RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
At 2/28/2007 08:19 AM, you wrote: Bob You seem to want to lump what is characteristically a complex impedance (R+or-jX) into a single number in order to simplify your argument that a non conducting RF output transistor is an open circuit because the transistor is not having any RF drive to the base (as in a class C amp with no current flowing in the collector / emitter circuit), and ignoring the Xc or XL remaining which will and is being transformed to an impedance different than the impedance originally designed to operate into as a load (50 ohms). Even then your argument again fails because the transformed complex impedance (+or-jX) will result in a source impedance from the transistor into something also complex, either capacitive or inductive, with little or no resistive component, and is never seen or sourced as a high impedance by any stretch of the imagination. I use the term high impedance loosely here to mean no resistive component, hence quasi-infinite VSWR, low return loss, mag. S11~=1 or however you want to put it. In reality, the impedance at the collector of the transistor is going to be pretty high. Yes it gets transformed around the Smith chart to a capacitance, through a short @ 1/4 wavelength, then inductive back to an open as you move away from it but I think that's irrelevent to this discussion. Why do you think that this (high impedance) is the case? Even in RF amplifiers operated as class A or AB, there is always current flow thru I'm talking about class C amplifiers, the ones normally found in repeater RFPAs. They draw no current when not TXing. Bob NO6B
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
At 2/28/2007 08:19 AM, you wrote: Bob You seem to want to lump what is characteristically a complex impedance (R+or-jX) into a single number in order to simplify your argument that a non conducting RF output transistor is an open circuit because the transistor is not having any RF drive to the base (as in a class C amp with no current flowing in the collector / emitter circuit), and ignoring the Xc or XL remaining which will and is being transformed to an impedance different than the impedance originally designed to operate into as a load (50 ohms). Even then your argument again fails because the transformed complex impedance (+or-jX) will result in a source impedance from the transistor into something also complex, either capacitive or inductive, with little or no resistive component, and is never seen or sourced as a high impedance by any stretch of the imagination. I use the term high impedance loosely here to mean no resistive component, hence quasi-infinite VSWR, low return loss, mag. S11~=1 or however you want to put it. In reality, the impedance at the collector of the transistor is going to be pretty high. Yes it gets transformed around the Smith chart to a capacitance, through a short @ 1/4 wavelength, then inductive back to an open as you move away from it but I think that's irrelevent to this discussion. Why do you think that this (high impedance) is the case? Even in RF amplifiers operated as class A or AB, there is always current flow thru I'm talking about class C amplifiers, the ones normally found in repeater RFPAs. They draw no current when not TXing. Bob NO6B
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
Since when is the Xc of the Collector-Base capacitance of an output transistor or the Drain-Gate capacitance of a FET considered an open circuit at RF? Allan Crites WA9ZZU Jeff DePolo [EMAIL PROTECTED] wrote: Bypassing the relay shouldn't have an effect on the TX output Z when not TXing, as the final RF output transistor is going to look like an open too. Bob NO6B But the open transistors would be at a different electrical distance away from the duplexer than the open T/R relay was.
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
At 2/27/2007 13:30, you wrote: Since when is the Xc of the Collector-Base capacitance of an output transistor or the Drain-Gate capacitance of a FET considered an open circuit at RF? Allan Crites WA9ZZU OK, maybe not a million ohms but high enough compared to the nominal 1 ohm or so output Z of the transistor (remember that the output of these guys has to be transformed up from a very low impedance to 50 ohms because of the output power low voltage). Bob NO6B
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
Bob Dengler wrote: At 2/23/2007 12:50 PM, you wrote: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? In my experience, yes. In fact, we have had several repeaters that the sensitivity actually gets BETTER with the transmitter active. (due to the correct 50 impedance being applied to the TX port of the duplexer) Hmmm, that sounds rather unusual. I can see the non-50 ohm impedance at the TX port pulling the notches on the RX side, but I wouldn't expect it to affect the much broader RX pass response to the point of degraded RX sensitivity. I'm assuming he had the antenna relay in line, and it was still switching when keyed/unkeyed. I would either hardwire the relay in tx mode, or jumper it out. -- Jim Barbour WD8CHL
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
