VHF Low Band antenna interaction

[RFI-EMI-GUY]

So my mobile project is back on. I decided to retire my low miles 2001 Expedition. Not because of mechanical problems, it runs fine but needs paint. So I found a 2013 with great mechanical s and paint is fine, within my repaint budget. So off to the races.

The roof on the XLT model is 104 inches of genuine US Steel sheet metal front to back. Centered on this roof I plan to have a 6 meter antenna , NMO base loaded type. And fore and aft of the 6 meter antenna an 11 meter and 10 meter, also base loaded NMO mount. Assuming this geometry, the 10 meter and 11 meter antennas will be mounted about 52 inches from each other, and the 6 meter antenna 26 inches from the 10 and 11 meter antennas. (There will be various VHF and UHF NMO's interspersed. Of the V and U, I don't anticipate much interaction.)

What kind of interaction should I expect with respect to VSWR tuning of these three antennas, 6, 10 and 11M ?

Will I be playing Whack-A- Mole? Tuning strategy?

 

[slowmover]

Maybe a fleet of Tesla slaved to follow lead car. 😁

 

[prcguy]

So my mobile project is back on. I decided to retire my low miles 2001 Expedition. Not because of mechanical problems, it runs fine but needs paint. So I found a 2013 with great mechanical s and paint is fine, within my repaint budget. So off to the races.

The roof on the XLT model is 104 inches of genuine US Steel sheet metal front to back. Centered on this roof I plan to have a 6 meter antenna , NMO base loaded type. And fore and aft of the 6 meter antenna an 11 meter and 10 meter, also base loaded NMO mount. Assuming this geometry, the 10 meter and 11 meter antennas will be mounted about 52 inches from each other, and the 6 meter antenna 26 inches from the 10 and 11 meter antennas. (There will be various VHF and UHF NMO's interspersed. Of the V and U, I don't anticipate much interaction.)

What kind of interaction should I expect with respect to VSWR tuning of these three antennas, 6, 10 and 11M ?

Will I be playing Whack-A- Mole? Tuning strategy?

I would not expect much tuning interaction as the 10/11m antennas should be high impedance on 6m The 6m antenna is about 1/8 wavelength on 10/11m and not that bad. There probably be some pattern skewing.

I have a couple of Laird wideband 10/11m antennas that cover roughly 26.8 to 30MHz with no tuning and they have whips over 60in long. They easily handle both 10 and 11m in one antenna and they are NMO.

 

[jeepsandradios]

FWIW I had a 2003 with Lowband (46.xx) and a CB antenna on the roof and both tuned fine. I used the Larsen NMO27b and Larsen NMO40b. Along with those there was also a 1/4 wave VHF (black) and 1/4 wave UHF and 800 pepper shaker on the roof. For the most part all worked very well considering the amount of RF there. I definately missed the space on the F150. Its even worseo n my new Frontier.

 

[RFI-EMI-GUY]

I would not expect much tuning interaction as the 10/11m antennas should be high impedance on 6m The 6m antenna is about 1/8 wavelength on 10/11m and not that bad. There probably be some pattern skewing.

I have a couple of Laird wideband 10/11m antennas that cover roughly 26.8 to 30MHz with no tuning and they have whips over 60in long. They easily handle both 10 and 11m in one antenna and they are NMO.

I might consider the Laird WB antenna. But the 60 inch had me considering the separate antennas which are about 1 or 2 feet shorter. I already sketched out a circuit for a single antenna changeover relay between two radios. plus woops termination load since I probably won't operate both at same time.

Would you expect interaction of VSWR between two NMO 10/11 with ~ 40 to 47 inch whips?

 

[RFI-EMI-GUY]

View attachment 153964

Maybe a fleet of Tesla slaved to follow lead car. 😁

Yeah, not going for that look!

 

[prcguy]

I might consider the Laird WB antenna. But the 60 inch had me considering the separate antennas which are about 1 or 2 feet shorter. I already sketched out a circuit for a single antenna changeover relay between two radios. plus woops termination load since I probably won't operate both at same time.

Would you expect interaction of VSWR between two NMO 10/11 with ~ 40 to 47 inch whips?

