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Yet another antenna question....

Looking for info, or if it's even possible, to stack two antennas. I want to be able to put up an directional antenna to point south to pick up the Valley Com trunk and then I want to put up a discone so I can rec'v anything else in the area. Such as WSP or Skagit. Then have them both connect to my one coax line that runs in to my house. And no, I will not be transmitting.

Any info or direction would be much appreciated.

Yes, you can do it. Maybe it will do what you want.

To put two antennas (or two radios) on the same end of a coax, it would be best to a multicoupler. The resulting signal strength won't be the simple sum of the two inputs no matter what you do, but the coupler should help. An alternative would be to add a remote controlled switch so you pick the antenna from downstairs.

Putting two antennas near each other will result in altering the performance of each. More spacing would minimize that effect.

Flash

Truthfully the connectors and any match errors would probably negate any gain you got out of this arrangement.

Your best bet is to use high quality heliax if its any distance to your receiver and use the fewest connectors possible. This becomes more an issue with higher frequencies your trying to monitor.

A high gain omni antenna would do you good here also... More capture area...

Part of the job the directional antenna does is attenuate interference from the back side (on and off channel). Adding the second antenna would allow this "noise" in, but only if it was an issue.


:mrgreen:

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

I am already running LMR-400 cable. High quality stuff.

I did a quick search for a multicoupler, but did not turn up anything that looked right. Can you provide me with a link to what you had in mind? I assume this will have either PL259 or N type of connectors?

Thank you.....

What frequencies and how far is the run?

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Would this work?
Wideband Antenna Spliter/Combiner Diamond SS-500
http://www.wimo.de/cgi-bin/verteiler.pl ... nas_e.html

A couple things:

As a few have suggested, you are dealing with both gains and losses. Antennas can create gain in specific directions. Connectors, feedlines, couplers and distance of path introduce losses.

Basically it is a math game. And not necessarily an exact math game, either, depending on how you go about it.

The directional (beam / yagi) type of antenna is going to give you considerable gain, depending on specific antenna used. Anywhere from 6-9db for a small beam, up to 15-20 db for a longer beam (more elements).

As for conector loss, others who do this every day will know better the amount of loss to expect per connector. I usually use .5db per connector for rough math. The bottom line is to keep the number of connections to a minimum, and be sure you make them up properly if you install the connectors.

Cable loss is pretty easy to find, you should find listings for the LMR-400. Keep in mind cable loss per foot in db VARIES depending upon the frequency in use (150 MHz lower loss per ft vs. 800 MHz higher loss per ft).

Last, locate your coupler. It too will have a loss factor listed, and may vary over frequency as with feedline, but perhaps less loss over a broader frequency range.

From here it is addition and subtraction. Take the gain of your beam, subtract the loss of each component along the way, and you will have a theoretical total gain factor of your antenna system.

Something I am not sure of, but others can answer:
When combining 2 antennas through a splitter/combiner, does the signal from ONE antenna get split in half after passing through the combiner?

I know when dealing with high spec multi-couplers, the % split can be specified, such as 50% / 50%, as opposed to 25% / 75%.

73,
Nick
N7QOR

I have about a 50 foot run of LMR-400 connected to a tuned 860 antenna on top of the house. I want to use the directional antenna because I am sure I can pick up the Valley Com better using this method.

Basically I'm looking for the piece of hardware that will allow me to connect both antennas to the one LMR-400 cable running in to my house.

That the only piece I'm missing to try this out.

Your coax is good for just under 2dB of loss per 100ft at 860. Thats a lot. A multicoupler is minimum .5dB loss. With the connectors your gonna see 3dB of loss at a minimum, or half your signal. This kinda math is where allot of paid radio techs fail...

Ive got an 800 yagi that if memory serves is somewhere between 14 and 20 dB of gain. (Its almost three ft long if I remember right.) You'd be totally welcome to it. I live in Bremerton. You would be better off with an antenna that is tall with allot of capture area. (Read diversity) Yagis are real susceptible to aiming issues. This comes into play when the signal paths change in non line of site situations.

The easiest thing for you to do would be to build a phasing harness. Make it out of 75 ohm cable to get the correct match. Exactly equal lengths (but do some research as Ive never made one just read about them). Problem here is you end up using adapters due to the limited kinds of 75 ohm connectors. That adds up to more loss.

There are power dividers available. Spendy!

That link you provided seems to be for HF.

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

I read your writeup last night Nick while I was half asleep...

I just reread and saw what I missed last night... :mrgreen:

Good writeup! Ive basically re-iterated some of what you posted...


Heres a coax link I bet has been posted here before but I dont see it anywhere now... http://www.ocarc.ca/coax.htm

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Forgot to add...

If your in a simulcast overlap area and seeing issues with that then the yagi is the way to go...

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

chpalmer, thanks for the reply. And thanks for the offer on the antenna.

Right now, with my existing setup I pick up the Valley Com trunk okay. So I can only assume that tossing up a yagi will help the situation.

As far as my comment about only needing the hardware, I need to be pointed as to where I can get a piece of hardware that will allow me to connect both pieces of coax from the antennas to the one piece of LMR-400 that comes in to my house. Or a link to where I can buy a phasing harness. Building something like this would be out of my league.

I did find this, which seems to be on the right track.

http://www.scannerworld.com/content/pro ... del/SW8DPL

Or how about this piece of hardware...?

http://www.westcoastmall.net/ppp12-coph ... -1012.html

Those look like the harnesses that are used on dual cb antenna installs...

Ill look in a couple of supplier books today..

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

chpalmer. Sent u a PM.