RE: [Repeater-Builder] Re: Coax shielding
Hi Ian, I think I'd be taking a close look at both transmitters with a spectrum analyser and seeing if they are both suitable for repeater work. I'm not familiar with either radio, but usually radios designed for duplex work go to a lot more trouble with internal shielding than your average mobile set. The other issue to consider is the impedance matching between all the components in the system. If the SWR is bad somewhere then there will be RF voltage on the outside of the coax linking mis-matched devices, regardless of how good the coax is. For instance if the link transmitter is seeing a high SWR into it's bandpass cavity then the jumper cable could be radiating unfiltered noise straight into the repeater receiver cable. It could also be that putting the bandpass filter in line has upset the SWR seen by the Link Tx and now radiates MORE noise in the shack. I've also seen some cavities make PA stages become unstable, creating very broad band noise, requiring both the cavities and PA to be retuned to solve the problem. 73,Mark VK3BYY From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of kerincom Sent: Monday, 28 June 2010 08:19 AM To: mail=repeater-buil...@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Coax shielding Hi skip .The repeater radios are maxon sm4450sc and the link is a tait t2010.The test I have tried in the past have been definitely point to the link being the problem as when we turn the link off the repeater works to its full range but with it on we get desence. We used to have the link closer to the repeaters aprox 487mhz but we shifted it to 517mhz to fix desense and we find we are still having problems.I think the white noise could be the issue but I tried a notch on the link cable tuned to the repeaters receive and that seem to cause more interference and weaken the links Transmit range.I wondered about putting a BP cavity filter inline with the link but since our link frequencies are 5.2mhz apart I feel you can only tuned the filter for either TX or rx frequencies and not both Unless maybe you can install two in pararell ,one tuned to TX and the other rx . Thank You, Ian Wells, Kerinvale Comaudio, 3A Murchison Street,Biloela.4715 Ph 0749922449 or 0409159932 or 0749922574 www.kerinvalecomaudio.com.auhttp://www.kerinvalecomaudio.com.au/
RE: [Repeater-Builder] Direct Strike Lightning Detector
Jess, Tape an empty aluminium drink can to the side of the single point earth strap (or to the leg of the tower). The magnetic field from the few thousand amps of strike current should flatten the drink can in microseconds! Mark vk3byy From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Jesse Lloyd Sent: Thursday, 29 April 2010 10:56 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Direct Strike Lightning Detector We've followed the polyphasor book to the best that we can, using 3 copper strap everywhere, single point ground, etc, etc. I'm reasonably confident that if it does get hit we won't know. I'd just like something simple to indicate that all our efforts were worth it (so I can say to the boss we got hit and everything survived, told you so). From reading some specs and documentation on tower leg mounted strike counters I think the fuse idea might work. So far I haven't seen any that won't work's float by in the threat, so thats something I suppose. Jesse On Tue, Apr 27, 2010 at 8:44 PM, Gerald Pelnar wd0...@cox.netmailto:wd0...@cox.net wrote: Got tower? On a high spot? It gets hit!! If you can't tell, that's a good thing. Gerald Pelnar WD0FYF McPherson, Kansas - Original Message - From: Jesse Lloyd ve7...@gmail.commailto:ve7lyd%40gmail.com To: Repeater-Builder@yahoogroups.commailto:Repeater-Builder%40yahoogroups.com Sent: Tuesday, April 27, 2010 12:32 AM Subject: [Repeater-Builder] Direct Strike Lightning Detector Hey All, I am trying to think of a way to detect if a tower at one of our sites gets a direct hit. I was thinking of paralleling a ground strap with a 10mA amp glass fuse. Maybe make the two connections to the ground stap 2 ft apart and use a fuse holder for fuse testing and replacement. I suspect the fuse would blow if any significant current went down the ground strap (or would the whole thing melt? I suppose either way I'd know!). Ideas? I live in an area that doesn't see a lot of lightning, I'm curious if the tower gets hit. Jesse Yahoo! Groups Links
RE: [Repeater-Builder] Fw: FCC RO Involving the Amateur 70cm Band
