RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
And that works how in FM ???(last I heard the noise is AM, speech is FM ) At 08:52 PM 02/05/09, you wrote: What he is saying is , a lower gain preamp aplifies less noise in relation to the signal so the audio sounds better -- To: Repeater-Builder@yahoogroups.com From: lar...@hotmail.com Date: Fri, 6 Feb 2009 04:47:11 + Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp --- In mailto:Repeater-Builder@yahoogroups.comRepeater-Builder@yahoogroups.com, Joe Burkleo joeburk...@... wrote: If for example the site has a higher than normal noise floor a lower gain preamp will often times amplify more of the signal and less of the extra site noise, where a higher gain preamp may amplify both the noise and signal, giving you a signal with more noise than you would like. Joe, scratchin' my head here... Would you be able to clarify the above statement for me? Laryn K8TVZ -- Get what you want at ebay. http://a.ninemsn.com.au/b.aspx?URL=http%3A%2F%2Frover%2Eebay%2Ecom%2Frover%2F1%2F705%2D10129%2D5668%2D323%2F4%3Fid%3D10_t=763807330_r=hotmailTAGLINES_m=EXTGet rid of those unwanted christmas presents!
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
On Feb 4, 2009, at 9:16 PM, Bob Ricci wrote: My only thought that was as a preselector the Hamtronics might have something to offer. As I said, the Angle Linear is on the top of the list, but the piggy bank is getting low. The Decibel Product DB-4002 with a 10dB preamp will do for now. If my wife doesn't toss me and the repeater out soon :) How 'bout asking the users with puny radios to pitch in? They can't afford a mobile rig, or better antennas for their HT's, I know... but maybe five or six of them together could afford a pre-amp? ;-) Nate WY0X
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
I bet you were right at a null directly under the antenna. 15 feet is just sort of 2 wavelengths. -Kevin -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of n...@no6b.com Sent: Thursday, February 05, 2009 11:52 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp At 2/5/2009 15:03, you wrote: With that short of a run I would be more concerned with the repeater being in the near field of the antenna. -Kevin I've read other similar comments. Guess I've been lucky: the last 2 meter system I set up has the antenna barely 15 ft directly above the repeater. No desense. The antenna is almost directly above the repeater so that may help. Bob NO6B Yahoo! Groups Links
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Ralph S. Turk wrote: I have never seen or used a Hamtronics preamp. I don't know anything about their specs or how truthfull they are. Maybe some one out there in the great bits might have an answer. Skip? Eric? anyone?? I've been using one of their Gaasfet UHF preamps on UHF ham repeaters for nearly 20 yrs, and have had excellent results. I'm not using one with helicals, though, because, well, I just didn't need them. Repeaters have been either Motorola MSY (Motrac-style) or Micor. The only hitch is that the case they supply these in is open on the bottom, so it NEEDS to be screwed down to the metal chassis of the repeater somewhere. It CANNOT hang on the coax, like I've seen some do with ARR's, or screw to the wood or plaster wall.
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
n...@no6b.com wrote: At 2/4/2009 21:19, you wrote: The Vertex has a .20uV measured and the rest of the specs are just as good. You do not need a preamp. The RX might still need an extra pass cavity, but I'd go ahead try it with just the duplexer if there isn't much RF in your neighborhood. Another angle on this-the Vertex radios don't have much of a front end. That's how they get the extra sensitivity. A 2M repeater I used to be involved with in the 80's had a Spectrum repeater (cringe). The transmitter died (no surprise), and one of the members was able to obtain and RCA 500 series repeater pulled from service. While the Spectrum tested on the bench at abt .2uV for 20dB, and the RCA was more like .35, once installed, the RCA heard BETTER, because it had a better front end, and better a better IF/limiter chain. -another brief rant: Another BIG problem with made-for-ham FM rx's is the lack of enough gain in the limiters to put the detector in saturation, and get the benefits of FM noise rejection. I just can't say enough about a Micor or MastrII rx or a repeater.
