Amateur Radio, 2 Mtr antenna

Don The Ham · 08-28-2006, 07:51 AM

I removed the roof CB antenna (not the mount just the CB whip). Then installed a 19 inch whip, expecting the antenna to have a low SWR on the 2 mtr ham band. Instead, the antenna has a low SWR at 70 Mhz. Does anybody know if a 2006 Winnegago Adventurer has a loading coil for CB mounted some place in this coax line under the roof???

Don The Ham · 08-28-2006, 07:51 AM

I removed the roof CB antenna (not the mount just the CB whip). Then installed a 19 inch whip, expecting the antenna to have a low SWR on the 2 mtr ham band. Instead, the antenna has a low SWR at 70 Mhz. Does anybody know if a 2006 Winnegago Adventurer has a loading coil for CB mounted some place in this coax line under the roof???

smlranger · 08-28-2006, 08:20 AM

Don, welcome to the forum.com

. Your's is an interesting question and someone (perhaps John Canfield) may be along to answer. You might want to contact Winnebago directly.

Good to have you here and look forward to your sharing your RV experiences with us.

PioneerRV · 08-28-2006, 11:56 AM

Good question Don. I also would like to mount a 2 meter somewhere on my 2006 Meridian and hate to drill a new hole. Its still too new, right.Look forward to some answers.
Don
W6DUO

John_Canfield · 08-28-2006, 03:19 PM

Hi Don and welcome to the forum de wb5tht!

I can't state for sure, but I doubt the CB antenna has a remote loading coil. Is your antenna designed for no counterpoise? Maybe temporarily run three or four 19" radials around the shield part of the antenna mount and see if it will resonate on 2M.

73 - John

dirko · 08-28-2006, 10:30 PM

Hi Ho: I think that John has a handle on the problem. A 19" whip is only half of the antenna. The other half comes about through a counterpoise of ground system (a groundplane antenna for example). If the outer braid of the coax were effectively grounded where the whip is attached, this would probably work as well. An infinite ground plane is the same as a 1/4 wave counterpoise. One way to think about this is that there is no current flow at the outer end of the 1/4 wave counterpoise, so whether it is connected to something or not is of little consequence. Often the loading coil is an autotransformer and establishes the ground, so when it is removed the outer braid of the coax is connected to nothing. Good luck from Jena, Germany. Dirk W7KCC

teekay · 08-31-2006, 07:09 AM

I have a 06 Meridian, I did a similar thing but for the aircraft band. I took my MFJ SWR analyzer and found the following (MHz SWR):
60 5.5, 70 4.0, 80 1.4, 90 2.1, 100 2.2, 110 2.9, 120 3.9, 130 3.0, 136 1.0, 140 1.5, 150 1.5.

Next I'll install a counterpoise and see if that has any effect.

Don The Ham · 09-04-2006, 11:22 AM

Thanks for the responses.. I assumed that the Winnebago CB mount had the coax shield connected to the MH frame at the roof line. I verified the coax shield is connected to MH ground, but it may not be at the roof. I will try the ground plane suggestion, when I get my MH back from another try to fix the HWH leveling system. I need to call Winnebago on some issues with my 38J, so I will also ask for some tech support on the roof mount antenna conversion to 2 mtr and let everyone know their response.

Don, W3MIF

Don The Ham · 09-11-2006, 01:16 PM

More info on CB antenna conversion to 2 mtr.. Winnebago response to my questions on this antenna conversion: No loading coil is mounted under the roof in series with the coax cable. Coax shield is grounded to the frame at the roof area. Power protection for the 12 VDC CB power cable is the "misc" circuit breaker under the dash panel. I have not got my motor home back from the dealer yet (3 weeks), so I have not tried the counterpoise (radials) to lower the SWR on the 2 meter antenna.

Don W3MIF

NR4A · 09-11-2006, 01:28 PM

I looked at the CB antenna on the Horizon we are about to purchase and thought about doing the same thing, except with a short dual band antenna. I doubt there is much of a groundplane under the antenna mount, and have no clue how the CB antenna would have any efficiency (or low SWR/resonance) the way it was installed.

Try the radials if possible, or go glass mount on the top/left of the windshield.

Let us know how you make out?

