RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
Interesting, I actually sent this out on the 5th. Between Yahoo Bellsouth, who knows what bucket it was stuck in? Fred N4GER -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Fred Flowers Sent: Monday, February 05, 2007 10:00 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater? 1) No 2) Yes 3) Probably not. Fred N4GER -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Tony L. Sent: Monday, February 05, 2007 8:48 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power. Yahoo! Groups Links Yahoo! Groups Links
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
I'm sure you will get a few more more educated replies than mine- Here's my two cents. Double the power, the most you would theoretically get is 3db more signal. Will the end users notice- probably not very significantly. I have heard and experienced systems that ran *high powered* amplifiers on their repeaters, one in particular failed but only the users 50 miles away noticed a difference (and that was on pure exciter power). What are the downsides- consume more power, potentially introduce more de-sense. You will create more heat in the cabinet as well. Is it worth it? You could probably argue it either way. If the money is sitting there to burn and it makes some people happy, what the heck, give it a shot and let us know your results. Is it going to make the machine full-quieting 60dB over S-9 OM everywhere it hears? Likely not. Remember, the next complaint from the other people is I hear it full scale but I cant get in! and your next post is about voters! Tom W9SRV - Original Message From: Tony L. [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Monday, February 5, 2007 8:47:34 AM Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power. Yahoo! Groups Links Looking for earth-friendly autos? Browse Top Cars by Green Rating at Yahoo! Autos' Green Center. http://autos.yahoo.com/green_center/
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
double the power is a 3DB increase, which will result in 1/2 S-unit increase in signal. There will be very little, if any, difference. Unless you can do the upgrade for free, it is not worth it. -- Original Message -- Received: Mon, 05 Feb 2007 08:47:45 AM CST From: Tony L. [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power.
RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
1) No 2) Yes 3) Probably not. Fred N4GER -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Tony L. Sent: Monday, February 05, 2007 8:48 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power. Yahoo! Groups Links
RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
Good idea and when you install the amplifier you will want to install this filter pre amp at the same time. http://www.anglelinear.com/custom/custom.html they are worth there money and the results are unbelievable. Oregon Repeater Linking Group Mike Mullarkey 6539 E Street Springfield, OR 97478 [EMAIL PROTECTED] www.orlg.org -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Tony L. Sent: Monday, February 05, 2007 6:48 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power.
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
You've already gotten reasonable answers that I won't rehash. Let's consider this, assuming that bumping the power up to 100 Watts doesn't degrade your receiver, how do the users perceive things? Flea powered HTs are the bane of repeater builders (or, at least, me), but people love them. Most are designed with rather hot receivers that give reasonable receive range with their small rubber-duck antennas. Now let's assume that your current setup works such that as the repeater is getting noisy in their receiver that they are dropping out of the repeater, i.e. the repeater is still balanced (do you see where I'm going?). Now you bump the power and suddenly the HT user is hearing the repeater full-quieting. Naturally he'll assume that he's in a better coverage area but will find that he's dropping out (as before) even though he's hearing the machine so much better. Of course, the complaints begin. What has been gained? A different set of complaints (from personal experience). It sounds to me like your repeater is reasonably balanced and I wouldn't do anything to upset that. I would leave it up to those that need the needle pinned to improve their own stations. 73, de Nate -- Wireless | Amateur Radio Station N0NB | Successfully Microsoft Amateur radio exams; ham radio; Linux info @ | free since January 1998. http://www.qsl.net/n0nb/ | Debian, the choice of My Kawasaki KZ-650 SR @| a GNU generation! http://www.networksplus.net/n0nb/ | http://www.debian.org
RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
Upping the power changes the balance , if you really need to fiddle with it improve the antenna for a boost both ways and at no additional running cost . From: Tony L. [EMAIL PROTECTED] Reply-To: Repeater-Builder@yahoogroups.com To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? Date: Mon, 05 Feb 2007 14:47:34 - One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power. _ Advertisement: 50% off on Xbox 360, PS and Nintendo Wii titles! http://www.play-asia.com/SOap-23-83-4lab-71-bn-49-en-84-k-40-extended.html
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
If you ever do install the amp, I would suggest lying to the users when it goes on line. Tell them that it is on low power when it is on high and vice versa but don't announce it the instant you change. Wait a while before announcing it. You will very quickly find out who can actually tell the difference. At least that is what we found about 20 years ago when we did a major rearrangement of antennas and lowering power. Nobody honestly could tell the difference and those who agreed with our false conditions were shown to not have a clue (I never did tell them what the experimental results were :-) Burt VE2BMQ Tony L. wrote: One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power.
