RE: [Repeater-Builder] Spectra Audio Popping after Capacitor replacement
At 03:38 PM 11/25/09, you wrote: Hi Mike, Thanks for the info. Yes, I've cleaned it up good... I use a q-tip with a baking soda/water combo, then wick solder on the pad till it flows... sometimes gotta scrape a shiny spot first. Then soldersuck the pad clean up with wick. Then another qtip with lacquer thinner (contains MEK) - does great job of cleaning the flux. Nice sparkly clean. The dried capacitor poop occasionally seeps under an adjacent component (capillary action) . Sometimes you have to lift an adjacent resistor or two to get access to all of it. The smell of the solder on the corroded pad reminds me of some solder I have that has a water soluble rosin. Kinda smells like fish. It's probably the audio amp, but it's not objectionable enough to make me want to change it out. It's amazing how many dead radios are coming back to life after re-capping! I agree! From the emails that WA1MIK (the author of the recapping article) and I have received over 70% of the problems in surplus Spectras are cap problems. Of course some of the problems were traces that had disappeared! Which is why Will Martin KA6LSD of Echo Communications wrote (in the recapping article) There have been cases where the corrosion has eaten away so much of the pads that I have had to use leaded components and solder to other locations on the board to restore the functionality. I saw one radio that Will fixed where he soldered one cap lead to one of the two original pads but the other lead had no pad... so he left the lead long, sleeved it and ran it a few inches over the components on the board and soldered it to another component. The guy is a genius at Spectras. He even found the manufacturer that made the audio module for Moto and buys them direct for a lot less than Moto sells them for. Things like that allow him to be more reasonable on repair pricing. I was over at his shop a while back and he had radios (awaiting service) on the shelf from a dozen 2-way shops and police agency shops in 7 states and 2 European countries - radios they couldn't fix. The outgoing shelf had radios from 4 states plus Canada and Mexico. The first thing he does is recap the radio. Then he starts working on the problems the customer complained about. Thanks, Tim Mike WA6ILQ
[Repeater-Builder] zetron model 48 repeater manager
Folks, Got this Zetron 48 at a hamfestnow, I need to unlock it...can you do it over the air like a 38A? I have the book but it is not clear at allNeed info on how to program this beastHappy Thanksgiving. Ron
RE: [Repeater-Builder] Re: pre-amp placement
Hi Skip, Happy Thanksgiving first off. Go to the Angle Linear web site and read Chip's documentation he has provided. I don't know too many people that has a better product than him and his stuff if installed correctly works like no other. Mike Mullarkey K7PFJ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of skipp025 Sent: Wednesday, November 25, 2009 10:37 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: pre-amp placement Hello John, W3ML w...@... wrote: Hi, not since high school... :-) I have now read two different things about where to put the pre-amp. Only two? One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? Depends and it does matter... based on how busy your radio site is, where any other rf activity is relative to your frequency, the type of preamplifier, how it's constructed, your receiver front end, your duplexer type with number of cavities, your Tx Power level and a few other tidbits... got a headache yet? I'd venture to say... if your receiver front end is of decent Q (quality) and reasonably narrow band-width along with a decent duplexer... then the preamp might best go after the duplexer, between it and the band-pass cavity. If your receiver front end is average or fairly broad (a few MHz band-width) there might be a case to include the extra band pass cavity after the preamp before the receiver input. Some of this option depends on the duplexer and TX Power Level. The point of what I write above is about trying to obtain the best overload prevention performance and or damage control when the preamplifier is overloaded and generating unwanted signals. Many but not all the variables are are in the list. You could of course try both positions and measure the system performance. s. No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.426 / Virus Database: 270.14.83/2526 - Release Date: 11/25/09 19:43:00
Re: [Repeater-Builder] Spectra Audio Popping after Capacitor replacement
On the spectras, if you keep using the radio after the caps go bad, it can damage the audio ic chip. The popping is one of the symptoms as well as distorted audio. Another thing I have seen is a tantalum chip cap that is the isolator cap between the audio chip and the previous chip. Just follow the audio-in line backwards from the audio chip to find it. ( am doing this from memory and not looking at a book or would give part numbers) The audio chip from mot last time I bought one was about $24.00 dealer price if I remember right. Hope this helps. Happy Thanksgiving Everybody !!! Mike Specialized Communications KB5FLX - Original Message - From: Tim Ahrens To: Repeater-Builder@yahoogroups.com Sent: Tuesday, November 24, 2009 10:32 PM Subject: RE: [Repeater-Builder] Spectra Audio Popping after Capacitor replacement Hi David, Is the Hear Clear board only on the 900 mhz spectras? I was looking in my service manual, and it talks about the board plugging into P501, but on my VHF spectras, this plug is unpopulated.. As a side note, when I went to replace the capacitors, I noticed that a fire ant had given it's life while spanning a couple of pins on the audio output TDAxxx part. There seemed to be some 'liquid ant residue' remaining, so perhaps it damaged the audio amp. I guess I'll have to look at the thing with the scope see what's going on in comparison to one that works 'correctly'. Thanks! Tim