At 2/26/2007 08:27 AM, you wrote: Bob Dengler wrote: At 2/23/2007 12:50 PM, you wrote: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? In my experience, yes. In fact, we have had several repeaters that the sensitivity actually gets BETTER with the transmitter active. (due to the correct 50 impedance being applied to the TX port of the duplexer) Hmmm, that sounds rather unusual. I can see the non-50 ohm impedance at the TX port pulling the notches on the RX side, but I wouldn't expect it to affect the much broader RX pass response to the point of degraded RX sensitivity. I'm assuming he had the antenna relay in line, and it was still switching when keyed/unkeyed. I would either hardwire the relay in tx mode, or jumper it out. Bypassing the relay shouldn't have an effect on the TX output Z when not TXing, as the final RF output transistor is going to look like an open too. Bob NO6B
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
Bypassing the relay shouldn't have an effect on the TX output Z when not TXing, as the final RF output transistor is going to look like an open too. Bob NO6B But the open transistors would be at a different electrical distance away from the duplexer than the open T/R relay was.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? (Z-Matcher)
Keep in mind that a Z-Matcher in a GE radio has it's own test point to tune it, as do some other Z-Matchers. You don't need to use a wattmeter and worry about the line length. Chuck WB2EDV - Original Message - From: Mike Morris WA6ILQ To: Repeater-Builder@yahoogroups.com Sent: Saturday, February 24, 2007 2:53 AM Subject: Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? (Z-Matcher) At 10:19 PM 02/23/07, you wrote: In a message dated 2/23/2007 6:36:24 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: In regards to the question of a wattmeter adding length to a cable, in places where I use Z-matchers, I actually leave an N-barrel connector in line that can be removed for inserting the wattmeter without adding any cable. So when you put that barrel back, you're pretty darn close. ... Not necessarily. At low band VHF frequencies, you could probably discount the error produced by the Bird. But in high band VHF and up, it becomes progressively more critical. The constant is the physical length of the Bird line section which is 3 13/16 inches but including the terminating N connectors, the length is 5 1/8 inches. This is where it gets interesting. The line section is air line and has a different velocity constant than RG142 or RG214. Section 3-35 states: Using the THRULINE you will be inserting a 4 inch length of 50 ohm air line and the load on the transmitter will be changed from its original condition without the THRULINE. But Section 3-40 states: Since the length of line between a mismatched load and the source transforms the impedance of the load as seen at the source, line length now becomes critical. If the adjustments for maximum power transfer were made with the Model 43 in place, removing it shortens the line by four inches, plus two connectors. (emphasis mine). So one section says to allow 4 inches while the other section says to allow 5 1/8 inches. Go figure. In any event, the use of a single barrel would miss the mark at 2 meters and above. I read it as he opens up one of the male-to-barrel connections and inserts the combination of a Bird with the jumper cable that makes it plus the cable a half wave. This way nothing changes. Mike WA6ILQ -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.3/699 - Release Date: 2/23/2007 1:26 PM
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
Yes, and as the article referenced below points out, switching the UHF Mastr II to High Side Injection eliminates the problem. We originally thought that HSI eliminated the problem totally on 220, but it didn't, there is an overlapping range that one side or the other doesn't fix; that is what is referenced in the text below. Kevin mch wrote: Weren't there some 440 frequencies that had issues, too? Joe M. Kevin Custer wrote: I'm not Scott, but maybe I'll do... grin See Below Yes, there is sufficient isolation for single box conversion with absolutely no internal desense from the MASTR II Mobile, with the exception of the frequency ranges between 223T940/222R340 thru 224T060/222R460. Why don't these frequencies work? http://groups.yahoo.com/group/GE-MastrII/message/6972
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? (Z-Matcher)
[EMAIL PROTECTED] wrote: In a message dated 2/23/2007 6:36:24 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: In my most critical applications, I use permanent in-line Bird samplers. Then, cabling lengths don't change because I don't remove the samplers; and you know exactly what you have and where If you can afford to leave Bird 4275s in your cables, please be sure that my name is correctly spelled in your will. Actually, if you look on eBay, there are (still) deals on these type of things from time to time. I rarely buy anything like this new, because I don't have the largest budgets either, but, I will spend the money to be sure of things in critical applications. Here is one: http://www.kuggie.com/ahra/hmft.html http://www.kuggie.com/ahra/hmftinfo.html Kevin
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