This is already happening in Australia. Amateurs are secondary users for 420-450MHz, with military and radio location being primary. A few years ago our ACMA introduced Low Interference Potential Devices license class (any modulation, for any purpose, 25 mW maximum, no license required). Allegedly this was to allow luxury cars to be imported without modifying their electronic door and security keys. Not surprisingly there are a few luxury cars still parked near amateur repeaters that can't be unlocked :-) Due to poorly written legislation, a whole lot of other devices have now flooded the market, including continuously transmitting data modules, and all cause a lot of trouble to amateur operators and repeaters. The bottom end of the band 420-430MHz of the amateur band has also been eroded by government digital radio networks (because it's cheaper to import equipment from overseas that's already in that band). Amateurs in parts of the country are no longer allowed to use that part of the band. I hope the FCC doesn't follow suit although it sounds like they already are! Mark, VK3BYY _ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Richard Sent: Thursday, 4 March 2010 07:11 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Fw: FCC RO Involving the Amateur 70cm Band I feel a little pessimistic about this, in that I expect it to happen more frequently as time passes. I hope I'm wrong, but I can't help feeling that we are going to gradually lose our spectrum as companies with deep pockets buy our frequencies out from under us. Richard www.n7tgb.net http://www.n7tgb.net/ Government's first duty is to protect the people, not run their lives. -- Ronald Reagan _ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of George Henry Sent: Wednesday, March 03, 2010 11:15 AM To: repeater-builder@yahoogroups.com Subject: [Repeater-Builder] Fw: FCC RO Involving the Amateur 70cm Band Re: the waiver request by ReconRobotics for 420 - 450 MHz operation. Hams get the shaft again... George, KA3HSW / WQGJ413
RE: [Repeater-Builder] Re: Can the 4th harmonic of 1250 AM keep UHF repeaters locked up?
I would have thought good grounding practices on the feeder and equipment at the base of the tower would have pretty well bypassed any 1.25MHz stuff. Ferrite 'beads' will reduce common mode pickup on coaxial cables without any effect at all on the signal inside the coax. Don't expect too much attenuation though - usually they are only good for 8-15dB at UHF frequencies, and somewhat less at low frequencies (choose your ferrite material carefully!). 73, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of DCFluX Sent: Wednesday, 24 February 2010 09:35 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Can the 4th harmonic of 1250 AM keep UHF repeaters locked up? How about 1.25 MHz RF coming down the outer jacket of the UHF antenna and into the ground of the system? You have about 200 ft or so of coax? Try a mag mount antenna temporarily. Not really sure how you'd cure that though. Not sure if snap on RF beads would work on coax with a signal going in the center.
RE: [Repeater-Builder] Re: Can the 4th harmonic of 1250 AM keep UHF repeaters locked up?
Hi Tony, Are you using a duplexer on this repeater? A lot of cavity filters act as a short circuit to DC and low frequencies, so additional filtering is unlikely to help. I can only think of one type of cavity that has a DC path between from input to output (via an internal inductor) and not to ground. This type could I guess pass low frequencies. It's simple to test - disconnect the antenna and receiver leads and measure the DC resistance with a meter between the centre and outer on the cavity connectors. If it's 0 ohms then it's likely to be a very good high pass filter for broadcast frequencies! Also, using a temporary attenuator you should be able to determine if there is an intermod problem within the receiver, or parts of the antenna filtering system on the receive side of a Duplexer. Inserting an attenuator will reduce the interference (and desired signal) by the same amount if everything on the receiver side of the attenuator is functioning correctly. If instead the interference drops by 2-3 times (in dB, and the desired signal drops only by the attenuator value) then you've found your problem! Placing a power attenuator in the duplexed antenna line is more complicated because you are attenuating both the Tx and Rx signals. You would expect the interfering signal to drop by more than double the attenuation value, and you can't really tell if the problem is in the antenna, antenna feeder, or something external. 73, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of KT9AC Sent: Wednesday, 24 February 2010 09:02 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Can the 4th harmonic of 1250 AM keep UHF repeaters locked up? I was able to match up the audio coming through the repeater and the local AM station. My latest theory is that their signal is so strong that its blowing into the receiver's front end and multiplying/mixing there (past the bandpass filters and all). They are heterodyne receivers after all. I'm considering an ICE broadcast high-pass filter that cuts off at 1.8Mhz (model 402). I have an email into them to see how well it might work at 448 Mhz. Tony
RE: [Repeater-Builder] Can the 4th harmonic of 1250 AM keep UHF repeaters locked up?
