Help troubleshooting new base install

[rob_d]

I just installed an antenna in my attic:
Antenna: Diamond Super Discone D3000N, mounted to antenna pipe which is mounted to a wood rafter and is grounded to electrical conduit
Lightning Arrester: Diamond SP-Series Lightning Arrester SP3000W, mounted to a wood rafter and is grounded to electrical conduit
Cable: LMR-240 with a 90 foot run to my scanner desk

After install, I can't even pick up weather frequencies so I know something is wrong.

I checked for a short between the center pin and the shield and there is no short.

Any suggestions on the basics? Maybe I missed something simple? Or did a beginner mistake?

Thanks for the help!

 

[ka3aaa]

Why the lightning arrester in the, are you expecting a strike inside your attic?????????????????

 

[mmckenna]

I just installed an antenna in my attic:
Antenna: Diamond Super Discone D3000N, mounted to antenna pipe which is mounted to a wood rafter and is grounded to electrical conduit
Lightning Arrester: Diamond SP-Series Lightning Arrester SP3000W, mounted to a wood rafter and is grounded to electrical conduit
Cable: LMR-240 with a 90 foot run to my scanner desk

After install, I can't even pick up weather frequencies so I know something is wrong.

I checked for a short between the center pin and the shield and there is no short.

A discone will show as an open circuit. So that should be good.
However, the open may also be due to a break in the cable or a damaged connector.

Any suggestions on the basics? Maybe I missed something simple? Or did a beginner mistake?

Thanks for the help!

What is your roofing material? Is there any metal at all? Even foil backed insulation/vapor barrier?

Attic installations can put the antenna closer to noise sources in the house. Are you not picking up anything, or is it masked by noise?

Why the lightning arrester in the, are you expecting a strike inside your attic?????????????????

Roofing materials will not magically shield from a lightning strike.
And it's not just a direct strike that would be of concern. Even a nearby strike can induce enough energy into the antenna to cause issues.

 

[rob_d]

A discone will show as an open circuit. So that should be good.
However, the open may also be due to a break in the cable or a damaged connector.





What is your roofing material? Is there any metal at all? Even foil backed insulation/vapor barrier?

Attic installations can put the antenna closer to noise sources in the house. Are you not picking up anything, or is it masked by noise?





Roofing materials will not magically shield from a lightning strike.
And it's not just a direct strike that would be of concern. Even a nearby strike can induce enough energy into the antenna to cause issues.

Roofing material is typical asphalt shingles and plywood sheets. Rafters are wood, siding is vinyl and Tyvek barrier.

Would I need to ground the cable shield at the antenna side with a cable grounding kit? Or is the assumption it is grounded by means of grounding the antenna mounting base pole?

Also, how would I check for noise interference aside from shutting off power to the entire house? Is there some other way to troubleshoot this potential issue?

 

[mmckenna]

Roofing material is typical asphalt shingles and plywood sheets. Rafters are wood, siding is vinyl and Tyvek barrier.

Would I need to ground the cable shield at the antenna side with a cable grounding kit? Or is the assumption it is grounded by means of grounding the antenna mounting base pole?

At minimum, you should have the coaxial cable shield grounded where it enters your home, ideally through a lightning discharge device.

Also, how would I check for noise interference aside from shutting off power to the entire house? Is there some other way to troubleshoot this potential issue?

Take the antenna off your scanner and sniff around. Shutting off breakers can work, but in closely spaced dwellings, you won't be able to shut off your neighbors power and the noise could absolutely be coming from there.


I'd take a close look at all your connections, look for corrosion, damage, etc.

Also:
90 feet of LMR-240 is going to lose 2/3rd's of your signal on the UHF bands before it even reaches your radio. Almost 80% loss on 800MHz.
Since discone antennas have zero gain, you've got a less than ideal setup. You would need to either shorten your coaxial cable, or upgrade to something with less loss.

 

[rob_d]

At minimum, you should have the coaxial cable shield grounded where it enters your home, ideally through a lightning discharge device.



Take the antenna off your scanner and sniff around. Shutting off breakers can work, but in closely spaced dwellings, you won't be able to shut off your neighbors power and the noise could absolutely be coming from there.


I'd take a close look at all your connections, look for corrosion, damage, etc.

Also:
90 feet of LMR-240 is going to lose 2/3rd's of your signal on the UHF bands before it even reaches your radio. Almost 80% loss on 800MHz.
Since discone antennas have zero gain, you've got a less than ideal setup. You would need to either shorten your coaxial cable, or upgrade to something with less loss.

Antenna is inside the attic and coax goes through a lightning arrester about 4 feet from the antenna base. The arrester is grounded to electrical conduit in the attic. Is this enough or do I need to ground the coax with a grounding kit?

I'll check the connections again but this is a brand new install. I guess I didn't do my homework on the LMR-240 for a 90 foot run. I thought it would be ok. I suppose I should at least be able to pick up something and not attribute the inability to pick up any signals due to loss?

Also, how does one sniff around with the antenna off the scanner? I'm not familiar with the terminology but I'm guessing put the scanner on close call and watch the bands if any light up?

I appreciate the help!

 

[mmckenna]

Antenna is inside the attic and coax goes through a lightning arrester about 4 feet from the antenna base. The arrester is grounded to electrical conduit in the attic. Is this enough or do I need to ground the coax with a grounding kit?