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
The preamp had better amplify all things equally! If it doesn't then it is non linear and you have an intermod generator connected to your receiver. But if the preamp is driven hard enough by a strong signal(s) to drive it into compression then it becomes non linear. A condition that you want to avoid. Amplifying noise along with signal is a common result of any amplifier. If the noise is already there at the site the preamp is not going to increase the signal to noise ration no matter how much or little gain it has. Once you have site noise that is higher than the noise figure of your receiver or preamp then any more or less gain or better noise figure front end will do nothing for you as to signal to noise ratio. In other words it won't help you hear any better. Adding a preamp to a receiver reduces the intermod rejection capability of a receiver by the amount of gain added by the preamp. A 10 db gain preamp reduces original IM spec of the receiver by 10 db. This is the main reason you want to add only enough preamp gain as necessary. There are two ways to increase intermod performance in a receiver. One is to reduce the bandwidth of the receiver front end to limit or reduce the total amount of energy reaching the receiver. This was commonly done by using the helical and other type of front end filters in older radios. The other way to increase intermod performance is to have higher dynamic range front ends in the receivers. This is the case with more of the modern receivers and is why you don't see as many with the multiple front end filters that the earlier radios had. The front ends are capable of handling more energy (greater number of signals entering) without overloading. The sharper the filter ahead of the receiver or preamp the less total energy enters the receiver. Here I am talking about off channel energy, the stuff you don't want. All signals that reach the receiver add together and reduce the total energy handling capability of the receiver. 73 Gary K4FMX _ From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Barry Sent: Thursday, February 05, 2009 11:52 PM To: repeater-builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp What he is saying is , a lower gain preamp aplifies less noise in relation to the signal so the audio sounds better _ To: Repeater-Builder@yahoogroups.com From: lar...@hotmail.com Date: Fri, 6 Feb 2009 04:47:11 + Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp --- In Repeater-Builder@ mailto:Repeater-Builder@yahoogroups.com yahoogroups.com, Joe Burkleo joeburk...@... wrote: If for example the site has a higher than normal noise floor a lower gain preamp will often times amplify more of the signal and less of the extra site noise, where a higher gain preamp may amplify both the noise and signal, giving you a signal with more noise than you would like. Joe, scratchin' my head here... Would you be able to clarify the above statement for me? Laryn K8TVZ _ Get what you want at ebay. Get rid of those unwanted christmas presents! http://a.ninemsn.com.au/b.aspx?URL=http%3A%2F%2Frover%2Eebay%2Ecom%2Frover% 2F1%2F705%2D10129%2D5668%2D323%2F4%3Fid%3D10_t=763807330_r=hotmailTAGLINES _m=EXT
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Again, 20 ft. of 7/8 for 2 meters is an unnecessary expense. 20 ft. of RG-214 has only 0.5 dB of loss @ 146 MHz - quite acceptable for a first-rate system, and it won't cost you that much even if you have to buy it @ retail $$. Bob NO6B If your repeater cabinet and the antenna are only separated by 20' and you're operating on 2m, there's a very good chance you're going to have other problems... --- Jeff WN3A
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
I agree. I recently moved a 2 meter repeater to a temporary location with approx. 25 feet of coax and have problems. I had to move the repeater cabinet around until I got rid of the desense. A better site is in the planning, but we need to get rid of some snow first. 73, Joe, K1ike If your repeater cabinet and the antenna are only separated by 20' and you're operating on 2m, there's a very good chance you're going to have other problems... --- Jeff WN3A
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Most sites will NOT allow RG214 to be used outside. Use 1/2 hard line for runs less than 50-75 ft - Original Message - From: Jeff DePolo j...@broadsci.com To: Repeater-Builder@yahoogroups.com Sent: Thursday, February 5, 2009 6:31:22 AM GMT -07:00 U.S. Mountain Time (Arizona) Subject: RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp Again, 20 ft. of 7/8 for 2 meters is an unnecessary expense. 20 ft. of RG-214 has only 0.5 dB of loss @ 146 MHz - quite acceptable for a first-rate system, and it won't cost you that much even if you have to buy it @ retail $$. Bob NO6B If your repeater cabinet and the antenna are only separated by 20' and you're operating on 2m, there's a very good chance you're going to have other problems... --- Jeff WN3A
