GMRS attic antenna not working

[tjcasper93]

I have a GMRS base station at my house with the Sirio CX455 antenna located in the attic (LMR400 cable). In car tests with my brother I lost him after a 1/2 mile. However with the same antenna in my kitchen we can talk both ways for miles. I've tried the attic antenna in various places, and have used different cables in the attic but get the same results.  I'm not running the LMR400 along any power cables.  We both use Midland MXT500. Any help getting the attic antenna to work is appreciated. 
 

[WRXB215]

Do you have a layer of that foil barier in your roof?

[tjcasper93]

No, just asphalt shingles.  Not sure about the underlayment but as I recall there wasn't any foil.  But if there was foil wouldn't it affect the kitchen set up as well since the signal has to go through the ceiling and then through the roof?

[WRXB215]

The signal is line-of-sight and travels mostly horizontal. If there is a window in the attic you may have better luck putting the antenna there.

[WRUE951]

11 minutes ago, tjcasper93 said:

I have a GMRS base station at my house with the Sirio CX455 antenna located in the attic (LMR400 cable). In car tests with my brother I lost him after a 1/2 mile. However with the same antenna in my kitchen we can talk both ways for miles. I've tried the attic antenna in various places, and have used different cables in the attic but get the same results.  I'm not running the LMR400 along any power cables.  We both use Midland MXT500. Any help getting the attic antenna to work is appreciated. 
 

Many years ago i tried a UHF antenna in an attic of a two story house and never had any luck with that setup..  Always puzzling because talking on portables from the garage down stairs worked much better..  There are lots of things in an attic that hampers single quality..  i.e. HVAC vents, wiring, vents etc..   I ended up putting the antenna in a tree next to the garage and had pretty good results..   Flag poles work well too if you can get away putting one up..  Experiment.  

[tjcasper93]

Thanks.  Interestingly I have tried putting the antenna on the roof and get the same results.  I thought I'd try the attic since the kitchen worked so well but no luck.  I also have to abide by the HOA rules.  I like the idea of a flag pole.  Perhaps I can get one to stick out above a tree so the HOA doesn't get too mad.

[tjcasper93]

Thanks WRXB215.  Unfortunately no windows in the attic.

[Socalgmrs]

Yea. That’s just not going to work very well at all.   Nothing to do with the cable.   Unfortunately with the 50w midland and the 2.5db gain j pole your only radiating 78w that’s not very much.   If you can get a higher gain antenna out side the house your going to do much better,.    Even a 20 watt radio with a good antenna will radiate 140 watts nearly double.   I’d say if you just have no way of getting the antenna out side a higher gain antenna with more punch is very much needed.   If you can do a 9db antenna you’re going to radiate 350 watts. That’s much much better then the 78w your doing now.  

[tjcasper93]

OK, but why does this antenna work so well from my kitchen?  My brother and I can talk for miles as he's driving around.  Trying to figure this out is baffling.  

[tjcasper93]

I forgot to mention that I went with a lower db antenna due to the hills in our area.

[tjcasper93]

WRUE951, how long was your cable when you put the antenna in the tree?

[WRUE951]

38 minutes ago, tjcasper93 said:

WRUE951, how long was your cable when you put the antenna in the tree?

45’ of 400.    

[tjcasper93]

Thanks.

[WRXL702]

The Sirio CX455 Is A 3/4 Wave Antenna, With A Radiation E Plane At 50 to 60 Degrees From The Horizontal. I Have Mine Mounted On A 7 ft Pole Outside & Connect To Repeaters 45 to 50 Miles Away. (Using 22' of RG8X)

This Antenna Does Not Work Well In A Attic, As The Majority Of The Signal Is Aimed Right Into The Roof Sheathing.  A 3/4 Wave Antenna Is Not The Best Choice For Simplex Applications, Due To The Lack Of Horizontal Plane, But Works Very Well If You Have A Low ASL Elevation Attempting To Access Repeaters.

