Which antenna and why? monitoring P25 Phase II system 769-775mhz

[Ronnierozier2]

I'm looking at two different antennas to monitor a P25 Phase II system operating from 769-774Mhz. these are the two antennas I'm looking at. Which would be better monitoring the P25 system at those frequencies. Also if you dont mind tell me why you chose the antenna you did.

Diamond Discone D130NJ

Diamond® Antenna ~ D130NJ Super Discone Antenna

DPD Productions Omni

700 MHz UHF Vertical Outdoor Base Antenna (769-775 MHz)

Specs Gain: 6 dBi SWR: 1.5:1 or Less on Center Pattern: Omni-directional Wavelength: Multiple 1/2 Tuned: 769-775 MHz Band: 700 MHz Safety Connector: N Female Cable: RG8X Cable Length: 24 Inches Height: 57" Width: 1 1/4" Weight: 2 lb Wind Area: 0.50 Sq Feet Features Ready Made...

dpdproductions.com

 

[DS506]

The vertical built for that band. Why? The 6db gain in the band you want.

 

[a417]

How far away are you from those systems? Will you be monitoring anything else outside of them? If signal strength is the predominant issue, as @DS506 said, you want the gain. If you are going to be listening to things all over the bands and all around you, I'd go with the discone.

 

[majoco]

"A gain of 6dbi" . The reference "i" refers to the theoretical isotropic radiator - an antenna hanging out in free space that is omni-directional and wideband and physically impossible. It's 'gain' is actually -2.15dB compared to a dipole as the dipole radiation pattern is a 'figure of eight' and therefore does have some gain. Your 6dBi is actually 3.85dBd which it probably gets from stacked dipoles and therefore a pattern aimed at the horizon.

 

[n5ims]

One big question you need to have answered prior to getting a good answer on what antenna you should use is this. "Is the system you're trying to monitor a simulcast system of not?" With a simulcast system, they broadcast using several tower sites on the same frequencies as a way to better provide handheld coverage in the area. The typical scanner has quite a bit of difficulty decoding a simulcast system if it picks up more than just a single tower site. You are often better off with a lower gain antenna than a higher gain antenna since your chance of picking up more than a single tower increases with your antenna gain.

Often it's better to use a very directional antenna pointed at a single tower (and no other on the system in the direction that antenna is pointed) than a high gain omnidirectional antenna. Now most likely that highly directional antenna will have quite a bit of gain, but that's OK since the directional pattern will only pick up the single tower site you have it pointed at. Be aware that depending on the system and tower site pattern you may actually need to point at a more distant site than the closest one if your closest one has another site along the same (or nearly the same) path.

To help answer your specific question, you most likely do NOT want the discone since it has a very wide frequency range coverage so you're wasting most of your antenna and its performance where you won't be listening. Also, most discones are rather poor at the 700+ MHZ range. Instead of designing it for that range, they chose to make it work from the VHF-Low, VHF-Hi, and UHF (below 500 MHZ) ranges and basically just hope that it will pick up the higher frequencies.

Including a link to the system or systems you're wanting to monitor will help us best answer your question.

 

[Ronnierozier2]

How far away are you from those systems? Will you be monitoring anything else outside of them? If signal strength is the predominant issue, as @DS506 said, you want the gain. If you are going to be listening to things all over the bands and all around you, I'd go with the discone.

The system im monitoring is bouncing off three towers. 2 to the East of me 16 and 19 miles away roughly and to the west about 15 miles away. Note this is not a simulcast system. I'm only interested in listening to the MSWIN state system here in Mississippi as everything around me is on that system. Currently I have an omni supposidly 6dbi gain frequency range of 698-2700mhz but it is an amazon 35.00 antenna so i would imagine it is what it is a cheap antenna. it does ok but my signal levels are about -85 to -100 and this antenna is about 40' on the eave of my house. I moved the antenna about 19' above the eave of the house but suprisingly to me the reception was horrible. the reception is better about 3'7" above my metal roof. explaine that one, i thought a metal roof would obstruct signal not turn into constructive interference .

 

[Ronnierozier2]

One big question you need to have answered prior to getting a good answer on what antenna you should use is this. "Is the system you're trying to monitor a simulcast system of not?" With a simulcast system, they broadcast using several tower sites on the same frequencies as a way to better provide handheld coverage in the area. The typical scanner has quite a bit of difficulty decoding a simulcast system if it picks up more than just a single tower site. You are often better off with a lower gain antenna than a higher gain antenna since your chance of picking up more than a single tower increases with your antenna gain.