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
I was thinking the same thing. It sounds like the poster's RX has good sensitivity as it is. LMR400 and antenna too close to repeater may be causing desense, thus the indication that receive isn't working as it should. Get rid of the LMR400 first and check for desense. If it's still there, move antenna further away and check again. Chuck WB2EDV - Original Message - From: Joe k1ike_m...@snet.net To: Repeater-Builder@yahoogroups.com Sent: Thursday, February 05, 2009 9:48 AM Subject: Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp I agree. I recently moved a 2 meter repeater to a temporary location with approx. 25 feet of coax and have problems. I had to move the repeater cabinet around until I got rid of the desense. A better site is in the planning, but we need to get rid of some snow first. 73, Joe, K1ike If your repeater cabinet and the antenna are only separated by 20' and you're operating on 2m, there's a very good chance you're going to have other problems... --- Jeff WN3A
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Hi All -- Here is my take on the preamp vs no preamp situation -- and with Vertex repeaters -- First -- Preamps are not the solution to most of our troubles, in fact it has been my experience over the years that they are more trouble than they are helpful I agree with Skipp and others when it is said to get rid of the LMR-400 and replace it. For inside the box use 142b or 223, something with low loss but is manageable to use on the duplexer and interconnects. rg-214 is way over the top for most of this stuff. For antennas, don't use less than 1/2 heliax. Even '214 will get noisy if there is any flex or it is out in the weather a couple of seasons. No-Preamps, we as amateurs look a preamps as a panacia for many things, including the lack of perceived receiver sensitivity. But it is interesting to note a couple of things. One, a 0.4 uv receiver is as good as it is going to get, in most cases because of the fact your setting in a high place and the MDS combined with the power out, 50 to 75 watts, is going to be about equal with a 4 pole antenna. Not rocket science, and you can actually run that test iif your on a hill and have the proper equipment to do so. Secondly, preamps, even at 10 db gain, really only add about 3 db of signal and the rest is just moving the noise floor higher. And in some cases really create a need for more signal to open the repeaters receiver. If your having issues with the reciever, it would be my recommendation to set down and take a hard look at the equipment, duplexer, antenna, and cables. There are so many variables here in just those 4 items that it will take sometime to optimize each of them to your needs. Coax, again I agree with all of those on here that LMR, 214, 213, RG-8 etc on a repeater is just not a good idea. Use hardline - Vertex, I have nothing bad to say abobut them other than my experience with 2 UHF machines. Both of them exhibit the same characterisitcs so I will just speak in general terms. What I found was that there was/is a lot of crosstalk in the repeater box itself and even though the duplexer was well tuned we could not get the isolation down on the system as a whole. The second problem I found was that the LO runs all the time! This not good it interferes with others on the site and can cause strange mixes within the box that could desense your receiver, especially if there is a signal within the IF of the repeater, either high or low. How did we fix it? We went to a GE box, LOL! So, I guess in conclusion here, before spending your hard earned dollars, for preamps, helical resonators, and the like take good gander at the situation and try to break it down to a common denominator, with a clear picture as to what your seeing. Do all of the things necessary for good repeater operation and then look again. I'll bet you just haven't found the right place to look yet. rick NU7Z On Thu, Feb 5, 2009 at 10:18 AM, skipp025 skipp...@yahoo.com wrote: Hi Ralph, Ralph w7...