tune a dual band antenna

[Joe]

Does anyone have info on how to tune a dual band mobile mag mount antenna?

2M/70cm

Stock out of the bag I get 1:2 in the mid level of 2 meter and about 1:4 on the low and the high, but when I switch to 70cm I get around 1:4 and 1:5

I have the FT7800R and a friend of my dads gave me a MFJ's Power Gain MFJ 1729. I realize the antenna is not top of the line but it was a gift

Thanks

 

[Captain Kilowatt]

I have yet to see a dual band VHF/UHF mobile antenna that needed to be tuned.If you try to tune one band you WILL mess up the other one.The SWR figures you have are fine.Run it like it is.1.5 is no big deal.My 2m band is good and my 70cm band is a bit worse than yours and I have no problems whatsoever.Trust me I am not going to risk smoking my FT-857.

 

[Joe]

I have yet to see a dual band VHF/UHF mobile antenna that needed to be tuned.If you try to tune one band you WILL mess up the other one.The SWR figures you have are fine.Run it like it is.1.5 is no big deal.My 2m band is good and my 70cm band is a bit worse than yours and I have no problems whatsoever.Trust me I am not going to risk smoking my FT-857.

Thanks QRN

I was getting a little worried when I saw 70cm at just over 1:5/1:6

as far as 2 meter goes its 1:2 and 1:4 max


I figured it would be tough to tune a 2 band antenna LOL I guess you learn something new every day

 

[Captain Kilowatt]

Unless you are running some really high power it is nothing to worry about.I run just 50w on 2m and 20w on 70cm and would not even think about trying to retune unless I was running well over 100 watts.You could try moving the antenna around a bit to see if that changes things any.

 

[Joe]

Unless you are running some really high power it is nothing to worry about.I run just 50w on 2m and 20w on 70cm and would not even think about trying to retune unless I was running well over 100 watts.You could try moving the antenna around a bit to see if that changes things any.

Thanks

Maybe its the antenna, its not the top of the line but it was free

I may look into the Larson NMO mag mount in the near future

 

[Chuck Bravo]

Hi Joe,
Consider a Tram dual band NMO. Good performer at a reasonable price.

Honest Bob will fix you up.
http://www.mapleleafcom.com/

I don't know if he will be at the York Hamfest next Saturday or not... worth a look, they are a well made antenna.

 

[Captain Kilowatt]

I've done business with Bob a couple times and I must say that the honest part is right on.He sent me the parts to repair my tribander HF beam after a severe winter storm wrecked havoc with it and sent the bill along with the parts.He told me to send him the payment AFTER I received the parts.He just wanted to get me fixed up as fast as he could.Gotta respect a man that will do that.Also gotta make sure you use him as right as he uses you. Bob is "good people".

 

[Joe]

thanks guys

Bob will be at the Hamfest I may pop over and see him, I also have heard good things about him

 

[bunnieman]

Stock out of the bag I get 1:2 in the mid level of 2 meter and about 1:4 on the low and the high, but when I switch to 70cm I get around 1:4 and 1:5
Thanks

Honestly, thats great! I wouldnt putz with it in anyway shape or form.

Dont forget, dummy loads are 1:1

 

[W5LZ]

Joe,
Tuning a dual band antenna isn't difficult ~electrically!. Mechanically, it's a different story! Basically, it amounts to adjusting the length of the lowest frequency antenna, then adjusting the length of the higher frequency antenna. (That means adjusting above the coil for the higher band, below the coil for the lower band.) Alternate back and forth between the two till you get the best results.

I'm not sure I'm reading your numbers correctly. If you mean an SWR of something around 1.5:1 or less, leave it alone, nothing wrong with that at all. If you meant something like 2:1 or 7:1, then it does need some attention.
- 'Doc