Omnix scanner question

[nick223]

So I put up an OmniX ( DPD Productions) scanner base antenna on a roof eave mount. Picking up analog vhf pretty good but P25 (700-800) not the greatest.
The scanner with a radio shack center load telescoping antenna picks up p25 a lot better from inside the room were the scanner sits.

The scanner is in a room almost right below the Onnix antenna. The coax run is about 30 feet use RG8 which I purchased from DPD productions. Also tried lmr400 with little difference is the signal.
Did I do something wrong? I would think the outside antenna should Out preform the telescoping antenna off the scanner.
I’ll add some pictures of the OmniX antenna.

 

[nick223]

Another picture

 

[jonwienke]

That antenna is designed for UHF and VHF, not 800. The only design that really covers vhf-800 is a discone.

 

[iMONITOR]

The specs on the antenna include up to 900 MHz so it should be fine. How distant

Tuned: 118-137, 148-175 & 225-900 MHz

OmniX Scanner Base Antenna

Specs Gain: 3 VHF 4 UHF dBi Pattern: Omni-directional Wavelength: 1/2 Elements: 3 Tuned: 118-137, 148-175 & 225-900 MHz Band: UHF & VHF Connector: N Female Cable: RG8X Cable Length: 16 Inches Height: 45" Width: 30" Weight: 2 lb Features Multi Band-Wide Coverage: The uniquely...

dpdproductions.com

What are you using for coax and did you use the proper Type N connector and weather proofed?

 

[popnokick]

The DPD Omni-X is good up to 900 mHz and should perform much better than the telescoping antenna on your scanner. Have you checked for a problem with your coax? Specifically the connectors? The Omni-X uses N connectors, so three possibilities arise regarding how you connected your coax -
1 - Purchased the exact length with the N-connector already on the coax cable.
2 - Attached the N-connector yourself to the coax.
3 - Using adapters to go from N to PL-259 (or other connector)
Which of the above was it? And now... did you test everything with a multimeter and the antenna DISconnected to ensure -
1 - Continuity from end to end of the cable for the center conductor?
2 - Continuity from end to end of the cable on the outer shield?
3 - No connection / short between the center and outer conductors?

 

[nick223]

The specs on the antenna include up to 900 MHz so it should be fine. How distant

Tuned: 118-137, 148-175 & 225-900 MHz

OmniX Scanner Base Antenna

Specs Gain: 3 VHF 4 UHF dBi Pattern: Omni-directional Wavelength: 1/2 Elements: 3 Tuned: 118-137, 148-175 & 225-900 MHz Band: UHF & VHF Connector: N Female Cable: RG8X Cable Length: 16 Inches Height: 45" Width: 30" Weight: 2 lb Features Multi Band-Wide Coverage: The uniquely...

dpdproductions.com

What are you using for coax and did you use the proper Type N connector and weather proofed?

RG8X Coax Cable with N connector and bnc connector into the scanner also used coax weather seal

 

[nick223]

The DPD Omni-X is good up to 900 mHz and should perform much better than the telescoping antenna on your scanner. Have you checked for a problem with your coax? Specifically the connectors? The Omni-X uses N connectors, so three possibilities arise regarding how you connected your coax -
1 - Purchased the exact length with the N-connector already on the coax cable.
Yes purchased with N to Bnc directly from DPD Productions
2 - Attached the N-connector yourself to the coax.
No
3 - Using adapters to go from N to PL-259 (or other connector)
No
Which of the above was it? And now... did you test everything with a multimeter and the antenna DISconnected to ensure -
1 - Continuity from end to end of the cable for the center conductor?
2 - Continuity from end to end of the cable on the outer shield?
3 - No connection / short between the center and outer conductors?
I tried 3 different coax cables with almost the same result on signal tried RG8x, RG6, and LMR400
i did not use a multi meter but i will next time im at the antenna.

 

[prcguy]

Have you checked for overload from nearby cell phone towers, etc, by switching on an attenuator to see if it receives better?

Another thing is, how tall are the center fat elements? I believe the Omni-X starts as a fat dipole for roughly the 225-400 range and each dipole element would be about 8-9" each if that's the case. Then it appears there is a 1/2 wave dipole favoring the VHF air band and another for probably mid 150 range. I've never had one but am giving it my best guess.

If what I think is true then there are no specific elements for 800 and it would rely on some larger elements working as multiple quarter wavelengths and that can result in strange radiation patterns or a null at the horizon in the 800 range.

 

[nick223]

Have you checked for overload from nearby cell phone towers, etc, by switching on an attenuator to see if it receives better?

No i have not, but i will

 

[kruser]

My guess is it could be an LSM (simulcast distortion) issue where the indoor antenna is only seeing signal from one tower while the new OmniX is allowing several towers signals in.

What scanner make/model?

 

[nick223]

My guess is it could be an LSM (simulcast distortion) issue where the indoor antenna is only seeing signal from one tower while the new OmniX is allowing several towers signals in.

What scanner make/model?

The telescoping antenna was receiving 5 tower sites with about 2-4 bars depending on the site, The OmniX was receiving 3 sites, 1-2 bars signal strength

 

[kruser]

The telescoping antenna was receiving 5 tower sites with about 2-4 bars depending on the site, The OmniX was receiving 3 sites, 1-2 bars signal strength

If it's not an overload issue doing something funny with the radio's front end, then it does sound like something with the antenna with you trying different coax types.
Good luck.

 

[jonwienke]

I'm not seeing any antenna elements 1/9th the length ofbthe VHF elements, so I'm not buying the claim it performs well at 900MHz. And it doesn't have enough of the long elements to make a biconical traveling-wave design.

 

[prcguy]

A person could probably add an 800MHz angled dipole to the feedpoint and tune for best match. I bet that would perk it up.

I'm not seeing any antenna elements 1/9th the length ofbthe VHF elements, so I'm not buying the claim it performs well at 900MHz. And it doesn't have enough of the long elements to make a biconical traveling-wave design.

 

[nick223]

My guess is it could be an LSM (simulcast distortion) issue where the indoor antenna is only seeing signal from one tower while the new OmniX is allowing several towers signals in.

What scanner make/model?

Uniden 996P2

 

[737mech]

As suggested get a volt meter and check center conductor to shield shorting. I have the dpd omni x mil air version and it handles 800/900 just fine. I have it in my garage because I use it for remote setups. I thought to try it because of this post. I can monitor just fine with a GRE PSR-500 Phase 2 Clark County NV SNACC system. It really sounds like a coax or connection problem. I hope you find something and start to enjoy that antenna many here have them they work great! Did you try the scanner attenuated? Another thing to check the contacts on the scanner BNC squeeze them toward center a little with a paper clip. Even try a little crc contact cleaner? Another great product for contacts is Deoxit.

 

[mule1075]

Also double check it is assembled correctly. I had a problem with my receive because I failed to seat the radials properly 1st time round.

 

[sflmonitor]

I would definitely check the coax for a short or some other issue. Maybe the antenna has a factory defect. I've had mine for about a year and absolutely love it. I can receive 800 MHz systems from over 25 miles away without a problem. Distant VHF/UHF signals are also received with ease including aircraft from as far out as 250 miles. Good luck.