I never suggested that the cable between the TX and the duplexer had to be an exact length and if the TX output is a true 50 ohms then any cable length produces no consequence at the cavity input. But if the TX impedance is not 50 ohms, I think any cable length other than half wave will make the cable a line transformer affecting the impedance presented to the cavity with a quarter wave producing the greatest impedance shift. That's not necessarily a bad thing because the impedance match of a random length cable is statistically as likely to improve the TX/cavity match as it is to degrade it. Exactly!!! Diddling around with this proved to be so frustrating that I eventually caved in and installed a Z-matcher at the TX output and tuned it for maximum cavity output at the pass frequency. It seemed (and seems) to me that this is a cleaner way to deal with the matching issue than trying to adjust BP/BR cavities with an input other than 50 ohms. If you want to use a Z-matcher to make your transmitter happy, you really need to monitor current draw when adjusting it in addition to power measurements. Just because you can install a Z-matcher and diddle with its caps to get a fraction of a dB more apparent power out doesn't indicate it's properly tuned. It could just be that the transmitter makes a little more power when looking into a load that's not 50 ohms, but at the possible expense of higher DC current draw, lower efficiency, and increased RF currents, all of which can be detrimental to the longevity of the PA. Also, apparent increases in TPO may be due to the generation of spurious products which are more likely when the transmitter is looking into a badly-matched load, which a Z-matcher is quite capable of creating. A spectrum analyzer would help tell the whole story (cleanliness is next to godliness when it comes to a mountaintop transmitter!). I'd rather see an isolator between the PA and duplexer, and if the PA is still not happy with that, fix/replace the PA. Also, when you're using a Z matcher at the output of the PA, the load Z (duplexer/feedline/antenna/etc.) is the other half of the equation. The Z of the antenna system is anything but constant. Electrical cable lengths (phase) vary with changes in temperature, thereby rotating the antenna feedpoint Z around the Smith chart. The antenna feedpoint Z is being transformed to some other Z at the end of the line, so the Z you are matching into is going to change as the electrical length of the line changes. As a practical example, a 200 foot length of Heliax on UHF has about a 20 degree phase change between 0 and 100 degrees F, and Heliax is much more phase-stable than most other cable types (especially solid polyethylene dielectric cables). The antenna feedpoint Z itself will also change with humidity/rain/icing, etc. Bottom line - matching to an antenna system is always unpredictable when done at the far end of the feedline. What looks good on the day you do the tuning may look ugly six months from now. It is for these reasons that I have always been against makeshift matching techinques, including cable length games, to make a system perform properly, for the performance improvements you think you're getting are likely to change due to factors you have little or no control over. I'd rather have everything on the ground kept as close to 50+j0 as possible, leaving only the antenna feedpoint Z as the variable you have no control over. And if the antenna Z is poor under normal weather conditions, it needs to be replaced. You mentioned that the power adjustment levels would not affect TX output significantly on an M II or Micor. I'm not familiar with the power control network they employ but does the collector voltage on the output devices remain constant during power changes? If not, how do you avoid significant output impedance shifts? On both M2 and Micor, the collector voltage of one of the early PA stages is varied to adjust the net gain (output) of the amplifier. The finals always have full 13.8V on the collectors (or emitters, in the case of PNP highband Micor transistors). --- Jeff
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
Ken Harrison wrote: Thanks for the recommendation, Don. Though I'm sure a MastrII would be a great conversion for 220, we (in the group sense) want to try to save some of our money to get a remote base setup going on our repeater, too. Our small savings would be wiped out to replace the entire repeater, in spite of it being handy to have a complete spare should there be a problem in the future. Thanks, Ken Um-converting a MastrII or other commercial station is MUUCH cheaper then buying one of those made-for-ham pieces of junk. You'll spend $1000-1500 for a Maggiore/Kendecom/Spectrum, where you can convert an MII for a couple of hundred. -- Jim Barbour WD8CHL
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
For Scott: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? Tks Bruce K7IJ In a message dated 2/22/2007 7:02:38 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: Ken, We not only do complete repeaters, we can custom build just about anything you want or need. We can simply build a rock-solid high-quality 220 receiver for you. We have done several receivers in the past that are rack mountable in a 2 unit rack space. I have a GE mastr II receiver that I am just finishing up. It came out looking so nice that I am going to take pictures as a show piece. Micor receivers would be VERY similar in construction. In my opinion, 2 things: 1. A Micor makes a much better repeater on 2M and 220 than a GE MII. (sorry GE loyalists!!) I think a Mastr II makes a much better repeater on UHF (sorry Micor loyalists!!) I would suggest a Micor for your 220 Machine. 