I know of one amateur repeater where a distant AM broadcast signal mixed with a commercial Tx operating on the same tower to produce interference on the repeater input. The problem was tracked to a rust joint between the galvanised iron roof and the guttering of the equipment hut. The broadcast station was more than 30 miles away, so rusty joints can work as pretty efficient broad band mixers! The only solution was to fix the roof as moving frequencies of the other players wasn't possible :-) Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Tony KT9AC Sent: Monday, 22 February 2010 08:53 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Can the 4th harmonic of 1250 AM keep UHF repeaters locked up? Thanks Jeff. The AM station has the same power both day and night, just goes from 2 towers to 4 to change the pattern. Rusty bolt or fence line etc seems the most likely. The problem does seem to disappear when its raining out, which helps verify this theory. It might be a needle in a haystack trying to find this, so maybe remoting the receiver might be the easiest. Thanks and I'll continue to investigate. I can try temporarily moving the frequencies apart about 100Khz and see if my 5Mhz theory holds water. Tony Jeff DePolo wrote: So, if we take the 1250Khz signal or 1.25Mhz x 4 = 5Mhz. I realize that the 4th harmonic of a 5KW broadcast station isn't very powerful Well...it *shouldn't* be very strong. It has to be attenuated 43 + 10 * log (Pwatts) as measured in the field (not at the transmitter output terminals). If you have access to a field intensity meter that covers up to 5 MHz, or a spectrum analyzer and a calibrated antenna, you can measure it yourself. AM stations that change power and/or pattern at night sometimes use a different transmitter between day and night depending on the power levels. Some stations also have pre-sunrise, post-sunset, or critical hours authorizations that are intermediate power levels between day and night power levels, or as an adjunct to daytime-only authorization. Bottom line - the 4th harmonic content may vary due to a combination of pattern, transmitter power output, or even different transmitters. but being in its nearfield might be enough to cause a mix with the UHF transmit output. Well, 1 or 2 miles isn't really near-field, but in any case, the field intensity may be relatively high depending on all of the other variables (power, pattern, etc.). Usually interference to VHF/UHF involving mixes with AM broadcast occur somewhere at or near the VHF/UHF site, not at the AM site. In some cases, the problem can actually be caused within the equipment on the ground rather than externally at the antenna or on the tower. If it's an in-the-cabinet mix, it could be caused by inadequate RF shielding. Before going on a wild good chase, I'd ensure that everything is properly RF-shielded, shielded cables are used for interconnects, grounding is good, all shields are in place, all mechanical connections (e.g. screws) are tight, no oxidizes or corroded connectors, etc. To rule out a lot of AM coming down the coax (which is fairly unlikely for most VHF/UHF antenna designs), install a high-pass filter. Even a shorted quarter-wave stub should give a fair amount of attenuation down in the MW range. If you have any in-line lightning protection (Polyphasers, et al), try removing them. But, more than likely, if in fact the AM station is the cause (either its fundamental or a harmonic), you have a passive intermodulation mix, the old rusty bolt problem. It could be in your antenna, on your tower, in your duplexer, in a corroded connector, who knows where. Divide and conquer is the only way to try to isolate it. --- Jeff WN3A Yahoo! Groups Links
RE: [Repeater-Builder] Can we tuning duplexer with this equipment?