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
At 06:47 AM 02/05/07, you wrote: One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Might want to ask the knowledge base here for recommendations and/or warnings... This group has over 3,000 members and they can tell you what works or doesn't work. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. OK, so the surrounding equipment can handle it. But can the receive side? Might want to mention what repeater you are using, and if you have any RF neighbors at the same site. This can be significant... for example if you have a 375w base on a UHF paging channel in the same building then our recommendations might be a bit different. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. Good. Your system isn't an alligator (all mouth and no ears) or an elephant. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. Big question: Do you want/need the increased activity? The increased power will raise the signal strength out in the fringe areas, and make it easier to hear, but can the users out there get back in? Yes, 3db can be difference between the repeater being heard or not in a fringe area... but it makes ZERO difference if the user can't get into the repeater. That's where the receive side of your system comes into play. If it can't hear them, they all you've done is raise the frustration level because the users expect that if they can hear it then they can get back into it (and if they have supersensitive flea-powered HTs then the ball game is different than if they have 50w mobiles) If you don't meet those expectations then you will have a different set of complaints to handle. Years ago I worked with a midwest group that had a similar coverage problem on 2m. Their solution was unique: they were on a low-end 147MHz channel with a plus offset and simply added a minus offset receiver for the other end of town. They told the users that if they were on the east side to use plus offset and if on the west side to use minus offset. If you boost the transmit power and find yourself up against the physics in repeater receiver performance the only way to get back to a balanced system is to add outlying receivers and linking them back in and voting them. Note that going to a voted environment is a HUGE can of technical worms. See these two articles: http://www.repeater-builder.com/tech-info/remotereceivers.html http://www.repeater-builder.com/tech-info/votingcomparators.html We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? Is there another system at the same site (or nearby) that runs higher power? Can you use them as a test? For example, is there a UHF commercial repeater(even a police/fire one) that has the same or similar ERP of your 100w system? If so, do a coverage check on that channel. If you are friends with the tech people of that system they may already have done a plot. Maybe download a copy of Radio Mobile and do a set of plots for yourself. You will find that boosting the antenna system performance makes more of a change. Remember that 3db more gain or 3db less loss in the antenna system will help the receive side and the transmit side and do it as much as the transmit side gets by doubling the power, and without changing out the transmitter. Note that in many areas coverage can depend on your geography more than the power level. Locally one popular system is limited by the fact that it's in a valley. Twenty watts into 6db does a great job of covering it, but they use 40w only because that's what was on hand. You could boost it from the current 40 to 1,000 watts and all you would do is raise the s-meters (and get further into the underground parking garages). In that environment once you've covered the valley floor, all you end up doing is spinning the AC mains power meter faster. If you have a flat-as-a-pancake service area then increasing the power level makes your footprint larger. But picture this: if you double the area of the footprint (which the 3db won't do, but for simple math, lets say it does), how much larger is the radius? So the answer is, it depends, but usually not as much as you'd like. BTW, this question was asked on this group back in 2004 and answered in 2005... Check out http://www.repeater-builder.com/antenna/3db.html 2) Will we risk generating additional receiver noise by doubling our
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
On 2/5/07, Burt Lang [EMAIL PROTECTED] wrote: If you ever do install the amp, I would suggest lying to the users when it goes on line. Tell them that it is on low power when it is on high and vice versa but don't announce it the instant you change. Wait a while before announcing it. You will very quickly find out who can actually tell the difference. At least that is what we found about 20 years ago when we did a major rearrangement of antennas and lowering power. Nobody honestly could tell the difference and those who agreed with our false conditions were shown to not have a clue (I never did tell them what the experimental results were :-) Burt VE2BMQ Agreed Burt -- or if not lying, not saying a word. Sounds dumb, but there are a million factors OTHER than the repeater that affect how a particular user is hearing the machine -- and many don't know how to logically remove the changes THEY'RE making from the changes happening to the repeater... if they THINK it sounds worse after a change... then they'll complain, even if the system is actually performing BETTER. Nate WY0X
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
On 2/5/07, Barry C' [EMAIL PROTECTED] wrote: Upping the power changes the balance , if you really need to fiddle with it improve the antenna for a boost both ways and at no additional running cost Unless you're running separate antennas, how would changing the gain of the antenna make a difference in additional gain for RX that wouldn't be also seen in additional gain for TX? But unless I'm missing something here (deep nulls and fading due to terrain or something?) the added gain of a better antenna on receive would translate to the same on TX, doesn't it? The only reasonable way to get more RX without affecting TX would be (pre-)amplification of the receive chain and additional filtering if necessary to avoid desense, etc. If there's a suspicion that the system isn't performing as absolutely well as it can on RX, a usable receiver sensitivity test with a weak signal injected into the RX chain with the antenna connected also, would be the way to find out. Jeff's article about measuring the sensitivity of a receiver WITHOUT the site noise/antenna connected is here: http://www.repeater-builder.com/tech-info/receiversensitivity.html And doing it WITH the site noise/antenna is here: http://www.repeater-builder.com/tech-info/effectivesens.html If there's 2 or 3 more dB available between the site noise floor and the receiver's best sensitivity measurements -- then sure, maybe you can squeak all of that out with better filters, a good LNA and balance the added TX power. That will take additional money/time/effort beyond just swapping the PA for a bigger one and checking for desense. And... no one's posted this here in the discussion yet... http://www.repeater-builder.com/antenna/3db.html ... which of course, is a good discussion of the situation too, since it actually starts with the same theoretical question (should I add 3dB to my transmitter?) and tackles the analysis of adding 3dB to a system mathematically. Hopefully the above articles help. And if you haven't done the Effective Sensitivity test, do it BEFORE you make any changes. It will give you a baseline so you know if relatively you're making things better, or worse, overall on RX. Nate WY0X
