> [EMAIL PROTECTED] wrote: > I disagree. If your TX can't handle the near pure reactance > of the duplexer at the reject frequency, the proper remedy > is an isolator. Now there's some low Q. If the RX can't > handle it, replace the preamp with one that is unconditionally > stable.
You appear to assume all problems are directly related to or generated by/in the Tx or Rx radio equipment hardware. Not always the case... > The one place a pad (or lossy coax) can go without affecting > system performance is between the preamp & RX, My turn... "I disagree" but you want to label standard coax as excessively lossy when in fact my point is to use a lower Q cable where the loss is an acceptable and reasonable amount. > but even then the solution affording the greatest dynamic > range is the one where the preamp has only enough gain so > as to make the noise contribution from the RX insignificant. > The GaAsFET preamps I use have 16 dB of gain, just enough > to satisfy the above criteria on stock GE UHF RXs without > sacrificing dynamic range. Kind of off topic but whatever floats the boat further down the river... > > I'd trade away a pesky grunge - gremlin or glitch problem > > for less than a dB additional loss most any day of the week. > > One could achieve the same result by turning up the noise > squelch threshold. You appear to be totally missing the main point. > Whether you hide the real source of the problem by doing > this or throwing a pad in front of the RX or TX, you are > avoiding the actual source of the problem. What if the source of a grunge problem was directly related to or supported by unwanted energy in a high Q network/cable path that otherwise might not even be there when using slightly lower Q cable like RG-214? especially when the problem/unwanted energy comes from external sources... One transmit combiner system we heard about on the group here a while back had a serious grunge problem without some of the other-leg repeater hardware even being connected. I suspected the fault was actually unwanted contributions or mix products made or supported by the (relatively) higher-Q transmission hardware within the combiner... > Granted, depending on the level of system performance needed > vs. quality of equipment involved it may not be worth > the effort to properly remedy the interference. My point > is that if one is trying to fully maximize system performance > (maximum power output, maximum possible effective sensitivity), > padding the TX or RX is not the answer to an interference > problem. ... what you're now talking about above is slightly off the original topic. If you have a pesky grunge problem... the proper use of lower Q coax versus say... hard-line and some higher-end coaxial lines MIGHT HELP suppress unwanted energy within a system, which could make the difference of a potential undesired mix even happening. If by using lower Q hardware you don't have a question of interference then wouldn't have to come up with an answer to... > The short lengths involved do not introduce significant > loss, We're talking about different cable and related hardware Q for the same-length of two different types of cable. > & I believe RG-400 is lossier (hence "lower Q") than > RG-214. Perhaps you meant to say hardline, superflex or > some other lower loss cable. The manufactures data sheet tells the spec. > Of course, those cables are more expensive & would drive > the unit cost up as well. When a customer or radio club is fighting a real pain in the pazzoo grunge problem they sometimes have to reach deeper into their wallet. If you've quoted a radio system with an included un-contained grunge dragon that person might possibly be you. > However, I believe there are several on this list that > have in fact replaced their duplexer & interconnect cables > with Superflex. Nothing wrong with using higher quality materials when you can. Most well designed antenna combiner systems and duplexer assemblies don't incorporate a grunge problem by design or desire. When one is unlucky enough to have a grunge problem the fix can include any number of unconventional methods not mentioned in the initial system design. > >You've never had a gremlin or grunge problem at a low-level site? > > None that had to be solved by adding attenuation on the RX or TX. > Bob NO6B Never even changed out a problematic run of LMR-400 yet? Then... Got Milk? :-) s.