If you wanted to do things to code, grounding to conduit is not acceptable. The arrestor needs to be bonded to the ground rod for the structure, and if that isn't directly under the antenna, you'd need to add a ground rod AND bond that to the existing one.

That's if you want to do it to code.

Grounding to the conduit ~should~ be sufficient for just grounding things, but it's not to code and probably isn't causing your issues.

Unless you are going to add the ground rods/bonding, I'd not spend a whole lot of time focusing on that. I bet you'd find that 95% of hobbyists don't ground anything and somehow survive.

I'll check the connections again but this is a brand new install. I guess I didn't do my homework on the LMR-240 for a 90 foot run. I thought it would be ok. I suppose I should at least be able to pick up something and not attribute the inability to pick up any signals due to loss?

Make 100% sure your outdoor connections are fully waterproofed. If you did not do that, its possible water got in and corroded something.

As for being able to pick up something, I don't know about that.
The discone antenna isn't doing you any favors with zero gain.
The long/lossy coax isn't doing you any favors by losing that much signal.
Having the antenna low and behind the building isn't doing you any favors.
Without knowing exactly where you are in relation to the systems you want to listen to, no one would be able to confirm or deny that you should be able to hear something.

But, hearing zero, that's usually a sign that something isn't connected somewhere, something failed, or the coax was cut/damaged. No way we can determine that from the photo or the evidence you have provided.

Also, how does one sniff around with the antenna off the scanner? I'm not familiar with the terminology but I'm guessing put the scanner on close call and watch the bands if any light up?

I appreciate the help!

Remove the antenna, walk around and see if the signal level peaks around electronics.

But, I don't think that is your problem, and having your antenna outside is going to be one of the best things you can do to eliminate that.


I really think you need to start at one end of your antenna system. Inspect every single inch of coaxial cable, each connector, each device, everything very carefully, and you'll likely find some issue(s).

 

[wtp]

back to basics...
take the radio up to the attic with a stock antenna(known good) on it.
then what do you get ?

 

[popnokick]

Can yo take your scanner … or a handheld scanner - up into the attic and connect a short jumper coax from the discone to the scanner? If you don’t have a battery powered scanner, pull an AC extension cord up there. This will immediately tell you if the discone is receiving anything- or if the long coax run and connectors are at fault. Then you can say either “Well I got lotsa stuff on the discone. The problem must lie in the coax and / or connectors.” Or you’ll be able to say, “This discone in the attic is not gonna work. It’s not picking up diddly.”

 

[rob_d]

Up in attic, scanner in hand with portable antenna and pick up signals loud and clear.
I attached the scanner directly to the attic antenna and static.
When I remove the antenna from the mounting pole, the signals come in fine. As soon as it it touching the mounting pole, the signal drops.

 

[mmckenna]

Up in attic, scanner in hand with portable antenna and pick up signals loud and clear.
I attached the scanner directly to the attic antenna and static.
When I remove the antenna from the mounting pole, the signals come in fine. As soon as it it touching the mounting pole, the signal drops.

Can you post a photo of the antenna mounted to the pole?

Are any of the antenna elements touching the pole?

Is this a conduit that is carrying any wiring?

 

[rob_d]

Can you post a photo of the antenna mounted to the pole?

Are any of the antenna elements touching the pole?

Is this a conduit that is carrying any wiring?

No elements touching pole or anything else. Mounting pole is a kit with pole and bracket and is mounted to a wood rafter.

 

[mmckenna]

Up in attic, scanner in hand with portable antenna and pick up signals loud and clear.

That's a very good sign.

I attached the scanner directly to the attic antenna and static.

There isn't much to a discone. Big concern would be a short between the two halves, and that would likely not cause static.

When I remove the antenna from the mounting pole, the signals come in fine. As soon as it it touching the mounting pole, the signal drops.

Try isolating the mount from the support mast and see if that helps.

 

[rob_d]

I checked the continuity between the two halves and there is none, so they aren't connected.
I isolated the mount from the support mast and it helped, but the small antenna on my scanner still gets better reception in the attic than the discone. I think the issue is electrical noise. I tried moving the discone around the attic but still hear slight static in all locations when listening to the weather channel. Again, the small antenna on my scanner (while up in the attic) is way more clear than when connected directly to the discone.

Is the discone more sensitive to electrical noise?

 

[WA0CBW]

Did you test the coax end to end?
BB

 

[rob_d]

All coax and connectors are good. Continuity checks out on all coax.

All of my in attic testing was done with a short 5 foot coax connected directly to the discone.

 

[mmckenna]

Is the discone more sensitive to electrical noise?

On its own, no. They do have funky radiation patterns, which may mean it's hearing things from down in your home easier than the handheld will.

Moving it around the attic was going to be my next recommendation, but sounds like you already tried that. I'm thinking that the addition of the mount to the bottom half of the discone was probably making it pick up noises from in the house easier, but I could be wrong.

You could try shutting circuit breakers off one by one and see if there is a specific breaker that feeds something that is making the noise. Then just track down what device that is. Might be something you can relocate or replace.

So, sounds like two issues:
Local noise
Lots of coaxial cable adding to loss.

 

[KevinC]

What model scanner are you using?

 

[rob_d]

What model scanner are you using?

Uniden BCD436HP

 

[KevinC]

Uniden BCD436HP

Ok, disregard then.