2. If you're going to spend money on a new receiver, why not spend a bit more and get a completely new machine. Think about it, if your receiver is not 100%, what's saying that your transmitter is running at 100%? The notable thing about spectrum repeaters is that they lived up to their name, they took up the WHOLE spectrum. This might even be what is happing that you assume is a bad receiver. Instead of a bad receiver, you may have a spurious transmitter that is totally wiping your receiver off the map. Duplexers are meant to isolate, but there is only so much they can isolate. If you'd like a quote on a new machine or a quote for a new receiver, feel free to e-mail or call. Scott - Owner Repeater-Builder (the company) _www.repeater-www.repeaterwww.repeater_ (http://www.repeater-builder.com/custombuilt/) Scott Zimmerman Amateur Radio Call N3XCC 474 Barnett Road Boswell, PA 15531 - Original Message - From: _Ken Harrison_ (mailto:[EMAIL PROTECTED]) To: [EMAIL PROTECTED] (mailto:Repeater-Builder@yahoogroups.com) Sent: Thursday, February 22, 2007 8:39 PM Subject: [Repeater-Builder] Re: 220 repeater receiver recommendations? Thanks for the recommendation, Don. Though I'm sure a MastrII would be a great conversion for 220, we (in the group sense) want to try to save some of our money to get a remote base setup going on our repeater, too. Our small savings would be wiped out to replace the entire repeater, in spite of it being handy to have a complete spare should there be a problem in the future. Thanks, Ken --- In [EMAIL PROTECTED] (mailto:Repeater-Builder@yahoogroups.com) , Don KA9QJG [EMAIL PROTECTED] wrote: Ken first of All I noticed You stated Our group, so I would assume You have others kicking in to the Cost, I do not and I had Scott build Me up a 220 Repeater System, He did it in the process of Building a house and Moving All I had to do was Program the Controller, Hook up the Amp, Power Supply Duplexers, and Ant, I have never had any Problems for over a Yr. BRBRBR**BR AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
[EMAIL PROTECTED] wrote: For Scott: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? At UHF-categorically yes, because both the MII and the Micor were avialable from the factory in full duplex versions for certain applications. 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? It probably isn't exactly 50 ohms, but should be close. And the cables from the duplexer to the radio do NOT *REPEAT* NOT need to be an exact length. This again indicates an impedance mismatch in the duplexer and it should be retuned. (or a bad antenna/load) 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? No it should not. The load on the 3rd port of the isolator is still 50 ohms, so it should not be an issue. And I don't see the impedance of a good PA like an MII or Micor changing off of 50 ohms enough to matter. Other brands, who knows. -- Jim Barbour WD8CHL
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? In my experience, yes. In fact, we have had several repeaters that the sensitivity actually gets BETTER with the transmitter active. (due to the correct 50 impedance being applied to the TX port of the duplexer) The only problems we have had with in-cabinet de-sense go back to issues with a transmitter multiple getting into a sensitive spot of the receiver. This is a well known phenomenon on UHF Mastr II's, but it also happens on converted 220 micors and MII's. I have been wanting to write up this research for some time. I will try to do it as soon as I can. 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? As others have stated, it may not be *exactly* 50j0, but it's close enough. Realize that most of the 50 ohm coax cable actually spec'd to be 52 ohm nominal!! I would think that the cable being 2 ohms off would be more detriment than the 50ohm designed output / input impedance that might move fractions of an ohm in impedance due to being tuned a few MHz from it's design frequency. If you want to get that picky, should a PA's output be tuned for 50 ohms when the frequency is changed from let's say 155.xx to 158.xxx? I would think that if the designers would have thought the port impedance to be that critical, they would have made provisions to adjust it. As far as our 220 modifications go; we use a M57774 power module. We DO NOT modify/retune the VHF pa to 220. If we did, we might run into design issues where impedance problems might rare their ugly head. We just use an off-the-shelf solution that works well. If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? Can't say. I have no experience. I will defer this question to others. Scott Scott Zimmerman Amateur Radio Call N3XCC 612 Barnett Rd Boswell, PA 15531 - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, February 23, 2007 2:24 PM Subject: Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? For Scott: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? Tks Bruce K7IJ In a message dated 2/22/2007 7:02:38 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: Ken, We not only do complete repeaters, we can custom build just about anything you want or need. We can simply build a rock-solid high-quality 220 receiver for you. We have done several receivers in the past that are rack mountable in a 2 unit rack space. I have a GE mastr II receiver that I am just finishing up. It came out looking so nice that I am going to take pictures as a show piece. Micor receivers would be VERY similar in construction. In my opinion, 2 things: 1. A Micor makes a much better repeater on 2M and 220 than a GE MII. (sorry GE loyalists!!) I think a Mastr II makes a much better repeater on UHF (sorry Micor loyalists!!) I would suggest a Micor for your 220 Machine. 2. If you're going to spend money on a new receiver, why not spend a bit more and get a completely new machine. Think about it, if your receiver is not 100%, what's saying that your transmitter is running at 100%? The notable thing about spectrum repeaters is that they lived up to their name, they took up the WHOLE spectrum. This might even be what is happing that you assume is a bad receiver. Instead of a bad receiver, you may have a spurious transmitter that is totally wiping your receiver off the map. Duplexers are meant to isolate, but there is only so much they can isolate. If you'd like a quote on a new machine or a quote for a new receiver, feel free