Application, Application Should Always Enter Into Your Antenna Decisions & Choices.

[Riktar]

When you are trying the antenna in the attic, did you try having your friend drive in multiple directions?

Do a range check with a direction that is parallel to the roof line. Then do a check perpendicular to the roof line.

If you  find a notable increase in range when you are parallel then I would guess that you have some metal barrier in the underlayment.

Just a thought.

 

[WRXB215]

10 hours ago, tjcasper93 said:

Interestingly I have tried putting the antenna on the roof and get the same results

It could be that from the kitchen you are actually getting the signal through under the thick part of the trees. There was another guy here a few months ago that was dealing with that same issue.

[nokones]

What are the VSWRs?

My attic antenna is working great under a metal roof tiles. Your need to make sure you're using a non-ground plane and definitely check the VSWRs

[WRXL702]

See Link Below For E Plane Patterns On The 1/4, 1/2 & 3/4 Wave Antennas.

https://practicalantennas.com/designs/verticals/5eights/

[tjcasper93]

WRXL702, Thanks for the info on the Sirio Antenna.  I am going to try a roof mount again tomorrow.  If it works I guess I'll keep it until the HOA notices it.  Maybe they will let me keep it up.

[tjcasper93]

WRXB215, you make a good point about the reception from the kitchen.  Maybe my kitchen setup is low enough to get around all of the interference.  

[tjcasper93]

nokones, you have a very nice, clean set up.  What antenna are you using?

[tjcasper93]

Riktar, great idea.  Tomorrow my brother and I will test out your theory.

[BoxCar]

17 minutes ago, tjcasper93 said:

WRXL702, Thanks for the info on the Sirio Antenna.  I am going to try a roof mount again tomorrow.  If it works I guess I'll keep it until the HOA notices it.  Maybe they will let me keep it up.

I would put the antenna where its not obvious from the street if possible. It's also best to mount it while doing something else such as hanging lights or cleaning gutters. People don't pay attention if they see an expected task.

[LeoG]

On 9/16/2024 at 8:55 AM, WRXB215 said:

It could be that from the kitchen you are actually getting the signal through under the thick part of the trees. There was another guy here a few months ago that was dealing with that same issue.

That would be me I think.

[tjcasper93]

Problem solved!  It was the LMR400 cable!  More specifically the connectors.  When I was reattaching the LMR400 coming from the attic to the radio this morning I noticed that the connection seemed a little loose, even though it was finger tightened.  Nonetheless we proceeded with our test from base to car and got the same results.....not very far.  So once again I set up the kitchen antenna and, just like before, we were talking from base to car for miles.  So I thought what the he** and I ran the shorter, RG58 cable ( which I was using in the kitchen) from the radio to the attic and connected it to the Sirio Antenna, which was just leaning against a board.  With that setup we went 19.6 miles as the crow flies using only simplex, and that was with hills and trees.  Obviously it got a little fuzzy and stat-icky when the car was in dense foliage or in a valley but we were ecstatic!   

[SteveShannon]

9 minutes ago, tjcasper93 said:

Problem solved!  It was the LMR400 cable!  More specifically the connectors.  When I was reattaching the LMR400 coming from the attic to the radio this morning I noticed that the connection seemed a little loose, even though it was finger tightened.  Nonetheless we proceeded with our test from base to car and got the same results.....not very far.  So once again I set up the kitchen antenna and, just like before, we were talking from base to car for miles.  So I thought what the he** and I ran the shorter, RG58 cable ( which I was using in the kitchen) from the radio to the attic and connected it to the Sirio Antenna, which was just leaning against a board.  With that setup we went 19.6 miles as the crow flies using only simplex, and that was with hills and trees.  Obviously it got a little fuzzy and stat-icky when the car was in dense foliage or in a valley but we were ecstatic!   

Good job figuring it out. What brand of LMR400 and connectors were they?