Signal loss/ jumper cable

[jody_clarke]

Greetings everyone and thanks for checking out this thread as I need a bit of expert advice as I'm nearing the end of setting up my little Rx'ng antenna system. Here's a bit of background info- Thus far I've purchased a Diamond D-130NJ discone along w/ 85 foot of LMR-400 coax. Before I ask the two questions I have for you guys(the latter question being somewhat absurd) let me give you a quick run down of my geographic situation as well as what I'm trying to pull in- I live in a very (we call them mountains down here- although they are actually very large hills as I've traveled enough to know what true mountains look like) so very hilly terrain, and happen to live at the very base of one of these very large hills in a very steep valley with a very large hill directly blocking the South- South Eastern view as we are surrounded by trees & lots of them.What I'm attempting to monitor is approx. 20 miles l.o.s.-if I had a clear l.o.s. to the majority of transmitters(mostly Public Safety 155MHZ some VHF-low Electric-coop,, as well as some 440MHz.)
First question- Now that I've finally got my antenna and coax I'm starting to doubt my decision about using a jumper cable- if you read my geographical information you can understand signal loss concerns of ANY. The coax is an 85 foot run of LMR-400 with an N-male connector to antenna to a male N connector. The jumper cable I'm referring to is made up of 6 feet of 9913 with a N-female and a BNC to radio. The only reason I went with a jumper cable to begin with was this cable run is for a handheld. Although in the past I've ran RG/8 to a handheld and simply laid it on it's side- no biggie. Guess what I'm getting at (not that it matters but connectors are at least heat shrunk) is even with my using the stretchy splicing tape along with quality 3M 33+ electric tape to wrap and fully( to the best of my ability) insulate the connectors could anyone give me any idea as to how much signal loss I'm looking at using this jumper cable, as mentioned I could get an LMR-400 BNC connector and have someone put it on the LMR-400 directly. Realize no one can tell me exactly how much loss I'm going to incur but any ideas .5db's, 1db, possibly more?? Any estimates, guesstimates, or suggestions on this would be greatly appreciated!!! One other quick question related to signal loss is the Times Microwave LMR-400 grounding kit were you have to strip 2 inches of the coax jacket, attach grounding kit and tape back up correctly, If done correctly how much signal loss can I expect from this?, while I realize all these things may be minimal in and of there-selves seems to me that eventually that they're bound to add up -.5 here, -.25, her, -.75 there, -1.2 db's for coax run-before I know it
there goes half my signal? Is the grounding kit necessary, I've read how important it is to ground your antenna/mast-but coax? Maybe I simply don't know- not to take away from my previous question-Thanks, for anyone's input!!

Secondly, I know the deal the higher you can get your antenna the better- yet there's always the trade off w/ length of coax. Have a fairly good idea about this but figured I'd ask to ensure I was correct? Considering my geographical location wanted to ensure this remains the same, although I somehow doubt the fact that I live in a deep valley anything would change my guess given the area I live in the more height the better regardless of how deep of a valley I'm in but wanted to double check w/ the experts, as I'm always tend to over think such simple matters and realize my living in a hole doesn't change the laws of physics. Guess my question would be (considering my geographical location) is getting my antenna about 10 feet above apex of roof (40 feet from ground)- saving about 20 foot of coax from my originally planned 85 foot run & placing antenna up to 20 feet above roof apex- 60 ft. from ground a better option or would I be correct in my assumption that regardless of how deep of a hole I'm in the higher the better particularly in my situation? As mentioned I tend to over think these things and I've yet to purchase my mast/pole So please don't blast me for asking what to most will sound and most likely is a ridiculous question-Thanks for your patience!

Just Curious:For some reason w/ a mobile mag mount on peak of metal roof I'm able to receive NOAA WX radio out of Birmingham-due South blocked by huge hill directly across a (creek/ finger off of very large lake)-approx. 30 yards South of house) and approx. 45 miles l.o.s. stronger than I can receive NOAA WX radio out of Huntsville @ approx. same distance due North both broadcasting @ 1000 watts? -Realize this could incorporate many factors mostly geography, simply curious if anyone might have any specific ideas.

 

[WA1ATA]

The spec for Belden 9913 coax is 1.4dB/100' at 100MHz, 1.8dB/100' at 200MHz, 2.6 @ 400MHz, 3.6 @ 700MHz. So the loss in 6' of cable will be around 0.1dB at 160MHz and about 0.2dB at 460MHz.