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
In a message dated 2/23/2007 12:00:13 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: It probably isn't exactly 50 ohms, but should be close. And the cables from the duplexer to the radio do NOT *REPEAT* NOT need to be an exact length. This again indicates an impedance mismatch in the duplexer and it should be retuned. (or a bad antenna/load) I never suggested that the cable between the TX and the duplexer had to be an exact length and if the TX output is a true 50 ohms then any cable length produces no consequence at the cavity input. But if the TX impedance is not 50 ohms, I think any cable length other than half wave will make the cable a line transformer affecting the impedance presented to the cavity with a quarter wave producing the greatest impedance shift. That's not necessarily a bad thing because the impedance match of a random length cable is statistically as likely to improve the TX/cavity match as it is to degrade it. Diddling around with this proved to be so frustrating that I eventually caved in and installed a Z-matcher at the TX output and tuned it for maximum cavity output at the pass frequency. It seemed (and seems) to me that this is a cleaner way to deal with the matching issue than trying to adjust BP/BR cavities with an input other than 50 ohms. You mentioned that the power adjustment levels would not affect TX output significantly on an M II or Micor. I'm not familiar with the power control network they employ but does the collector voltage on the output devices remain constant during power changes? If not, how do you avoid significant output impedance shifts? BRBRBR**BR AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
... but does the collector voltage on the output devices remain constant during power changes? If not, how do you avoid significant output impedance shifts? Yes. The final stages are kept at B+, the power set is done in the first stage in the PA; commonly known as the pre-driver or possibly pre-pre-driver stage. Using your logic, one could ask if a change in B+ voltage would skew the output impedance?? Say the difference between 11v and 15v (not ALL power supplies are created equal.) Scott Scott Zimmerman Amateur Radio Call N3XCC 612 Barnett Rd Boswell, PA 15531 - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, February 23, 2007 4:06 PM Subject: Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? In a message dated 2/23/2007 12:00:13 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: It probably isn't exactly 50 ohms, but should be close. And the cables from the duplexer to the radio do NOT *REPEAT* NOT need to be an exact length. This again indicates an impedance mismatch in the duplexer and it should be retuned. (or a bad antenna/load) I never suggested that the cable between the TX and the duplexer had to be an exact length and if the TX output is a true 50 ohms then any cable length produces no consequence at the cavity input. But if the TX impedance is not 50 ohms, I think any cable length other than half wave will make the cable a line transformer affecting the impedance presented to the cavity with a quarter wave producing the greatest impedance shift. That's not necessarily a bad thing because the impedance match of a random length cable is statistically as likely to improve the TX/cavity match as it is to degrade it. Diddling around with this proved to be so frustrating that I eventually caved in and installed a Z-matcher at the TX output and tuned it for maximum cavity output at the pass frequency. It seemed (and seems) to me that this is a cleaner way to deal with the matching issue than trying to adjust BP/BR cavities with an input other than 50 ohms. You mentioned that the power adjustment levels would not affect TX output significantly on an M II or Micor. I'm not familiar with the power control network they employ but does the collector voltage on the output devices remain constant during power changes? If not, how do you avoid significant output impedance shifts? -- AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.3/699 - Release Date: 2/23/2007 1:26 PM
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
At 2/23/2007 12:50 PM, you wrote: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? In my experience, yes. In fact, we have had several repeaters that the sensitivity actually gets BETTER with the transmitter active. (due to the correct 50 impedance being applied to the TX port of the duplexer) Hmmm, that sounds rather unusual. I can see the non-50 ohm impedance at the TX port pulling the notches on the RX side, but I wouldn't expect it to affect the much broader RX pass response to the point of degraded RX sensitivity. I have experienced this phenomenon before, but without a duplexer (or anything except a load for the TX) connected to the radio. In my case it was due to leaking the RX RF from the signal generator (in this case just an HT) through the radio's case the RF taking different paths through the radio to the RX between the TX on TX off conditions. Sometimes the RX would degrade with the TX on (as expected), sometimes it would improve. Both conditions were eliminated when the sig. gen. was properly coupled to the RX's RF input. Bob NO6B
