Hi Eric and the Group -- Thanks for your comments and yes, Rg-400u is a good substitute as well. I completely forgot about that one -- old age I guess LOL!
73 - Rick NU7Z On Thu, Feb 5, 2009 at 11:05 AM, Eric Lemmon <wb6...@verizon.net> wrote: > Rick, > > You made some very good points. I can offer two comments: For hookups > within the repeater cabinet, use RG-400/U coax instead of RG-142/U. RG-400 > has a stranded center conductor, while RG-142 has a solid steel center > conductor that breaks easily when repeatedly flexed. > > Regarding the Vertex UHF repeaters, I corrected an in-cabinet desense > problem by replacing all three internal jumpers- which were unmarked > gray-jacketed single-shield cables- with double-shielded RG-400 cable. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: Repeater-Builder@yahoogroups.com<Repeater-Builder%40yahoogroups.com> > [mailto:Repeater-Builder@yahoogroups.com<Repeater-Builder%40yahoogroups.com>] > On Behalf Of Rick Beatty > Sent: Thursday, February 05, 2009 10:46 AM > To: Repeater-Builder@yahoogroups.com <Repeater-Builder%40yahoogroups.com> > Subject: 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 panacea 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 you're 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 you're 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 repeater's receiver. If you're > having issues with the receiver, it would be my recommendation to sit 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 some > time > 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 about them other than my experience with > 2 > UHF machines. Both of them exhibit the same characteristics 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 you're 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<skipp025%40yahoo.com> > <mailto:skipp...@yahoo.com <skipp025%40yahoo.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 receiver). > > My personal suggestion is that you replace the LMR-400 > coax with almost anything else... with relatively short > VHF lengths RG-214 mil spec is probably a great choice > if you don't have access to free-bee (gratis) hard line. > > As previously reported many times... I source a lot of > repeater problems back to LMR-400 cable so I jerk it out > of all our duplex (repeater)operations. The Internet Wifi > guys like and swear by it a lot (because of the lower cost) > but their operations are mostly half duplex (simplex). > Half duplex radio operations don't appear to suffer the > LMR-400 type grunge problem nearly as much as the many > repeater (full-duplex) gremlins we've had to resolve. But > I have seen a fair number of Wifi problems related to > using LMR-400 but a lot of that sort of blame gets put > off on the path being bad or co-channel interference. > > It's very smart of you to pay attention to the antenna > beam-width related to both your elevation and location of > the majority users. > > A smaller part about how much Transmit Power you use is > modestly inter-related to your hardware and how hot you > want the receiver side of things. Less TX Power Out is > easier to deal with... but I do like a very solid TX > signal on/at the user end. > > There are a gazillion pre-amp and filter options possible... > for me it comes full circle back to the receiver performance > and how it's laid out (constructed). > > Commercial mobile two-way radios can be decent repeater > receivers and some can be "not so good". > > cheers, > skipp > > >