It depends on the type of duplexer. Certainly a spectrum analyser with tracking generator, or better still a network analyser, is ideal for tuning notch type duplexers, but you can get away with simpler equipment with bandpass type cavity duplexers. Indeed I have tuned several repeater duplexers with nothing more than a SWR meter, power meter, handheld TX, Attenuator, and dummy loads. A harmonic marker generator with a tunable receiver can be used as a rather crude substitute for a spec-an. I have a marker generator that produces the equivalent of a few tens of microvolts at 100kHz spacings across 2 meters. By tuning back and forth between the rx and tx frequencies of the duplexer you can get an rough idea of the notch and bandpass tuning prior to applying more power. It's not much good at measuring deep notches because you'd need a receiver with about 0.01uV sensitivity to measure a 60dB notch, but you can at least measure individual cavities. Mark Harrison VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Azam Sent: Wednesday, December 23, 2009 8:20 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Can we tuning duplexer with this equipment? I found this simple and cheap rf measurement kit at http://www.foxdelta.com/products/pm3.htm http://www.foxdelta.com/products/pm3.htm Can it be used to tune a duplexer? rgds azam
RE: [Repeater-Builder] DTV ch 2 vs 6m
Here in Australia all the digital stations are somewhat lower power than the analogs, so as far as interference to your receivers goes, that may be a saving grace. I would imagine that if you live near a TV station that your front ends will need to have pretty good on intermod performance (I don't expect too many amateur 6m handhelds are going to cope very well!). I have noticed that the picture from my set top box usually drops out or pixilates badly when I transmit on 2 meters FM, but the antennas are only a few feet apart. I wouldn't expect the overload performance of a $39 set top tuner to be great, and it's not :-) 73, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Glenn Little WB4UIV Sent: Sunday, 11 January 2009 3:08 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] DTV ch 2 vs 6m If you interfere with the digital signal, the viewer will not know anything as to there being interference. All they will see is that they cannot see the channel 2 TV station. On the flip side, the digital wide band noise generated by the TV station will probably render 6M totally useless. The digital transmitter has a Mask filter between the transmitter and the antenna. The skirts on this filter are almost vertical. This is a very effective filter. The in specification out of band noise can be very high. 73 Glenn Little WB4UIV Chief Engineer WCIV TV Paul N1BUG wrote: I think this is on topic for the list since it could affect some 6 meter repeater owners. After transition I will have a local channel broadcasting DTV on their low VHF channel 2 assignment. I'm curious... does anyone know whether DTV will be more (or less) susceptible to interference from ham radio transmissions than analog TV? Thanks 73, Paul N1BUG
RE: [Repeater-Builder] Does anyone else think of Power Factor like SWR?
Yes, SWR is a problem for long power distribution lines, but only the very long ones. There was a case I think in Canada where they ran into this problem. The transmission lines from one side of the continent to the other was an odd multiple of a quarterwave (1,250 km). Since a quarterwave acts as an impedance transformer, when they put a low impedance load at the far end, the cable transformed this to a high impedance at the generator end and they couldn't get power into it. The solution? Either fit impedance correction devices along the cable, or transmit DC power and convert it back to AC at the load end (they do that with a power cable running between the mainland of Australia and the island of Tasmania). Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of kb9bpf Sent: Wednesday, 17 September 2008 4:26 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Does anyone else think of Power Factor like SWR? The main difference is that at 60 Hz, the wavelengths are EXTREMELY long. I'm wondering if engineers and technicians who deal with cross- country power distribution must have to consider SWR effects on the power transmission line. In practice in homes and small factories, I would think, the SWR on the line caused by a mismatch between the characteristic impedance of the transmission line and the load is an insignificant factor, like worrying about the SWR measurement shift caused by a two-foot RG-213 jumper on 160M. At least as far as the transmission line is concerned - no significant voltage and current nodes and loops developed along the line like on an RF transmission line. A simplistic or impractical way of looking at things? I don't know. Maybe. Works for me. ... Ramble off. 73, Brad KB9BPF ---
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Hi Eric, I agree with most of what you say, except the bit about generators and horsepower. I've always understood poor power factor to be a problem because the generator and distribution system needs to carry higher currents to deliver the same energy into a poor load. That's a problem because the power companies either suffer higher resistive (and financial) losses in their systems, or they need to use heavier distribution wiring and thicker wires in their transformers and generators (increasing the infrastructure costs). To offset these costs they financially discourage anyone from using poor power factor loads. It's the same in a generator set. The difference between the 1,000 Watt/ 1250 KVA rating is that with a bad load up to 250 Watts are wasted in resistive losses in the generator windings, requiring a bit more torque from the engine to provide the extra 250 Watts and some extra energy to further cool the generator. Electronic power supplies, especially older switch modes, cause a whole new set of problems. While they show up as poor power factor loads, they also create harmonics in the supply network, and that could show up on electronic power meters very inaccurately! Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Wednesday, 17 September 2008 11:22 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert Yahoo! Groups Links
RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power)
Ooops - typo - should have written 1.250 KVA, not 1250KVA as that would mean 1.250 MegaVA ! Mark -Original Message- From: Mark Harrison [mailto:[EMAIL PROTECTED] Sent: Wednesday, 17 September 2008 2:54 PM To: 'Repeater-Builder@yahoogroups.com' Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hi Eric, I agree with most of what you say, except the bit about generators and horsepower. I've always understood poor power factor to be a problem because the generator and distribution system needs to carry higher currents to deliver the same energy into a poor load. That's a problem because the power companies either suffer higher resistive (and financial) losses in their systems, or they need to use heavier distribution wiring and thicker wires in their transformers and generators (increasing the infrastructure costs). To offset these costs they financially discourage anyone from using poor power factor loads. It's the same in a generator set. The difference between the 1,000 Watt/ 1250 KVA rating is that with a bad load up to 250 Watts are wasted in resistive losses in the generator windings, requiring a bit more torque from the engine to provide the extra 250 Watts and some extra energy to further cool the generator. Electronic power supplies, especially older switch modes, cause a whole new set of problems. While they show up as poor power factor loads, they also create harmonics in the supply network, and that could show up on electronic power meters very inaccurately! Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Wednesday, 17 September 2008 11:22 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Albert, You are forgiven, because you pose an important question! The spinning aluminum disk in the kilowatthour meter found on most residential service-entrance panels measures true power in kilowatts versus time, which equals energy. Thus, your electric utility charges you for the true power you use, not for volts times amperes- known as reactive power. Although the utility must provide the capability to supply all of the amperes you need, some of those amperes are given back to the utility due to a lower than unity power factor. That is why many utility companies charge a kVAR Penalty to certain industrial power users whose volt-ampere demands far exceed their watt demands, meaning that the power factor is low. Industrial power users strive to keep their power factors at 0.95 or above, to avoid some really painful penalties! The power factor, or PF, is simply watts divided by volts time amperes. The issue of power factor is why large Diesel generator sets have ratings such as 1000 kW/1250 kVAR. In simple terms, any AC generator requires torque (engine horsepower) to meet true power demands, and excitation (field flux intensity) to meet reactive power demands. When the generator load is reactive, that is, it has a power factor less than unity, the generator must not only have the horsepower to supply the energy in watts, but it must have excess capacity to handle the additional current required by motors and other low-power-factor loads. In a nutshell, that is why a 1000 watt generator may be unable to keep running a refrigerator that uses only 900 watts; the fridge may require 1200 VA to operate because it has a low power factor, and the small generator has no ability to handle such loads. Because of its relatively small amount of spinning mass, such a small generator probably could not even handle the refrigerator's starting current- which is about 5 to 6 times its running current. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Albert Sent: Tuesday, September 16, 2008 2:13 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Volt-Amp (Re: APC UPS Charging Power) Hopefully, you will forgive me for hijacking the post, but this brings up a question I have had for a long time. What on earth is a volt-amp? My logic would state that is is the same as a watt, which is volts x amps, as you probably well know. So what on earth is it? Confused. Albert Yahoo! Groups Links
RE: [Repeater-Builder] Re: Wits End -- Desense (actual Cable-Q contributions)
Hi John, I'm not familiar with that particular radio, but would it be possible to disconnect the antenna feed at the Rx PCB and place a 50 ohm surface mount resistor in it's place? That may allow you to differentiate between shielding problems in the receive antenna cabling and other possible issues of control wires and receiver board shielding. I guess it's a bit hard then to feed in a signal on the receive frequency, but you may still be able to detect a change in unsquelched noise when the Tx operates. On another note, I presume you've probed around on the receive frequency as well as the Tx frequency, and everything in between, including I.F. frequencies? Once I had a repeater that was being upset by a 5 volt three terminal regulator chip that burst into oscillation at 50MHz when the supply dropped slightly during transmit. Another repeater had a similar problem with sidebands appearing a couple of MHz either side of the transmitter. It turned out to be a another voltage regulator oscillating at about 1MHz (a discrete component circuit this time). Surprisingly a tiny bit of this got past all the bypass capacitors and found it's way into the PA pre-driver where it mixed and produced the sidebands. Although the sidebands were more than 40dB below the fundamental, even after the diplexer they presented a significant signal on the receive frequency at the receiver input. Of course the sidebands