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
A half wave length cable will act as an impedance transformer too. In this case it will be a 1:1 transformation and if the output of the transmitter is not 50 ohms then whatever impedance it is will be transformed to the cavity input. 73 Gary K4FMX _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Friday, February 23, 2007 4:06 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? In a message dated 2/23/2007 12:00:13 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: It probably isn't exactly 50 ohms, but should be close. And the cables from the duplexer to the radio do NOT *REPEAT* NOT need to be an exact length. This again indicates an impedance mismatch in the duplexer and it should be retuned. (or a bad antenna/load) I never suggested that the cable between the TX and the duplexer had to be an exact length and if the TX output is a true 50 ohms then any cable length produces no consequence at the cavity input. But if the TX impedance is not 50 ohms, I think any cable length other than half wave will make the cable a line transformer affecting the impedance presented to the cavity with a quarter wave producing the greatest impedance shift.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
I'm not Scott, but maybe I'll do... grin See Below [EMAIL PROTECTED] wrote: For Scott: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? Yes, there is sufficient isolation for single box conversion with absolutely no internal desense from the MASTR II Mobile, with the exception of the frequency ranges between 223T940/222R340 thru 224T060/222R460. Why don't these frequencies work? http://groups.yahoo.com/group/GE-MastrII/message/6972 I have built intermittent duty 2 meter repeaters from Mastr II and Micor Mobiles with 110 watt PA running at 140+ watts and have seen no sign of internal cabinet desense. 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? We don't recommend operating a mobile conversion at greatly reduced power because the amplifiers are run in Class C, and reducing the power will generate spurious emissions. For the 220 conversion, we totally build a new power amplifier as seen in this Micor 220 conversion - GE is similar. See here: http://www.repeater-builder.com/pix/220micorpa.jpg http://www.repeater-builder.com/products/ampbd.html For other bands, we recommend the 45 watt version of the PA which will run rated power, continuously. 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? Any time you convert commercial equipment to ham band operation, you likely won't have a perfect 50 ohm terminal impedance at the receiver or transmitter port, so yes, as all better repeaters builders know, the equipment might have to be tuned as a system using custom cabling lengths or Z Matchers for optimal performance. Kevin Custer Repeater Builder (the company)
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
In a message dated 2/23/2007 4:32:54 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: as all better repeaters builders know, the equipment might have to be tuned as a system using custom cabling lengths or Z Matchers for optimal performance. Can you comment on a difference of opinion regarding how a Z matcher should be adjusted? One school tunes for maximum smoke downstream of the cavities which is the approach I adopt. The other school tunes for minimum reflected SWR between the first cavity and the TX. My academic preference is for the latter, but as a practical matter it's a pain in the buns to do because you have to account for the line section that the Bird meter adds to the cable. Beyond that, using just a meter, what is it that is actually being measured since it could possibly be a composite of both on-channel energy and and off-channel reflected spurs and harmonics. BRBRBR**BR AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
[EMAIL PROTECTED] wrote: I'm particularly interested in any shortcomings of the G.E. that are not easily overcome. Repeatability of a band split conversion, out of band (high-band to 222) conversion, (where sensitivity is concerned) and tuning stability. It seems that *some* MASTR II receivers will come out better than others. You can have 3 like receivers in high-band with the same high-band sensitivity and tune them 2M and have 3 different sensitivity values. 220 is similar, some come out good, some don't. Anything can be made work if messed with long enough. You usually don't have to mess with the MICOR stuff much; it works equally well with each conversion. Very very few VHF MICOR receivers that work well originally don't convert well, 220 or otherwise. The UHF MICOR is a whole other story Here is an overview of my opinion. This is based on converting literally hundreds of receivers, MVP, MASTR II, EXEC II and MICOR: http://groups.yahoo.com/group/Repeater-Builder/message/49667 In my opinion, the only 'real' shortcoming of the GE receivers that isn't easily overcome is tuning stability due to their use of ceramic tuning capacitors. Kevin
RE: [Repeater-Builder] Re: 220 repeater receiver recommendations?
_ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Kevin Custer Sent: Friday, February 23, 2007 8:34 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? [EMAIL PROTECTED] wrote: In a message dated 2/23/2007 4:32:54 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: as all better repeaters builders know, the equipment might have to be tuned as a system using custom cabling lengths or Z Matchers for optimal performance. Can you comment on a difference of opinion regarding how a Z matcher should be adjusted? One school tunes for maximum smoke downstream of the cavities which is the approach I adopt. The other school tunes for minimum reflected SWR between the first cavity and the TX. My academic preference is for the latter, but as a practical matter it's a pain in the buns to do because you have to account for the line section that the Bird meter adds to the cable. Beyond that, using just a meter, what is it that is actually being measured since it could possibly be a composite of both on-channel energy and and off-channel reflected spurs and harmonics. I think you answered your own question, however I'll bite In *most* of the instances where I employed impedance matching between the transmitter and first cavity, the place where best return loss and least insertion loss was found, is very close to one another -tuning wise. I usually use the maximum smoke approach first and see what I have, then go from there. In my most critical applications, I use permanent in-line Bird samplers. Then, cabling lengths don't change because I don't remove the samplers; and you know exactly what you have and where Kevin Do you use a cable with the bird that makes it a ½ wavelength total line length when you insert it in line? That should not change things when the wattmeter/cable are removed. With a PA that does not exhibit a 50 ohm output I would think that it would be best to tune the Z match for maximum output looking at the antenna connection (output of the cavities). The reason being if you put the wattmeter between the Z match and the radio and tune the Z match for minimum reflected power as noted on the wattmeter then you are tuning the Z match to match the cavity input to 50 ohms that the wattmeter line section is setup for. But that is not what the transmitter really is so you end up with a flat reflected power between the cavity and the transmitter but it does not match the transmitter. 73 Gary K4FMX
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
Weren't there some 440 frequencies that had issues, too? Joe M. Kevin Custer wrote: I'm not Scott, but maybe I'll do... grin See Below Yes, there is sufficient isolation for single box conversion with absolutely no internal desense from the MASTR II Mobile, with the exception of the frequency ranges between 223T940/222R340 thru 224T060/222R460. Why don't these frequencies work? http://groups.yahoo.com/group/GE-MastrII/message/6972
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? (MVP?)
Yep, There are several conversions on the RB site for the MVP. They are loosely based on the MII conversions. I haven't done many MVP conversions of any particular band, but the ones I have done have not had any internal desense issues. Scott Scott Zimmerman Amateur Radio Call N3XCC 474 Barnett Road Boswell, PA 15531 - Original Message - From: skipp025 [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, February 23, 2007 5:06 PM Subject: [Repeater-Builder] Re: 220 repeater receiver recommendations? (MVP?) What about the GE MVP Scott..? Would the conversion be available and similar for the MVP Mobile? skipp Scott Zimmerman [EMAIL PROTECTED] wrote: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? In my experience, yes. In fact, we have had several repeaters that the sensitivity actually gets BETTER with the transmitter active. (due to the correct 50 impedance being applied to the TX port of the duplexer) The only problems we have had with in-cabinet de-sense go back to issues with a transmitter multiple getting into a sensitive spot of the receiver. This is a well known phenomenon on UHF Mastr II's, but it also happens on converted 220 micors and MII's. I have been wanting to write up this research for some time. I will try to do it as soon as I can. 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? As others have stated, it may not be *exactly* 50j0, but it's close enough. Realize that most of the 50 ohm coax cable actually spec'd to be 52 ohm nominal!! I would think that the cable being 2 ohms off would be more detriment than the 50ohm designed output / input impedance that might move fractions of an ohm in impedance due to being tuned a few MHz from it's design frequency. If you want to get that picky, should a PA's output be tuned for 50 ohms when the frequency is changed from let's say 155.xx to 158.xxx? I would think that if the designers would have thought the port impedance to be that critical, they would have made provisions to adjust it. As far as our 220 modifications go; we use a M57774 power module. We DO NOT modify/retune the VHF pa to 220. If we did, we might run into design issues where impedance problems might rare their ugly head. We just use an off-the-shelf solution that works well. If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? Can't say. I have no experience. I will defer this question to others. Scott Scott Zimmerman Amateur Radio Call N3XCC 612 Barnett Rd Boswell, PA 15531 - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, February 23, 2007 2:24 PM Subject: Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? For Scott: With respect to using the GE MII mobile frame for repeater applications: 1. Can you say categorically that there is sufficient TX/RX shielding to prevent any desense at any power level the conversion is capable of operating? 