Stubby Antenna Install - Testing the loss of gain in the radio

[Radio Guy]

I swapped my antenna out for a 13" rubber coated one with copper coil, yada yada inside. I reported the results in another thread but the bottom line is a shortened antenna will be worse than stock for several reasons.

The stock antenna is roughly 1/4 wavelength in the middle of the FM broadcast band and its a microscopic fraction of a wavelength in the AM broadcast band operating in a completely different mode. In the FM broadcast band the whip will be fairly low impedance and on the AM band its extremely high impedance and probably several thousand ohms. The coaxial cable from antenna to radio is a special high impedance coax and all AM/FM radios are designed to match up with the equivalent of a roughly 30-32" whip antenna with the special coax.

When you shorten the stock antenna you can coil wire inside to make it electrically the equivalent of a 30-31" whip but the efficiency goes down. It doesn't matter if the coil is copper or made of solid gold, if you swap a 31" long antenna with a 13" you will loose a lot of reception and you can't get it back by any means. Its gone and aint commin back.

When I swapped my antenna I took note of various strong and weak AM and FM stations then visited them again after installing the 13" replacement and many weak stations were gone, could not receive anything. Some stations that were fine got noisy and some strong stations did not seem to change. This happened across both AM and FM bands.

If a station is really strong and you degrade it a bunch with a tiny antenna it could still be really strong and you just won't perceive a change on the radio, but if you hook a test receiver or spectrum analyzer to the antenna lead you will see exactly how much degradation there is. I may do this some day when I have time but its more for the benefit of others as I know and accept the degradation from my swapping antennas.

Years ago most car radios had a small variable capacitor to match the antenna on the AM band since the combination of antenna and length of coaxial cable can affect the circuit. The variable capacitor was accessible either on the back of the radio or through the cassette door opening (what's that??). I have not serviced car radios in many years and don't know if they still have a variable capacitor for antenna matching, but if they do you will get back some of the lost reception on AM by adjusting the capacitor if it has one.

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[MyRight]

I installed this 6" stubby a few days ago. Where I live in northern Georgia, even with the stock antenna I could only reach a couple of channels strong enough for the auto tuner to pick up on FM.
I saw no noticeable difference once the stubby was installed.
Today, I had to drive in to work, so I was near enough population where more stations are within range.
I was able to pickup all of the popular stations...many in HD and didn't notice any difference at all.
I didn't try AM, as I rarely ever listen to anything available on there.

I am completely happy with the change and for the benefits of appearance, as well as not having the metal antenna slapping the Jeep when running though the auto car wash is a huge plus for me.

 

[jac04]

I have tried:
- stock
- cut-down stock
- 13" AntennaX https://antennax.com/i-24623578-off...ru-2021-jeep-wrangler-jk-jl-gladiator-jt.html

AntennaX states "99.9% of the time reception stays the same OR improves". Well, I guess I'm part of the .1%, because reception was lousy. I have the same one on my JK and it seems to work much better than on my JT.

Cut-down stock (24", IIRC), was better than the 13" stubby, but still not as good as stock.

I ended up scuffing & painting my stock antenna black. The only reason I changed to the stubby was for asthetics. Now that my stock antenna is black, I don't even notice it.

 

[Radio Guy]

I have tried:
- stock
- cut-down stock
- 13" AntennaX https://antennax.com/i-24623578-off...ru-2021-jeep-wrangler-jk-jl-gladiator-jt.html

AntennaX states "99.9% of the time reception stays the same OR improves". Well, I guess I'm part of the .1%, because reception was lousy. I have the same one on my JK and it seems to work much better than on my JT.

Cut-down stock (24", IIRC), was better than the 13" stubby, but still not as good as stock.

I ended up scuffing & painting my stock antenna black. The only reason I changed to the stubby was for asthetics. Now that my stock antenna is black, I don't even notice it.

AntennaX lied. When you start with a roughly 1/4 wavelength antenna, anytime you shorten it the performance or efficiency will go down in proportion to how much you shorten it. There are very few exceptions like starting with a thin stainless steel antenna of a certain length (stainless has measurable loss in antennas) and you go to a slightly shorter but fatter antenna say 5 to 10% % shorter and made of copper which is a much better conductor at RF and you might come out even in performance. This is if you make the shorter antenna resonant by some means to be the electrical equivalent of the original antenna.

