Railfan Technology > Here’s a weird scanner installation question

OK, I have a scanner in my workshop, with the antenna in the attic. Unfortunately, that puts it under a steel roof. Surprise, surprise, the reception is horrible. 

I had had the bright idea of buying a magnetic mount antenna, similar to the one that performed quite well on my last car, and putting it on top of the steel roofing, high enough up on the roof so it won’t get removed by snow slides in the winter. (We’re in upstate NY here, so snow is an issue. )

Heres the catch:  there’s enough steel roof exposed to hold the mag mount, but most of the roof is covered with photovoltaic solar panels. 

Anybody know now if those panels would behave as a ground plane for the antenna?  They have aluminum frames, but I have no idea if the collection grid itself is conductive enough to work. 

Opinions welcome, especially if you know more about radio than I do. It doesn’t take much actual knowledge to reach that level...
 

Well, I can't see the solar panels doing any harm to reception. Go for it!

Have you considered building a J-pole antenna (link) and, say, mounting it to your chimney? 

Arved Grass
Fleming Island, FL

Make sure the antenna is grounded.  It should be grounded to the same grounding that grounds the house wiring.  I've seen lightning strikes hitting ungrounded antennas start structure fires.  Yes, it's unlikely, but it can happen.  This past summer I had a lightning strike less than 200 yards from my house.  Yes, my antenna is grounded.  No damage.

Interesting dilema. The general idea of a ground plane for an omni-directional antenna is that it is the same dimension of the antenna but in a full circle.

Putting an antenna on the roof gives better reception for a number of reasons, putting anything metal in front of it reduces that advantage. Installing an antenna on the metal frames would lose the advantage of a continuous ground plane, there may be other noise contributions as well. It would be a try it and see what happens and then justify the results later on.

Literally above all else there's the lightning safety factor, sticking anything metal above everything else means the installation needs to be designed to be hit by lightning.

Consider mounting the antenna on the side of the building where most of the radio traffic would be. Less likely to be hit by lightning and much less complex installation.

WW Wrote:
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> Make sure the antenna is grounded.  It should be
> grounded to the same grounding that grounds the
> house wiring.  I've seen lightning strikes
> hitting ungrounded antennas start structure
> fires.  Yes, it's unlikely, but it can happen. 
> This past summer I had a lightning strike less
> than 200 yards from my house.  Yes, my antenna is
> grounded.  No damage.

Well, if you want to get technical, and legal, there's a whole slew of grounding and bonding requirements in the National Electric Code. ARRL has some nice information (link) explaining everything, from why to how.

Arved Grass
Fleming Island, FL

I use PolyPhaser lightning protection devices on all of my antennas, both ham and ATCS.
If there are going to be severe storms, I try to disconnect the antennas.
Most of my antennas are around 20 feet in the air, but to lightning that doesn't mean anything.
I have seen lightning strike the ground right next to a 400-foot tower where I was working at.  I decided the vehicle was safe than being in the radio equipment building.
Good luck.
Pat
WA5VRO

If you want good reception and less exposure to other wiring, you might consider mounting an antenna on a pole attached to the side of the building away from all other obstructions.  The antenna would bolt on the top of the pole and the bottom of the antenna should clear the roof line.
It's good practice to keep clear of all other wiring including solar panels, keeps the path to ground along a straight path and hopefully keeps stray currents such as lightning or static charges from following a path into the building.  Be sure to ground the mounting pole with a heavy wire right down straight to a driven ground rod.  Resist the temptation to use a water pipe because that usually leads into the building and is not code approved anyway.
A good 5/8 wave vertical with ground plane would work well at roof height and cover all directions.  The ground plane radials are only about 18 inches long so shouldn't be a problem to clear the roof and pole.
Use a good feedline like LMR400 50 ohm coax for low losses.
Signal reception should be fine depending on how high you can get the antenna.

Arved Wrote:
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> Well, I can't see the solar panels doing any harm
> to reception. Go for it!
>
> Have you considered building a J-pole antenna
> (link) and, say, mounting it to your chimney? 

