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Author Topic: Reducing Location Noise  (Read 2036 times)
AE5QB
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Posts: 269




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« on: February 14, 2013, 08:00:19 AM »

I am the sponsor and trustee of a middle school club station.  We were awarded a Butternut HF9V antenna as part of an ARRL station grant.  We just recently got on the air and are getting our feet wet with the School Club Roundup.  We seem to have a very noisy site here at the school as our noise levels on 20m and 40m are near S7/8 just about all of the time.  I assume it is due to the noisy motors in our ventilation system, lighting, etc.  I would say we do not have the optimal installation as it is not permanent.  We have to store our radio in a lockable cabinet and roll up the radio end of the coax and store it in a mechanical room when not in use.  So we have a very dynamic and nonsecureable (is tha a word) location without the ability to run massive permanent grounding busses etc.

So  I am just looking for a few anecdotal and professional suggestions on how we might manage the noise levels a little.  On the top of my list is to replace the vertical with a horizontal antenna.  Even a dipole or maybe a hex beam would be a lot quieter but I assume this environment would still be noisey even with that.  I can't personally think of many options other than attempting to ground the station to the electrical bus ground or running a fairly lengthy ground connection outside to a ground rod, but then I am not an expert in grounding and noise control and don't know how much that might help. If I could get the noise down to less than S6 I think I would be pleased.

Regards,
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N8BOA
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« Reply #1 on: February 14, 2013, 09:25:21 AM »

id bet you are hearing the electronic ballest in all of those fixtures. I would start ans see how far away you can hear the noise on a AM radio if you had a hand held unit. perhaps you can locate the antenna out of the way.
Good luck
And Good Job
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WB2WIK
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« Reply #2 on: February 14, 2013, 09:34:43 AM »

There are things you can do to "track down" noise sources, but an S7/S8 noise level on 40m really isn't bad.

Many times my noise level on 40m is S9 at home (with no man-made noise sources at all -- it's all atmospheric) and it's easy to make lots and lots of contacts, since "station" signals are well above that.

The Butternut needs a good radial system, of course.  What kind of radial system are you using?
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WB6BYU
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« Reply #3 on: February 14, 2013, 09:44:53 AM »

We had a simlar problem with the HF stationat the County Emergency
Operations Center:  a noise floor of S8 to +10 over on many bands.
Adding a coax choke at the antenna dropped the noise by 2 S-units
and allowed us to make more contacts.  (Adding one at the station
end didn't help, but we left it there for good measure.)

First, make sure you have a good ground system on the antenna,
then try adding a feedline choke right at the antenna.

There is no guarantee that a horizontal antenna will be any quieter.
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AA4PB
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« Reply #4 on: February 14, 2013, 09:47:03 AM »

I assume your antenna is mounted on the roof. If so, you will need a good radial system as described in the manual. You might also try making a multi-turn coil of the coax (a choke) feedline near the antenna connection. That would help to minimize noise pickup on the coax shield due to common-mode currents. You should ground the coax shield to "building steel" somewhere before it goes down into the building for lightning protection. Grounding connections made directly to the radio equipment aren't normally of much help in reducing noise anyway so I wouldn't worry about the temporary setup.

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W5WSS
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« Reply #5 on: February 14, 2013, 11:58:16 AM »

Yeah noise ingress is a function of an incomplete vertical system where radials should restore balance.

The HF9v vertical portion is OK but operating  devoid of a good second portion the radials whether ground mounted or tuned elevated and tuned resting atop the ground or rooftop is really beneficial of either function transmitting and receiving. Noise ingress is the product of voltage rising about the equipment and this action makes noise and is heard by the receiver.

You would benefit by automatically adding them axially spread apart by a couple feet even two tuned after laying them on the rooftop and resting in their final position be sure to route them traveling away and opposite yes a set of two per band will probably reduce the noise considerably 73
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AE5QB
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« Reply #6 on: February 14, 2013, 06:27:42 PM »

Thanks for the feedback folks.  We are just getting started so experimentation is the word.  I will say the kiddos are quite excited as we have been operating in our first SCR this week.  In spite of the noise we have made a number of contacts just operating after school for a couple of hours each day.  We are at 2500 points with tomorrow left to go.  I know that is not a big gun number for any contest, but looking at the last results it could be included in the "also ran" category.  So we are OK with that, but I digress.

I do have a ferrite bead choke kit from Palomar Engineering but haven't assembled it yet.  I will put that together and install it at the antenna and see if that helps.  We don't have the vertical on the roof yet (red tape) so we have it elevated on a 4 foot tripod out in the school yard.  We have 4 tuned radials for the 2 bands (20/40) that we have been working.  The radials start at the base of the antenna slope down to about 1 foot off the ground.  So yes it is a very minimal and compromised antenna install.

