass and reject - used a 10 db / 50 Ohm attenuator between the duplexer and the test equipment to make for a better match. I have never used a network analyzer, but I have used several different service monitors with tracking generator. Steve NU5D Can you describe this test setup and procedure a little clearer; perhaps with a drawing? What was the attenuator for? Feel free to send it to me directly ([EMAIL PROTECTED]). Thx. Vern (W6NCT)
[Repeater-Builder] Re: Tuning duplexers with sweep generator?
--- In Repeater-Builder@yahoogroups.com, Gary Schafer [EMAIL PROTECTED] wrote: W6NCT: Please see response posted at 3:37. For some reason it isn't being nested correctly when sorting by topic.
[Repeater-Builder] Re: measuring coax for duplexer
see responses/questions embedded below --- In Repeater-Builder@yahoogroups.com, Gary Schafer [EMAIL PROTECTED] wrote: Cables between cavities include the length of the coupling loops in the cavities. They are measured from the bottom of one loop, the cable, to the bottom of the loop in the next cavity. You need to figure the velocity factor of the cable and the velocity factor of each loop separately as the cable has a specific velocity factor and the loop will have a velocity factor of air. The cables that go to the T are measured from the bottom of the loop again as above to the center of the T connector. A notch cavity will provide about 30 to 35 db of notch depth. Each interconnecting cable provides an additional 10 db or so of notch depth when its length is right. W6NCT: Ok, I understand that they include the lengths inside the cavities; but how can I determine how much is inside the cavity without disassembling them? If I measured an unterminated (test) cable before I connected it to the cavity, could I connect it between the MFJ analyzer and the cavity and measure the additional electrical length added by the cavity? If I made the actual cables that much shorter would the system be resonant; ot do I need to do it iteratively? Would I need to start off with the test cable being a specific wavelength by itself, so that the in-cavity length (and associated velocity factor) would be more easily determinable? ... Don't forget that the transmit side cables are tuned to the receive frequency just like the transmit notches are. W6NCT: Why are the cables in the Tx cavities tuned to the Rx frequency? This seems counter-intuitive to me. I would expect that the Tx cables and cavites should be resonant at the Tx frequency to have the best performance and SWR match. Similarly, I would expect that the Rx cavities would be resonant at the Rx frequency for the best RF throughput to the receiver. What am I missing? The cable on the transmit side to the T provides a high impedance at the receive frequency because the notch in the transmit cavity is a short circuit at the receive frequency. That reflects a high impedance or open circuit at the center of the T connector thru the quarter wave length at the receive frequency. The cable on the receive side provides a high impedance at the transmit frequency at the T because the notch in the receive cavity is tuned to the transmit frequency and provides a short there. The quarter wave length cable reflects that short to a high impedance or open circuit at the T to the transmit frequency. W6NCT: I don't quite understand this; and it doesn't help me understand why the Tx cavities' cable lengths should be for the Rx frequency. I'm still missing something, I guess. Sorry. Ideally you could disconnect the receive cable at the T and it should not effect the transmit power flow to the antenna. W6NCT: I don't understand this either; since I'd expect the unterminated stub of the T to act like a really short antenna. Since it is not an odd multiple of the Tx quarter wavelength, I'd expect its open circuit reflections to impact the Tx path's operation and SWR. Again, I must be missing something. When the transmit energy gets to the T connector it sees a high impedance going to the receiver and a lower impedance (50 ohms) going out to the antenna line so it takes that path. When a receive signal comes in it sees a high impedance in the transmit path at the T and a low impedance (50 ohms) to the receiver path. W6NCT: This piece makes sense to me; and it is fundamentally why the duplexer works. Right? I suspect it should be giving me a hint what I am missing above; but unfortunately it doesn't just yet. The cables that connect to the T connector are necessary to provide transmitter/receiver isolation so power flows in the right direction. If they were not properly tuned there would be a lot of suck out of transmit power and receive energy going to the wrong path. W6NCT: Ok, I can see/understand this. The same thing is done on a transmit combiner where each transmitter has a pass band cavity (it could be done with notch cavities instead). The cavity isolation between transmitters needs to be around 10 db on each side in order to provide the isolation so that the power goes to the antenna and not to the other transmitter. So the other transmitter must be 10 db down on the skirt of the opposite transmitters pass band skirt. You can think of these cavities as switches. The same type of thing goes on at the T connection of a duplexer. W6NCT: I can also understand this for a combiner for multiple transmitters. 73 Gary K4FMX W6NCT: I'm sorry if I seem a little dense on a couple of these notions; some of the concepts seem counter-intuitive to me. That being said, I still need a methodology to determine the proper physical length
