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Do reradiating antennas work?


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Without more specific information, it is hard to give a definitive answer.

 

There are two general types of "reradiating antenna systems", passive and active.

 

A passive reradiating antenna is simply two antennas that are coupled together, often by coaxial cable, and one is placed inside the area of weak signal and the other (called the "donor" antenna) is placed in an area where good signal can be had.

 

An active reradiating antenna system has a donor antenna in a location of good signal coupled to an amplifier (in the case of cellular or 2-way, this would be a bi-directional amplifier), whose output is connected to an antenna inside the poor signal area.

 

To answer the basic question:

 

Passive = NO

 

Active = YES

 

The passive antennas which you typically paste on inside and outside of the windshield are just gimmicks. The problem in any passive system is that in most cases the coupling loss from the inside antenna to the mobile device is greater than the donor antenna gain from being in a better signal area and its own pattern gain. This usually results in a very small advantage in the system - if any at all.

 

An active antenna will always have a power source independent of the mobile device and if properly designed, manufactured, and installed, can have a substantial benefit. (There a really big bold word in this sentence, read carefully :anicute: )

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I built my own reradiating antenna and have had decent sucess with it. The results I got are shown on the page. It helps for hiding caches but with all the LPCs and guardrail caches around I find I don't even need the GPSr, let alone a better signal. But a fun project nonetheless.

BRDAD!!!!!!!!!!!!!!!! LTNS.

 

For those to young to know, Brdad and I worked on these antenna's at the same time. We shared info and both worked well. The link on the bottom of my page goes to his. He has some really great charts and tests. My design was functional, his was really clever.

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Pretty cool projects.

 

i like the:

Things to consider concerning a reradiating antenna:

1. GPS signals are low power, high frequency (1.57542 GHz) digital signals. As long as the GPS is getting a clear signal from a particular satellite, amplifying the signal will do little for your accuracy.

2. A reradiating antenna will only amplify signals from satellites that are in view; If the GPS is picking up 4 satellites and all the others are near the horizon, odds are you will only pick up 4 with the reradiating antenna.

3. Where the reradiating antenna will help is under heavy cover, where the signal strength is not enough for the GPS to get a clear signal.

 

3. IMO Only if the donor antenna can be put outside the tree cover will it make a significant difference

 

I see the rating of gain is 27-33 Db.

 

Cable loss is approximately 28Db / 100 feet at 900 MHZ using RG-174/u (typical ultra-miniature coax) this would extrapolate to perhaps 40Db at 1.5 Ghz.

 

Therefore the shorter the better on the cable, but a 10 foot length loses about 4Db (not counting connectors and any poor construction practices that might be encountered in homemade projects)

 

The other important factor is coupling loss between the "transmitting antenna" gimmick and the receiver.

 

I don't know what would be a good estimate of coupling loss, but considering the factors of an untuned transmitting natenna with an unknown VSWR and resultant losses in the TX antenna cable and the variables of actual coupling, I would expect a coupling loss of at least 20Db.

 

Adding all this up, +33 -4 -20 = net gain of about +9Db

 

Technically speaking, I would consider it a very good project for getting a better signal inside the vehicle (with the antenna outside), but I would consider the advantages outdoors in heavy tree cover subjective at best.

 

There. Did I successfully convince anyone that a bumble bee cannot fly (from an engineering perspective)?

Edited by Confucius' Cat
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Just like the bee, inspite of the assumed numbers you used it works. I have mine on the end of a pole that extends 15 feet and I get a greatly improved signal in places where tree cover is causing problems. So it works in spite of the assumptions you made about construction. Which is really all that counts. :anicute:

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Just like the bee, inspite of the assumed numbers you used it works. I have mine on the end of a pole that extends 15 feet and I get a greatly improved signal in places where tree cover is causing problems. So it works in spite of the assumptions you made about construction. Which is really all that counts. :anicute:

The 15 foot pole is the key. You go from a location of poor signal to a better location. At 1.5 Ghz that might only require a 6 inch change in location. That is why such tests are subjective. The simple movement of the leaves in the wind could easily affect as much "gain" as the external antenna.

 

I guess you could just as easily attach the GPSr to the 15 foot pole and hold it up and take a reading.

 

if it works for you that's great. Others in other cases might find it not worthwhile.

 

it is interesting that i have been caching for four years and tried such active antennas (directly connected) with my Garmin (old as the hills) Street pilot back when I first started. The active antenna certainly helped the ancient Garmin, no question (but the old garmin has an external antenna jack, thus eliminating the questionable coupling of the "transmit" antenna gimmick).