@... wrote: I have never seen or used a Hamtronics preamp. I don't know anything about their specs or how truthful they are. Maybe some one out there in the great bits might have an answer. Skipp? Eric? anyone?? I'll answer up to the anyone label... Through the years Hamtronics has offered up a number of quite different RF Preamplifier kits and assembled boards. Relative to the industry they are truthful and their products are a good dollar value. Even more valuable is the experience and knowledge many people receive for constructing and setting up their kits. The RF Preamplifier you're probably talking about is not a true helical filter design. Hamtronics no longer offers the HRA series with the on board Toko (brand) helical filter. Their current products (when I last looked) were broad-band and some with modest tuned circuits, which is not really a true helical layout. After completing a recent very large vhf receiver site distribution project... I'm now not so keen on using and depending on or trusting the classic (Toko) type Helical filter assemblies in front receiver pre-amplifiers at locations with strong adjacent signals. The shining star in this most recent project was the now famous GLB pre-amplifier. Please don't confuse my description of the small Toko helical filter assemblies with the helical filters built into many receiver front end circuits/layouts. However, both the performance of your receiver can be and is often directly related to both... but you often can't easily change the receiver (as-built) front end assembly. You get what you get built into the receiver as supplied by the manufacturer. After reading your posts and all the answers... I can write is how I personally would want to know more about the Vertex radio receiver front-end layout before I started making changes. Directly dependent on the receiver front- end layout and performance... would say a lot about what you can successfully park in front of it (the
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
With that short of a run I would be more concerned with the repeater being in the near field of the antenna. -Kevin I am blessed with my location and yes, noise can be high. I'll try without the preamp first and see where I'm at, and the use of the proper antenna will help. I've spent so much alreqady that a few more buckis for 7/8 won't make a difference and will err on the side of caution with intermod. Again, 20 ft. of 7/8 for 2 meters is an unnecessary expense. 20 ft. of RG-214 has only 0.5 dB of loss @ 146 MHz - quite acceptable for a first-rate system, and it won't cost you that much even if you have to buy it @ retail $$. Bob NO6B Yahoo! Groups Links
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/5/2009 15:03, you wrote: With that short of a run I would be more concerned with the repeater being in the near field of the antenna. -Kevin I've read other similar comments. Guess I've been lucky: the last 2 meter system I set up has the antenna barely 15 ft directly above the repeater. No desense. The antenna is almost directly above the repeater so that may help. Bob NO6B
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
What he is saying is , a lower gain preamp aplifies less noise in relation to the signal so the audio sounds better To: Repeater-Builder@yahoogroups.com From: lar...@hotmail.com Date: Fri, 6 Feb 2009 04:47:11 + Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp --- In Repeater-Builder@yahoogroups.com, Joe Burkleo joeburk...@... wrote: If for example the site has a higher than normal noise floor a lower gain preamp will often times amplify more of the signal and less of the extra site noise, where a higher gain preamp may amplify both the noise and signal, giving you a signal with more noise than you would like. Joe, scratchin' my head here... Would you be able to clarify the above statement for me? Laryn K8TVZ _ Get rid of those unwanted christmas presents! Get what you want at ebay. http://a.ninemsn.com.au/b.aspx?URL=http%3A%2F%2Frover%2Eebay%2Ecom%2Frover%2F1%2F705%2D10129%2D5668%2D323%2F4%3Fid%3D10_t=763807330_r=hotmailTAGLINES_m=EXT
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Here is a true Hamtronics Helical Resonator preamp for 220 MHZ and 440 MHZ http://www.hamtronics.com/pdf/Manuals/HRA.pdf. 73 W4CSO - Original Message - From: Barry To: repeater-builder@yahoogroups.com Sent: Thursday, February 05, 2009 11:52 PM Subject: RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp What he is saying is , a lower gain preamp aplifies less noise in relation to the signal so the audio sounds better -- To: Repeater-Builder@yahoogroups.com From: lar...@hotmail.com Date: Fri, 6 Feb 2009 04:47:11 + Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp --- In Repeater-Builder@yahoogroups.com, Joe Burkleo joeburk...@... wrote: If for example the site has a higher than normal noise floor a lower gain preamp will often times amplify more of the signal and less of the extra site noise, where a higher gain preamp may amplify both the noise and signal, giving you a signal with more noise than you would like. Joe, scratchin' my head here... Would you be able to clarify the above statement for me? Laryn K8TVZ -- Get what you want at ebay. Get rid of those unwanted christmas presents!