drifted in frequency across the receive frequency, changing with temperature just to make diagnosis all that more interesting! Good Luck and 73, Mark VK3BYY Melbourne, Australia From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of John Transue Sent: Thursday, 4 September 2008 9:25 AM To: Repeater-Builder@yahoogroups.com Cc: [EMAIL PROTECTED] Subject: RE: [Repeater-Builder] Re: Wits End -- Desense (actual Cable-Q contributions) Skipp, Thanks for the suggestion. I have tentatively concluded that the desense problem is not classic desense caused by too much RF from the TX getting into the RX. I have used a spectrum analyzer and a sniffer probe to locate the RF. But the only RF I can find is at the TX frequency. I don't see any at the RX frequency. The dynamic range of the spectrum analyzer appears to be at least 40 or 50 dB. With the duplexer adding another 79 or so dB and the receiver having selectivity, I can't see how the RF level from the TX can be a problem. Nevertheless, when the repeater transmits, the receiver doesn't hear as well as otherwise. I'm thinking that the COR board might have a problem that is somehow feeding into the receiver. Have you ever heard of such a case? The problem seems to be independent of the external cables and feedline and antenna. I have experienced it with dummy load, with antenna, without the duplexer, with various lengths of cables, etc. I'd like to have some RG214 for test purposes, and I'd like to have some additional RG400. Getting cable is a two-hour round trip for me, so I can't do that for a few days. I hope to get to the cable store (The RF Connection) soon. Thanks for all the help, Skipp. With you an others from Repeater Builders holding my hand, this problem might actually get solved. JohnT
RE: [Repeater-Builder] Wits End -- Desense
For a better pickup loop, solder a 50 ohm surface mount resistor in series with the loop at the end of the coax, and put a few ferrite RFI beads or clamps at random distances along the coax. This reduces pickup by the coax itself which can otherwise cause misleading measurements. Since the loop is now terminated you can also drive the loop safely with a low power signal generator (perhaps even a handheld on low power if the 50 ohms resistor is a 1 Watt type), and use this to find out where noise is getting into the receiver. 73, Mark VK3BYY _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Derek J. Lassen Sent: Monday, 1 September 2008 4:20 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Wits End -- Desense Try putting a one inch dia, single turn loop on the end of a coax feed line to a receiver. Use it to sniff around inside the box to find the RF. 73 de KN6TD (s) Derek At 11:42 AM 8/31/2008 -0400, you wrote: Ive tried everything, it seems, and I still have desense!! Even when I connect only the repeater (Yaesu Musen FTR-1510) and a controller (needed to make the repeater transmit) and put a dummy load on the TX out, I get desense. Following up on Erics suggestion about holes leaking RF, I sealed the edges and holes in the TX and RX units inside the repeater, and I built a shield to enclose the back side of the TX connector that is on the back side of the repeater. That might have reduced the desense a little bit, but not much. I even ran the TX feedline to an outside wire-mesh chair in an effort to reduce any possible radiation getting from the dummy load to the receiver. There was still the same desense. The desense is at least 10 dB. It appears to me that the desense has to be occurring inside the repeater cabinet, but for the life of me I cant see how this can be. Everything seems to be well shielded. So, Id very much like to hear your theories and suggestions. Is there some way to find the source of the desense radiation? Is there some way that unshielded control lines, audio lines, and power lines can carry RF to the receiver? I have looked at the output of the repeater TX with a spectrum analyzer [tnx Tom N4ZPT] and it is clean. While I dont think the following is significant, for completeness I note that the repeater RX and TX both appear to be several kilohertz low in frequency. However, I do not have a frequency counter, and I am only checking the frequencies by the use of an HT and mobile, both modern transceivers by Yaesu. Your thoughts, suggestions, and sympathy will be appreciated. John AF4PD
RE: [Repeater-Builder] Re: Interference on a 6 meter repeater
Hi Skipp, I was only suggesting a lower gain antenna as an alternative to using a power attenuator. It will work if all the sources for the IM mix come from external sources, and won't be nearly as useful if the mix frequencies include your repeater TX and you are using a duplex antenna system. I've certainly experienced IM problems when a low gain antenna has been upgraded to a high gain antenna. It's been due the signal strength of the two adjacent off-channel signals increasing. As you say, filtering doesn't help there because they are adjacent channels, but some attenuation is enough to reduce the signals below the overload point of the receiver. And yes, an attenuator in front of the receiver in a duplex repeater helps more than a reduction in antenna gain because you are reducing the local TX signal too. No doubt there are situations where, say, a 6dB attenuator and a 6dB higher gain antenna would kill off IM with no loss in repeater sensitivity. Cheers, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, 14 February 2008 4:23 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Interference on a 6 meter repeater Mark Harrison [EMAIL PROTECTED] wrote: Hi Skipp and Joe, BTW, You could also use a lower gain antenna instead of a power attenuator. High gain antennas are not always a good idea :-) 73, Mark vk3byy In 97.5% plus examples an antenna replacement wouldn't solve the problem. You could try antennas and cavity filter setups until the cows come home and this radio would still be problematic. cheers, s.
