COMPACtenna SCAN-III

[KevinC]

The latest sweeps are a little more believable.

 

[vagrant]

Thank you for those plots. It is appreciated.

 

[cbehr91]

I haven't heard good things with regards to the quality. One user here on RR claimed his leaked and had water inside it. I don't think the NMO center connector would hold up over time if you installed/removed it very often. One light whack would snap that like a pretzel! The price seems high, $114.00. I think half of that would be plenty. Thanks for posting however.


View attachment 83576

That was me that had a leak. It was the original 11" V/U/7/800. Dr. Jack wanted me to return it and it replaced it for free since it was within the one-year warranty period. My replacement was a different model, though, as I think the original model was already out of production. Shorter, about 7.5", and didn't seem to work as well on VHF as the original. (I suspect it's either the 2m/440 model or 2m/220/440 version -- I don't have an analyzer to test it). Also, at least with my Larsen NMO mounts (magnet and hole) if you use the supplied rubber gasket under the antenna the center pin on the antenna doesn't make contact with the mount, so you have to go without the gasket.

 

[JoshuaHufford]

Okay I'll eat crow now. Sorry I forgot I had my splitter involved and grabbed the wrong coax. Don't sweep antennas while in a hurry!

SWR:

Return Loss:

Smith Chart:

Phase:

I'm not very familiar with how to interpret what I'm seeing in these images, and they are hard to read on my screen. Am I understanding properly that the lowest SWR is at 418MHz?

I would be very interested to see what the SWR is at 160-162, 450-460, 895-960MHz as those are where my primary interests are.

I have the 2M/440 model now, I picked it up used at a decent price, but I've thought about getting the Scan model for wider range.

 

[devicelab]

I would be very interested to see what the SWR is at 160-162, 450-460, 895-960MHz as those are where my primary interests are.

The sweep is 30 Mhz to 1 Ghz.... look at the first picture.

 

[JoshuaHufford]

The sweep is 30 Mhz to 1 Ghz.... look at the first picture.

Is there a way I can pinpoint the ranges I specified on the graph? I can't enlarge the picture any more than how it is posted in the thread.

 

[vagrant]

Joshua, based on what you noted, the Larsen tri-band would be better suited for your frequency needs. It sweeps better than the Scan III in the 140-165, 440-470, and it may be even on 895-960 range. You're also lucky as the Larsen 150-450-800 is half the price. I believe there's a new model out with a spring. I could be wrong.

For my needs, the Scan III looks like a better solution. My placement will not be the same though, but one must experiment.

 

[JimD56]

Has anybody tried this antenna on an NMO mast mount up high on the house? I'm surrounded by 770-860mhz.

 

[JoshuaHufford]

Joshua, based on what you noted, the Larsen tri-band would be better suited for your frequency needs. It sweeps better than the Scan III in the 140-165, 440-470, and it may be even on 895-960 range. You're also lucky as the Larsen 150-450-800 is half the price. I believe there's a new model out with a spring. I could be wrong.

For my needs, the Scan III looks like a better solution. My placement will not be the same though, but one must experiment.

I assume you are referring to this one?

https://www.theantennafarm.com/catalog/larsen-nmo150-450-800-1050

I'll have to see if I can still pull into my garage with it on my car, that is why the Scantenna is on my radar.

 

[JoshuaHufford]

The sweep is 30 Mhz to 1 Ghz.... look at the first picture.

I'm also curious what kind of ground plane you were using when you did the sweep? I seem to recall the inventor saying this antenna works best when it is a the edge or corner of it's ground plane, which I don't understand why.

 

[JimD56]

I meant putting the CompacScantenna III on something like this 1465 NMO Mount CB Mobile /Base Ground Plane Antenna Kit 727932011804 | eBay
I have this set up now with the https://www.theantennafarm.com/catalog/larsen-nmo150-450-758-8932 not sure if this "magic" antenna would give me better performance in the ranges I listen to most 770-860mhz with no simulcast

 

[vagrant]

Yes, I am referring to that particular Larsen antenna. I also understand your concern with the height and garage. I use a motorized mount for my VHF/UHF mobile antenna.

As to the ground plane during the sweep, I presume it was in the middle of the vehicle roof which was previously noted in the thread. Everyone's needs are different, that means placement location, so that sweep may not look like mine or it may look very close once in place. I would need to put it near my AM/FM antenna near the passenger side front fender. Again, one must experiment as the results can be different.