[Repeater-Builder] Re: pre-amp placement
k7...@... Mike wrote: Hi Skipp, Hello back, Happy Thanksgiving first off. Go to the Angle Linear web site and read Chip's documentation he has provided. I don't know too many people that has a better product than him and his stuff if installed correctly works like no other. Thank you very much... same to you... I have been to Chip's web site and in years past talked to him more than once. Chip is a nice enough guy... as is anyone who takes the time to talk with people on the phone for as long as he often does. He makes great products and they do work well... but we have had different opinions (which is just fine, really) about some VHF Preamp applications. If you'd be interested in rolling your own You can build your own Phempt Preamplifier using the information from the sonic web page, which is found at: http://www.radiowrench.com/sonic/ and the specific description page is: http://www.radiowrench.com/sonic/so02145.html Chip's products installed do work like other similar preamplifiers... his stuff is good however, he is not alone in the Phempt Preamplifier world. I personally prefer to use different band-pass cavity products but again... his stuff does work well and he does provide very good customer support. cheers s.
RE: [Repeater-Builder] Re: pre-amp placement
Skipp, It seems as if both of your answers suggest that the preamp be installed in the same place- between the duplexer and the bandpass cavity. Perhaps your intent for the second situation was to suggest that the preamp be placed between the bandpass cavity and the receiver input. The site noise level is a major factor when determining the placement of the preamp. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of skipp025 Sent: Wednesday, November 25, 2009 9:37 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: pre-amp placement Hello John, W3ML w...@... wrote: Hi, not since high school... :-) I have now read two different things about where to put the pre-amp. Only two? One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? Depends and it does matter... based on how busy your radio site is, where any other rf activity is relative to your frequency, the type of preamplifier, how it's constructed, your receiver front end, your duplexer type with number of cavities, your Tx Power level and a few other tidbits... got a headache yet? I'd venture to say... if your receiver front end is of decent Q (quality) and reasonably narrow band-width along with a decent duplexer... then the preamp might best go after the duplexer, between it and the band-pass cavity. If your receiver front end is average or fairly broad (a few MHz band-width) there might be a case to include the extra band pass cavity after the preamp before the receiver input. Some of this option depends on the duplexer and TX Power Level. The point of what I write above is about trying to obtain the best overload prevention performance and or damage control when the preamplifier is overloaded and generating unwanted signals. Many but not all the variables are are in the list. You could of course try both positions and measure the system performance. s.
[Repeater-Builder] Re: pre-amp placement (previous post correction)
I've got to lay off the hard stuff so early in the morning... please allow me to correct the following. I'd venture to say... if your receiver front end is of decent Q (quality) and reasonably narrow band-width along with a decent duplexer... then the preamp might best go after the duplexer, between it and the band-pass cavity. Should have said: then the preamp might best go after the duplexer and the trailing band-pass cavity, between the the BP Cavity and the receiver front end that is all... tnx s.
Re: [Repeater-Builder] Re: pre-amp placement
The main way of thinking is that you want to put the pre-amp after the band pass filter. The reason for this is that if it is before the b/p filter, it amps anything it sees, noise and unwanted stuff alike. If its behind the b/p filter, it only amps the signals that are left and need it. You might need to add a several DB attenuator between the pre amp and the receiver to keep from overdriving the front end. Advanced Receiver Research makes very good low noise preamps as so do several other companies. Hope this helps, Mike Specialized Communications KB5FLX - Original Message - From: skipp025 To: Repeater-Builder@yahoogroups.com Sent: Wednesday, November 25, 2009 11:36 PM Subject: [Repeater-Builder] Re: pre-amp placement Hello John, W3ML w...@... wrote: Hi, not since high school... :-) I have now read two different things about where to put the pre-amp. Only two? One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? Depends and it does matter... based on how busy your radio site is, where any other rf activity is relative to your frequency, the type of preamplifier, how it's constructed, your receiver front end, your duplexer type with number of cavities, your Tx Power level and a few other tidbits... got a headache yet? I'd venture to say... if your receiver front end is of decent Q (quality) and reasonably narrow band-width along with a decent duplexer... then the preamp might best go after the duplexer, between it and the band-pass cavity. If your receiver front end is average or fairly broad (a few MHz band-width) there might be a case to include the extra band pass cavity after the preamp before the receiver input. Some of this option depends on the duplexer and TX Power Level. The point of what I write above is about trying to obtain the best overload prevention performance and or damage control when the preamplifier is overloaded and generating unwanted signals. Many but not all the variables are are in the list. You could of course try both positions and measure the system performance. s.