Often it's better to use a very directional antenna pointed at a single tower (and no other on the system in the direction that antenna is pointed) than a high gain omnidirectional antenna. Now most likely that highly directional antenna will have quite a bit of gain, but that's OK since the directional pattern will only pick up the single tower site you have it pointed at. Be aware that depending on the system and tower site pattern you may actually need to point at a more distant site than the closest one if your closest one has another site along the same (or nearly the same) path.

To help answer your specific question, you most likely do NOT want the discone since it has a very wide frequency range coverage so you're wasting most of your antenna and its performance where you won't be listening. Also, most discones are rather poor at the 700+ MHZ range. Instead of designing it for that range, they chose to make it work from the VHF-Low, VHF-Hi, and UHF (below 500 MHZ) ranges and basically just hope that it will pick up the higher frequencies.

Including a link to the system or systems you're wanting to monitor will help us best answer your question.

thank you for the information friend. please see my comment to a post above. the system im ONLY interested in monitiring is MSWIN here in mississippi and its a P25 Phase II system. look above for my comment about this system bouncing around three towers in my area but it's not simulcast.

I live in lefore county Mississippi and if you look on the MSWIN website they have a site map. I can reach three towers from my current location. I have these three sites programmed in my SDS100 and I hear traffic from all three sites.

the three sites im monitoring is Carrollton, North carrollton and Morgan City

 

[Ronnierozier2]

"A gain of 6dbi" . The reference "i" refers to the theoretical isotropic radiator - an antenna hanging out in free space that is omni-directional and wideband and physically impossible. It's 'gain' is actually -2.15dB compared to a dipole as the dipole radiation pattern is a 'figure of eight' and therefore does have some gain. Your 6dBi is actually 3.85dBd which it probably gets from stacked dipoles and therefore a pattern aimed at the horizon.

Thanks for the post, today ive been studying up on antennas and what you mentioned in your post is exactly what was covered in the youtube video is the radiation patterns of Dipole, omni, and directional antennas.

i am very interested in what you mentioned above about my 6dbi antenna actual gain is -2.85db that the listed 6dbi. can you take a moment and explaine that in a little more detail or point me in a direction where that calculation is ?

 

[Ronnierozier2]

I live where the red crosshairs are located on the map. I should have used a different color than red. Right in the middle of town and from my home outsude in the yard with a remtronix antenna i cant get any signal from any of the three towers. thats why i have an omni on the house. Even with the Omni my signal levels from all three sites range from -85 to -100 when im connected to the cheap amazon omni. thats why im wondering if a discone or the DPD antenna would work better than my cheap 698-2700mhz omni meant for wifi stuff

 

[a417]

Currently I have an omni supposidly 6dbi gain frequency range of 698-2700mhz but it is an amazon 35.00 antenna so i would imagine it is what it is a cheap antenna. it does ok but my signal levels are about -85 to -100 and this antenna is about 40' on the eave of my house. I moved the antenna about 19' above the eave of the house but suprisingly to me the reception was horrible. the reception is better about 3'7" above my metal roof. explaine that one, i thought a metal roof would obstruct signal not turn into constructive interference .

if it's the same variation of the $35.00 amazon yagi that I tried last year, it's absolute garbage. Find someone with a VNA or test equipment and they will show you... it's complete and utter trash. That antenna is misrepresented as what it can do, just recycle it. If its still in the return window, ship that back, and ask them to return your hard earned shekels.

Get a good discone, get it up in the air, and reap the benefits.

 

[Ronnierozier2]

if it's the same variation of the $35.00 amazon yagi that I tried last year, it's absolute garbage. Find someone with a VNA or test equipment and they will show you... it's complete and utter trash. That antenna is misrepresented as what it can do, just recycle it. If its still in the return window, ship that back, and ask them to return your hard earned shekels.

Get a good discone, get it up in the air, and reap the benefits.

here is the antenna im currently using on top of my house for now. I do have access to some very expensive test equipment, we have an Anritsu spectrum analyzer and Anritsu Site Master. I'm going to bring home the sitemaster this weekend cause i need to test my LMR400 anyway. I've really never used either one being im in a management position but im sure there are some youtube videos out there that will show me how.

https://www.amazon.com/dp/B08NV48VTL?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[a417]

Ok, that's not the yagi I thought you were referring to, but the tech specs and sales flim-flam are eerily similar. Sweep it and lets see.