I am using an indoor gain antenna to monitor rail traffic in my area. Currently the antenna is attached to the inside of an exterior wall on the 3rd floor of my townhome. If I moved the antenna to the attic what kind of increased reception range could I expect? I would think signals would more easily penetrate the roof then a wall with plywood and drywall. Anyone have thoughts on this, or can speak from experience of moving an indoor antenna to the attic?
indoor antenna placement thoughts?
- Thread starter Andrewo
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It would help us to know a little more about the antenna. Can you post a pic? In general though, barring obstacles like aluminum foil insulation and metal ductwork, your antenna is going to do better in the attic. How much more coax is that going to require?
It would help us to know a little more about the antenna. Can you post a pic? In general though, barring obstacles like aluminum foil insulation and metal ductwork, your antenna is going to do better in the attic. How much more coax is that going to require?
I am using the traintenna blade indoor antenna, which is nice because it doesn't require a ground plane. The antenna came with 18' of coax which should allow me to run it from the attic above to my Yaesu.
DPD Productions - TrainTenna Railroad Band Antennas for Commercial & Hobbyist Applications
DPD Productions - TrainTenna Railroad Band Antennas for Commercial & Hobbyist Applications
I looked on that site and that "blade" antenna appears to be a simple 1/2 wave vertical, the 'blade' just being a name. It should yield the same performance as any 1/2 wave vertical antenna. 1/2 wave antennas have no gain, by the way. They are what are used as a standard that other antennas are compared with.
I can say that I have 'doubt's about any company that claims an omnidirectional pattern from a log-periodic (LP) antenna. That seems kind of odd.
An antenna in your attic may produce better results than against a wall. It would depend on what the building's roof consists of, and the extra height wouldn't hurt anything.
Good luck.
- 'Doc
I can say that I have 'doubt's about any company that claims an omnidirectional pattern from a log-periodic (LP) antenna. That seems kind of odd.
An antenna in your attic may produce better results than against a wall. It would depend on what the building's roof consists of, and the extra height wouldn't hurt anything.
Good luck.
- 'Doc
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WA1ATA
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It is common to have gain specified with something other than a 1/2 wave antenna. A very common reference is an isotropic antenna that has equal radiation in all directions.
A 1/2 wave antenna in freespace will have 2.15dB gain over isotropic. In real life, mounted above ground they generally have slightly higher gain. DPD claims 3dBi gain. Note the little "i". That means the 3dB is referenced to isotropic.
The blade antenna appears to be a 1/2 wave end fed antenna with fed via a matching stub. More commonly referred to as a J-pole. In this case, made out of ladder line rather than copper tubing.
Please explain. I don't see any such claim in the link provided by the original poster, DPD Productions - TrainTenna Railroad Band Antennas for Commercial & Hobbyist Applications . Perhaps you are misreading the 3D plot. Note that the origin is not in the center of the big ball. The two other graphs give more quantitative info.
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The confusion might be that the first antenna shown on the linked DPD webpage is in fact a log periodic. But the TrainTenna "blade" being used by the OP... pictured further down the page... is definitely not an LP.
TO THE OP- Assuming you have enough height in your attic to keep the antenna vertically oriented. and are able to locate the antenna away from large metal surfaces, chances are performance will improve in the attic. Go for it... and let us know what happens.
The confusion might be that the first antenna shown on the linked DPD webpage is in fact a log periodic. But the TrainTenna "blade" being used by the OP... pictured further down the page... is definitely not an LP.
TO THE OP- Assuming you have enough height in your attic to keep the antenna vertically oriented. and are able to locate the antenna away from large metal surfaces, chances are performance will improve in the attic. Go for it... and let us know what happens.
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This is what I'm referring to with the 'omni-directional' thingy.
"Flexible Design: Unlike Yagi designs, the LP design has more useful lobes to the sides and back. This gives the antenna a better 360 degree omni ability, with the added benefit of gain in the direction it's aimed. Why use a unity gain discone or ground plane, when you can have omni ability and directional gain as well with the LP."
