Yaesu ATAS-120A

[tweiss3]

I've been working a local parks on the air program and have had limited success with my 817 due to the park rules (not allowed to toss a string up in the tree, etc). I'm trying not to get ALL my contacts on my fall back 2m mobile in the car. I have a FT-450D sitting in the closet as a backup rig. I see it is compatible with the ATAS-120A, and would open up some possibilities.

My intent for use is to power from a vehicle, and toss the antenna on the roof/rack for the operation, then take it down before pulling out of the parking lot. I'm not looking to drill a hole for this at this time, though I already have 2 holes drilled in the roof.

The fine print for the antenna I see is to make sure the antenna has a strong ground, which lead to the following train of thought.
1) I have roof rack bars on the intended car, but the bars are rubber isolated from the body, so that isn't a great option without some large grounding straps. This is less than ideal, I don't really want anything hanging that could get yanked by some knucklehead walking by.
2) Go magmount on the roof. While normally magmount is not idea, temporary operational it fits the bill, and will keep it secure. But would this provide enough "grounding" to be effective. It would allow it to be put center of the roof.
3) I could also get the "rail" counterpoise, but that's even more expensive and I believe it makes the antenna directional.

Any input on the above options? Any experience with this screwdriver antenna?

 

[prcguy]

The Yaesu ATAS series of antennas are at the bottom of the performance scale for screwdriver antennas. The coil diameter looks smaller than the guys index finger in this picture and the wire size is tiny.



A cheap Hamstick will usually put out a better signal but people still keep buying the ATAS. Its interesting how a good screwdriver antenna with larger diameter coil will have a feedpoint impedance well under 50 ohms and more in the 10-15 ohm range and need external matching where the ATAS can match close to 50 ohms due to its excessive internal losses. But side by side with an ATAS, another brand of screwdriver antenna will seem like you have a 100w amp on your FT-817 and its the antenna that's making the difference.

You might look at other known good performing antennas and the Little Tarheel II should run circles around an ATAS, especially when using it with a 6ft whip. Tarheel Antennas - Little Tarheel II I have a larger Tarheel 100HP and a Hi-Q 160-10 version with 5" dia coil. Its a monster and not for everyone but it puts out a huge signal from a mobile compared to any other tunable antenna I've tried.

Otherwise I've used various screwdriver antennas on temporary mounts and even mag mounts with excellent results. The key is to have the antenna high on the vehicle and to have a good ground or with a mag mount having good capacitive coupling to ground. Here is my HF mag mount setup that has an 8 1/2" X 11" sheet of copper foil stuck to an equal size flexible refrigerator magnet as a huge capacitive ground. This mount measured identical to a hard mounted and grounded ball mount in both impedance measurements and signal strength. With this setup you can use a cheap Hamstick or various screwdriver types on the vehicle roof then take it all apart with no trace left on the vehicle.

I will add a warning that a big tri or quad magnet mount can be very difficult to remove due to the strong magnets.

 

[tweiss3]

I kind of forgot about the Hamstick (now HamTenna). For the $$, I think I going singleband HamTenna and magmount is going to be the way to go.

It's hard to see the difference between the Tarheel II and the ATAS120, they seem similar in overall length and diameter, but I'll take your word for it on performance, I haven't found any of your recommendations wrong yet. I'll kick a screwedriver antenna down the road for a bit, and see where we are after messing around with the HamTenna.

For that matter, I'm going to give it a shot with the FT817 and a HamTenna, only jump out with the 450D if I'm still "underpowered".

 

[prcguy]

The coil diameter is much larger on the Little Tarheel II.

I kind of forgot about the Hamstick (now HamTenna). For the $$, I think I going singleband HamTenna and magmount is going to be the way to go.

It's hard to see the difference between the Tarheel II and the ATAS120, they seem similar in overall length and diameter, but I'll take your word for it on performance, I haven't found any of your recommendations wrong yet. I'll kick a screwedriver antenna down the road for a bit, and see where we are after messing around with the HamTenna.

For that matter, I'm going to give it a shot with the FT817 and a HamTenna, only jump out with the 450D if I'm still "underpowered".

 

[tweiss3]

Fair enough. Its hard when all photos are junk and complete dimensions aren't available.

 

[prcguy]

Looking at the picture of the ATAS above and measuring my finger, I estimate the ATAS coil to be about 1/2" to 5/8" diameter. Looking at the pictures of a Little Tarheel II and knowing the lower mast is 1 1/2" dia, I would estimate the coil diameter to be very close to the mast dia, or about 1 3/8" to 1 1/2". That is small for a screwdriver antenna but huge compared to the ATAS and it ups the efficiency quite a bit.