[Repeater-Builder] MVP Audio Popping
The recent discussion on Spectra audio popping prompts this post. Has anyone cured the audio popping on a GE Custom MVP. The speaker pops every time that the squelch opens. I have several radios that this happens on, some worse than others. Chuck WB2EDV
Re: [Repeater-Builder] Re: pre-amp placement
Anyone have a spare bandpass filter tunable for the UHF amateur band like a DCI? Thanks! Alan - Original Message - From: Mike Dietrich To: Repeater-Builder@yahoogroups.com Sent: Thursday, November 26, 2009 10:09 AM Subject: Re: [Repeater-Builder] Re: pre-amp placement The main way of thinking is that you want to put the pre-amp after the band pass filter. The reason for this is that if it is before the b/p filter, it amps anything it sees, noise and unwanted stuff alike. If its behind the b/p filter, it only amps the signals that are left and need it. You might need to add a several DB attenuator between the pre amp and the receiver to keep from overdriving the front end. Advanced Receiver Research makes very good low noise preamps as so do several other companies. Hope this helps, Mike Specialized Communications KB5FLX - Original Message - From: skipp025 To: Repeater-Builder@yahoogroups.com Sent: Wednesday, November 25, 2009 11:36 PM Subject: [Repeater-Builder] Re: pre-amp placement Hello John, W3ML w...@... wrote: Hi, not since high school... :-) I have now read two different things about where to put the pre-amp. Only two? One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? Depends and it does matter... based on how busy your radio site is, where any other rf activity is relative to your frequency, the type of preamplifier, how it's constructed, your receiver front end, your duplexer type with number of cavities, your Tx Power level and a few other tidbits... got a headache yet? I'd venture to say... if your receiver front end is of decent Q (quality) and reasonably narrow band-width along with a decent duplexer... then the preamp might best go after the duplexer, between it and the band-pass cavity. If your receiver front end is average or fairly broad (a few MHz band-width) there might be a case to include the extra band pass cavity after the preamp before the receiver input. Some of this option depends on the duplexer and TX Power Level. The point of what I write above is about trying to obtain the best overload prevention performance and or damage control when the preamplifier is overloaded and generating unwanted signals. Many but not all the variables are are in the list. You could of course try both positions and measure the system performance. s.
[Repeater-Builder] Re: pre-amp placement
Hi Eric, Eric Lemmon wb6...@... wrote: Skipp, It seems as if both of your answers suggest that the preamp be installed in the same place- between the duplexer and the bandpass cavity. You caught that just as I was posting the correction. Perhaps your intent for the second situation was to suggest that the preamp be placed between the bandpass cavity and the receiver input. Actually, I meant the converse... The site noise level is a major factor when determining the placement of the preamp. 73, Eric Lemmon WB6FLY Yes, but I make a case to install Rx Pre-amplifiers in some locations where others might say they are not effectively contributing all the time. As long as the pre-amplifier isn't over-loaded and causing grief, I like to have them in operation. The advantage of the installed preamplifier is fairly obvious in relative system comparisons. And just to throw another log on the fire (keeping the subject nice and warm)... I often use pre-amplifiers with T/R (coax path) Relay bypass capacity. For more than one reason I can and do remotely toggle pre-amps in and out of operation. s.
[Repeater-Builder] Re: pre-amp placement
Mike Dietrich m.dietr...@... wrote: The main way of thinking is that you want to put the pre-amp after the band pass filter. The reason for this is that if it is before the b/p filter, it amps anything it sees, noise and unwanted stuff alike. If its behind the b/p filter, it only amps the signals that are left and need it. It's a good way of thinking... but many of us in the commercial radio world are thinking more along the lines of what happens to the preamplifier and the receiver during large input signal events. How does the preamp and the receiver perform during signal over-loads and how to best prevent those over-loads from causing grief. The best placement of the added RX Preamp is not always the convention thinking best/first choice. You might need to add a several DB attenuator between the pre amp and the receiver to keep from over driving the front end. In some cases, one might need an attenuator... which sort of highlights why I had previously mentioned the receiver front-end performance. More time to freak everyone out... we have more than a few applications with two series Rx Pre-amplifiers. There's a lot more hardware going on (in place) than just parking two Pre-amplifiers in series so please don't be mislead by my initial description. But yes, we do often use two Rx Pre-amplifiers and when properly done they work killer (very, very well). Advanced Receiver Research makes very good low noise preamps as so do several other companies. Hope this helps, Mike I like ARR and Angle RX Preamplifiers... ARR makes a T/R Relay switched version, which for a number of reasons is really neat to be able to remotely control. cheers. s.