Re: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
Spend the money on a more modern receiver designed for repeater ops, get a fresh antenna like a Station Master, and use the best run of heli-ax and premium connectors you can afford and you will see just as much improvement if not better. External power Amplifiers and more power output will do some things you might not like. Your receiver noise floor will increase. Any filters you have in line with the low power setting might now act up on the higher power output. Ditto with the coaxial connectors. You might see more intermod and have to install more gadgets that would go wrong or go wrong when you least want to. Ask yourself if you want a gadgety repeater or one that will operate when the lights go out or even when there is bad weather out there. I build a couple and learned the hard way. Adam Kb2jpd On 2/5/07, Nate Duehr [EMAIL PROTECTED] wrote: On 2/5/07, Barry C' [EMAIL PROTECTED] atec77%40hotmail.com wrote: Upping the power changes the balance , if you really need to fiddle with it improve the antenna for a boost both ways and at no additional running cost Unless you're running separate antennas, how would changing the gain of the antenna make a difference in additional gain for RX that wouldn't be also seen in additional gain for TX? But unless I'm missing something here (deep nulls and fading due to terrain or something?) the added gain of a better antenna on receive would translate to the same on TX, doesn't it? The only reasonable way to get more RX without affecting TX would be (pre-)amplification of the receive chain and additional filtering if necessary to avoid desense, etc. If there's a suspicion that the system isn't performing as absolutely well as it can on RX, a usable receiver sensitivity test with a weak signal injected into the RX chain with the antenna connected also, would be the way to find out. Jeff's article about measuring the sensitivity of a receiver WITHOUT the site noise/antenna connected is here: http://www.repeater-builder.com/tech-info/receiversensitivity.html And doing it WITH the site noise/antenna is here: http://www.repeater-builder.com/tech-info/effectivesens.html If there's 2 or 3 more dB available between the site noise floor and the receiver's best sensitivity measurements -- then sure, maybe you can squeak all of that out with better filters, a good LNA and balance the added TX power. That will take additional money/time/effort beyond just swapping the PA for a bigger one and checking for desense. And... no one's posted this here in the discussion yet... http://www.repeater-builder.com/antenna/3db.html ... which of course, is a good discussion of the situation too, since it actually starts with the same theoretical question (should I add 3dB to my transmitter?) and tackles the analysis of adding 3dB to a system mathematically. Hopefully the above articles help. And if you haven't done the Effective Sensitivity test, do it BEFORE you make any changes. It will give you a baseline so you know if relatively you're making things better, or worse, overall on RX. Nate WY0X
RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
Tony, As you can tell from the number of replies, this is a topic that generates a great deal of interest! I agree with the majority of posters who state that a power increase will have relatively minor positive effect, and MAY have significant negative effects. In fact, one fellow posted a comment a year or two ago, that his 50 watt PA died, and he connected the exciter directly to the duplexer in place of the PA for several weeks- a 100:1 change in power output- and none of the regular users noticed the difference! In this particular case, the repeater was far from being balanced. Nevertheless, it does lend credence to the oft-repeated statement that increased power does not equate to increased coverage. It has been stated many times on this and other sites that the primary limitation of repeater coverage is the ability of the repeater to hear the radios in the field. If the pipsqueak-power handheld portable radios in the field cannot reach the repeater's receiver, no amount of power increase will make any difference. Quite the contrary, as many have pointed out, more power will possibly increase receiver noise and/or desense, intermodulation, and other ills. These MAY have the effect of reducing the coverage area! I strongly suggest that a thorough analysis be performed on the entire system, to ensure that the feedline loss is as low as it can possibly be, the antenna gain and pattern is appropriate for its location, and the receive chain is as efficient and noise-free as possible. If your site noise floor is low, you MAY be able to profoundly improve your coverage with a couple of bandpass cavities followed by a very good preamp, between the duplexer output and the receiver input. A preamp is never the final answer but when appropriately filtered CAN result in a significant improvement. Please note that I have emphasized the words MAY and CAN. I have learned from experience that effective site engineering comes from a proper consideration of all factors. Moreover, the knee-jerk suggestion that an increase in power output will solve repeater coverage issues is laughably misguided. I sincerely hope that you can convince your repeater users that a careful analysis of the repeater operation may reveal other, more effective means to improve its coverage. 73, Eric Lemmon WB6FLY From: Tony L. [EMAIL PROTECTED] mailto:railtrailbiker%40yahoo.com Reply-To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? Date: Mon, 05 Feb 2007 14:47:34 - One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating additional receiver noise by doubling our output power, thus losing coverage in the process? 3) Will using a higher power level shorten the life of other system components over time (e.g., power supply)? By the way, our frequency coordination would be valid even if we doubled our output power.
RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater?
I may as well chime in here too. When adding a pre-amp don't overlook the fact that you may not always get out of the addition of the pre-amp what you think you will. Every cavity that is ahead of the pre-amp has loss. Sometimes it requires additional cavities which increases the loss over what you had without the pre-amp. You may end up with a total receiver noise figure the same as when you started depending on how bad the receiver is in the first place. But in most cases it should help some. Be prepared to start chasing IM problems though! Not that a pre-amp is an IM generator but you will see many more problems that may have been hidden before. I think someone mentioned measuring site noise as a first step. If you don't do that you may waste many many hours chasing problems of why the pre-amp doesn't work that could have been easily discovered up front. Desense and site noise measurements are on the top of the list. 73 Gary K4FMX _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon Sent: Monday, February 05, 2007 8:54 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Effects of doubling RF output on UHF repeater? Tony, As you can tell from the number of replies, this is a topic that generates a great deal of interest! I agree with the majority of posters who state that a power increase will have relatively minor positive effect, and MAY have significant negative effects. In fact, one fellow posted a comment a year or two ago, that his 50 watt PA died, and he connected the exciter directly to the duplexer in place of the PA for several weeks- a 100:1 change in power output- and none of the regular users noticed the difference! In this particular case, the repeater was far from being balanced. Nevertheless, it does lend credence to the oft-repeated statement that increased power does not equate to increased coverage. It has been stated many times on this and other sites that the primary limitation of repeater coverage is the ability of the repeater to hear the radios in the field. If the pipsqueak-power handheld portable radios in the field cannot reach the repeater's receiver, no amount of power increase will make any difference. Quite the contrary, as many have pointed out, more power will possibly increase receiver noise and/or desense, intermodulation, and other ills. These MAY have the effect of reducing the coverage area! I strongly suggest that a thorough analysis be performed on the entire system, to ensure that the feedline loss is as low as it can possibly be, the antenna gain and pattern is appropriate for its location, and the receive chain is as efficient and noise-free as possible. If your site noise floor is low, you MAY be able to profoundly improve your coverage with a couple of bandpass cavities followed by a very good preamp, between the duplexer output and the receiver input. A preamp is never the final answer but when appropriately filtered CAN result in a significant improvement. Please note that I have emphasized the words MAY and CAN. I have learned from experience that effective site engineering comes from a proper consideration of all factors. Moreover, the knee-jerk suggestion that an increase in power output will solve repeater coverage issues is laughably misguided. I sincerely hope that you can convince your repeater users that a careful analysis of the repeater operation may reveal other, more effective means to improve its coverage. 73, Eric Lemmon WB6FLY From: Tony L. railtrailbiker@ mailto:railtrailbiker%40yahoo.com yahoo.com mailto:railtrailbiker%40yahoo.com Reply-To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: [Repeater-Builder] Effects of doubling RF output on UHF repeater? Date: Mon, 05 Feb 2007 14:47:34 - One of our 70cm Amateur Radio repeaters is currently outputting 50 watts into the duplexer. We're considering replacing the existing RF power amp with a 100 watt model. Current draw on the 50 watt unit is 8 amps. The 100 watt unit will draw 20 amps. Our power supply is rated at 36 amps continuous, and the duplexer is rated at 250 watts. Half of our users believe that the repeater's output power is perfectly matched to its receiver. That is, users of high powered mobile radios generally lose repeater reception at about the same time the repeater's receiver loses them. However, the other half of our users believe doubling the repeater's power output would generate increased activity since the repeater could be heard more comfortably. We could upgrade without changing any of our other infrastructure. However, these questions arise: 1) Will the hundreds we pay to upgrade actually translate into significantly increased range? 2) Will we risk generating