Fair enough. Its hard when all photos are junk and complete dimensions aren't available.

 

[tweiss3]

Looking at the picture of the ATAS above and measuring my finger, I estimate the ATAS coil to be about 1/2" to 5/8" diameter. Looking at the pictures of a Little Tarheel II and knowing the lower mast is 1 1/2" dia, I would estimate the coil diameter to be very close to the mast dia, or about 1 3/8" to 1 1/2". That is small for a screwdriver antenna but huge compared to the ATAS and it ups the efficiency quite a bit.

I did look at the Tarheel photos more closely, and their lineup. Very nice units, and not tiny. If only they had a turnkey fully automatic tuning version. I know, they have options for auto controllers, but still.

Well I bought a 10m and 20m HamTenna and tri-magmount (i know its going to be hard to pull down). Pick it up tomorrow from DX (wife said I have something else to do at home immediately after work). Any idea on the bandwith of a HamTenna? Documentation is vague. I'm just wondering if I need to tune the middle of the band and use the tuner to get all of 20, or if I need to tune in the voice portion in order to get the tuner to cover the voice band.

 

[vagrant]

That reminds me of that Diamond brand tiny magnet thing they make ( MAT50 ) to help with capacitive coupling. The difference is yours is four times the size and probably costs four times less.

I like the flat ground strap as well. It appears your soldered that. Would a shallow head short bolt with some washers work instead? Put that through the copper sheet first with the smooth head on the downside and then cover that with the whole sheet adhesive backed magnet to protect the roof. Hmm...I'm going to make one and do some testing with different band Hamsticks. Ohh, they have a sheet at Lowes that's 12" x 24" for $16.

View attachment 105316

 

[N4GIX]

I have had an FT-857 and ATAS120 on my little Toyota Camry for three years now. It has been a solid performer for my uses.

I highly recommend taking the time to ground bond all doors, hood, trunk lid, and all fenders. It greatly improves your signal as well as reducing noise. I used 1/2" ground strap for the bonds.

 

[N2IXX]

I had the original ATAS-120 and it worked well for me, I used a trunk lip mount. It worked better than a ham stick and I would still be using it if it didn't meet with an unfortunate accident with my garage door. I now have a Little Tar Heel II lip mounted on the trunk lid and it works quite well coupled to an IC-7000 with an autotuner. You could use a trunk lip mount and just remove it when done. Just giving another option.

 

[prcguy]

I bought the copper foil and magnet off Ebay. I could have used thin stainless steel or brass or whatever, a little larger than the 8.5 X 11" magnet sheet and cut it out with scissors so the sheet had a built in tab that stuck out beyond the magnet material and would reach the ground bolt on the mag mount. A bolt would work on the magnet side except for making a lump between the foil and magnet material. It was very easy to solder the braided strap to the copper foil and I did that before sticking it to the magnet material, which has a peel off adhesive side and that's what sticks to the copper foil.

That reminds me of that Diamond brand tiny magnet thing they make ( MAT50 ) to help with capacitive coupling. The difference is yours is four times the size and probably costs four times less.

I like the flat ground strap as well. It appears your soldered that. Would a shallow head short bolt with some washers work instead? Put that through the copper sheet first with the smooth head on the downside and then cover that with the whole sheet adhesive backed magnet to protect the roof. Hmm...I'm going to make one and do some testing with different band Hamsticks. Ohh, they have a sheet at Lowes that's 12" x 24" for $16.

 

[N4GIX]

You could use a trunk lip mount and just remove it when done. Just giving another option.

Many years ago (20?) I bought a Diamond fold-over mount that allows my ATAS-120A to fold into the trunk whenever I get the car washed, or have to park in a multi-level garage such as that at the VA Hospital in Chicago.

For some reason Diamond ceased production and I've only seen one show up on FleaBay over the past ten years. Stupidly, I didn't buy that one. I'd sure like to get another one!

 

[N2IXX]

Many years ago (20?) I bought a Diamond fold-over mount that allows my ATAS-120A to fold into the trunk whenever I get the car washed, or have to park in a multi-level garage such as that at the VA Hospital in Chicago.

For some reason Diamond ceased production and I've only seen one show up on FleaBay over the past ten years. Stupidly, I didn't buy that one. I'd sure like to get another one!

I remember those an knew a handicapped ham who used one since he couldn't reach up to fold an antenna over manually. It worked well for him. Wonder why no one offers something like that.

 

[N4GIX]

It's a remarkably simple mount. The part that holds the antenna base uses a piano hinge and easily folded into the trunk. When folded, nothing remains visible! It's completely hidden.

I can only guess that they weren't selling well so Diamond just decided to stop manufacturing them. I don't recall the price exactly, but it was a bit south of $100