Re: [Repeater-Builder] pre-amp placement
--- On Wed, 11/25/09, W3ML w...@arrl.net wrote: From: W3ML w...@arrl.net Subject: [Repeater-Builder] pre-amp placement To: Repeater-Builder@yahoogroups.com Date: Wednesday, November 25, 2009, 10:46 PM Hi, I have now read two different things about where to put the pre-amp. One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? 73 John As always it is one of the it depends answer. You want the preamp as close to the antenna as you can get it. This sets the noise figure or in simple terms the minimal signal you can detect. Idealy it should be right at the antenna. This is not possiable with a repeater and single antenna so you want it right after the duplexer going to the receiver. Sometimes if you are in an area with lots of transmitters that are overloading the receiver or causing other problems (which is probably your case or you would not need the banpass cavity) then the preamp goes between the banpass cavity and the receiver. Most preamps do not have very much selectivity and many duplexers don't either to signals outside the tuned frequencies. This lets the preamp amplify many undesired signals and can cause all kinds of problems. If your repeater is located very far away from other transmitters this is not usaully a problem. If there are several transmitters near by then you may have a problem without a band pass filter.
[Repeater-Builder] Re: pre-amplifier brands
Advanced Receiver Research makes very good low noise preamps as so do several other companies. And we've seen Angle Preamps mentioned in these post. I wanted to make sure the GLB Series of Preselector Preamplifiers were mentioned. I really like the GLB Rx pre-selector preamp products: http://www.aria-glb.com/products/reset_frames.htm?/products/preselector.htm A bit less gain, but for a good reason... The models I use have very decent protection before and after the active device. IE the included pre-selector name in the description. I have a few GLB Preselector Preamplifiers working where less protected higher gain boxes don't function well. A bit more costly but don't be thrown off by the higher initial price tag. s.
[Repeater-Builder] Re: pre-amp placement
Thanks Glenn, I think I will it where it is since it is a Adv Receiver Research Gasfed. I don't remember the article mentioning helical resonators. Was just wondering why there would two different places in the articles. 73 John --- In Repeater-Builder@yahoogroups.com, Glenn Little WB4UIV glennmaill...@... wrote: If the preamp has helical resonators on the input, it should not matter. If the preamp does not have preselection, after the bandpass filter, unless you like the intermod that will be generated in the preamp. 73 Glenn WB4UIV At 10:46 PM 11/25/2009, you wrote: Hi, I have now read two different things about where to put the pre-amp. One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? 73 John Yahoo! Groups Links
[Repeater-Builder] Re: pre-amp placement
Ralph you bring up a good point of thought. The ham that built our repeater placed the Decibel Products 4002 Bandpass behind the Wacom 6 can duplexer and then followed by the ARR Gasfed P144VDG to the radio. Now where he built it was his tower site (an old ATT brick building) full of transmitters. Now that we have it, it is located here at my house in my ham shack. So, the only transmitters are my 2 meter and HF when I am on HF. The HF doesn't bother it at all and I run low power on 2 meter when I am on that. So, with your thought, I could probably do away with the bandpass all together run the preamp right out of the cans to the radio (which is a GE Mastr II mobile). Right (after fixing a lot of problems which most of you should remember) it is working good. Of course, you always to improve something even if it works like handheld access, so when I came across that article it made me want to ask where should the preamp go. I looked on the ARR site and they have no info on placement that I could find at all. Now maybe, if we had bought a new one, it might have came with a paper. Thanks for the advice. 73 John --- In Repeater-Builder@yahoogroups.com, Ralph Mowery ku...@... wrote: --- On Wed, 11/25/09, W3ML w...@... wrote: From: W3ML w...@... Subject: [Repeater-Builder] pre-amp placement To: Repeater-Builder@yahoogroups.com Date: Wednesday, November 25, 2009, 10:46 PM Hi, I have now read two different things about where to put the pre-amp. One says before the Bandpass and one after. What I have now is the 6 can duplexer is hooked to the bandpass and then on the other side the pre-amp is connected and then a cable goes from preamp to radio. The other article I read this past week says the preamp should go between the cans and the bandpass. Which is right? Or does it matter? 73 John As always it is one of the it depends answer. You want the preamp as close to the antenna as you can get it. This sets the noise figure or in simple terms the minimal signal you can detect. Idealy it should be right at the antenna. This is not possiable with a repeater and single antenna so you want it right after the duplexer going to the receiver. Sometimes if you are in an area with lots of transmitters that are overloading the receiver or causing other problems (which is probably your case or you would not need the banpass cavity) then the preamp goes between the banpass cavity and the receiver. Most preamps do not have very much selectivity and many duplexers don't either to signals outside the tuned frequencies. This lets the preamp amplify many undesired signals and can cause all kinds of problems. If your repeater is located very far away from other transmitters this is not usaully a problem. If there are several transmitters near by then you may have a problem without a band pass filter.
