COMPACtenna SCANNER

[N9JIG]

Mine is the Scanner version, but to be honest I don't know if there really is a difference.

 

[cbehr91]

I still don't know what to think of the little antenna. I just did a listening comparison again vs. a 1/4 wave whip on the NOAA WX channels. Same NMO mount, coax, and Icom radio, and they were neck-and-neck with the COMPACtenna doing slightly better on WXJ93 from Cridersville, OH (I am in Columbus), but slightly worse than the 1/4 wave on KJY68 from Chillicothe.

One thing I have found -- at least in my experience -- is that the COMPACtenna definitely does better in the middle of the car roof, and not in the corner like the product literature says...not sure why that is.

 

[Ubbe]

One thing I have found -- at least in my experience -- is that the COMPACtenna definitely does better in the middle of the car roof, and not in the corner like the product literature says...not sure why that is.

Middle of the roof are always suggested as the best placement for an antenna.


/Ubbe

 

[prcguy]

In the brief playing around I've done the match on 2m gets worse when its in the middle of a large metal surface and better near the edge. This tells me there is a lot of capacitance to ground and the impedance is probably much lower than 50 ohms when in the center of a roof. The radiation pattern will still be better at the center of the roof but the mfr recommends the roof edge for matching purposes.

Looking at the patents for this antenna with some drawings indicating the antenna might start with a large flat large surface area circuit board type of material, then its rolled up into a log, its no wonder it might have a lot of capacitance to ground. Especially if the base of the radiating element is wide and has a lot of surface area close to ground.

Maybe the design could benefit from a cone shaped feed point where the point of an upside cone attaches to the NMO contact then it widens out after an inch or so and the rolled up log attaches to the wide part of the cone? That would reduce some capacitance at the feed point. Maybe I'll have to sacrifice my Compactenna one day and cut it open to see what's inside and maybe play around with some ideas.

I suspect the inventor borrowed some ideas from existing antennas and it may not be engineered as far as it could have been.

 

[cbehr91]

Middle of the roof are always suggested as the best placement for an antenna.


/Ubbe

I know middle of the roof is optimal...I was rhetorically asking why when the COMPACtenna product literature says corner of the roof is best it actually works best in the traditional center roof location (at least the two models I've had anyway).

EDIT: read prcguy's post regarding its radiation pattern, and I'd have to agree. Since I'm not using the antenna to transmit, at least based on his observations the middle of the roof is still best.

 

[RadShackFan]

Okay, I guess I'll step into this lions den. Ordered the 2m/440 version from Universal Radio. Wanted to be able to drive into the garage without having to remove the antenna. It arrived early this morning so I've been putting it through some tests.

First test was conducted with the Yaesu FTM-100DR that is currently in my vehicle. I could not detect any difference in the antennas performance and the Laird 1/4 wave I had been using. I could only measure SWR on VHF since I do not have a meter capable of UHF. (I don't really use the UHF side except to monitor the local VFDs.) SWR on VHF hovered around 1.8 throughout the band. Totally acceptable for my intended APRS use.

Now for the scanner test. Used the Whistler 1098 I use in my shack to monitor the Montgomery P25 and AFRN systems. Connected it up in the car and was pleasantly surprised. With the car in the garage the scanner locked on to both systems control channels with 3 bars signal strength. AFRN was not seeing much use, so I turned that off. The scanner tracked the Montgomery system and I could hear the radio traffic clearly.

Taking the car for a ride was even better. Once outside the garage the signal bars were a full 5 and I had no problems following the conversations. I was only monitoring the Bald Knob and simulcast sites.

Now I have to decide which radio to have in the car.

I don't really understand the physics behind this design, and really don't care, but the antenna works.

 

[prcguy]

If possible test the Compactenna against another so we will know its better or worse than brand or type X.

Okay, I guess I'll step into this lions den. Ordered the 2m/440 version from Universal Radio. Wanted to be able to drive into the garage without having to remove the antenna. It arrived early this morning so I've been putting it through some tests.

First test was conducted with the Yaesu FTM-100DR that is currently in my vehicle. I could not detect any difference in the antennas performance and the Laird 1/4 wave I had been using. I could only measure SWR on VHF since I do not have a meter capable of UHF. (I don't really use the UHF side except to monitor the local VFDs.) SWR on VHF hovered around 1.8 throughout the band. Totally acceptable for my intended APRS use.

Now for the scanner test. Used the Whistler 1098 I use in my shack to monitor the Montgomery P25 and AFRN systems. Connected it up in the car and was pleasantly surprised. With the car in the garage the scanner locked on to both systems control channels with 3 bars signal strength. AFRN was not seeing much use, so I turned that off. The scanner tracked the Montgomery system and I could hear the radio traffic clearly.

Taking the car for a ride was even better. Once outside the garage the signal bars were a full 5 and I had no problems following the conversations. I was only monitoring the Bald Knob and simulcast sites.

Now I have to decide which radio to have in the car.

I don't really understand the physics behind this design, and really don't care, but the antenna works.

 

[RadShackFan]

If possible test the Compactenna against another so we will know its better or worse than brand or type X.

Per your request: I have an older version of the Larsen tri-band I used on my work vehicle when Montgomery used the EDACS system before I retired. I tested it with the scanner only since, I assume, you would be interested in the 700/800mhz performance. I drove the same route and monitored the Montgomery P25 system. (The scanner did lock on to the AFRN control channels, but there is rarely any activity on it.) I even sat in a few different places and switched back-and-forth between the Larsen and the Compactenna. I really could not tell any difference in the quality of the signals.