 

Since I bought my first Magellan and subsequently, my second Magellan, I have never had any trouble with tree cover- even in places where the cache owner posted such things as "was not able to get good readings due to heavy tree cover."

 

I don't think that it is due to Magellan being "better" than Garmin as much as it is that it is a newer unit.

 

I have found that if signal is questionable, all i have to do is stand still and hold the unit upright for a few seconds and the sat signals pop right up.

 

An illustration from related radio stuff:

I'd like a nickel for every police, fire and commercial 800MHz base (control) station I have had to "service" because they used a magnet mount antenna inside the dispatch center or firehouse. They will complain about loss of signal or static. Moving the antenna a few inches "fixes" the problem (until next week/month).

 

The real problem is that they were too cheap to pay to have a proper and legal antenna installed OUTSIDE.

 

The OP requested "do they work". The answer is "maybe" - especially with "homebrew". I don't want to give false hopes.

 

It would be much better, if the point is to use an external antenna, to buy a unit that has an antenna jack. With the direct connection at least you get full benefit of the active antenna without losing MOST of the gain in the connection gimmick.

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Just like the bee, inspite of the assumed numbers you used it works. I have mine on the end of a pole that extends 15 feet and I get a greatly improved signal in places where tree cover is causing problems. So it works in spite of the assumptions you made about construction. Which is really all that counts. :anicute:

The 15 foot pole is the key. You go from a location of poor signal to a better location. At 1.5 Ghz that might only require a 6 inch change in location. That is why such tests are subjective. The simple movement of the leaves in the wind could easily affect as much "gain" as the external antenna.

 

I guess you could just as easily attach the GPSr to the 15 foot pole and hold it up and take a reading.

 

if it works for you that's great. Others in other cases might find it not worthwhile.

 

it is interesting that i have been caching for four years and tried such active antennas (directly connected) with my Garmin (old as the hills) Street pilot back when I first started. The active antenna certainly helped the ancient Garmin, no question (but the old garmin has an external antenna jack, thus eliminating the questionable coupling of the "transmit" antenna gimmick).

 

Since I bought my first Magellan and subsequently, my second Magellan, I have never had any trouble with tree cover- even in places where the cache owner posted such things as "was not able to get good readings due to heavy tree cover."

 

I don't think that it is due to Magellan being "better" than Garmin as much as it is that it is a newer unit.

 

I have found that if signal is questionable, all i have to do is stand still and hold the unit upright for a few seconds and the sat signals pop right up.

 

An illustration from related radio stuff:

I'd like a nickel for every police, fire and commercial 800MHz base (control) station I have had to "service" because they used a magnet mount antenna inside the dispatch center or firehouse. They will complain about loss of signal or static. Moving the antenna a few inches "fixes" the problem (until next week/month).

 

The real problem is that they were too cheap to pay to have a proper and legal antenna installed OUTSIDE.

 

The OP requested "do they work". The answer is "maybe" - especially with "homebrew". I don't want to give false hopes.

 

It would be much better, if the point is to use an external antenna, to buy a unit that has an antenna jack. With the direct connection at least you get full benefit of the active antenna without losing MOST of the gain in the connection gimmick.

 

Again you assume that the construction is of such that it really causes problem. An active antenna is not for everyone. If you want or need one they work. If you don't then its easy to spout tech-speak and make them sound like they are worthless. There are days when an additional 2 db would mean the difference between a lock and a DNF.

Edited by CO Admin
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Just like the bee, inspite of the assumed numbers you used it works. I have mine on the end of a pole that extends 15 feet and I get a greatly improved signal in places where tree cover is causing problems. So it works in spite of the assumptions you made about construction. Which is really all that counts. :anicute:

The 15 foot pole is the key. You go from a location of poor signal to a better location. At 1.5 Ghz that might only require a 6 inch change in location. That is why such tests are subjective. The simple movement of the leaves in the wind could easily affect as much "gain" as the external antenna.

 

I guess you could just as easily attach the GPSr to the 15 foot pole and hold it up and take a reading.

 

if it works for you that's great. Others in other cases might find it not worthwhile.

 

it is interesting that i have been caching for four years and tried such active antennas (directly connected) with my Garmin (old as the hills) Street pilot back when I first started. The active antenna certainly helped the ancient Garmin, no question (but the old garmin has an external antenna jack, thus eliminating the questionable coupling of the "transmit" antenna gimmick).

 

Since I bought my first Magellan and subsequently, my second Magellan, I have never had any trouble with tree cover- even in places where the cache owner posted such things as "was not able to get good readings due to heavy tree cover."