So I'll try the choke first and then go from there.  Right now we have nothing grounded.  My impression is that with an elevated system you really don't want the coax and radials grounded to earth.  Maybe that is incorrect.  Anyway, I appreciate the data point on 40m noise levels elsewhere.  On hunting down the noise source, I am not sure it is one or two sources.  To me it just sounds like a high level of white noise.  I do have relatively high noise on 40m at my home QTH but probably 2 S units lower than at the school.  At home 20 meters is actually pretty good and nothing like what I am seeing at the school.  20m is my primary concern.

Anyway, thanks for the information.  We'll keep experimenting.  I have some foxhunting equipment so maybe when we get some time we'll do some snooping around and see if we can find anything specific.

73,

Tom/AE5QB
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W3HKK
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« Reply #7 on: February 15, 2013, 02:52:31 AM »

Here's another solution. 

Dipoles are way less susceptible to  man made noise than verticals are.   So put up a  single dipole fed with a single line of coax.  Try 40 meters for starters. 

Then if you find it is much quieter,  add  elements  and convert it to a fan dipole with single coax feed, and  individual antennas cut for the bands you want to operate. The higher the frequency  ( 40 20 17 15 10) the better for noise reduction.  Perhaps try  try 40-20-17-10 .

 
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W5DXP
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« Reply #8 on: February 15, 2013, 07:01:05 AM »

There is no guarantee that a horizontal antenna will be any quieter.

But since a lot of local noise is vertically polarized, it might be worth a try given all that free student-power available.

Two QTHs ago, the noise level on my horizontal dipole was two S-units lower than for my vertical on 40m. Sometimes I used the vertical for transmitting and the dipole for receiving.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5WSS
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Posts: 1732




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« Reply #9 on: February 15, 2013, 07:11:26 AM »

Hello Tom, OK fb. The 4 tuned, elevated, sloping, and Isolated from Earthing radial sets for two bands is really good.

Your radial system potentially offers excellent system balance then because is more of center feed when these measures are taken.

The noise may subside some and as wb2wik mentioned could be normal and not indicative of a system deficiency per say.

Look at my call sign Eham picture the antenna is a fullsize 20m antenna with sloping isolated radials.

An interesting observation I made while using it was Engine noise and the positioning of the radials I could rotate the whole set of 4 around keeping everything even and eliminate allot of the engine noise.

This was best when the two that were nearest the front were dividing evenly their position apx 45 degrees from the engine.

IE the radials were placed from quarter panel diagonally relative to the engine compartment splitting the difference relative to the noise source.

So perhaps you can rotate your radials as a set about the antenna evenly and quiet things down, Along with repositioning the coax on the ground and adding the balun choke when you can.

This anecdote is NOT meant to say that your system is working poorly but rather are adjustments that are available relative to noise.

If you add a safety Earthing rod for the station listen to the noise when connecting themhave a helper make and break this connection and If it changes or gets stronger then noise ingress is suspect. The symptom is usually indicative of an antenna system radial deficiency.

Congratulations on the SCR accomplishments.

When you relocate the antenna to rooftop are you going to use the same tripod? And reuse the same tuned radial arrangement?
You may need to re tune the antenna some but in either case whether or not you add more horizontal radials axially around the semi circle the return of power back towards the vertical will not be much more than your sets of 4 tuned after laying them on the roof.

If so then,

Place the radials on the rooftop then use an analyzer to tune the radials this offsets any loading effects that nearby conductors and materials have on them.
Repeat the  same procedure for the vertical.
Now check the system feed point RR. Match the system and enjoy!

If you plan to duplicate a ground mounted vertical that is upon a rooftop then simply encircle the vertical with the radials as symmetrically as possible traveling away from the center no need to tune them if you can get enough then perhaps the system will return enough power back to the vertical to rival the sloped tuned sets.

The rooftop height above ground relative to the tripod on the ground system should completely change the noise source geometry and perhaps be quieter by default.

Have fun enjoy the system.

New hams learning 73
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AE5QB
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Posts: 269




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« Reply #10 on: February 15, 2013, 08:09:19 AM »

Thanks for the advise.

I never really considered the direction of the radials so that is very good information.  I'll try that this evening.  We have power lines and the AC cooling system from another school next door that I can point the radials away from.  Those potential sources are about 300 feet away so I don't know if they could be a problem or not.  I'll also try the grounding test suggested.