Connector losses are less than 0.1dB each when properly installed. More specifically, the N connector is 0.15dB at 10GHz, so at 460MHz it should be less than 1/4th that or under 0.04dB. The BNC connector (which you have to have one way or another) is a bit higher, about 0.1dB at 1GHz or about 0.07dB at 460MHz.

So the two extra N-connectors are about 0.08dB + 0.2dB for the 6' cable means about 0.3dB loss at 460MHz in the jumper cable vs. terminating the LMR400 in a BNC connector.

For 160MHz, it will be about 2x 0.19 + 0.1 = 0.14dB loss in the jumper cable at 160MHz.

To put these estimated losses into perspective, 0.3dB at 460MHz is the loss from 11' of LMR400. At 160MHz, the 0.14dB loss is about the same as a 9' run of LMR400. In other words, the 6' jumper has about the same loss as 10' of LMR400.

 

[WA1ATA]

is getting my antenna about 10 feet above apex of roof (40 feet from ground)- saving about 20 foot of coax from my originally planned 85 foot run & placing antenna up to 20 feet above roof apex- 60 ft. from ground a better option or would I be correct in my assumption that regardless of how deep of a hole I'm in the higher the better particularly in my situation?

My guess is that once you are high enough to get a clear line of site to the ridge line / mountaintop or whatever else is the highest thing in the line of sight between you and the transmitter, then additional height doesn't do much for you.

Generally, 160MHz will diffract more than will 460MHz or 800MHz. So your reception of the Birmingham NOAA wx station may be the combination of a good line of sight from the ridgeline to the transmitter, coupled with the ridgetop bending/diffracting a bit of the signal down into your valley.

What's between you and the Huntsville transmitter? Is it on a high enough hill to have line of sight to your area?

 

[jody_clarke]

What's between you and the Huntsville transmitter? Is it on a high enough hill to have line of sight to your area?

It's hard to say, the terrain surrounding my house is quite unique- but everything you've suggested makes a lot of sense, and thanks for the signal loss guidelines- I can live with those numbers! Still am not 100% sure to go with the full 85' coax run, yet I figure since I already have descent coax w/ quality N type connectors on them might as well use it.
Thanks, for the information J.C.

 

[LtDoc]

All things considered, the amount of loss with that 9913, the connectors, etc, is negligible. If you can get an 'extra' 20 feet or so of height, I think it would be worth doing. Also considering the short lengths typically used for 'jumpers', even RG-58 wouldn't be terrible.
- 'Doc

 

[WA1ATA]

Also considering the short lengths typically used for 'jumpers', even RG-58 wouldn't be terrible.
- 'Doc

At some point it does start catching up with you though. I use an 18" sma to bnc adaptor from Universal Radio. Comet HS05 Comet HS10 Amateur HT Antenna Adapter

That jumper uses the very thin RG-174 that has a loss of 18dB/100' at 460MHz, so even a tiny 18" jumper has about about 0.3dB loss; and at 860MHz is has 25dB/100' loss, so 18" is almost 0.4dB.

 

[Fast1eddie]

All excellent points to consider, but will your ears be able to tell the difference??? Think the signal magnitude has to be logarithmic for us to understand....but anyway, I say go for the height and seriously consider your cable run. The shorter the run will help to minimize your signal loss, the jumper is cool.

Similar setup here, Icom discone into a very short run with a 3ft jumper. It works.

 

[WA1ATA]

.... but will your ears be able to tell the difference??? Think the signal magnitude has to be logarithmic for us to understand....

Similar setup here, Icom discone into a very short run with a 3ft jumper. It works.

RF losses cause noise, not a change in audio level. On a practical basis, only a small percentage of signals fall into the zone between "very strong" and "undetectable" where a change of a couple of dB in the RF signal level will make a noticeable change in the quality of reception.

Most signals have many dB of excess signal strength, so cable losses, less than optimum antennas and even inserting a 10dB attenuator doesn't have much effect.

For a typical FM receiver, there is only 6 or 10dB difference between undetectable and nearly full quieting. In fact, it may take only 2 dB increase in RF signal level to go from a noisy 12dB SINAD reception to a good, clean strong reception with 25+dB SINAD (nearly noise free).

If your antenna and the transmitting antenna are both stationary, only a very few signals are likely to fall in that range where a couple of dB make a difference. If either of you are moving, then getting some excess gain in the system helps as the signal fades in and out as the antennas move.

For most repeater systems, they will have more than enough power to have a strong signal all the way out to the radio horizon. Small low power handheld transceivers are the ones that will challenge an antenna/scanner system, but luckily, in most cases we have the option of monitoring a much more powerful repeater transmitter.