Two antennas on virtually the same band and less than 1/4 wavelength apart will skew the pattern a lot. That will also be influenced by having the unused antenna open, grounded or attached to a 50 ohm load. I suspect you have one radio that does both 10 and 11m so why not one antenna to cover both?

 

[RFI-EMI-GUY]

Two antennas on virtually the same band and less than 1/4 wavelength apart will skew the pattern a lot. That will also be influenced by having the unused antenna open, grounded or attached to a 50 ohm load. I suspect you have one radio that does both 10 and 11m so why not one antenna to cover both?

I have two radios, the Syntor X9000 that yes, does have 10M plus an Itinerant at 27.490 of lower importance. And I will have a multimode FCC certified CB 11/M. I can definitely see the advantage of the one antenna shared by a relay. I have solved my 6 meter "problem" for the X9000 with a Comet CF360 diplexer. Its just so very frickin long, the WB antenna.

67.5 inches!

 

[mm]

I might consider the Laird WB antenna. But the 60 inch had me considering the separate antennas which are about 1 or 2 feet shorter. I already sketched out a circuit for a single antenna changeover relay between two radios. plus woops termination load since I probably won't operate both at same time.

Would you expect interaction of VSWR between two NMO 10/11 with ~ 40 to 47 inch whips?

Stay away from the Laird WB models, I had 2 of them each one was the model covering ~27.75 to 30 MHz and in the matching/wideband network in the base the toroidal core cracked on each one.

I ended up redesigning mine to use a new toroid core which has heavily protected from further vibration damage but the retuning of the matching network to cover 10 meters was a major pain due to the stray capaitance of the new material used to keep the core from cracking. The second replacement that i received from the dealer had core overheating issues when used with my GE 110 watt Orions and RANGR's and this one was fine with my 60 watt models. Eventually this second one had the same toroid core damage from vibration as the first one.

 

[RFI-EMI-GUY]

Stay away from the Laird WB models, I had 2 of them each one was the model covering ~27.75 to 30 MHz and in the matching/wideband network in the base the toroidal core cracked on each one.

I ended up redesigning mine to use a new toroid core which has heavily protected from further vibration damage but the retuning of the matching network to cover 10 meters was a major pain due to the stray capaitance of the new material used to keep the core from cracking. The second replacement that i received from the dealer had core overheating issues when used with my GE 110 watt Orions and RANGR's and this one was fine with my 60 watt models. Eventually this second one had the same toroid core damage from vibration as the first one.

Do you have a schematic of the "innards"?

 

[RFI-EMI-GUY]

I am wondering why Laird does not specify rated power for these antennas?

 

[prcguy]

I am wondering why Laird does not specify rated power for these antennas?

I see the CW27 and the CW37 both rated at 200 watts.

 

[RFI-EMI-GUY]

I see the CW27 and the CW37 both rated at 200 watts.

Where did you find that?

 

[prcguy]

Where did you find that?

I did a search on Laird CW27 and CW37, two models that I have and then found factory specs.

 

[RFI-EMI-GUY]

I did a search on Laird CW27 and CW37, two models that I have and then found factory specs.

I have found that on some reseller sites. But not Laird. I cannot find any mention of VHF low antennas on Laird websites,

 

[prcguy]

Go to page 10 in this Laird catalog then look for the technical data, it states 200 watts maximum power for the various wide band models.

 

[RFI-EMI-GUY]

Go to page 10 in this Laird catalog then look for the technical data, it states 200 watts maximum power for the various wide band models.

Thanks. Yes 200 watts. That catalog is 15 years old per the document properties. I wonder if they are still carried? I am also curious why mm's antennas failed, and was it mechanical or electrical? It does look to be the way to go, and I can make one of the three central mounts a contingency for unanticipated bands.

 

[prcguy]

Thanks. Yes 200 watts. That catalog is 15 years old per the document properties. I wonder if they are still carried? I am also curious why mm's antennas failed, and was it mechanical or electrical? It does look to be the way to go, and I can make one of the three central mounts a contingency for unanticipated bands.

You should be able to find some here and there, I got two off ebay over the years for really good prices. I've never run more than 100w and mine are just fine. I upgraded the whip on one to a much thicker one, not that that improves performance but it sticks up straighter at freeway speeds.