Usable low profile 10m/6m antenna

[N9JIG]

Here is my current boggle:

I have a decent dual band radio in the car and am considering replacing it with a new IC7000 or another mobile that covers 6m, 10m as well as 2m and 70cm.

Most of these use a separate antenna for 6 and 10m (as well as other HF bands). What I need is a decent mobile antenna with an NMO mount that will give usable performance on 10m and 6m and be under 16 inches tall off the roof. (Garage clearance etc.)

I know I wouldn't get great performance out of a small antenna like that, I already have a performance antenna for times I need one, but I need something I can use for everyday traveling to and from work etc. and not have it whack off every tree branch on the way.

 

[popnokick]

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Assuming you'll be transmitting and not simply receiving, the laws of physics will burn your RF output finals and/or antenna if you run any usable power into something 16 inches or less on 6 or 10. You'll find 16 inch dualbanders for 2m & 70cm (I have one). You might have some crappy reception on 6 & 10 with one, and we could all take bets on what will pop first when you key up on those freqs.

 

[rfradioconsult]

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Assuming you'll be transmitting and not simply receiving, the laws of physics will burn your RF output finals and/or antenna if you run any usable power into something 16 inches or less on 6 or 10. You'll find 16 inch dualbanders for 2m & 70cm (I have one). You might have some crappy reception on 6 & 10 with one, and we could all take bets on what will pop first when you key up on those freqs.

Ok a couple of things; let's look at the "Hamstick" style of HF mobile antennas, they make ones that cover 75-80 Meters along with the rest of the HF bands, the length is roughly 7 feet for each band. Compare to a 1/4 antenna as a standard a 1/4 wave at 75 M is roughly 65 feet, so if we have a shortened antenna of roughly 7 feet the Hamstick is roughly 9.5% in length;however you have to calculate the antenna efficency is about 3-5% so your 100W radio is actually radiating a signal of about 3-5 W ERP.

Back in the heyday of 11 Meter CB there were a number of antennas sold that had a center loading coil with an overall length of about 16-18 inches. So yes you can have a shortened antenna but expect about a 12 dB reduction in your signal.

With modern radios, both commercial and amateur almost all utilise a built-in Forward/Reverse power montioring circuit to reduce the RF drive to reduce the potential of damage to your radio in the event of a fault in the antenna system.

 

[N9JIG]

I was thinking some sort of loading coil would at least get it resonate. I realize it wouldn't work real well, but should be enough for local use.

 

[rfradioconsult]

Here is a link that discribes the DDRR antenna that would meet your height requirements, if you are willing to construct one. Many years ago there were a couple of manafacturers selling these.

http://www.cq-vhf.com/AntennasFall07.html

 

[popnokick]

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Have you considered a 1/4 wave whip mounted someplace other than rooftop? You would at least be able to tune/load to full power. When you go into the garage just bend the whip over and attach to a gutter clip on you vehicle. Mount as high as you can on vehicle. Trunk or hood lip, side body, or bumper (in order of preference).

 

[jim202]

Here is my current boggle:

I have a decent dual band radio in the car and am considering replacing it with a new IC7000 or another mobile that covers 6m, 10m as well as 2m and 70cm.

Most of these use a separate antenna for 6 and 10m (as well as other HF bands). What I need is a decent mobile antenna with an NMO mount that will give usable performance on 10m and 6m and be under 16 inches tall off the roof. (Garage clearance etc.)

I know I wouldn't get great performance out of a small antenna like that, I already have a performance antenna for times I need one, but I need something I can use for everyday traveling to and from work etc. and not have it whack off every tree branch on the way.

Your not asking for much, but sure have a good dream.

Been in the 2 way field for better than 45 years now and can plant my feet and say that it will never
happen. Getting an antenna for 6 and 10 meters that is 16 inches or less I don't think is even a dream.
The law of physics just won't let that happen. Those antennas are just plain going to be long. Accept
that fact and deal with it. The rest of the frequencies may come closer to that, but your still going
to have issues.

 

[c5corvette]

I have to agree with eveyone else - a 16 inch or less NMO mount type antenna will have to have a hell of a transmatcher hidden somewhere in feedline.

Why not try a commercial company like stico.com or licenseplateantenna.com ? When I did law enforcement radio installs back in the 80's we used AM/FM look-alikes all the time for lowband and they worked as good or better than a normal antenna.

If you are going to use for both ends of the spectrum (for example, both 30 and 50), you can try a glass mount antenna made for 10/11 meters. You will need to find one specifically rated for your power output requirments (I have used ones rated up to 50 watts before for FD lowband and it works marginally ok.)

 

[popnokick]

I've used glass mount/thru the glass antennas and had some success with VHF low band and 10M, BUT FOR RECEIVING ONLY. You do not want to TRANSMIT into a glass mount antenna. This thread began with the rig in use as possibly an IC-7000, and presumably wanting to transmit. If we take transmitting out of the problem, and start talking receive only... then there are more antenna options.

 

[c5corvette]

This thread began with the rig in use as possibly an IC-7000, and presumably wanting to transmit.

I'd have to agree - any glass mount wont handle 100 watts. 50 is about the max I have seen 10/11m thru glass antennas rated.