Help with a New Ground Plane for VHF Low Band

Elpablo

Member
Joined
Feb 26, 2003
Messages
46
I just installed a new ground plane antenna on my roofline to receive VHF low band specifically. This is made up of a Tram 1465 Ground Plane base kit, a Larson NMO 40 whip (50” tall), a 2 foot gavanized steel mast and 30 feet of MPD digital 400 coax (similar to LMR400 but white and flexible). I have grounded the mast to 8’ rod (properly by an electrician).
My problem is the audio quality is very noisy on low band frequencies compared with the same antenna on my NMO mount on my SUV. My signal strength is mainly 5X5 on all the low band frequencies I want to listen to in a 50+ mile radius based on the signal meter on the Uniden BCD536HP. I have noticed that noise reduces at night a good deal but still not as clear as I was expecting based on my mobile use with the antenna. Oddly, it’s sounds great on 800 MHz.
I connected it to my SDS100 and see RSSI levels of -83 to -89 dBm on the stronger, closer signals and -99 to -104 dBm on some of the further, weaker signals. I know this radio is not the best for this VHF Low Band.
This is my first attempt at a mounted outdoor antenna. Might you all have any suggestions on how to improve the audio quality?
Thanks in advance.
 

Arkmood

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Joined
Dec 19, 2002
Messages
232
Location
Taney County MO
This is my first attempt at a mounted outdoor antenna. Might you all have any suggestions on how to improve the audio quality?
Thanks in advance.
Antenna: You're using a base loaded antenna (compromise), try one cut for target freq.
Audio: Don't know how much audio DSP goes on in SDS100 - there are stand alone units...
Ground Plane: You have a much better GP on SUV vs Tram kit.
 

nd5y

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Joined
Dec 19, 2002
Messages
8,929
Location
Wichita Falls, TX
This is made up of a Tram 1465 Ground Plane base kit,
If the base kit has 20" or so radials then it is designed for VHF high band or higher and will be useless on low band.
You basically have no ground plane. That's why the same antenna works properly on your vehicle. The radials need to be at least 1/4 wavelength at the lowest operating frequency. That's 4 to 8 feet for low band.
 

Elpablo

Member
Joined
Feb 26, 2003
Messages
46
Thanks for the input. So it seems like the main issue is the proper ground plane. The Tram kit does have the 20" radials which is apparently not designed for low band. @nd5y what you said makes sense, the radials should be about the same length as the whip for what I intend to listen to. I do see that Larson makes a low band GP kit that I am think of swapping to. I confirmed it's radials are 54" long. https://productfinder.pulseeng.com/product/BSA45C/
 

prcguy

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Jun 30, 2006
Messages
9,745
Location
So Cal - Richardson, TX - Tewksbury, MA
As mentioned the ground plane is a bit small for that frequency range and that antenna but its probably not related to the noise issue. Try temporarily ungrounding the mast so you only have the antenna and feedline connected to the radio and nothing else. You might even take the antenna off the mast and set it on the roof by itself to see if it improves the noise. If you have a lot of noisy equipment in the house noise can travel through the ground system to the antenna where its picked up. If the electrician did a proper legal job he bonded the new ground rod to the house main electrical panel ground with no less that #6 copper wire. If he didn't do that it violates code.



Thanks for the input. So it seems like the main issue is the proper ground plane. The Tram kit does have the 20" radials which is apparently not designed for low band. @nd5y what you said makes sense, the radials should be about the same length as the whip for what I intend to listen to. I do see that Larson makes a low band GP kit that I am think of swapping to. I confirmed it's radials are 54" long. https://productfinder.pulseeng.com/product/BSA45C/
 

Groeteschele

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Premium Subscriber
Joined
Apr 6, 2020
Messages
46
Location
Munich
I just installed a new ground plane antenna on my roofline to receive VHF low band specifically. This is made up of a Tram 1465 Ground Plane base kit, a Larson NMO 40 whip (50” tall), a 2 foot gavanized steel mast and 30 feet of MPD digital 400 coax (similar to LMR400 but white and flexible). I have grounded the mast to 8’ rod (properly by an electrician).
My problem is the audio quality is very noisy on low band frequencies compared with the same antenna on my NMO mount on my SUV. My signal strength is mainly 5X5 on all the low band frequencies I want to listen to in a 50+ mile radius based on the signal meter on the Uniden BCD536HP. I have noticed that noise reduces at night a good deal but still not as clear as I was expecting based on my mobile use with the antenna. Oddly, it’s sounds great on 800 MHz.
I connected it to my SDS100 and see RSSI levels of -83 to -89 dBm on the stronger, closer signals and -99 to -104 dBm on some of the further, weaker signals. I know this radio is not the best for this VHF Low Band.
This is my first attempt at a mounted outdoor antenna. Might you all have any suggestions on how to improve the audio quality?
Thanks in advance.
If room permits Laird/Cushcraft Ringo-Ranger series low band aerials are an affordable choice. The CRS2, CRS3 and CRS4 and the BR3 and BR4 are band split aerials There are also commercial, land mobile and military grade aerials that are extremely expensive and usually the choice for purist who monitor low band signals with laboratory grade receivers. The members in the Skip/Tropo subforum can advise you for what's best from personal experience. A number of them use Laird/Cushcraft Ringo Rangers aerials.