There is no way on this planet where you can take a 1/4 wavelength antenna in the FM broadcast band of about 31" and shorten it to 13" and have the 13" antenna outperform the 31" antenna.

 

[Mac]

I bought one off Amazon 31” black very pleased with the results, I don’t like the look of stubby antennas.
AntennaMastsRus - 31 Inch Black Antenna is Compatible with Jeep Wrangler JK - JL | Gladiator (2007-2020) - Spiral Wind Noise Cancellation - Spring Ste https://www.amazon.com/dp/B00ZJNIIZW/ref=cm_sw_r_cp_apip_NynC87HxINaAK

 

[21Moja]

I’m going to relocate my stubby to the bolt location for the soft top with a homemade mount. I’ll test it in both locations top on/top off and see how it does. I have a hardtop and it will fit underneath when top is on.

Do you ever get this done? Wondering what the results were...

 

[Summitsearcher]

Nope. Ran into a supply problem for the connectors and wire I needed. I did find you can run wire through the top bar to the back instead of the floor. I’ll get it done as soon as clips are available.

 

[Summitsearcher]

AntennaX lied. When you start with a roughly 1/4 wavelength antenna, anytime you shorten it the performance or efficiency will go down in proportion to how much you shorten it. There are very few exceptions like starting with a thin stainless steel antenna of a certain length (stainless has measurable loss in antennas) and you go to a slightly shorter but fatter antenna say 5 to 10% % shorter and made of copper which is a much better conductor at RF and you might come out even in performance. This is if you make the shorter antenna resonant by some means to be the electrical equivalent of the original antenna.

There is no way on this planet where you can take a 1/4 wavelength antenna in the FM broadcast band of about 31" and shorten it to 13" and have the 13" antenna outperform the 31" antenna.

Maybe you can locate what I need for this location project?

 

[LostWoods]

AntennaX lied. When you start with a roughly 1/4 wavelength antenna, anytime you shorten it the performance or efficiency will go down in proportion to how much you shorten it. There are very few exceptions like starting with a thin stainless steel antenna of a certain length (stainless has measurable loss in antennas) and you go to a slightly shorter but fatter antenna say 5 to 10% % shorter and made of copper which is a much better conductor at RF and you might come out even in performance. This is if you make the shorter antenna resonant by some means to be the electrical equivalent of the original antenna.

There is no way on this planet where you can take a 1/4 wavelength antenna in the FM broadcast band of about 31" and shorten it to 13" and have the 13" antenna outperform the 31" antenna.

Someone bumped this old thread but while you cannot cut a 1/4 wave antenna down to a shorter length, it is possible to make a 1/4 wave with a shorter length. Much like a Firestik CB antenna, the rod itself doesn't have to be the antenna and you can coil wire around a non-conductive shaft to maintain the same 1/4 wave. This is pretty much how most quality aftermarket flex antennas are made though there's probably more shit on the market than good.

 

[Radio Guy]

Someone bumped this old thread but while you cannot cut a 1/4 wave antenna down to a shorter length, it is possible to make a 1/4 wave with a shorter length. Much like a Firestik CB antenna, the rod itself doesn't have to be the antenna and you can coil wire around a non-conductive shaft to maintain the same 1/4 wave. This is pretty much how most quality aftermarket flex antennas are made though there's probably more shit on the market than good.

Absolutely true! But when you shorten it by winding wire into a coil around a fiberglass rod the efficiency and performance goes down. Go from a 31 inch long solid 1/4 wave whip for FM broadcast to half length or about 15 1/2" you loose at least 50% of the performance or more than 3dB. Go to something 1/3 the length like 10-11 inches and its even worse like around 75% or 6dB.

Some mfrs advertising will lead you to believe their 10" long flexible rubber replacement made with oxygen free solid copper wire, gold plated connections and other exotic materials will work better than stock but its a complete lie.

 

[j.o.y.ride]

I removed my antenna altogether

 

[TimC]

Some mfrs advertising will lead you to believe their 10" long flexible rubber replacement made with oxygen free solid copper wire, gold plated connections and other exotic materials will work better than stock but its a complete lie.

Whaaat? My oxygen-free, center loaded 102” plutonium plated whip was a rip-off at $600???

 

[Radio Guy]

Whaaat? My oxygen-free, center loaded 102” plutonium plated whip was a rip-off at $600???

And you wondered why you've been followed by black helicopters.

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