[Repeater-Builder] RE: preamp
I just read back what I typed while XYL was talking to me. You could tell I missed breakfast and she was talking about food as it is not a gas fed, but GaAS FET preamp. Now only 4 more hours before I get fed. Have a great holiday. 73 John
Re: [Repeater-Builder] RE: preamp
Most people gas after their fed. Alan - Original Message - From: W3ML To: Repeater-Builder@yahoogroups.com Sent: Thursday, November 26, 2009 11:37 AM Subject: [Repeater-Builder] RE: preamp I just read back what I typed while XYL was talking to me. You could tell I missed breakfast and she was talking about food as it is not a gas fed, but GaAS FET preamp. Now only 4 more hours before I get fed. Have a great holiday. 73 John
Re: [Repeater-Builder] Re: pre-amp placement
At 11/26/2009 07:31, you wrote: Mike Dietrich m.dietr...@... wrote: The main way of thinking is that you want to put the pre-amp after the band pass filter. The reason for this is that if it is before the b/p filter, it amps anything it sees, noise and unwanted stuff alike. If its behind the b/p filter, it only amps the signals that are left and need it. It's a good way of thinking... but many of us in the commercial radio world are thinking more along the lines of what happens to the preamplifier and the receiver during large input signal events. How does the preamp and the receiver perform during signal over-loads and how to best prevent those over-loads from causing grief. Sounds like the best answer to the above is Mike's comment above yours. I personally find very few situations where I'd want to put a preamp ahead of a pass cavity filter. I guess that has to do with the quality of the radios I use (GEs). MVPs Mastr IIs don't need pass filtering unless they have the UHS preamp installed. If the preamp goes ahead of the pass filtering, it's vulnerable to overload from out-of-band signals as well as lightning damage. If the preamp has integral filtering (helical resonators), it may not be as prone to the above, but it won't have the low noise that a good coaxial cavity filter/PHEMT preamp combo can achieve. You might need to add a several DB attenuator between the pre amp and the receiver to keep from over driving the front end. Not if you use a good receiver, or not use a preamp with too much gain. Bob NO6B
Re: [Repeater-Builder] Re: pre-amplifier brands
At 11/26/2009 07:43, you wrote: Advanced Receiver Research makes very good low noise preamps as so do several other companies. And we've seen Angle Preamps mentioned in these post. I wanted to make sure the GLB Series of Preselector Preamplifiers were mentioned. I really like the GLB Rx pre-selector preamp products: http://www.aria-glb.com/products/reset_frames.htm?/products/preselector.htm I think we've covered this before, but I'll say it again: the noise figure spec, the most important spec on any preamp, is missing! Would you buy a power amplifier that only spec'd 10 dB gain? I also don't see a P1dB spec either. Perhaps these are good preamps nonetheless, but be advised: you'll never get as good of a noise figure as using an ordinary GaAsFET preamp with a 0.25 or even 0.5 dB loss pass cavity in front of it. Perhaps this isn't so important on antenna noise-limited VHF bands, but in SoCal on 220 440 it is. The only place I'd use a GLB preselector would be a space-constrained application where a 1/4 wave resonator simply couldn't fit. Bob NO6B
Re: [Repeater-Builder] Re: pre-amp placement
At 11/26/2009 08:14, you wrote: Thanks Glenn, I think I will it where it is since it is a Adv Receiver Research Gasfed. Good choice IMO. If you want to maximize your sensitivity, just make sure your pass cavity is very low loss. If the loops are or adjusted for 2 dB loss, you could easily pick up 1.5 dB. Note that the pass filters that Chip sells at http://anglelinear.com/filters/coax_filters.html are only 0.3 to 0.4 dB loss per cavity. A bit pricey IMO, so I look for something used. Bob NO6B
Re: [Repeater-Builder] Re: pre-amp placement
You might need to add a several DB attenuator between the pre amp and the receiver to keep from over driving the front end. Not if you use a good receiver, or not use a preamp with too much gain. Bob NO6B What defines too much gain can vary wildly. One trick I learned in building transverters for the microwave bands, and one I now apply to VHF/UHF preamps is to check the overall noise figure of the system as a whole. You'd be surprised at what just a few db too much gain can do, and it doesn't necessarily show up with a quick sensitivity check. A preamp can be placed in front of a receiver and, yeah, now the receiver is more sensitive. But if it's a .5 DB NF preamp, and you're not careful, your system noise figure can end up going from, say, 6 db for the barefoot receiver, to 4 db with the preamp - an improvement to be sure, but not nearly as good as the preamp may be capable of. If that preamp is driving the receiver front end even just a little bit into compression, you've lost a lot of potential. Even with a good receiver. Carefully balancing preamp gain with attenuation on the output can be extremely useful. Not everyone has a noise figure meter, though, and measuring NF on an FM receiver is a pain in the neck. A sinadder can be used to the same effect, even if the actual noise figure isn't known. It can be interesting to observe insertion of a few db of pad between the preamp and a receiver, and watch the sinad sensitivity of a receiver improve by a few tenths of a microvolt.