RE: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
I expect wiki will answer it better than I but the amps are not linear so do not increase signals at a flat rate . To: Repeater-Builder@yahoogroups.com From: lar...@hotmail.com Date: Fri, 6 Feb 2009 05:16:17 + Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp --- In Repeater-Builder@yahoogroups.com, Barry ate...@... wrote: What he is saying is , a lower gain preamp aplifies less noise in relation to the signal so the audio sounds better Not trying to be superpicky here, but this is something I need to understand better... Why, and how, would the lower-gain preamp amplify less noise than signal? Would the preamp not amplify anything presented to it's input that is within it's operating parameters an equal amount? Laryn K8TVZ _ Get rid of those unwanted christmas presents! Get what you want at ebay. http://a.ninemsn.com.au/b.aspx?URL=http%3A%2F%2Frover%2Eebay%2Ecom%2Frover%2F1%2F705%2D10129%2D5668%2D323%2F4%3Fid%3D10_t=763807330_r=hotmailTAGLINES_m=EXT
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Hi Bob All duplexers have very poor out of band attenuation. The extra cavity is to narrow the bandwidth. Cavity should have 2-3db of insertion loss (equates to sharp slopes). Preamp gain is adjusted by use of a step attenuator. Determine how much attn is needed to just raise the limiter by about 10% max. This way you make up for loss of system plus about 10%. Too much gain will just lead to overload of the front end of the RX. Ralph - Original Message - From: Bob Ricci b...@af6d.com To: Repeater-Builder@yahoogroups.com Sent: Wednesday, February 4, 2009 3:25:14 PM GMT -07:00 U.S. Mountain Time (Arizona) Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp The WA-COM 642 duplexer are Bp/Br cavities. The bandwidth is already limited. Are you saying a 7th cavity adding further loss? And why limit the gain? I remain teachable. Those that don't know, ask... --- In Repeater-Builder@yahoogroups.com , Ralph S. Turk w7...@... wrote: You would still need a pass cavity in front of the Preamp. Unless the Helical is similar to the old Motorola vintage L, H or M receivers the cavity is still needed to limit the bandwidth going to the preamp. You might also need an attenuator after the preamp to limit the gain. Ralph - Original Message - From: Bob Ricci b...@... To: Repeater-Builder@ yahoogroups .com Sent: Wednesday, February 4, 2009 2:08:14 PM GMT -07:00 U.S. Mountain Time (Arizona) Subject: [Repeater-Builder] Hamtronics Helical Resonator Preamp or Advanced Research Preamp Hamtronics has a preamp with a helical resonator with a 18dB preamp. I am at a high elevation with noise all around me. Advanced R3esearch has a 24dB preamp with a low NF and 1dB compression point. Either would be behind a WACOM 642 6 cavity duplxer . Which would be the better approach? The ultimate goal is to improve reception of handhelds in a mountainous region. __ ._,_. __ _ Messages in this topic ( 1 ) Reply (via web post) | Start a new topic Messages | Files | Photos | Links | Members Yahoo! Groups Change settings via the Web (Yahoo! ID required) Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe Recent Activity • 15 New Members • 1 New Links • 1 New Files Visit Your Group Sell Online Start selling with our award-winning e-commerce tools. Group Charity Be the Change A citizen movement to change the world Special K Group on Yahoo! Groups Join the challenge and lose weight. . __ ,_._, __ _
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
