Base A-99 and Neighbors?

[M0GVZ]

I do have a 12t on 3" choke up there now, and it actually did help with rf in my stereo. I have no idea if it is causing any other issues though.

I also got a ground rod sunk at the mast, but I haven't actually grounded anything yet. I'm not sure what I want to use for equipment grounds yet. I should probably figure that out and get on that.

No idea what that is choking but it is nowhere near actual measured air wound chokes for 11m, chances are its choking lower, much lower. 5 turns of RG58 or RG213 on a 4.25" diameter is perfect for 11m, covering 26-28MHz giving 8k Ohms or more. Add just 5 more turns and it drops the frequency of that 8k Ohms down to 16-18MHz . Choose one of the below. Ideally you'd want one where there's a black line under the 11m section as well as that means its resistive, not reactive choking but it does mean using a ferrite core.

Ground rods don't do anything for RF grounding.

 

[loosecannon]

I appreciate the help. I am going to ground the mast for lightning protection. I couldn't find a ground rod at the utility box to use. I figured that being insulated with rubber and wood that I should probably give lightning a safe path home.

What ferrite mix is the proper one to use?

I just don't understand the antenna needing the coax. Why wouldn't it use the metal mast? Is the wound choke completely ineffective, to the point that 8.5' of coax is still part of the antenna? If so, and I put ferrite chokes at the feed point, the vswr would be off the chart. Maybe I will try ferrite at 8.5', then insulate the antenna from the mast and snap some ferrite at the feed point.

yes you are right that the antenna will just use the mast if you choke off the coax.
I did not know how your antenna was mounted so i did not assume that there would be 10 or so feet of mast below the antenna in your setup.

isolating the antenna from it's mast and then choking the coax at the proper point is the ideal installation, but can be hard to accomplish.
you can't just insulate the connections between the antenna and the mast, as the current on the shield of the coax will just induce itself right back on to it.

you need to use some sort of non-conductive substrate for your mast.
MFJ and DXengineering sell fiberglass telescoping masts that would be perfect for your set up, but they will run you a couple hundred bucks.
(if you choose to get one, buy one longer than you think you need, and then just don't use the top two sections, as they are only 3/4" and 1" anyway)

then install a lightning arrestor (a real one, not the 10 dollar ones) right where the coax meets the ground, and install your 4 foot ground rod there. then run coax from the arrestor to the radio.

this way, the only link from your antenna to your system is the coax, which is running through the lightning arrestor.
the thinking here is that any strike close enough to zap you will melt the coax and hopefully the arrestor stops the rest.
LC

 

[LeapFrog]

yes you are right that the antenna will just use the mast if you choke off the coax....

..isolating the antenna from it's mast and then choking the coax at the proper point is the ideal installation, but can be hard to accomplish...
you can't just insulate the connections between the antenna and the mast, as the current on the shield of the coax will just induce itself right back on to it....

...you need to use some sort of non-conductive substrate for your mast...
LC

LC, I was working under the presumption that the first 100 & something odd inches of the mast metal acts as the 1/4 wave for the half wavelength over 1/4 wavelength design of the A99 (if no GPK used). I guess i'll have to read the frickin' manual (if i can find a copy) and see if they mention anything at all about the topic, lol I don't know .

Best Regards
-LeapFrog

 

[Sonar]

I just installed an A-99 on my camper. It has a push up pole, but I don't have a tool to raise it at the moment. I tested it out at roof level, and the vswr was acceptable so I transmitted voice. I was blown away by the very loud and crystal clear talkback on my stereo. At 5 watts ssb I don't hear anything. 7 watts makes a little noise, and 40 is loud as heck through the old stereo.

Will raising it 10 to 20 feet above the roof make a huge difference? Are modern electronics less prone to interference than my 70's pioneer?

Defeneyly make an ugly balun (RF choke) as suggested, and it wouldn't hurt to add a low pass filter. Drake made a very good one. The Drake low pass filters are readily available on eBay. $20-$50. There's also a company that manufacturers new ones. I forgot the name of them but I've read that they work very well. 73 PS Getting above the roof line as high as possible should help. Adding the low pass filter and RF choke might be something you'd consider even if you get the antenna above the roof line.

 

[M0GVZ]

LC, I was working under the presumption that the first 100 & something odd inches of the mast metal acts as the 1/4 wave

It would if it were 102 inches long but it isn't, its longer. As it increases in length over 102 inches its impedance increases for 27MHz. By the time you get to 204 inches or a half wavelenght long the impedance of the mast is several thousand ohms. Current takes the path of least resistance so if the impedance of the coax is less than the mast the current will flow more down the coax. That's why you use a RF choke so the RF current sees the braid of the coax as hopefully higher impedance than the mast or radials and sends the current down those instead.

 

[2RT307]

Defeneyly make an ugly balun (RF choke) as suggested, and it wouldn't hurt to add a low pass filter. Drake made a very good one. The Drake low pass filters are readily available on eBay. $20-$50. There's also a company that manufacturers new ones. I forgot the name of them but I've read that they work very well. 73 PS Getting above the roof line as high as possible should help. Adding the low pass filter and RF choke might be something you'd consider even if you get the antenna above the roof line.

Bencher makes new lpf's, but you are on target with the old Drake units. EF Johnson also made some good ones that handle about 1.5kw, and you can usually find used ones in the same 20-50 dollar range.