Re: [Repeater-Builder] MVP Audio Popping
At 11/26/2009 07:14, you wrote: The recent discussion on Spectra audio popping prompts this post. Has anyone cured the audio popping on a GE Custom MVP. The speaker pops every time that the squelch opens. I have several radios that this happens on, some worse than others. The speaker audio comes from pin 12 of AR901 on the SAS board. The schematic calls out 6.6 V unsquelched 0.1 V squelched. C921, a 220 uF coupling cap couples the audio to the speaker. Off hand I don't see any way to get rid of the DC step short of replacing/redesigning the audio amp. You could try replacing C921 with a smaller value cap to reduce the low frequency content of the step. Bob NO6B
RE: [Repeater-Builder] MVP Audio Popping
I agree about the MVP audio design. After all, the Custom MVP was GE's economy line radio, so we should not expect it to perform as well as the Mastr II. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of n...@no6b.com Sent: Thursday, November 26, 2009 9:39 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] MVP Audio Popping At 11/26/2009 07:14, you wrote: The recent discussion on Spectra audio popping prompts this post. Has anyone cured the audio popping on a GE Custom MVP. The speaker pops every time that the squelch opens. I have several radios that this happens on, some worse than others. The speaker audio comes from pin 12 of AR901 on the SAS board. The schematic calls out 6.6 V unsquelched 0.1 V squelched. C921, a 220 uF coupling cap couples the audio to the speaker. Off hand I don't see any way to get rid of the DC step short of replacing/redesigning the audio amp. You could try replacing C921 with a smaller value cap to reduce the low frequency content of the step. Bob NO6B
Re: [Repeater-Builder] Re: pre-amp placement
At 11/26/2009 08:30, you wrote: Ralph you bring up a good point of thought. The ham that built our repeater placed the Decibel Products 4002 Bandpass behind the Wacom 6 can duplexer and then followed by the ARR Gasfed P144VDG to the radio. Now where he built it was his tower site (an old ATT brick building) full of transmitters. Now that we have it, it is located here at my house in my ham shack. So, the only transmitters are my 2 meter and HF when I am on HF. The HF doesn't bother it at all and I run low power on 2 meter when I am on that. So, with your thought, I could probably do away with the bandpass all together run the preamp right out of the cans to the radio (which is a GE Mastr II mobile). Yes, but it will offer some protection from your 2 meter radio so you'll desense your repeater a bit less. It also offers some protection from the EMP of nearby lightning strikes: less bandwidth between the strike preamp means less EMP energy reaching the preamp's input. The DB4002 came with either 0.5, 1 or 3 dB loops. If yours has 3 dB loops, then you'll probably see some improvement in sensitivity by removing the can. If it has 0.5 dB loops, you won't notice a difference. 1 dB is somewhere in between, but if you have any amount of site noise you probably won't notice a difference as well. Here in SoCal you can put a 6 dB pad in front of a preamp not notice a difference in effective sensitivity. Needless to say, I don't use them on 2 meters here - the stock sensitivity of an MVP or Mastr II is perfectly matched to our environment. I have noticed that away from this area, the noise floor on 2 meters can be much lower. Bob NO6B
Re: [Repeater-Builder] MVP Audio Popping
You are telling me what I suspected - that it's the design, not a component going bad or failed. Chuck WB2EDV - Original Message - From: n...@no6b.com To: Repeater-Builder@yahoogroups.com Sent: Thursday, November 26, 2009 12:38 PM Subject: Re: [Repeater-Builder] MVP Audio Popping At 11/26/2009 07:14, you wrote: The recent discussion on Spectra audio popping prompts this post. Has anyone cured the audio popping on a GE Custom MVP. The speaker pops every time that the squelch opens. I have several radios that this happens on, some worse than others. The speaker audio comes from pin 12 of AR901 on the SAS board. The schematic calls out 6.6 V unsquelched 0.1 V squelched. C921, a 220 uF coupling cap couples the audio to the speaker. Off hand I don't see any way to get rid of the DC step short of replacing/redesigning the audio amp. You could try replacing C921 with a smaller value cap to reduce the low frequency content of the step. Bob NO6B Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.709 / Virus Database: 270.14.83/2528 - Release Date: 11/26/09 04:10:00