[Repeater-Builder] Controller connection to RPT-21
Has someone successfully connected a controller and ComSpec CTCSS module to a Standard Radio RPT-21? If so, could you provide me schematic changes to reflect these connections. I am just learning about repeaters, and have an idea how this might be done; but I lack the confidence, and would appreciat the help of someone who has already done it. For reference, I have a NHRC-5 controller, ComSpec TS-32 (or TS-32P, if any better) CTCSS module, and an S-COM analog delay line. I think that these are the right pieces; all I think that I need is how to hook it all up. Thank-you. Vern (W6NCT)
[Repeater-Builder] Re: RPT-21
Did you find this information? If not, and if you still need it, maybe I can help. vern
[Repeater-Builder] Re: Standard RPT21 Manual
Did you ever find what you needed for this; if not, maybe I can help? vern
[Repeater-Builder] measuring coax for duplexer
PRIMARY CONCERN: I am in the process of building a 70cm repeater and need to know how to measure and test the physical and electrical length of the short coax cables linking the (band-pass/notch) duplexer cavities. I read somewhere that these cables should be an odd multiple of 1/4 wavelength at the operational frequency. In my case, a 1/4 wave cable won't easily reach between cavities; so I am using one that is approximately 3/4 wavelength. QUESTION #1: Due to the Tx/Rx split, I would expect these cable lengths might need to be different between the Tx cavities and the Rx cavities, assuming that I can make the cables this close to a target length. However, I am now wondering how much this small of a difference might matter. Should I be concerned about this small of a difference in the cable lengths (i.e., approximately 0.2)? QUESTION #2: My next problem came when I tried calculating the physical length for these cables. I did the calculations for my operational frequency on the test pair, even trying to allow for the velocity factor (Vf = 0.695) for the RG-400 cable; but I'm not sure where to measure the cable length with respect to the type-N connectors. At 70cm even a 1/4 will impact the effective wavelength of these jumper cables; so this measurement seems relativel critical. CALCULATIONS: wavelength(ft) = 983.6 / [frequency(MHz) * Vf] for 3/4 wavelength cables,... Tx @ 446.860MHz (L = 3 * 4.5893 = 13.7679) Rx @ 441.860MHz (L = 3 * 4.6413 = 13.9239) If I install the type-N connector on one end of a 14 piece of RG-400, at what point should I measure and cut it for the other type-N connector? QUESTION #3: When I prototyped up a couple cables, I tried to confirm that I was in the right ball-park for their length. I tried measuring their electrical using my MFJ-269 analyzer. For reference, I set the analyzer for a 270 degree (i.e., 3/4 wavelength) cable length, and tried to measure the electrical cable length of the initial (approximately 14 long) cables; before I cut and installed the second type-N connectors. Adjusting the frequency even closer, I came out with a resonant frequency (i.e., lowest SWR) at around 420 MHz, presumably indicating that the cables were long. The analyzer also indicated a 1.2' length for the initial setting of 270 degrees; which seemed about right. Assuming a target frequency at around 444 MHz (i.e., mid-way between Tx and Rx frequencies for test case), a 420 MHz resonance would indicated that the cables should be cut down to approximately 95% of their length. If this is correct, I should cut the cables down to somewhere around (14 * 0.95) 13.3. This seemed quite a bit shorter than the caculated length (around 13.8 (+/- 0.1)); so wanted to validate my test methodology as well. Am I doing this correctly? Thank-you in advance for your assistance.
[Repeater-Builder] Tuning duplexers with sweep generator?
I was recently told (by another ham) that I could ONLY tune up my 70cm duplexer cavities using something called a tracking generator. Unfortunately I do not have one; and judging the prices I have seem for things with that name on the web, I doubt that I can easily budget to purchase one. For some reason, I thought that my father used to tune up resonant cavities using a sweep generator, oscilloscope, and a frequency counter; but I don't recall the exact setup he used. I inherited his Wavetek (Model #1080, 1GHz) sweep generator, oscilloscope, and frequency counter. I also have access to an IFR-1100 service monitor, if I need it (i.e., can be borrowed from a friend). Can I tune up my 70cm duplexer cavities using the equipment I have? If so, could someone please indicate the test setup and procedure. Thank-you.