I have never seen or used a Hamtronics preamp. I don't know anything about their specs or how truthfull they are. Maybe some one out there in the great bits might have an answer. Skip? Eric? anyone?? - Original Message - From: Bob Ricci b...@af6d.com To: Repeater-Builder@yahoogroups.com Sent: Wednesday, February 4, 2009 7:21:37 PM GMT -07:00 U.S. Mountain Time (Arizona) Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp I do have another bandpass cavity that has 55dB attenuation. Rather than use the 24dB preamp I can always use the one with less gain because I too was concerned with overloading the front-end. The Hamtronics is a preselector helical resonator preamp, so doesn't it already do what the extra cavity does by way of the helical resonator? I'm not stuck on Hamtronics. I just want the best solution. --- In Repeater-Builder@yahoogroups.com , Ralph S. Turk w7...@... wrote: Hi Bob All duplexers have very poor out of band attenuation. The extra cavity is to narrow the bandwidth. Cavity should have 2-3db of insertion loss (equates to sharp slopes). Preamp gain is adjusted by use of a step attenuator. Determine how much attn is needed to just raise the limiter by about 10% max. This way you make up for loss of system plus about 10%. Too much gain will just lead to overload of the front end of the RX. Ralph - Original Message - From: Bob Ricci b...@... To: Repeater-Builder@yahoogroups.com Sent: Wednesday, February 4, 2009 3:25:14 PM GMT -07:00 U.S. Mountain Time (Arizona) Subject: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp The WA-COM 642 duplexer are Bp/Br cavities. The bandwidth is already limited. Are you saying a 7th cavity adding further loss? And why limit the gain? I remain teachable. Those that don't know, ask... --- In Repeater-Builder@yahoogroups.com , Ralph S. Turk w7hsg@ wrote: You would still need a pass cavity in front of the Preamp. Unless the Helical is similar to the old Motorola vintage L, H or M receivers the cavity is still needed to limit the bandwidth going to the preamp. You might also need an attenuator after the preamp to limit the gain. Ralph - Original Message - From: Bob Ricci bob@ To: Repeater-Builder@ yahoogroups .com Sent: Wednesday, February 4, 2009 2:08:14 PM GMT -07:00 U.S. Mountain Time (Arizona) Subject: [Repeater-Builder] Hamtronics Helical Resonator Preamp or Advanced Research Preamp Hamtronics has a preamp with a helical resonator with a 18dB preamp. I am at a high elevation with noise all around me. Advanced R3esearch has a 24dB preamp with a low NF and 1dB compression point. Either would be behind a WACOM 642 6 cavity duplxer . Which would be the better approach? The ultimate goal is to improve reception of handhelds in a mountainous region. __ ._,_. __ _ Messages in this topic ( 1 ) Reply (via web post) | Start a new topic Messages | Files | Photos | Links | Members Yahoo! Groups Change settings via the Web (Yahoo! ID required) Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe Recent Activity • 15 New Members • 1 New Links • 1 New Files Visit Your Group Sell Online Start selling with our award-winning e-commerce tools. Group Charity Be the Change A citizen movement to change the world Special K Group on Yahoo! Groups Join the challenge and lose weight. . __ ,_._, __ _
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 14:25, you wrote: The WA-COM 642 duplexer are Bp/Br cavities. The bandwidth is already limited. Only in-band. Out of band they pass almost everything. Bob NO6B
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
--- On Wed, 2/4/09, Ralph S. Turk w7...@comcast.net wrote:
From: Ralph S. Turk w7...@comcast.net
Subject: Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or
Advanced Research Preamp
To: Repeater-Builder@yahoogroups.com
Date: Wednesday, February 4, 2009, 9:11 PM
#yiv258189647 p {margin:0;}
Hi Bob
All duplexers have very poor out of band attenuation. The extra cavity is to
narrow the bandwidth.
Cavity should have 2-3db of insertion loss (equates to sharp slopes).
Preamp gain is adjusted by use of a step attenuator. Determine how much attn
is needed to just raise
the limiter by about 10% max. This way you make up for loss of system plus
about 10%. Too much gain will
just lead to overload of the front end of the RX.
Ralph
Most do have the poor out of band rejection. Years ago I was involved with a
repeater that had a 4 cavity 2 meter Wacom duplexer . It had all kinds of
intermod. Must have been 100 transmitters within about a 10 block radius.
Shipped it to Wacom and had them add a pass cavity to each side. Worked fine
then. I think after that they offered one that way in their catalog.