Re: [Repeater-Builder] Re: pre-amp placement
So what is the recommendation to set the loss of the BP cavity? I have a setting as to 3 db, 1 Db, .5 Db Etc. Running the ARR preamp on a UHF repeater, it seems the preamp is a little too much and we get a little desense. I am only running a 4 cavity duplexer and a notch cavity with the preamp. de KM3W From: n...@no6b.com n...@no6b.com To: Repeater-Builder@yahoogroups.com Sent: Thu, November 26, 2009 12:50:18 PM Subject: Re: [Repeater-Builder] Re: pre-amp placement At 11/26/2009 08:30, you wrote: Ralph you bring up a good point of thought. The ham that built our repeater placed the Decibel Products 4002 Bandpass behind the Wacom 6 can duplexer and then followed by the ARR Gasfed P144VDG to the radio. Now where he built it was his tower site (an old ATT brick building) full of transmitters. Now that we have it, it is located here at my house in my ham shack. So, the only transmitters are my 2 meter and HF when I am on HF. The HF doesn't bother it at all and I run low power on 2 meter when I am on that. So, with your thought, I could probably do away with the bandpass all together run the preamp right out of the cans to the radio (which is a GE Mastr II mobile). Yes, but it will offer some protection from your 2 meter radio so you'll desense your repeater a bit less. It also offers some protection from the EMP of nearby lightning strikes: less bandwidth between the strike preamp means less EMP energy reaching the preamp's input. The DB4002 came with either 0.5, 1 or 3 dB loops. If yours has 3 dB loops, then you'll probably see some improvement in sensitivity by removing the can. If it has 0.5 dB loops, you won't notice a difference. 1 dB is somewhere in between, but if you have any amount of site noise you probably won't notice a difference as well. Here in SoCal you can put a 6 dB pad in front of a preamp not notice a difference in effective sensitivity. Needless to say, I don't use them on 2 meters here - the stock sensitivity of an MVP or Mastr II is perfectly matched to our environment. I have noticed that away from this area, the noise floor on 2 meters can be much lower. Bob NO6B
RE: [Repeater-Builder] Re: pre-amp placement
A total insertion loss of about 1.0 dB works well, in my experience. With two 8 bandpass cavities in series, this gives at least 25 dB of isolation from the transmitter carrier at a 600 kHz split. Bear in mind that your notch cavity has the same deficiency as the typical BpBr duplexer- there is relatively little bandpass effect. A pass-notch cavity is a poor substitute for a bandpass cavity. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Pointman Sent: Thursday, November 26, 2009 10:09 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: pre-amp placement So what is the recommendation to set the loss of the BP cavity? I have a setting as to 3 dB, 1 dB, .5 dB etc. Running the ARR preamp on a UHF repeater, it seems the preamp is a little too much and we get a little desense. I am only running a 4 cavity duplexer and a notch cavity with the preamp. de KM3W
RE: [Repeater-Builder] Re: pre-amp placement
Most of the time you will want as much selectivity as you can get in front of the preamp. The only time that I can think of off hand where you might want a filter behind a preamp is if you are getting a receiver feed from a receiver multicoupler that has a preamp in it, giving a few megs wide signal out of the multicoupler. Overload of a preamp depends on the total amount of power that gets into it. The wider the window in front of it the more total power that has potential for getting in from many other transmitters. This can cause IM products to be generated in the preamp itself. Once that happens you have opened the barn door and there is not much you can do after the preamp to help the receiver. Sometimes if is good to use a preamp that doesn't necessarily have the best noise figure but maybe has a higher dynamic range (higher intercept point) if your site has lots of nearby transmitters and noise that could overload the preamp. Having a very low noise figure doesn't do you any good if the preamp causes IM to be generated. The second thing is not to run too much gain in the preamp so that the added gain overloads the front end of the receiver. For every Db of gain the preamp provides that reduces the receivers IM rejection ability by the same number of Db. So again if you have lots of strong adjacent