73,
Brett

 

[357magnum]

Buy a Gainmaster.

No disrespect Mud Foot but why a gain master ? I have been looking @ new antennas to go with my Sirio 27-4 beam and thought about a gain master but after watching forum member Marconi's review and others I might add it doesn't seem it worth it's wait in salt ?

 

[Robb]

No disrespect Mud Foot but why a gain master ? I have been looking @ new antennas to go with my Sirio 27-4 beam and thought about a gain master but after watching forum member Marconi's review and others I might add it doesn't seem it worth it's wait in salt ?

When I was deciding for a different vertical antenna, I narrowed it down between the GM and the Vector 4000. Cost was the deciding factor, as I reasoned that - although different by design concept - they both were efficient radiators. I went with the V4000. But had a local friend that used the GM, and was very impressed with its performance on both RX and TX.

End fed half wave antennas - like the A99 - come with issues regarding proper setup.
Nature of the beast.

 

[Sonar]

End fed half wave antennas - like the A99 - come with issues regarding proper setup.
Nature of the beast.[/QUOTE]
I didn't know there was an inherent issue with the a99. I guess I read all the good things and skipped the bad. The a99 replaced my 11 meter wire dipole and I was happy with it. I did eventually replace the a99 with an imax 2000. Only because I had to take down the a99 to replace a bent mast. I thought since I had to take down the a99 I might as well put up what I read was a better antenna and that's when I put up the 2000. I'm very happy with it and noticed a nice 1 s-unit gain in my recive. I'm assuming the verticals you're mentioning are far superior to 2000 and of course the a99. My choice for the a99 then the 2000 were strictly ease of installation and not cost. I'd love a better antenna but the thought of having to fuss getting it right after it's up is why I'm sticking with the 2000. Not to mention my 2000 works fine just 7' off the ground. I just don't have the room in the yard to add guy wires and with a new roof am not willing to put anything on top of it. My swr is 1.3:1. I suspect the improper height is the cause of the high, but acceptable swr. In all honesty it works well even at 7'. Sorry for getting side tracked.
73

 

[357magnum]

When I was deciding for a different vertical antenna, I narrowed it down between the GM and the Vector 4000. Cost was the deciding factor, as I reasoned that - although different by design concept - they both were efficient radiators. I went with the V4000. But had a local friend that used the GM, and was very impressed with its performance on both RX and TX.

End fed half wave antennas - like the A99 - come with issues regarding proper setup.
Nature of the beast.

Thanks Robb , never even considered the V4000 but now I will check into it , I really thought it would be the GM but it seems it might be a little lacking in construction to hold up to the wind and WX in the NE corner but I must ad I have never seen one up close to check one out .

 

[Marconi]

Thanks Robb , never even considered the V4000 but now I will check into it , I really thought it would be the GM but it seems it might be a little lacking in construction to hold up to the wind and WX in the NE corner but I must ad I have never seen one up close to check one out .

357, consider this. If you're the least bit concerned with wind and weather at your location...the New Vector is probably not for you.

The GM, Vector, and Imax are higher gain, but the A99 is not that far behind. If you compared them close in the real world you might not even be able to tell the difference at times.

Below are two models. The New Vector 4000 vs. A99 with both in Free Space. I added an overlay of these two with patterns compared.

I also posted my real world antenna comparison results showing RX average S units from 5 of my well known local buddies. The A99 did show up last as expected, but the report does not show a big signal difference among them all...at my location.

 

[357magnum]

357, consider this. If you're the least bit concerned with wind and weather at your location...the New Vector is probably not for you.

The GM, Vector, and Imax are higher gain, but the A99 is not that far behind. If you compared them close in the real world you might not even be able to tell the difference at times.

Below are two models. The New Vector 4000 vs. A99 with both in Free Space. I added an overlay of these two with patterns compared.

I also posted my real world antenna comparison results showing RX average S units from 5 of my well known local buddies. The A99 did show up last as expected, but the report does not show a big signal difference among them all...at my location.

Thank You Sir ! Great info as usual I did watch a vid on You Tube of the 4000 in wind and yes you are right it's not the antenna for me with the Wx we get here .

 

[M0GVZ]

Part of the reason for the difference in performance of the A99 over the Imax for local contacts is a very high angle lobe on the Imax which is absent on the A99 and would benefit local contacts up to a few hundred miles.

 

[Marconi]

Part of the reason for the difference in performance of the A99 over the Imax for local contacts is a very high angle lobe on the Imax which is absent on the A99 and would benefit local contacts up to a few hundred miles.

Connor you could be right, but my models for the Imax/A99, both without the GPK, shows similar patterns at the lowest angles. The Imax shows a little more gain at a lower angle. IMO this is primarily due to the Imax being the taller antenna when both are mounted at 36' feet.

Do you have a modeling reference that shows the Imax with a very high angle lobe that is absent as compared to the A99? If you do, then I will have to revisit my models to see if I have some mistake.

 

[wavrider]

I have not seen any information posted about what type radio or power level you have?
If the radio is super whack packed top gun modulated then could be spurious RF SPLATTER being transmitted.
I have used A99 verticals and never had any problems with RFI,,choke wrapped on the coax at fed point and clean modulation from the rig,