I then scanned the local Ham VHF/UHF repeaters, the Troopers and the Sheriff departments in Macon and Autauga counties. Both antennas were equal in signal strength, but the Compactenna had some white noise on both Sheriffs departments that are VHF. (According to Google maps I was 21 miles from the Autauga county radio tower and 26 miles from the Macon county radio tower. (When listening in my shack using the same scanner but an antenna in my attic @ 18' there is no white noise.)

I did not drive into the downtown area during this or yesterdays tests.

The antenna works well enough for me, so I guess it comes down to personal choice. The only thing that I found to be strange is the screw in the side near the bottom of the antenna. I hope it's not a future "leak" spot.

 

[iMONITOR]

Yet another variation on Dr. Jack Nilsson's, N8NDL COMPAC antenna. Replacing the COMPAC SCANNER antenna, comes COMPAC SCAN III antenna. He changes antennas frequently, but I guess that's a good thing. It was mentioned here on RR that his original COMPAC SCANNER antenna developed a water leak. It appears the new version would not be ideal for civilian/commercial VHF Air Band. Might work well for 750-850 public safety. But it's about 6" taller than it needs to be for that. I'll probably never get any sleep until I actually try one of these.

COMPAC SCANNER $84.98
100MHz-1500MHz
+3 dBi
7.5" tall

COMPAC SCAN III $114.95
100MHz-1500MHz
+3 dBi
9.5" tall
It is optimized for 136-174, 378-512 and 750-960 MHz.

 

[RadShackFan]

Well that didn't last very long. Went to the Mall last night and was inside about 40 minutes. Came out and the Compactenna was gone. Someone stood in my truck bed and removed it from the NMO mount in my roof. It was on pretty tight so I know it didn't just come off.

I've had one or more antennas on my truck for 10 years and have never had a problem before.

 

[iMONITOR]

Well that didn't last very long. Went to the Mall last night and was inside about 40 minutes. Came out and the Compactenna was gone. Someone stood in my truck bed and removed it from the NMO mount in my roof. It was on pretty tight so I know it didn't just come off.

I've had one or more antennas on my truck for 10 years and have never had a problem before.

That's a shame. Some people!

 

[NC1]

Went to the Mall last night and was inside about 40 minutes. Came out and the Compactenna was gone.

Somebody knew what it was and had to relieve you of it. That really sucks.
I had an expensive dual band Diamond on the trunk of my car, amazingly nobody ever stole it.

 

[K4EET]

Well that didn't last very long. Went to the Mall last night and was inside about 40 minutes. Came out and the Compactenna was gone. Someone stood in my truck bed and removed it from the NMO mount in my roof. It was on pretty tight so I know it didn't just come off.

I've had one or more antennas on my truck for 10 years and have never had a problem before.

qslmark, hello there. I have been following this thread as I have two of Dr. Nilsson's antennas and absolutely love them (although one is now obsolete). More importantly though, I was speaking with Dr. Nilsson today and he would like for you to contact him at the COMPACtenna corporate eMail address that appears on the website (COMPACtenna) under the "Contact" menu item. BTW, I'm sorry to hear that somebody must have needed your antenna more than you did. Just remember, God was watching...

73, Dave K4EET

 

[TailGator911]

Quite happy with mine and they worked well on a recent RV trip to Tennessee. They are a curious contraption to the uninformed and I got a few questions at the campground. One lady actually told me she thought my Winnebago Via was a 'government vehicle', and when I asked her why she thought that, she said - "Those funny-looking antennas on your roof rack". They do invite questions.

JD
kf4anc

PS - k4EET, haven't seen you around lately, hope all is well, brother.

 

[prcguy]

Sorry to hear about the theft, I would be asking for surveillance video and going door to door until I found it.

I wonder if you can transmit on the scan III version across its stated frequency range? If so I might have to get one of those too.

 

[K4EET]

PS - k4EET, haven't seen you around lately, hope all is well, brother.

Hi JD, while I do have an illness called MELAS (Google it for details), I am still alive and kicking. I am subscribed to a lot of the forums and they seem to be getting along nicely without me. I'm in more of a reading and absorption mode right now. But rest assured, I have not gone away. Since I don't want to hijack this fine thread, you or anybody else feel free to PM me anytime. 73, Dave K4EET

 

[JoshuaHufford]

That is a shame. I was also thinking you should ask the mall if they have any video of the area you were parked in from that time.

 

[buddrousa]

Well I have ordered the COMPACtenna SCAN III scanner antenna comes in 5/18/2019 I will test next week and see how it works in my area.

 

[RFI-EMI-GUY]

Looking at the patent, that certainly seems like a "different" antenna.

I concur with PRCGUY, the matching section should be optimized to permit center of ground-plane mounting.

My thoughts are that at the lower frequencies, the antenna is going to favor horizontal polarization and that at the higher frequencies, there are going to be some notches in the VSWR due to resonances. But I could be wrong. I would love to see one of these tested on an antenna range at various frequencies and polarization's.

 

[JoshuaHufford]

Well I have ordered the COMPACtenna SCAN III scanner antenna comes in 5/18/2019 I will test next week and see how it works in my area.

I will be interested to see how this works for the railband if you feel like testing that.