Live in CA. Very rare to get lightning here. I assume 58 ohm cable, or can use 59?

Many coax cables are identified by an RG-number.

I think you are referring to RG-58  and RG-59 coax.

RG-58 is 53.5 ohm and 0.195 inch OD.

RG-59 is 73 ohm and 0.252 inch OD.

There are other sizes with similar impedance's, but they have different power ratings, and losses at different frequencies.

For a receiver, you don't care about the power rating, but if you need a "long" run loss matters at 160 MHz.    

For "base station" type of use, LMR400 is the preferable cable to use.  Its major disadvantage is that it is pretty stiff and higher diameter than RG-58 or RG-59, but it can be run for considerable distance with minimal signal loss. RG-58 and RG-59 are best used for only mobile applications.

I don't use RG-59 because it's TV cable and 75 ohms.  Might be ok for receive only if that is the only thing that is available.
Pat
WA5VRO

Well Children, Here's something you didn't think about.  I too have a solar array on my roof and I've found my problem is quite common. All those panels are connected to an invertor that converts the DC current the panels generate while the sun shines on them into Direct Current at low voltage, but what you want is Alternating Current at Moderately high voltage.  It dose this by digitizing the the generated power into pulses of voltage at varying frequencies and amplitudes and polarities, thus DC becomes AC and therefore useful.  It also has to synchronize it's output to the utility frequency so there are no shorts.  All this generates NOISE.  Now this may not be an issue for AM reception but I "GUARANTEE" it will be an issue for any digital signal you want to try to receive. Especially digital TV, Digital VHF or Digital UHF.  It will mess with digital signal processing systems inside your receiver because the 'noise' will be treated just like any other received signal.  The only solution is to separate the receiving antenna and the noise source as far as possible, OR  install specific tuned filters in the antenna circuit which can get complicated and expensive.  I suggest separation as the best practical method.
I've been there.  My 3kw solar system is saving me a bundle, but wiped out my over the air TV reception.  I'm now trying to relocate my TV antenna to the far side of my yard.

mrsaxtonsr Wrote:
-------------------------------------------------------
> Well Children, Here's something you didn't think
> about. 

Often called chopper noise. Common in anything using DC/DC converters or just about any self contained vehicle.

To make some sense out of Mr Sunshine's rant the idea is to run the DC through a circuit that quickly cuts the energy off and then restores it, the output of that circuit looks like somebody taking an axe to a log and chopping divets out of it hence the name chopper. The subsystem I'm familiar with used a frequency just below 20 kHz for example, so all the transmitters and Transponders in that system has that signature 20 KHz sideband to them. The chopper creates a bunch of noise with most of the energy in a series of harmonics, the same idea is used in many of the other circuits in an RF design that create harmonics or multiply frequencies but the DC circuit is at a greatly higher voltage and current. The design I'm familiar with creates a bunch of harmonics and then runs them through a transformer and power supply supply circuits designed for those power levels and frequencies, the same idea is used in the battery back up system ( UPS ) that folks plug their computers into. In a UPS simply described the AC goes through a circuit to be stored in the DC battery and then when neeeded the DC goes through a circuit to be output as AC. The ciruits would change depending on energy levels and cost.

If you spec a Solar System for cost performance there is little concern with UHF performance, it simply has to meet building electrical code. If designing from scratch the chopper frequency and EMI could be a critical concern so would be designed into the system. I have no idea what the 'best practices' for the consumer solar industry would be, being an RF kinda guy if I was purchasing a solar panel system I would certainly be looking for those effects on my radios. A receive system would certainly be impacted by all that noise, in that case power supply filtering, cable and enclosure shielding and a system described by Rick2582 ( who has a HAM License btw ) would be what you're looking for. It's a known issue, HAMs deal with it in remote  installations, it's described in Industry, in electronics school, in College, the idea has been cheaped out for low cost solar installations.



Edited 1 time(s). Last edit at 11/10/19 08:37 by TCnR.

By now, the orgional poster may have given up on the whole idea.  The Tech savy folks on TO are great, but only when you speak their "Talk".