RE: [Repeater-Builder] Re: Interference on a 6 meter repeater
Hi Skip and Joe, Yes, placing attenuators in line can tell you a lot about IM and interference problems. In Joe's case it would be interesting to know if placing an attenuator in the antenna line (assuming a shared receive/transmit antenna) produces an equivalent reduction in the NOAA signal, or a two or three fold reduction. That could provide some more clues as to the location of the actual mixing. BTW, You could also use a lower gain antenna instead of a power attenuator. High gain antennas are not always a good idea :-) 73, Mark vk3byy -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Tuesday, 12 February 2008 4:56 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Interference on a 6 meter repeater Re: Interference on a 6 meter repeater You are living one of my past nightmares... Let me give you the probable fix first. If you have them, try a number of attenuator pads in series with the Yaesu Radio. First might be a 10 dB pad and back the values down while testing for grunge. I ended up using a 3 dB pad in series with the Yaesu Radio... the problem generator radio still worked just fine in the intended operation and the 3dB pad fixed the problem. Of course the pad will have to take the attenuated transmit power value. Yes I tried cavities and shook my head when they didn't work (even multiple cavities and really high insertion loss settings) regardless of configurations. The front end of some Yaesu Radios can be a real serious problem maker... been there, done that, coffee mug and tee shirt. You can tell the Yaesu Owner their radio is probably causing other problems besides your issue and they should deal with it as best possible. My fix was the pad option short of replacing the radio. Try the high power pad... and hope the 3dB value is enough to knock the problem out of the ball park. Let us know if it works for you. cheers, s. Joe [EMAIL PROTECTED] wrote: I've been working on an interference problem on a 6 meter repeater and would like to pass it by the brain trust for some input. The repeater is on 53.85Mhz with the input on 52.85Mhz. When the repeater is keyed up, NOAA weather radio comes through the repeater output loud and clear. (Decode PL turned off) I identified the problem as intermodulation in a Yaesu VX-2500V transceiver at the site used for telemetery on a simplex frequency of 173.3375Mhz. The mix is: 4(53.85)-162.55=52.85 (repeater input) The VHF transceiver frequency is not involved in the mix, but the PA stage of the Yaesu is where the mix is being created. I proved this by disconnecting the coax to the Yaesu and the IM goes away. Also, when the Yaesu keys up on 173.3375, the interference goes away on the repeater. The IM is only being caused when the Yaesu transceiver is in the receive mode. No cavity is on the Yaesu, it goes directly to the antenna. The site is on a water tank, so there is only about 10 feet of horizontal separation between the telemetry antenna and the 6 meter repeater antenna. The NOAA station is running 500 watts 1.6 mile away, line of site. I added a VHF cavity tuned to 173.3375 to the Yaesu telemetry radio, but it did not fix the problem. (The can had about 25dB rejection at 162.55Mhz and about 40dB rejection at 53.85Mhz.) Prior testing showed that reducing the 6 meter repeater output from 25 watts to 2 watts solved the problem. My next thought is to put a highpass filter and the VHF cavity in series with the telemetry radio antenna. I am thinking of using a 6/2 meter diplexer, terminate the 6 meter port with 50 ohms, and connect the telemetry radio to the 2 meter port. The diplexer should give good rejection to the 6 meter signal going into the telemetry radio (along with the additional isolation of the VHF cavity) and the VHF cavity would give rejection of the NOAA radio signal. If this works, I will contact TX/RX and see what they can provide to make the installation professional. We are guests at the site and need to provide something professional to the water company. Any ideas? We already thought of changing frequency on the 6 meter repeater, but that would be difficult to coordinate. 73, Joe, K1ike
RE: [Repeater-Builder] Interference on a 6 meter repeater