My thought was to install the system in the same configuration on the roof.  I actually have a 10 foot mast on the roof to which I can mount the HF9V.  I could then slope the radials down and tie them off using UV cord and cinder blocks as anchors.  I was thinking of 16 radials, 4 each 10, 20, 15/40, 80. My thought was the slightly higher base position would make for a slightly greater slope and a slightly improved impedance match.  But I don't relish the idea of trying to tune the HF9V on top of a 10' mast.  Who knows.  I have the wire to lay down 32-50 foot radials so I may just mount it on the roof and go with a flat radial system.  That would be easier to install, adjust, and maintain.  The only problem there is anchoring the far ends of 32 radials.  Perhaps I could just tack them down using roofing tar a few spots along the length of each radial.

Anyway, thanks again, we are not stressing, just having a lot of fun. In this day and age of immediate gratification and black and white answers, it is great to show students that there is a lot of gray area and compromise in what we do.  Their number one question right now is, "Why isn't it working right?"  My answer is always, "Gee I don't know, what do you suggest we do to find out?"

73,

Tom/AE5QB
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W5WSS
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« Reply #11 on: February 15, 2013, 09:08:27 AM »

Excellent!

I am interested in the antenna system progress. Please keep us posted once in awhile.

73

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WB2WIK
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« Reply #12 on: February 15, 2013, 09:14:43 AM »

Be careful with the antenna installed so low to the ground on a tripod in the school yard.

Assuming it's not behind a big locked gate and wall and might be accessible to kids or others walking by, this is dangerous.

The roof is a much safer environment for a transmitting antenna.

Even up there, don't let the "ends" (tips) of the radials come in contact with the roof or come close to anything flammable.  In "wet weather" (very high humidity, or rain), people are most surprised how far an arc will travel even with a 100W transmitter.  The tips of the radials are all high voltage points, and I've arced right across and through what many would consider to be pretty good insulators -- usually in wet weather.

Use ceramic or glass insulators and lead ropes at the ends of all the radials. Wink
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AE5QB
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Posts: 269




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« Reply #13 on: February 15, 2013, 06:04:56 PM »

Be careful with the antenna installed so low to the ground on a tripod in the school yard.

Assuming it's not behind a big locked gate and wall and might be accessible to kids or others walking by, this is dangerous.


Point well taken.  We didn't have it behind a big locked gate but we did put in some wooden sticks and put some of that orange plastic construction fencing material around the location.  It wouldn't have kept out anyone bent on getting in, but it was a deterrence.  We didn't zap any kids so I guess it was effective enough.  But thanks for bringing up the reminder.

We finished the SCR this evening with 67 QSO's , 12 schools, and 3 DX stations.  We worked Brazil, St. Croix, and Aruba.  We heard Juan on the Canary Islands 59 +20 but couldn't bust the pileup.  We worked a member of a Yacht club in Illinois and an aeronautical mobile in a Cessna Citation flying from Colorado to El Paso, Texas.  We finished with, if I recall properly, 25 states and 6,070 points.  We had a good run on schools the last couple of hours adding 5 to the 7 school contacts over the previous 4 days.  It was a lot of fun and I am really proud of my students.  We had our share of mess-ups and I apologize for them, but overall the munchkins did pretty well.  For our first attempt at the SCR and with a marginal antenna system, I think we did pretty well.   I also want to thank all of the hams across the nation who so graciously, patiently, and enthusiastically support the School Club Roundup.  What a great way to get kiddos interested in the hobby.  Your responses to our kids, even when they messed up, were overwhelmingly positive, supportive, and encouraging. My school is a pretty poor title 1 school with most of my kids coming from broken families.  I certainly don't pitty them but I do find it sad they don't have the same opportunities and experiences that I did as a kid. I think their first ham radio experience was overwhelmingly positive.  Anyway, my kiddos were all smiles when we shut down and are already talking about the next one.

Now if I can just find funding and support for a 100 foot tower and a beam before October, we should be in good shape!

Tnx again, everyone.

73,

Tom/AE5QB 
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KC4MOP
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« Reply #14 on: February 16, 2013, 02:43:31 AM »

Tom
The stations worked for SCR is proof that your project was a very good success.
If you are a good talker and there is a lot of enthusiasm for Amateur Radio; THEN try to convince the school board to go for a 60 foot tower and a reasonable, practical Yagi.  100 foot tower is a not necessary. Even if they go for it. The Yagi (horizontal) antenna is always much less electrical noise.
In fact, a 100 foot dipole raised up on the roof with thirty foot poles would have been a winner. A remote antenna tuner at the antenna and barefoot power was all you needed.
The vertical was not goodness on top of an electrically busy building. Vertical polarization is where all of your electrical noise is.
We hope you have success to get Amateur radio into your school district. The Cub Scouts are still very receptive to Amateur Radio. I'm waiting to get my 7 yr old involved.
Fred
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