2. When these converted mobiles operate with reduced TX power, what happens to the output impedance of the TX? Is it still 50 ohms? If not, does this affect the physical length of the half wave interconnect cables often suggested between the TX and an isolator and/or the cavities? 3. If the output of the TX is other than 50 ohms as a result of a power level change, does it upset the adjustment of the downstream isolator that has been tuned by a tracking generator? Tks Bruce K7IJ In a message dated 2/22/2007 7:02:38 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: Ken, We not only do complete repeaters, we can custom build just about anything you want or need. We can simply build a rock-solid high-quality 220 receiver for you. We have done several receivers in the past that are rack mountable in a 2 unit rack space. I have a GE mastr II receiver that I am just finishing up. It came out looking so nice that I am going to take pictures as a show piece. Micor receivers would be VERY similar in construction. In my opinion, 2 things: 1. A Micor makes a much better repeater on 2M and 220 than a GE MII. (sorry GE loyalists!!) I think a Mastr II makes a much better repeater on UHF (sorry Micor loyalists
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
In a message dated 2/23/2007 6:15:19 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: Do you use a cable with the bird that makes it a ½ wavelength total line length when you insert it in line? That should not change things when the wattmeter/cable are removed. I'm not sure I understand what you are saying. The Bird constitutes part of the line section and if you remove it after tuning with the z match, haven't you effectively changed the length of the line? BRBRBR**BR AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations? (Z-Matcher)
In a message dated 2/23/2007 6:36:24 P.M. Pacific Standard Time, [EMAIL PROTECTED] writes: In my most critical applications, I use permanent in-line Bird samplers. Then, cabling lengths don't change because I don't remove the samplers; and you know exactly what you have and where If you can afford to leave Bird 4275s in your cables, please be sure that my name is correctly spelled in your will. BRBRBR**BR AOL now offers free email to everyone. Find out more about what's free from AOL at http://www.aol.com.
Re: [Repeater-Builder] Re: 220 repeater receiver recommendations?
At 2/22/2007 19:01, you wrote: Ken, We not only do complete repeaters, we can custom build just about anything you want or need. We can simply build a rock-solid high-quality 220 receiver for you. We have done several receivers in the past that are rack mountable in a 2 unit rack space. I have a GE mastr II receiver that I am just finishing up. It came out looking so nice that I am going to take pictures as a show piece. Micor receivers would be VERY similar in construction. In my opinion, 2 things: 1. A Micor makes a much better repeater on 2M and 220 than a GE MII. (sorry GE loyalists!!) Interesting conclusion. Care to state any specific advantages the Micor has over the G.E.? I'm particularly interested in any shortcomings of the G.E. that are not easily overcome. Bob NO6B I think a Mastr II makes a much better repeater on UHF (sorry Micor loyalists!!) I would suggest a Micor for your 220 Machine. 2. If you're going to spend money on a new receiver, why not spend a bit more and get a completely new machine. Think about it, if your receiver is not 100%, what's saying that your transmitter is running at 100%? The notable thing about spectrum repeaters is that they lived up to their name, they took up the WHOLE spectrum. This might even be what is happing that you assume is a bad receiver. Instead of a bad receiver, you may have a spurious transmitter that is totally wiping your receiver off the map. Duplexers are meant to isolate, but there is only so much they can isolate. If you'd like a quote on a new machine or a quote for a new receiver, feel free to e-mail or call. Scott - Owner Repeater-Builder (the company) http://www.repeater-builder.com/custombuilt/www.repeater-builder.com/custombuilt/ Scott Zimmerman Amateur Radio Call N3XCC 474 Barnett Road Boswell, PA 15531 - Original Message - From: mailto:[EMAIL PROTECTED]Ken Harrison To: mailto:Repeater-Builder@yahoogroups.comRepeater-Builder@yahoogroups.com Sent: Thursday, February 22, 2007 8:39 PM Subject: [Repeater-Builder] Re: 220 repeater receiver recommendations? Thanks for the recommendation, Don. Though I'm sure a MastrII would be a great conversion for 220, we (in the group sense) want to try to save some of our money to get a remote base setup going on our repeater, too. Our small savings would be wiped out to replace the entire repeater, in spite of it being handy to have a complete spare should there be a problem in the future. Thanks, Ken --- In mailto:Repeater-Builder%40yahoogroups.comRepeater-Builder@yahoogroups.com, Don KA9QJG [EMAIL PROTECTED] wrote: Ken first of All I noticed You stated Our group, so I would assume You have others kicking in to the Cost, I do not and I had Scott build Me up a 220 Repeater System, He did it in the process of Building a house and Moving All I had to do was Program the Controller, Hook up the Amp, Power Supply Duplexers, and Ant, I have never had any Problems for over a Yr. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.3/697 - Release Date: 2/22/2007 11:55 AM