Hi Joe, That's odd that the cavity in the telemetry radio feed didn't change things, but it goes away when the radio is disconnected from the antenna. A third condition to try would be with the cavity connected to antenna but leave radio disconnected. If the IM is still present then I'd be looking very carefully at the telemetry antenna, connectors, feedlines, lightning protection, etc. It could be that a parasitic diode junction is occurring somewhere in the antenna system, generating the IM, but only when the radio or cavity is just providing a DC path for the diode to self-bias (or perhaps the radio is even providing a small bias current up the antenna cable, as some radios do). When the telemetry transmitter comes on it probably swamps the parasitic diode so much it stops working as a diode for the duration. p.s. was it a bandpass or notch cavity? good luck, Mark vk3byy -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Joe Sent: Monday, 11 February 2008 1:02 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Interference on a 6 meter repeater I've been working on an interference problem on a 6 meter repeater and would like to pass it by the brain trust for some input. The repeater is on 53.85Mhz with the input on 52.85Mhz. When the repeater is keyed up, NOAA weather radio comes through the repeater output loud and clear. (Decode PL turned off) I identified the problem as intermodulation in a Yaesu VX-2500V transceiver at the site used for telemetery on a simplex frequency of 173.3375Mhz. The mix is: 4(53.85)-162.55=52.85 (repeater input) The VHF transceiver frequency is not involved in the mix, but the PA stage of the Yaesu is where the mix is being created. I proved this by disconnecting the coax to the Yaesu and the IM goes away. Also, when the Yaesu keys up on 173.3375, the interference goes away on the repeater. The IM is only being caused when the Yaesu transceiver is in the receive mode. No cavity is on the Yaesu, it goes directly to the antenna. The site is on a water tank, so there is only about 10 feet of horizontal separation between the telemetry antenna and the 6 meter repeater antenna. The NOAA station is running 500 watts 1.6 mile away, line of site. I added a VHF cavity tuned to 173.3375 to the Yaesu telemetry radio, but it did not fix the problem. (The can had about 25dB rejection at 162.55Mhz and about 40dB rejection at 53.85Mhz.) Prior testing showed that reducing the 6 meter repeater output from 25 watts to 2 watts solved the problem. My next thought is to put a highpass filter and the VHF cavity in series with the telemetry radio antenna. I am thinking of using a 6/2 meter diplexer, terminate the 6 meter port with 50 ohms, and connect the telemetry radio to the 2 meter port. The diplexer should give good rejection to the 6 meter signal going into the telemetry radio (along with the additional isolation of the VHF cavity) and the VHF cavity would give rejection of the NOAA radio signal. If this works, I will contact TX/RX and see what they can provide to make the installation professional. We are guests at the site and need to provide something professional to the water company. Any ideas? We already thought of changing frequency on the 6 meter repeater, but that would be difficult to coordinate. 73, Joe, K1ike Yahoo! Groups Links
RE: [Repeater-Builder] cavity duplexer
Hi Wayne, From memory the suggestion was to use 50 ohm double screened cable for the phasing harness and intercavity cables. RG-142 (not to be confused with the far more popular RG-214) has two layers of braid and there are other types from various other manufacturers. You may be able to pick up similar cable at hamfests in the form of commercially made jumper cables that come out of mobile phone base stations and the likes... Some double screened cables has a layer of aluminium tape covered with braid (like that used commonly for TV antennas). Probably should be avoided in this application due to potential problems with dissimilar metals and corrosion. If fact, some commercial guys recommend using nothing less than double shielded cables that have all conductors silver plated, and use silver plated N-type connectors all around. By the way, I've seen quite a few people say the QST cavities aren't the best and many have published improvements on the Internet (to improve performance and ease of construction) - it may be worth a quick search around the net! 73, Mark VK3BYY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of vk4cya Sent: Thursday, 10 January 2008 8:22 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] cavity duplexer Hello to the group, I have just joined the group.The local radio club that i'm in it putting together a cavity duplexer alot like the one in the july 1972 issue of qst.We are going ahead leaps and bounds but we have came across a problem it is suggested that we use rg55/u coax on the cavity's but the problem is that i can't find anyone in australia selling that type of coax.So is there anyone that could help me in suggesting what else could be used.I have found a couple of sites on the net that have rg55/u but in roll form.We are looking for around 2 metres of it only. Any help would be most great Thamks Wayne vk4cya
