Sirio WY 155n advice needed

[jimlg]

I am trying to monitor a P25 trunked system using this antenna, this site is 52 miles from my location, unfortunately there is another
site that uses 2 of the same frequencies 32 miles from me. Site 1 which I want to monitor uses a control frequency of 171.6750,
Site 2 uses a control frequency of 170.3875. When site 1 switches to frequency 170.3875 there is interference from from the control
channel on site 2, when site 2 switches to frequency 171.6750 it interferes with the control channel of site 1.

The signal strength for site 1 is ok as long as there is no interference from site 2, I have tried nulling out site 2 using the null points on the
antenna, it has helped some but not enough.

I would like to add another WY 155n for more forward gain and possible better side rejection, is this feasible, if so which is the better way
to mount them, side by side, or one above the other, also what frequency should the phasing harness be tuned to?

 

[prcguy]

I would get a larger Yagi like 6 elements. The 2 element version you have only has 3dBd gain and a very broad beamwidth.

 

[jimlg]

Sorry about that, I left out the 6 in the model. I actually have the WY 155 6N

 

[prcguy]

That is a very respectable antenna with a good pattern and F/B ratio. If combined at the proper spacing you will increase gain up to a maximum of 3dB and the pattern will be a little narrower. Its an expensive experiment to try out and it may or may not fix your problem. But one thing for sure is it will look really nice up there on your mast, and that is worth something I guess.

I would have to do research on spacing and most vertical Yagi's I've seen are spaced side by side. I believe you can space them vertically with the same result and the spacing would be similar to that of an exposed dipole array which is about 1 wavelength or a little more spacing.

For phasing the two antennas you can use a 50 ohm power divider and exact equal lengths of 50 ohm cables, any length. For a 75 ohm coax phasing harness its best to use an antenna analyzer to trim the lengths. You could use RG59, RG6 or RG11 TV coax with F connectors then use F to N adapters which have very little loss. A 3/4 wavelength cable from each Yagi to a T adapter will work so divide 2952 by the center frequency you want, then multiply by the velocity factor of the cable then multiply that by 3 to get your 3/4 wavelength in coax.

Since the world is not perfect its best to add several inches to that, put one connector on the cable and check with an antenna analyzer, it will show a short at the target frequency and if you cut the cables a little long it should show a short at a lower frequency than you need so you can test and trim to freq. Trim the cable until it shows a short about 500KHz above your desired freq then cut a second cable the same length and install connectors. A compression type F connector and N adapter will add to the length and that is why you cut it about 500KHz higher in freq at VHF to compensate.

You can also use PL-259s or N connectors but you would need to use a 75 ohm cable with a copper or tinned braid so you can solder for PL-259s or find a crimp type N connector for the specific cable and there are some for RG11. You can find F type T adapters on eBay for various prices, usually too much but there should be some for under $3 each if you search around.

Sorry about that, I left out the 6 in the model. I actually have the WY 155 6N

 

[jimlg]

That is a very respectable antenna with a good pattern and F/B ratio. If combined at the proper spacing you will increase gain up to a maximum of 3dB and the pattern will be a little narrower. Its an expensive experiment to try out and it may or may not fix your problem. But one thing for sure is it will look really nice up there on your mast, and that is worth something I guess.

I would have to do research on spacing and most vertical Yagi's I've seen are spaced side by side. I believe you can space them vertically with the same result and the spacing would be similar to that of an exposed dipole array which is about 1 wavelength or a little more spacing.

For phasing the two antennas you can use a 50 ohm power divider and exact equal lengths of 50 ohm cables, any length. For a 75 ohm coax phasing harness its best to use an antenna analyzer to trim the lengths. You could use RG59, RG6 or RG11 TV coax with F connectors then use F to N adapters which have very little loss. A 3/4 wavelength cable from each Yagi to a T adapter will work so divide 2952 by the center frequency you want, then multiply by the velocity factor of the cable then multiply that by 3 to get your 3/4 wavelength in coax.

Since the world is not perfect its best to add several inches to that, put one connector on the cable and check with an antenna analyzer, it will show a short at the target frequency and if you cut the cables a little long it should show a short at a lower frequency than you need so you can test and trim to freq. Trim the cable until it shows a short about 500KHz above your desired freq then cut a second cable the same length and install connectors. A compression type F connector and N adapter will add to the length and that is why you cut it about 500KHz higher in freq at VHF to compensate.

You can also use PL-259s or N connectors but you would need to use a 75 ohm cable with a copper or tinned braid so you can solder for PL-259s or find a crimp type N connector for the specific cable and there are some for RG11. You can find F type T adapters on eBay for various prices, usually too much but there should be some for under $3 each if you search around.

Thank you very much for the information. I agree it would look really nice. Fortunately most of my neighbors don't care how many antennas
I have up so I doubt they would even notice another one.

 

[Ubbe]

...I have tried nulling out site 2 using the null points on the antenna, it has helped some but not enough.... which is the better way to mount them, side by side, or one above the other...

In this case side by side and as far apart as possible. It will make a very narrow beam. If you get the distance between antennas right it will actually make them totally out of phase to the interfering transmitter. And the longer the distance between them the more out of phase they will be, until one antenna are 1/2 wave behind the other in relation to the direction of angle to the interfering transmitter. A 1/2 wave are 1 meter or 3ft.

Best thing would be if you could experiment and move one antenna forward and back while monitoring to get the best relation between max in phase to the wanted system and max out of phase to the offending system.

If you install antennas above each other it will only make the beam more narrow vertically and will not help with your issue.

/Ubbe

 

[jimlg]

In this case side by side and as far apart as possible. It will make a very narrow beam. If you get the distance between antennas right it will actually make them totally out of phase to the interfering transmitter. And the longer the distance between them the more out of phase they will be, until one antenna are 1/2 wave behind the other in relation to the direction of angle to the interfering transmitter. A 1/2 wave are 1 meter or 3ft.

Best thing would be if you could experiment and move one antenna forward and back while monitoring to get the best relation between max in phase to the wanted system and max out of phase to the offending system.

If you install antennas above each other it will only make the beam more narrow vertically and will not help with your issue.

/Ubbe

Looks like I have some work to do, thank you for the advice.