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Modifying an AS3900 Antenna for CB use

HoveringHMMWV

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I've gutted an AS3900 antenna for use with a CB radio. I understand that it's not an optimal choice but can be functional although limited. My question is: Where should I attach the ground strap to the antenna? Externally at the base of the spring/mount or somewhere internally on one of the metal components?
Thanks in advance!
 

NotThatGuy

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Two things to overcome.

Do you know how to use an SWR Meter and tune an antenna?

I'd have to see is the AS3900 has the bandwidth to tune for 11 Meters, ( 27Mhz, the CB Band)

Connecting the ground strap of an antenna is an important part of creating the "ground plane" part of the antenna.

What vehicle are you mounting the CB in?

I'm unsure if that antenna can be tuned for 11 Meters. Anyone?
 
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NotThatGuy

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It looks like the antenna is a Broadband antenna.

Your available power will more than likely be used up by using such a Broadband antenna.

Is there a Band Specific Mast that can be replaced for 27Mhz?

The other option is to call the manufacture and ask them if the antenna can be tuned (by altering its length), for 27 Mhz.

Or abandon using that antenna and use an 11 Meter (27Mzh) Band Antenna.

I wish I could help more but .mil vehicle chassis are new to me, (But not COMMS installs).
 

tennmogger

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The As-3900, if unmodified, would have presented a reasonable load to the CB transmitter but won't radiate much on CB frequencies. If "gutted", and a coax connection made to the feed point inside the base, the antenna now looks like a dipole for a much higher frequency than CB. (I am remembering mid-30-ish MHz.) That high resonance is the design of the antenna as a dipole with feedpoint near the middle, where the two antenna sections screw together. Half the dipole is the length of the short top section of the antenna, hence the high frequency. That length is nowhere near CB frequency. There is now no match to the antenna on CB. It might still work ok on receive but the transmitter won't like it.

What to do? I would get an automatic antenna tuner, like the LDG Z-11 PRO. These show up used but aren't too expensive new. Connect the radio to the LDG radio port, and the LDG antenna port to the modified AS3900. The tuner will match the CB to the antenna so the CB will like what it sees. Radiation from the antenna will not be optimum (like a true 102" whip) but I'd guess the signal output will far exceed what you would get out of the unmodified AS-3900.

Search on SS for AS-3900 and AS3900 because there is a lot of info already here.

On your grounding question, ground the antenna base's housing, and ground the coax shield to the housing. This won't ground the "antenna" because it is a dipole and a dipole does not need grounded.
 
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NotThatGuy

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Thanks for the help Clarification Ten,

I like to get guys with little radio experience to try and follow me and think out the obstacles.

I wasn't able to pull up specs/install manual on the antenna to figure out the type and tuning ability of the antenna.

Even if the antenna would resonate, having a wide-band SINGARS transmitter to use on 17 Meters is like buying a Formula 1 Race car without a transmission and expecting to win.

Btw, have you used this antenna on HF radios with a transmitter with a built in tuner?

What type of resonate SWR did you get?

I've always found that Mobile HF will be degraded due to the necessity of using a compromised antenna.

But once you park and throw out some wire, that's when HF shines and pulls its weight, (given the conditions are in your favor).
 

tennmogger

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I have not used a gutted AS3900 with a tuner but I have used a AS1729 with a tuner to provide a better load on 10 meters. Worked ok but no doubt was lossy. CB frequency is not far off. Your AS3900 might work better? I am really curious to know too. Who could try that with a tuner? Someone could send me a "bad" AS3900 HA HA.
 

NotThatGuy

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Over the years I haven't had too much luck trying to fit(i.e. tune) a broadband antenna to a mobile application.

Its a whole lot easier using a mobile antenna that designed to work in the frequency band of the transmitter.

Most adjustible load mobile HF Antennas are INHO not rugged enough for mobile use.
 
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