73,
Sam / NR4A

NR4A · 09-12-2006, 11:22 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by teekay:
I have a 06 Meridian, I did a similar thing but for the aircraft band. I took my MFJ SWR analyzer and found the following (MHz SWR):
60 5.5, 70 4.0, 80 1.4, 90 2.1, 100 2.2, 110 2.9, 120 3.9, 130 3.0, 136 1.0, 140 1.5, 150 1.5.

</div></BLOCKQUOTE>

teekay,
I wouldn't put all of my faith in that little MFJ-259 analyzer. With perfect (50 ohm) coax they are somewhat effective, however if you have a splice in the line or moisture contaminated coax, or are testing within close proximity of an external RF source, they will be far from accurate and give the erratic readings like you have observed.

I know it is not practical to read the SWR at the antenna itself, however it is the recommended way to do it. Since you're using it to primarily receive at those frequencies, I would tend to accept what I get. Transmitting is another story.

I used to be a dealer of those MFJ's, they're not too bad for $250, but far from being an expensive TDR or Service Monitor.

Enjoy!

Sam

W8RLM · 09-12-2006, 12:22 PM

I use a glass mount dual bander mounted near the top left side of the windshield. It seems to work on both 2 meter and 70 cm. I'm running a Yaesu FT100 with an ATAS 100 mounted near the top of the ladder in the back.

By the way, if any of you Hams out there can explain to me why the ATAS will tune on every band from 40 down to meters except 20 meters, I'd appreciate it. I have 50 feet of coax running from the antenna, under the motorhome and forward to the radio which is mounted under the dash board. The antenna is grounded to the motorhome frame under the motorhome at the left rear where Winnebago has some other circits grounded.

W8RLM - Bob

W8RLM · 09-12-2006, 12:23 PM

I guess I didn't read my own post very well. It shuld say that the ATAS will tune from 40 down to 6 meters except 20 meters.

W8RLM - Bob

NR4A · 09-12-2006, 03:59 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">.

By the way, if any of you Hams out there can explain to me why the ATAS will tune on every band from 40 down to meters except 20 meters, I'd appreciate it. I have 50 feet of coax running from the antenna, under the motorhome and forward to the radio which is mounted under the dash board. The antenna is grounded to the motorhome frame under the motorhome at the left rear where Winnebago has some other circits grounded.

</div></BLOCKQUOTE>

Bob - Dont confuse a D.C. ground for an R.F. ground. They are really not one in the same. Case-in-point, move an antenna from one side of an automobile to the other and it's resonance characteristics typically change. Back to the game of counterpoise / radials / aka antenna reference. Mount the ATAS on a pipe driven into the earth and bet it will tune just fine on all the bands.

BTW - I'm sure you are aware that it doesn't matter if you are running 50 feet or 100 feet or 2 feet of coax for that matter. It is not part of this equasion at all.

Hope this helps shed some light on curing the problem(?)

73,
Sam/NR4A

N8XV · 09-12-2006, 04:15 PM

We have 35U and at one time I tried using the CB antenna on 2 meters. On ours I found cutting the whip length to about 16" brought the SWR to a usable level. Just to try it take any wire that will stand up right and fit the hole. Keep cutting it off a 1/2" at a time and see if the SWR comes down.

73, Bill

Don The Ham · 02-18-2007, 03:02 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Don The Ham:
I removed the roof CB antenna (not the mount just the CB whip). Then installed a 19 inch whip, expecting the antenna to have a low SWR on the 2 mtr ham band. Instead, the antenna has a low SWR at 70 Mhz. Does anybody know if a 2006 Winnegago Adventurer has a loading coil for CB mounted some place in this coax line under the roof??? </div></BLOCKQUOTE>

UPDATEProblem solved, SWR now under 2:1 on 2 meters. ACCESS TO ANTENNA MOUNT COAX: On my 38J, open the storage area above the driver door, remove two screws on the front facing storage area liner, fold back liner and you have access to antenna mount. AS FOUND: Coax shield is grounded to a brace molded into the front top cap, ground wire is small gauge wire and about 18 inches long (Not good enough for an RF ground). MY SOLUTION: Leave as found ground wire in place, add 19 inches of braided shield around the feed coax, shield connected only to coax at antenna mount. Trim antenna element length >> NOW: 1.7:1 SWR at 146 Mhz. Modification results in a > Coaxial vertical < per ARRL VHF Manual.

From an amateur radio view > I miss my metal roof.