That tells me they are claiming some omnidirectional properties for their 'LP' antenna. And that is not what is typically considered a good characteristic for a log-periodic or any directional antenna.
I'm aware of how antenna modeling works and how the results are displayed. I've done that sort of thing for quite a number of years. I'm also aware of the limitations and qualifications when comparing actual antenna performance when compared to an isotropic antenna. If you cn factor in, model, all the 'left out' characteristics in an antenna's environment you still only end up with an -indication- of what it's capable of, not a factual representation. Close, but no cigar.
I can find no reference to the impedance matching system used by the 'blade' antenna. It certainly could be a 'J'-pole though. Or, considering it's physical length, a 'J'-pole array of more than one element. It could also be a center fed doublet, or several other possibilities. Without tearing one apart I wouldn't make a guess on that.
Just for grins, try using a length of wire as the receiving antenna. If that length is related to a resonant length for the frequency of interest, it will work surprisingly well. For RR frequencies (162 Mhz +/-) make it in multiples of about a foot and a half. The higher the better, and until it get's completely ridiculous, longer is better. If this thing is going to be where it won't be seen, who cares what it looks like, you know?
- 'Doc
"Flexible Design: Unlike Yagi designs, the LP design has more useful lobes to the sides and back. This gives the antenna a better 360 degree omni ability, with the added benefit of gain in the direction it's aimed. Why use a unity gain discone or ground plane, when you can have omni ability and directional gain as well with the LP."
That tells me they are claiming some omnidirectional properties for their 'LP' antenna. And that is not what is typically considered a good characteristic for a log-periodic or any directional antenna.
I'm aware of how antenna modeling works and how the results are displayed. I've done that sort of thing for quite a number of years. I'm also aware of the limitations and qualifications when comparing actual antenna performance when compared to an isotropic antenna. If you cn factor in, model, all the 'left out' characteristics in an antenna's environment you still only end up with an -indication- of what it's capable of, not a factual representation. Close, but no cigar.
I can find no reference to the impedance matching system used by the 'blade' antenna. It certainly could be a 'J'-pole though. Or, considering it's physical length, a 'J'-pole array of more than one element. It could also be a center fed doublet, or several other possibilities. Without tearing one apart I wouldn't make a guess on that.
Just for grins, try using a length of wire as the receiving antenna. If that length is related to a resonant length for the frequency of interest, it will work surprisingly well. For RR frequencies (162 Mhz +/-) make it in multiples of about a foot and a half. The higher the better, and until it get's completely ridiculous, longer is better. If this thing is going to be where it won't be seen, who cares what it looks like, you know?
- 'Doc
I agree the mention of omni properties on a log periodic is not a good attribute. Looking at the DPD log periodics I don't see a shorting stub at the rear of the antenna and that could be the cause of unwanted side lobes.
I read an analysis once where someone characterized a log periodic with and without the shorting stub and without the performance was significantly degraded.
prcguy
I read an analysis once where someone characterized a log periodic with and without the shorting stub and without the performance was significantly degraded.
prcguy
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This is an interesting question about the ideal design tradeoff.
Is the typical user of the antenna better served by a very high front-to-back ratio (and probably a fairly erratic side pattern with deep nulls); or is the user better served by more uniform pattern and lower front to back ratio.
My guess is that the more common requirement is high gain in one particular direction to pull in a weak station, with less gain (but nearly uniform response) in other directions in order to pick up the stronger stations.
I don't see the need to reject an unwanted on-frequency signal via high front-to-back ratio as a common requirement for scanner users or railroad fans.
As I understand the drawings, the forward gain is 9dBi. Front to back ratio is 18dBi, so the "omnidirectional" portion of the antenna response curve is -9dBi.
Is the typical user of the antenna better served by a very high front-to-back ratio (and probably a fairly erratic side pattern with deep nulls); or is the user better served by more uniform pattern and lower front to back ratio.
My guess is that the more common requirement is high gain in one particular direction to pull in a weak station, with less gain (but nearly uniform response) in other directions in order to pick up the stronger stations.
