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Scanner / Receiver Antennas - For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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Old 03-17-2016, 9:10 AM
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Default Is dual 800 Mhz Yagi possible?

Unlike some who want to mix a discone and a yagi, I want to be able to use two identical 800Mhz Wilson Yagi's to hit two different towers in my area. Currently I have two sites near me, one for the south end of my county and one for the north end. The discone does great on the south end but it's hit or miss on the north. Currently I have a 800 yagi pointed to the North site and it works great. For now I have to use two scanners and two separate antennas. I would like to only have the one scanner with dual 800 and this will free up the other scanner for discone use.
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Old 03-17-2016, 9:34 AM
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Hey new Modem or Router have an Dual Antenne Port. Maybe you search in the Manual for more information.
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Old 03-17-2016, 9:40 AM
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Thanks but that doesn't really answer my question. I know what you are referring to with routers but I'm talking about two antennas on the same band range for scanner use.
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Old 03-17-2016, 9:43 AM
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You can connect them to a splitter/combiner, but you could get some nullification, based on the phases of arriving signals.

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Old 03-17-2016, 10:01 AM
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You can combine them with either a T adapter and equal, critical lengths of 75 ohm coax, or with a good quality splitter and equal lengths of 50 ohm cable. When you do this and both Yagi's are pointed in the same direction and at a proper spacing, you can get up to 3dB of gain.

When pointed opposite directions you will get at least 3dB loss on top of whatever each antenna is rated for in gain but most 800 Yagi's have at least 10dBD gain so you will probably be ahead. There should not be much phase degradation from signals arriving at both antennas due to the side and rear rejection properties of the Yagi's.

Or better yet find a 4 bay or 8 bay exposed dipole array and set for an elliptical pattern.
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Old 03-17-2016, 10:11 AM
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Quote:
Originally Posted by Your_account View Post
Hey new Modem or Router have an Dual Antenne Port. Maybe you search in the Manual for more information.
Those are usually dual diversity receive. Different beast than what he's looking for, but good observation.
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Old 03-17-2016, 10:39 AM
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Thanks for all the great info.
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Old 03-17-2016, 4:28 PM
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Quote:
Originally Posted by prcguy View Post
You can combine them with either a T adapter and equal, critical lengths of 75 ohm coax, or with a good quality splitter and equal lengths of 50 ohm cable. When you do this and both Yagi's are pointed in the same direction and at a proper spacing, you can get up to 3dB of gain.

When pointed opposite directions you will get at least 3dB loss on top of whatever each antenna is rated for in gain but most 800 Yagi's have at least 10dBD gain so you will probably be ahead. There should not be much phase degradation from signals arriving at both antennas due to the side and rear rejection properties of the Yagi's.
And if you do get any odd phase degradation you should be able to do a minor tweak on one antenna or the other and kill whatever badness is happening. Between 10+ dBi of forward gain and easily -20 dBi (possibly much more) in a null, it would be easy to see 30+ dB of isolation between the two.

The short answer is yes, two Yagi's can work quite well, where two Omni's might be asking for problems.

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Old 03-17-2016, 4:46 PM
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Quote:
Originally Posted by wise871 View Post
Unlike some who want to mix a discone and a yagi, I want to be able to use two identical 800Mhz Wilson Yagi's to hit two different towers in my area. Currently I have two sites near me, one for the south end of my county and one for the north end. The discone does great on the south end but it's hit or miss on the north. Currently I have a 800 yagi pointed to the North site and it works great. For now I have to use two scanners and two separate antennas. I would like to only have the one scanner with dual 800 and this will free up the other scanner for discone use.
Dan the upside to using two antennas and two scanners is you would never miss a north or south call at the same time. But yes I see no reason why you should not try the two antenna solution . Just try to make your harness as close to the same length as possible.
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Old 10-07-2018, 10:32 PM
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Was thinking on doing the same with dual Yagi’s.
Have Wilson 301111 Yagi Antenna pointed to the West as of now.
Want to cover WNW & WSW to pick up more control towers.
Think I will give this a shot now.



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Old 10-08-2018, 6:38 AM
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Frank do google searches for making a co-phasing harness and keep the impedance matched for best performance. This is done all the time in ham radio.
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Old 10-08-2018, 6:56 AM
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Was just reading up on stacking antennas.
I have yet to find the correct spacing between the two or if they both have to be pointed in the same direction.
Already have the same length 400 coax for each.
Was planning on making sort of a “V” with two Yagi’s but it doesn’t seem to work that way it’s I read.
More or less just double the gain in one direction.
Back to reading and finding the one article that going to help solve this can or can’t do plan.



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Old 10-08-2018, 7:17 AM
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As the antennas are not being used to get more gain in the same direction, the spacing is not that critical. Except to have as much between the 2 yagi antennas as you can have. This way the interaction between them is minimal. Maybe something on the order of several wave lengths as a minimum. At 800 MHz. that is not a large distance. So go for much more.

Without 2 people working on your install, it will get frustrating to try and get a peak on each yagi for the signal your trying to get. The alternative is to use a portable and connect the antenna to it while you try to point it. This way you can see what is going on. Other wise one person will have to be watching the scanner while the second person is moving the yagi to peak the signal. Have a set of portable radios to communicate with each other.

Good luck on the install.
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Old 10-08-2018, 7:38 AM
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As Jim stated if you can one at the top and 6 or 8 feet down the second with the T for the coax in the middle should work good for you.
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Old 10-08-2018, 9:53 AM
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So green is the way the Yagi is now.
If I point two as the yellow lines are is co phasing is still required ? I’m not necessarily stacking these if they’re pointing in different directions.
Or I’m I reading it wrong and getting that 50 ohm signal back to the radio is the most crucial part.
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Old 10-08-2018, 11:50 AM
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That Wilson yagi have 8 elements and to make it broadbanded to cover the whole 700MHz-900MHz range they have 2 larger elements, probably tuned for 750MHz and 4 shorter elements, probably tuned for 850MHz. The say it has 10dB gain at 855MHz and it will be less at 700MHz and also have a wider loob at that frequency.

Try to keep the coax lenghts the same from antenna to the point where they are connected together within 1/2 inch. If you have something to monitor from due west and it stopped working then you have to direct both antennas more to the west and matching the cable lenghts will be important.

/Ubbe
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Old 10-08-2018, 11:55 AM
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After calling both big name scanner stores one wanted me to leave a voicemail other had no clue on co-phasing so I called DX Engineering and got my answer.
Co phasing isn’t needed when receiving only.
So using two Wilson 301111 Yagi antennas pointed in two different directions using a T connector is fine.
5 to 6 foot spacing between the two Yagi’s is required though.
Might try this before winter gets here.


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Old 10-08-2018, 6:15 PM
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Glad you got your answer I am old school and just like to keep the impedance matched for best performance.
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Old 10-08-2018, 6:29 PM
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That was my concern as well.
But he reassured me that in receiving only and the fact I wasn’t really stacking the two Yagi’s it wasn’t necessary.
Appreciate everybody’s feedback.
Leaning something new everyday.


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Old 10-09-2018, 4:23 AM
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The physics law doesn't change depending of if the antenna system are used for transmit or receive. The only difference are if the SWR are too high and the transmitter doesn't have any protection for it. All other things like gain, directivity, impedance and coax attenuation are the same.

It's always important to keep antennas away from any metal, including other antennas, and one wavelenght are more than enought, 1 foot at 800MHz.

Keep in mind than any signal that are received by both antennas will need the coaxes to be in phase. The lower the frequency in a yagis designed frequency range the lower the gain will be and also give a wider angle of reception.

/Ubbe
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