Mobile quad band antenna or duplex?

[ThisIsMeToo]

Novice here looking for some antenna advice. Seems like a lot of great advice here already but cannot find anything related to my question.

I acquired an TH-9800 mostly for the quad band aspect. Installed it mobile with a Nagoya NMO-200C antenna (155/460Mhz). This is ideal as it gets me to GMRS (I know please do not preach), that is required for or RV friends when we move. Tuning I should be doing today with the arrival of a new SWR meter. Need to read up on tuning a dual band on this. Ideally, I would like to keep the GMRS side and tune the other down to 2M.

Seeing I go the NMO-200C for cheap, and in reading I see a lot of people not recommending the quad band antennas and duplexing the antenna, this is the route I am investigating for 6M & 10M. I see that Comet makes the CF-530C duplexer (Low Pass = 1.3-90MHz & High Pass = 125-470MHz) just for this situation.

My wish would be for the best at GMRS and 10M.

So, the questions arise:

Is this a viable recommend path (granted I would need to add a dual band 6M/10M antenna to compliment)?
Is the duplexer and two dual bands really a better alternative than a single quadband antenna?
Tuning: Should I wait until the duplexer is inline before tuning? I would assume so but turn to the experts here.
If this is viable, any thoughts on a 6M/10M dual band to compliment?
Should I just toss the idea and go back to a quadband such as the Diamond CR8900A or Comet UHV-4?

Thanks in advance!

 

[prcguy]

I don’t know of any 10m/6m dual band antennas worth mentioning but you can easily make one with a full length 1/4 wave whip on each band and an adapter that holds them a few inches apart on the same mount. Then you would need a diplexer that has roughly a 90MHz low pass/high pass split to combine in the VHF/UHF antenna.

 

[ThisIsMeToo]

Hi PRC.
That sounds like an novel solution that took me a while to understand. At first I thought you were suggesting another duplexer, but the 90MHz you are suggesting is between the UHF antenna I already have and the VHF dual whip antenna you are suggesting. You are suggesting, more or less, making a dual band VHF antenna on the same mount? That sounds interesting and would give great tunability. AM I correct to assume that I just combine the 6M and 10M whips before going into the duplexer (meaning path of least resistance for the VHF antennas)?

Being mobile, I would obviously need to look at loaded whips.

Thanks!

 

[prcguy]

Hi PRC.
That sounds like an novel solution that took me a while to understand. At first I thought you were suggesting another duplexer, but the 90MHz you are suggesting is between the UHF antenna I already have and the VHF dual whip antenna you are suggesting. You are suggesting, more or less, making a dual band VHF antenna on the same mount? That sounds interesting and would give great tunability. AM I correct to assume that I just combine the 6M and 10M whips before going into the duplexer (meaning path of least resistance for the VHF antennas)?

Being mobile, I would obviously need to look at loaded whips.

Thanks!

It’s easy to combine two whips on bands like 10m and 6m on the same mount because on 6m the 10m whip will be about a half wavelength, very high impedance and little RF current will flow. When on 10m the 6m whip will be an insignificant 1/8 wavelength and little current will flow. If you went with a loaded 10m antenna about 5ft tall, a full 1/4 wave whip on 6m would be about the same length.

 

[ThisIsMeToo]

Thanks PRC,
That confirms what I was thinking with my limited knowledge - path of least resistance. Would be ideal for me with two antennas as they would be easier to tune, plus offer the flexibility to dismount if I needed for a semi-permanent base station.
5ft would be too tall. Mount is on top of a headache rack on a pickup, that must be almost 7.5ft up already. Granted it is towing a 5th wheel most of the time ...
Shark does have a line of mini 10m antennas as well as the corresponding 6m. Making a DYI bracket for the two would be easy, and would assume a Y cable connecting the two. I see hints of a dual brackets in the description for the Sharks, cannot find such premade. Elimination of the Y-cable would be KISS and less fail proof. I will keep searching.

As far as tuning, do I tune each of the three antennas (existing dual band and two new whips) individually or do I tune them from the duplexer?
Already have a struggle with the existing dual band, what was supposed to be "factory tuned" for GMRS has a center freq of 1.485 SWR and nothing close to 1:1 across the entire band. Off to find a good article on how to tune a dual band now.

Thanks again.

 

[prcguy]

Making a dual band 10m/6m antenna would put both whips on the same mount with a common coax, you can’t combine two separate antennas on two separate mounts with two separate feedlines.

 

[Project25_MASTR]

Making a dual band 10m/6m antenna would put both whips on the same mount with a common coax, you can’t combine two separate antennas on two separate mounts with two separate feedlines.

Unless the lengths of the individual feedlines were correctly matched...Motorola used to put out a low band diplexing chart for the Syntor X9000 that used two antennas on two mounts with two very specific lengths of RG-58 (which varied by frequency). From there the two lengths were simply Teed together with an off the shelf Tee.

 

[ThisIsMeToo]

Making a dual band 10m/6m antenna would put both whips on the same mount with a common coax, you can’t combine two separate antennas on two separate mounts with two separate feedlines.

Not sure I understand. So......
If I took the two Shark antennas I called out, made a bracket to mount both (or found one to purchase). Would I not Y=cable the two together there (at the mount) and then single cable back to the duplexer? The duplexer being 90MHz split one side going to the existing dual band UHF antenna and the other up to the Y-cable / 10m/6m array.