I don't see the need to reject an unwanted on-frequency signal via high front-to-back ratio as a common requirement for scanner users or railroad fans.
As I understand the drawings, the forward gain is 9dBi. Front to back ratio is 18dBi, so the "omnidirectional" portion of the antenna response curve is -9dBi.
"I don't see the need to reject an unwanted on-frequency signal via high front-to-back ratio as a common requirement for scanner users or railroad fans."
I tend to agree with you about the rejection thingy when speaking about signals that are not 'numerous' on a particular frequency. In my area there are seldom more than one train through here at one time. Im located to one side of the tracks. If I were between two tracks, if there were simultaneous transmissions being made from two directions at the same time (I really doubt that) thn I would see a need for rejecting that 'second' signal. On bands where there are a number of transmissions being made from several directions, sure, rejecting the undesired signals becomes more important (sides or back of the antenna). That's the 'beauty' of a directional antenna, it can do that, and is as important as having a high gain in the direction you point the thing. I think that's why having an omnidirectional antenna in addition to a directional one is a good idea. If that omnidirectional antenna also has some gain, that's even better.
At VHF/UHF the one thing that will mean more 'range' more than gain is antenna height. That's because of the 'line-of-sight' characteristics of those frequencies. The original poster's idea of moving the antenna to the attic is a pretty good one for that reason. It won't be a 'cure-all', but it will certainly help -IF- the construction of the building doesn't present too much attenuation. Mounting an omnidirectional antenna a 1/10 of a mile above the house would be even better! (That's just not practical in most cases though... RATS!) Sometimes, hearing too much is just as bad as not hearing anything...
- 'Doc
I tend to agree with you about the rejection thingy when speaking about signals that are not 'numerous' on a particular frequency. In my area there are seldom more than one train through here at one time. Im located to one side of the tracks. If I were between two tracks, if there were simultaneous transmissions being made from two directions at the same time (I really doubt that) thn I would see a need for rejecting that 'second' signal. On bands where there are a number of transmissions being made from several directions, sure, rejecting the undesired signals becomes more important (sides or back of the antenna). That's the 'beauty' of a directional antenna, it can do that, and is as important as having a high gain in the direction you point the thing. I think that's why having an omnidirectional antenna in addition to a directional one is a good idea. If that omnidirectional antenna also has some gain, that's even better.
At VHF/UHF the one thing that will mean more 'range' more than gain is antenna height. That's because of the 'line-of-sight' characteristics of those frequencies. The original poster's idea of moving the antenna to the attic is a pretty good one for that reason. It won't be a 'cure-all', but it will certainly help -IF- the construction of the building doesn't present too much attenuation. Mounting an omnidirectional antenna a 1/10 of a mile above the house would be even better! (That's just not practical in most cases though... RATS!) Sometimes, hearing too much is just as bad as not hearing anything...
- 'Doc
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The 52" height of the RR blade is about right length for a 1/2 wavelength section at 160MHz + a transmission line matching section of roughly 1/4 wavelength.. The Marine VHF blade (156-157MHz range) is listed as being 57" long.
Someone took apart a "Traintenna" and posted the details in this late 2009 thread: http://forums.radioreference.com/sc...67-traintenna-really-designed-160-161mhz.html . It appears that the blade is similar construction but without the weather housing. I notice that, unlike the indoor blade antennas, the outside antennas for both RR and marine are the same length. My guess is that they use the same housing/weather protection tubing.
I was particularly interested in that discussion since I often use a simple rollup J-pole of very flexible 300 ohm twinlead as a portable indoor antenna.
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Back to the original discussion ..........
The advantage of antenna like the blade is that you can move it around to different locations in a room to see if you can find a hot spot if there is just one specific weak station you are having trouble with. And of course, you can alway just climb up onto your roof or into your attic with the blade antenna and a handheld scanner and see what improvement you get before you go to the trouble of drilling holes and running coax.
As others have noted, height is key since normal propagation of VHF is more or less line-of-sight
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