www.theantennafarm.com/catalog/
 
Last edited:

Arkmood

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Joined
Dec 19, 2002
Messages
232
Location
Taney County MO
Noise: You can actively search for noise in home with a portable AM/FM radio - place it near appliances, power adapters,etc...
 

jim202

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Joined
Mar 7, 2002
Messages
2,644
Location
New Orleans region
While your waiting for your low band radials, it might be worth spending some time trying to see if you can locate any low band noise. There is a multitude of sources. Some can be generated right in your home and others can be external.

First off, let me point out some sources of noise. There it the noise that can be generated by computer displays and TV sets with large screens like plasma displays. Next comes the computers that can radiate noise. This may or may not be caused by the LAN cables. Some fish tank heaters have bad thermostats that arc and generate noise. Older houses have been known to have bad door bell transformers that generate noise. These are sometimes hard to even locate. Then there is sources outside the home like arcing high voltage insulators. Tree limbs touching the wires or touching the wires in the wind. These get worse with wet weather. Last one is an electric fence charger. This sounds like a pulsing noise.

The best way to start locating noise is to start by killing the main breaker for the house and running a receiver on battery power. If the noise goes away, your down to items in your home. If it stays, your in for the search that will take considerably more time.

Hope this was of some help. You have not asked for the info, but thought I would pass it along for what it's worth. We all go through the noise hunting eventually.

Jim
 

prcguy

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Joined
Jun 30, 2006
Messages
9,745
Location
So Cal - Richardson, TX - Tewksbury, MA
The Ringo series only covers a few MHz well then falls off rapidly. If you tune one for 40MHz it will work great from maybe 39 to 41MHz then ok from about 38 to 42MHz then it rolls off pretty fast. I have a commercial duty version here I retuned for 6m amateur and it works ok. If you want consistent broad band coverage there are a couple of military antennas that show up surplus. One is the COM201B and its a medium size ground plane that covers 30 to 90MHz with very good performance across the entire band. I've had a half dozen of them and when the price gets down to about $175 they are a good deal.

The predecessor to the COM201B was the big OE-254 Bicone which is about 16ft tall but it works well. Its surprising the COM201B at half the size has better specs but the OE-254 shows up on Ebay here and there and you can usually find just the center hub with balun and attach your own radials. I did that using 10ft long radials instead of the original 8ft and had a great antenna that covered CB, 10m, 30-50Mhz VHF lo, 6m amateur and more.

Then there is the really big Discones that are about 8ft tall and work really well but the neighbors will not like it. They are a little more hard to find but I have one in my garage that needs a new home. The big Discones give you near resonant 1/4 wave ground plane performance across 30 to 90Mhz and will work much higher with reduced specs. I have used all the antennas mentioned for VHF lo band reception and have settled on the COM201B due to its performance vs size and the neighbors input. Its a keeper if you can find one.

Update: If the OP can figure out and fix the noise problem and if he can extend the radials on the NMO base mount, there is some surplus CHP base loaded broad band antennas on Ebay now and then. These are special models that cover 39 to 46Mhz continuous with no tuning and they work really well with a 62" long whip. Its not the entire VHF low band but its a lot wider than a sharply tuned VHF base load or a Ringo.

If room permits Laird/Cushcraft Ringo-Ranger series low band aerials are an affordable choice. The CRS2, CRS3 and CRS4 and the BR3 and BR4 are band split aerials There are also commercial, land mobile and military grade aerials that are extremely expensive and usually the choice for purist who monitor low band signals with laboratory grade receivers. The members in the Skip/Tropo subforum can advise you for what's best from personal experience. A number of them use Laird/Cushcraft Ringo Rangers aerials.

www.theantennafarm.com/catalog/
 
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