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 18:21, you wrote: I do have another bandpass cavity that has 55dB attenuation. Rather than use the 24dB preamp I can always use the one with less gain because I too was concerned with overloading the front-end. The Hamtronics is a preselector helical resonator preamp, so doesn't it already do what the extra cavity does by way of the helical resonator? See my earlier post. Helical resonators are either lossy or have low Q. Can't get steep skirts in such a small filter without loss. I'm not stuck on Hamtronics. I just want the best solution. I don't recommend Hamtronics. I'm not biased, just has something to do with the observation that nothing I ever bought from them ever met their own specs. Bob NO6B
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
Bob Ricci wrote: Why then a preamp? Just to recover what I can from the LMR-400 and the cavities. LMR-400 on a repeater. Yuck. You need to study up on that stuff in duplex service. The cable length is so short that hard line isn't justified. Oh, but a preamp is justified - because you used inferior cable? Bad engineering practicesIMHO If a preamp is justified to recover loses from inferior cable, hardline is justified. Kevin Custer List Owner
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 18:11, you wrote: Hi Bob All duplexers have very poor out of band attenuation. The extra cavity is to narrow the bandwidth. Cavity should have 2-3db of insertion loss (equates to sharp slopes). A pass cavity shouldn't be quite that lossy. 0.5 to 1 dB is typical. The 10 diameter Motorola bottles have very good rejection only 0.5 dB loss. Preamp gain is adjusted by use of a step attenuator. Determine how much attn is needed to just raise the limiter by about 10% max. This way you make up for loss of system plus about 10%. Too much gain will just lead to overload of the front end of the RX. One reason I recommend the Angle Linear preamps is that the amount of gain they have (~16 dB) is the perfect amount of gain for G.E. Mastr II, Motorola Micor similar RXs. No attenuator is needed when used with these RXs. Bob NO6B
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 20:16, you wrote: My thoughts as well :) I know that the Big Bear repeater uses a Hamtronics and it does well enough but we needed far better quality and went commercial. My only thought that was as a preselector the Hamtronics might have something to offer. If we're talking about the LNP-146, I wouldn't even call that a helical resonator. Looks to me like 3 low-Q coils. Seriously, if your Vertex VHF RX needs help from a preamp, it's defective IMO. The noise floor in SoCal is fairly high in most areas that have a view of LA/San Bern./Riverside. If the 12 dB SINAD is 0.3 µV or less, you don't need a preamp here. Bob NO6B P.S: ditch the LMR400 - it will cause desense, sooner or later. If your antenna run is short enough to not need hardline, use RG-214. The silver-plated braid will keep the duplex scratchies away.
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 20:53, you wrote: Thanks, Bob. I sincerely appreicate your experience and the polite sharing of it. This is my first repeater and although I have an experienced mentor, I have things to learn. Experience is often best learned by doing and not reading. Like LMR-400 in duplex service. Some say yes; others say no. I have 20 feet to the antenna but I guess I could change it to 7/8 For 20 ft. @ 2 meters, 7/8 is a bit of overkill. RG-214 would be ideal, as the loss is minimal. If you want to go with 1/2 hardline just can't find a short chunk anywhere, I can probably part with one of my runs a pair of connectors. Bob NO6B
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 21:19, you wrote: The Vertex has a .20uV measured and the rest of the specs are just as good. You do not need a preamp. The RX might still need an extra pass cavity, but I'd go ahead try it with just the duplexer if there isn't much RF in your neighborhood. I am blessed with my location and yes, noise can be high. I'll try without the preamp first and see where I'm at, and the use of the proper antenna will help. I've spent so much alreqady that a few more buckis for 7/8 won't make a difference and will err on the side of caution with intermod. Again, 20 ft. of 7/8 for 2 meters is an unnecessary expense. 20 ft. of RG-214 has only 0.5 dB of loss @ 146 MHz - quite acceptable for a first-rate system, and it won't cost you that much even if you have to buy it @ retail $$. Bob NO6B
Re: [Repeater-Builder] Re: Hamtronics Helical Resonator Preamp or Advanced Research Preamp
At 2/4/2009 22:17, you wrote: Excellent advice, and thank you. We are experimenting with unity gain, 3dB, 6dB, and 9dB. The results have been quite interesting. Using three separate radios at the same location and manual voting we can hear that at one moment unity gain is better, while at another one of the other antennas is better. Choice of antenna will not be as easy as preamp/no preamp. As you've found, the lower gain antenna will probably do better in areas directly below you, while the GP9 will work best out at the horizon. If you really want to go for maximum performance, you may want to consider 2 antennas: a low gain antenna to duplex off of, a GP9 feeding a 2nd voted receiver. You'll need a little extra power on the TX feeding the low gain antenna to make up for the high gain of the GP9 at the fringe locations. We'll go for the best all around solution or maybe even two receivers, two antennas and voting. But there is a reason that the Forest Service uses unity gain -- it gets down into the canyons. If your primary concern is covering the mountains, the low to medium gain antennas are probably your best choice. Bob NO6B