signals at your site you don't want lots of preamp gain. Total receiver system noise figure is partially set by the preamp if its noise figure is lower than that of the receiver, which it usually is. Using a preamp with a .5 Db noise figure and a receiver with an 8 Db noise figure won't give you a total noise figure of .5 Db, but somewhere in-between. The more gain the preamp has the lower the overall noise figure will be in this case, unless you have enough gain to cause some of the other low noise figure stages in the receiver to go into compression as Mel eludes to. The stage that goes into compression in the receiver doesn't necessarily have to be the front end of the receiver. The first IF stages in most receivers have a pretty low noise figure and help establish the overall noise figure of the receiver as well as the front end of the receiver. So these stages can be overloaded with too much gain and cause a noise figure reduction. But the biggest problem with too much preamp gain is overloading the mixer in the receiver and causing it to generate IM products. By controlling the gain of the preamp (using attenuators after the preamp) or by other means you can usually find a happy medium of some gain to improve system noise figure (sensitivity) and not too much gain to destroy the IM performance of the receiver. One way to do that is to put in attenuation until the sensitivity just starts to degrade with the preamp in the circuit. That will give you good sensitivity and good IM performance. Any more gain and all you are doing is degrading the receiver IM performance. When shopping for preamps don't only look at gain figures and noise figures, also look at the intercept point to see how much signal it will handle before compression starts. That's where it will start generating IM products. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- buil...@yahoogroups.com] On Behalf Of Mel Swanberg Sent: Thursday, November 26, 2009 12:40 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: pre-amp placement You might need to add a several DB attenuator between the pre amp and the receiver to keep from over driving the front end. Not if you use a good receiver, or not use a preamp with too much gain. Bob NO6B What defines too much gain can vary wildly. One trick I learned in building transverters for the microwave bands, and one I now apply to VHF/UHF preamps is to check the overall noise figure of the system as a whole. You'd be surprised at what just a few db too much gain can do, and it doesn't necessarily show up with a quick sensitivity check. A preamp can be placed in front of a receiver and, yeah, now the receiver is more sensitive. But if it's a .5 DB NF preamp, and you're not careful, your system noise figure can end up going from, say, 6 db for the barefoot receiver, to 4 db with the preamp - an improvement to be sure, but not nearly as good as the preamp may be capable of. If that preamp is driving the receiver front end even just a little bit into compression, you've lost a lot of potential. Even with a good receiver. Carefully balancing preamp gain with attenuation on the output can be extremely useful. Not everyone has a noise figure meter, though, and measuring NF on an FM receiver is a pain in the neck. A sinadder can be used to the same effect, even if the actual noise figure isn't known. It can be interesting to observe insertion of a few db of pad between the preamp and a receiver, and watch the sinad sensitivity of a receiver improve by a few
Re: [Repeater-Builder] Re: pre-amp placement
So your suggestion is to get a Band pass/reject cavity instead? Or should I get 2 for the added isolation? keep in mind I am on UHF de KM3W From: Eric Lemmon wb6...@verizon.net To: Repeater-Builder@yahoogroups.com Sent: Thu, November 26, 2009 2:48:54 PM Subject: RE: [Repeater-Builder] Re: pre-amp placement A total insertion loss of about 1.0 dB works well, in my experience. With two 8 bandpass cavities in series, this gives at least 25 dB of isolation from the transmitter carrier at a 600 kHz split. Bear in mind that your notch cavity has the same deficiency as the typical BpBr duplexer- there is relatively little bandpass effect. A pass-notch cavity is a poor substitute for a bandpass cavity. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@ yahoogroups. com [mailto:Repeater-Builder@ yahoogroups. com] On Behalf Of Pointman Sent: Thursday, November 26, 2009 10:09 AM To: Repeater-Builder@ yahoogroups. com Subject: Re: [Repeater-Builder] Re: pre-amp placement So what is the recommendation to set the loss of the BP cavity? I have a setting as to 3 dB, 1 dB, .5 dB etc. Running the ARR preamp on a UHF repeater, it seems the preamp is a little too much and we get a little desense. I am only running a 4 cavity duplexer and a notch cavity with the preamp. de KM3W