 

I don't think that it is due to Magellan being "better" than Garmin as much as it is that it is a newer unit.

 

I have found that if signal is questionable, all i have to do is stand still and hold the unit upright for a few seconds and the sat signals pop right up.

 

An illustration from related radio stuff:

I'd like a nickel for every police, fire and commercial 800MHz base (control) station I have had to "service" because they used a magnet mount antenna inside the dispatch center or firehouse. They will complain about loss of signal or static. Moving the antenna a few inches "fixes" the problem (until next week/month).

 

The real problem is that they were too cheap to pay to have a proper and legal antenna installed OUTSIDE.

 

The OP requested "do they work". The answer is "maybe" - especially with "homebrew". I don't want to give false hopes.

 

It would be much better, if the point is to use an external antenna, to buy a unit that has an antenna jack. With the direct connection at least you get full benefit of the active antenna without losing MOST of the gain in the connection gimmick.

 

Again you assume that the construction is of such that it really causes problem. An active antenna is not for everyone. If you want of need one they work. If you don't then its easy to spout tech-speak and make them sound like they are worthless. There are days when an additional 2 db would mean the difference between a lock and a DNF.

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One thing you have to consider is the effect of water in blocking GPS signals. The primary ingredient of the human body, by far, is water. If you're holding your GPS at waist level, at least half the horizon is blocked entirely by your body. If your head is above the GPS, then even more is blocked. Getting the antenna above your body will give a greatly increased signal in almost all cases. I haven't tried any homebrew antennas, but the one sold by PC-Mobile, which runs on 3 AA batteries, does work very well, and is very portable. It can make a big difference, especially under heavy wet tree cover. A standard external antenna is probably better, but for GPSrs which have no external antenna connection a reradiating antenna is a good solution.

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[

Again you assume that the construction is of such that it really causes problem. An active antenna is not for everyone. If you want of need one they work. If you don't then its easy to spout tech-speak and make them sound like they are worthless. There are days when an additional 2 db would mean the difference between a lock and a DNF.

SORRY!

I didn't mean to call your baby ugly just:

The OP requested "do they work". The answer is "maybe" - especially with "homebrew". I don't want to give false hopes.

That's all.

Edited by Confucius' Cat
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[

Again you assume that the construction is of such that it really causes problem. An active antenna is not for everyone. If you want of need one they work. If you don't then its easy to spout tech-speak and make them sound like they are worthless. There are days when an additional 2 db would mean the difference between a lock and a DNF.

SORRY!

I didn't mean to call your baby ugly just:

The OP requested "do they work". The answer is "maybe" - especially with "homebrew". I don't want to give false hopes.

That's all.

 

You could say the same thing if someone asked if cars worked. The answer - maybe, especially with homebrew.

 

There is nothing I have ever heard of in this world, natural or man-made, which you can say always works. I'm pretty sure the OP can look at our information and make the assumption he may or may not have as much luck as I or Lap have. I don't see the need to beat into us the fact that it may not work great.

 

As my page suggests, it did help in my tests, for whatever reasons. I don't care if it's because the antenna was somewhere other than where I would usually hold the GPS, or if there are surveying hampsters in the unit adjusting my numbers. I would guess I have received 25 0r 30 emails from people all over the world who have made such units, all but two I think were happy with what they got for the price. One of them had the wiring incorrect, and I am almost guessing the other had a faulty reradiating antenna. I never heard back from either, so I am not sure.

 

If car salesmen didn't want to give false hopes, we'd still be riding horses. :blink:

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If car salesmen didn't want to give false hopes, we'd still be riding horses. :blink:

If the lottery didn't give false hopes, poor people would have more money.

 

other cool false hopes we can spend our time and money on:

 

natural male enhancement

millions of dollars from a sultan in Nigeria that can't access his bank account

free computer if you forward spam

better sight without glasses or surgery

social security

hurricane insurance

rent to own

payday loans

the "sure win" in a horse race

_________________(fill in the blank) get rich quick scheme

make millions in real estate without using any of your own money

 

... ad infinitum

 

Oh, and microwave frequency electronic construction projects done by people who might not even recognize a soldering iron if they see one on a Wal-Mart shelf. (A fact that is NOT indicated one way or the other by the OP, but I am sure does NOT apply to those who have successfully created "reradiating antenna systems", which everyone who has so far posted except myself and the OP has defined as "means of connecting an external antenna to a GPSr that is not designed to be connected to an external antenna").

 

I am happy for your success.

 

I was just trying to be helpful

I won't let it happen again

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