`Passive' Repeater?

[Halfpint]

OK... {WAN GRIN!} I wonder if anyone here has ever played with a `passive repeater'? *Many* years ago I set up such a thing for use on CB using a 5 element beam on the receive side and a `Supper Maggie' on the output side to enable us to talk into Casper, Wyoming from Alcova Lake. We mounted the antennas on a pair of towers about 5/8 wavelength apart and connected them together with exactly 1 wavelength of RG-8 coax suspended from a `runner' of fairly heavy-duty `wire rope' approximately every couple feet. While we were not originally able to get into Casper before after setting up the `lashup' we were able to get into just about all of Casper with a `readable' signal. The `problem' I now have is that I have forgotten just *how* it was that we had figured out just how it was we selected the antennas and the length of coax.

The reason I am trying to `revisit' this is that I have a Davis Vantage Pro2+ wireless weather station setup that I am having some reception problems with. It really is not totally a matter of not actually having enough signal strength already but, instead is a matter of `interference' that I have been experiencing. (Mainly it is people walking between the Instrument Sensor Suite, a couple temperature only stations, and the console though I do also have a few slight problems with our 900MHz DSS cordless phone now and then.) The weather station operates between 902MHz and 928MHz FHSS w/ around 8mw output. What I would like to be able to do is be able to put an antenna up outside our house that would be high enough to not have the signal path `walk through-able' *and* maybe also far enough away from the cordless phone to reduce it's effect on my reception. (If I could just get the outside antenna up just over roof level the metal roof would probably almost totally eliminate the interference from the phone as I suspect that the main interference from the phone is from the base not the handset.) Now there is another `kicker' in this... The `extra' temperature only stations are not on the same `line' from the console as the ISS. One is almost 180° behind the ISS and the other is close to 90° off to the side. The 180° degree one really isn't that much of a problem as it is actually inside our house and is approximately 20' or so away. The 90° one, OTOH, *is* a problem. That one is mounted just outside our pumphouse and is used to monitor the temp inside the pumphouse. We have it set to sound an alarm if something occurs and the temp drops low enough that we could have a problem and we have to get out to it and either start up a genset or hook up a backup propane tank to hopefully correct the problem. (Thankfully we have only have had to do either just a couple times. Last December and January was the last time when we had those 2 big snowstorms with their long series of below 0°F days. Our propane dealer was scheduled to come out about a half a week *after* the first wave came through and we ended up going through a 3/4 full 250# tank and had to hook up a backup 100# tank to get us through until he could finally get in to fill the main tank. We have since replaced the 250# with a 500# and the 250# is now our backup.) Hopefully I can use some sort of omni antenna (array) w/gain outside and a simple antenna inside? I am also wondering if I can use more than just one wavelength (Some multiple of 1 wavelength?) of coax between the two antennas?

 

[zz0468]

I design microwave systems, (not the part 15 crap, the real thing), and have incorporated passive repeaters in several system designs. So, yeah, I guess I could say I've played with them.

The length of feedline between the antennas is non-critical, in terms of wavelength. It IS critical in terms of wanting something low loss. So forget about the "1 wavelength" part of the equation. Assuming both antennas in the passive are matched to the coax, your vswr is low, and therefore the length is non-critical.

If the cordless phone is a problem, I would replace it with a 2.4 or 5.8 GHz unit. Eliminate THAT source of interference altogether. If I'm reading this right, you have one sensor 20' away, and the other further? You could get a yagi or corner reflector and aim it at the far one, and take your chances on the near one. In an application like this, I see no reason why you couldn't put two passives in, for each sensor that needs it.

 

[Halfpint]

I design microwave systems, (not the part 15 crap, the real thing), and have incorporated passive repeaters in several system designs. So, yeah, I guess I could say I've played with them.

OK!

The length of feedline between the antennas is non-critical, in terms of wavelength. It IS critical in terms of wanting something low loss. So forget about the "1 wavelength" part of the equation. Assuming both antennas in the passive are matched to the coax, your vswr is low, and therefore the length is non-critical.

I had always wondered about the coax length but just figured that it wasn't all that `bad' of an idea, at least in that particular `band'. I am considering using LMR-400 or similar for the coax but haven't yet decided upon antennnas.

If the cordless phone is a problem, I would replace it with a 2.4 or 5.8 GHz unit. Eliminate THAT source of interference altogether. If I'm reading this right, you have one sensor 20' away, and the other further? You could get a yagi or corner reflector and aim it at the far one, and take your chances on the near one. In an application like this, I see no reason why you couldn't put two passives in, for each sensor that needs it.

The phone is somewhat of a `non-starter' as I have tried *several* other brands/models and none of them have been able to cut it range-wise or features-wise. Plus the 2.4GHz models all interfered with our wireless security cameras, which also have problems with our microwave oven but that isn't as bad since we use that fairly little compared to talking on the phone. (We have a couple teenagers who seem to constantly are yakking. [And... Nope! We are *not* getting either one cellphones because they would just end up spending even *more* time yakking and less time doing homework or chores. Yeah... I *am* a tad bit of a `tyrant' about that. {WAN GRIN!} But, even though both SWMBO and I have the danged things *we* limit ourselves, too.]) The 5.8GHz ones are out because, despite all the claims to the negative, they caused interference to our wireless computer network. The old 900MHz phone doesn't cause nearly as much of a problem as what we experience from `walk-throughs'. On top of that I can go out to the furthest corner of our property, approximately .5 mile, and am still able to make and receive calls along with talking to the other handset, approximately another .25 mile away, clearly. None of the other phones were able to do so. (This is handset to handset not handset to base to handset.) Typically I see a drop to around 85% signal-wise from the phone on the two sensors that are outside the house and none with the sensor that is inside. With the `walk-throughs', however, I regularly experience 95% - 100% signal losses depending upon who walks through what sensor's `line of sight' to the console. (And, in the case of the one out at the well, because of the signal path and one of the paths between buildings the loss can be significant enough to cause enough data loss to trigger an unwarranted alarm. [If the system loses enough `packets' during an archive interval it starts screaming for help thinking it may have lost the whole sensor.] )

It took me quite a while to figure out that if someone managed to get themselves placed just right between a sensor and the console it would cause the dropouts I was having problems with. (In the case of SWMBO it took a*lot* longer as I really didn't want to believe that all she had to do was be either getting out or putting something into the 'fridge or fixing something on/in the stove! {GRIMACE!} I finally had to accept it after actually taking the time to keep track of the dropouts and just what she was doing, where she was while doing it, and the actual times. After that it was easier to also see where the rest of us were also causing dropouts. Unfortunately the two `worst offenders' have turned out to be SWMBO and our hired hand for some reason.) My reasoning about using the `passive repeater' is the hope that *if* I can get the external antenna up high enough to make the path between it and the sensors over everyone's heads I will be able to cut the majority of the dropouts. I realize that I will probably still have some from other sources but I hope to eliminate the `people' ones. The inside antenna will be fairly close to, if not possibly right next to, the console antenna which should then, hopefully, cut down on the phone interference. (*When* we are *finally* able to get moved and setup on a newer place I expect that a lot of what I have discovered here will make it a lot easier to set up things and we won't have all these assorted `hacks' we are currently having to do. When one is dealing with houses and buildings that the newest of which are over 50 years old and the oldest are rapidly approaching 100 years old it is a `cross one has to bear'. Especially if one is a farmer that is land rich and cash poor and dealing with a county `gummit' that favours `development' over `agriculture'. {FROWN!})

Oh, well... Just an `Olde Fart's' 2¢ worth. Thanks for the information and pardon my `rants'. {WAN GRIN!}