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Help! Antenna SWR

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N00b Ham question.

I have a mobile/base rig (Icom 7100). I have a mobile whip antenna for 2m/70cm plug into it (Tram 1185). The internal SWR meter is reading very high (beyond the 8:1 measurement). I'm only keying for a fraction of a section because I don't know what kind of internal protection the Icom has.

I'm not sure where to begin to get this matched. I checked the feedline and antenna for continuity and loss, and it looks fine. I don't have an external SWR meter yet to separately compare to the internal one. I'm afraid to do to much because I don't want to burn up the output stage with a massive impedance mismatch, although maybe the Icom has enough protection.

Anyway, I'm completely new to this. Please let me know if you have any suggestions.

Also, what other forums are you guys on for Ham?
 

cockpitbob

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First, set the Tx power to its lowest setting. The radio almost certainly has SWR protection, but I wouldn't risk it.

It's probably something simple, so please don't be offended by the dumb stuff I'm about to suggest.

* Are you sure you're transmitting in the 2M or 70cm band?
* Do you have the antenna connected to the correct connector on the back of the radio?
* Check for a short in the antenna cable (center to shield). There's a small chance it has a matching coil that will look like a short. My Hustler 2M/70cm is open circuit but I have a CB antenna that looks like a short.
* That's a cheap antenna. They do get good Amazon reviews, but you might have gotten unlucky.

I'm in Topsfield. If you're nearby you could swing by and try my 2M/70cm mag mount and we could look at your antenna with my antenna analyzer.
 
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Thanks cockpitbob. I was hoping you'd respond.

First, set the Tx power to its lowest setting. The radio almost certainly has SWR protection, but I wouldn't risk it.

It's probably something simple, so please don't be offended by the dumb stuff I'm about to suggest.

* Are you sure you're transmitting in the 2M or 70cm band?
* Do you have the antenna connected to the correct connector on the back of the radio?
* Check for a short in the antenna cable (center to shield). There's a small chance it has a matching coil that will look like a short. My Hustler 2M/70cm is open circuit but I have a CB antenna that looks like a short.
* That's a cheap antenna. They do get good Amazon reviews, but you might have gotten unlucky.

I'm in Topsfield. If you're nearby you could swing by and try my 2M/70cm mag mount and we could look at your antenna with my antenna analyzer.

- 2m band
- Yes, this was my first thought. Unless there's a misprint in the manual, I'm on the right connector.
- I'm pretty sure I checked this last night, but I'll check again tonight.

I would love to look at this on an antenna analyzer, so I might take you up on your offer after I try a few more things. I'm going to hit the Braintree radio club, too. I'm in metro-boston.

Something occurred to me this morning after posting. I tried this antenna indoors. I'm guessing the metal body of the vehicle acts as a ground plane for a mag mount antenna, correct? (Sorry, I know electronics, but my antenna knowledge is crap. I never took took that class in EE.)

So lack of a ground plane will affect characteristic impedance. Is the effect big enough to cause this? Tonight I'll be putting this mag mount on my car and running the test again.

Thanks again!
 
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yeh, not having a ground plane can do that......

stick it on top of your fridge (assuming the fridge isn't stainless or buried in a wall....)

antennas don't really like to be indoors though....
 

Evtide

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Doug, have fun with that radio. I picked up one in December and am loving it. Now I really have get cracking and finish studying for the General.

I do have an antenna analyzer (Rig Expert AA-170) and it works great, but the Icom's built in SWR meter works pretty good, too. If it's giving you a high match it probably is due to lack of a good ground plane or other local indoors influences. Checking the match on the antenna anywhere but where you intend to use it may not give you the real picture. Mag mounts like to be centered on a trunk or car roof for sure.
 
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It was lack of a ground plane. And yes, I used a giant cookie sheet to test it out. [grin] I'm just south of Boston and I picked up someone in RI with this little mag mount antenna. That's pretty cool. Can't wait to get the real antenna mounted on the roof.

Thanks for the help guys.

Evtide, the IC-1700 is pretty awesome. I wanted a (mostly) all band unit so I could focus on antennas, where I am clearly mentally challenged. [rofl]
 
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Drill holes and install proper mounts. That way you can install really good antennas that would probably blow off your vehicle with most mag mounts. I'm running a true 5/8 wave 2-meter antenna on my truck. It is tall, but works great. No loading coil losses.
 
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What kind of vehicle do you have?

Very old Ford Explorer. I really bought the cheap mag mount antenna for my equally cheap Baofeng HT. I'm putting money into the IC7100 and some antennas as a reliable base station.

I don't spend much time in my car, since I ride the T to work. If that changes, I'll probably go the permanent mobile antenna route.
 

cockpitbob

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Personally I like a (good) mag mount antenna. I too don't spend a lot of time in the car. I'll move the antenna from my car to the wifes, to a folding aluminum camping table. I have a cig lighter cord for my old FT-2600 2M rig and will just lay it on the seat in my wife's car. Yes, I need to remember to turn the power down to 25W for the 10A fuse behind the cig lighter. To each his own: I like flexability and portability.
 
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Personally I like a (good) mag mount antenna. I too don't spend a lot of time in the car. I'll move the antenna from my car to the wifes, to a folding aluminum camping table. I have a cig lighter cord for my old FT-2600 2M rig and will just lay it on the seat in my wife's car. Yes, I need to remember to turn the power down to 25W for the 10A fuse behind the cig lighter. To each his own: I like flexability and portability.

That's a good idea, especially getting more power than a typical HT.
 
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It is a long standing mantra in radio that you should put your money into quality antenna's and feedline. The mount is essentially part of the feedline. A mag mount is fine for lower frequencies, small antenna's and temporary use, but little else. As you move up in frequency, mag mounts will add capacitance at the base of the antenna. That capacitance will cause power loss, swr issues and other problems as your operating frequency rises. The fanciest radio in the world will not be heard if the feedline and antenna system are crappy.
 
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