 

[prcguy]

My take is the fat rolled up circuit board section would add a lot of capacitance to the ground plane, lowering the impedance and reducing the ground plane would raise the impedance back to something acceptable.

I'm also curious what kind of ground plane you were using when you did the sweep? I seem to recall the inventor saying this antenna works best when it is a the edge or corner of it's ground plane, which I don't understand why.

 

[buddrousa]

The COMPACtenna SCAN III, designed by Dr. Jack Nilsson N8NDL, is 9.5 inches tall, yet has wide VHF/UHF range covering 100 - 1500 MHz. It is optimized for 136-174, 378-512 and 750-960 MHz. The small, rugged, receive-only antenna provides high performance as a result of its unique electric/magnetic field diversity design. The patented design uses the the latest science to provide revolutionary performance in NLOS (Non-Line-Of-Sight) obstructed environments such as behind buildings, in garages, behind other vehicles and in valleys. Nominal gain +3 dBi. It features an NMO base.

This antenna requires an NMO type vehicle mount and coax which are not included. Please see table below for typical mounting methods. One year limited mfg. warranty. Made in the U.S.A.

This antenna may also be used as a high performance compact base antenna at the top of a metal mast such as with the optional Larsen BSAKIT. Specific instructions are provided on the Manufacturer Data Sheet provided with the antenna. For best results with this mount, carefully bend the ground plane radials downward 70 degrees below the horizon.

 

[JimD56]

Thanks buddrousa. Any idea if its performance would be better than the all band Larsen NMO I have on the house now? Also, my ground plane radials are straight out, no angle bends at all. Currently listen to air 108-137mhz, milair 225-380mhz, UHF 460mhz, and aforementioned 770-860mhz.

 

[Ubbe]

I also understand your concern with the height and garage. I use a motorized mount for my VHF/UHF mobile antenna.

Don't you have access to any other mounts that could work better in those situations?

A type that are used a lot in europe are one that can be completly installed from the outside, you don't need to have access to the hole from the inside.

The bottom part are cut to a 45 degree angle and are faced to either side of the car and the top part, that the antenna attach to, are secured to the bottom part with a bolt and have a rubber gasket between them to add friction. The bolt are tighten enough to keep the antenna upright at highway speeds.

If the antenna gets in contact with an object the top part twist and the antenna lays flat on the roof. You then just raise the antenna again to an upright position as if nothing had happened. Neither the antenna, the base or the roof are damaged. The rubber gasket usually has to be replace after 5 years or so, depending of the climate.




/Ubbe

 

[prcguy]

Nothing that I know of works better than an NMO mount for most vehicle installations. There is a reason every police car, fire truck, ambulance, Taxi, US Federal Govt, etc, has NMO mount antennas. Its been well proven over the last 52 years of its existence.

Prior to that I think the 3/8" snap in, or old Motorola mount was most popular.

Don't you have access to any other mounts that could work better in those situations?

A type that are used a lot in europe are one that can be completly installed from the outside, you don't need to have access to the hole from the inside.

The bottom part are cut to a 45 degree angle and are faced to either side of the car and the top part, that the antenna attach to, are secured to the bottom part with a bolt and have a rubber gasket between them to add friction. The bolt are tighten enough to keep the antenna upright at highway speeds.

If the antenna gets in contact with an object the top part twist and the antenna lays flat on the roof. You then just raise the antenna again to an upright position as if nothing had happened. Neither the antenna, the base or the roof are damaged. The rubber gasket usually has to be replace after 5 years or so, depending of the climate.


View attachment 83678

/Ubbe

 

[vagrant]

Thank you for the suggestion Ubbe. I could of course use an NMO mount, or the one you mentioned, and move/fold the antenna by hand at least twice a day. Additionally, a 1/4 wave height would easily hit the repeaters around me that are on average 900 to 1500 meters above the valley floor where I live and probably hit the garage door as well. I have about 25 cm from the roof of the vehicle to the door and therein lies the issue.

I use a Diamond motorized mount attached to the roof rack along with a Diamond NR770HB antenna. This antenna enjoys the entire roof all by itself and is used for my VHF/UHF mobile. I have two more TX antennas connected to the back tailgate of the SUV, one is specifically for UHF connected to a Motorola P25 radio and the other on VHF dedicated to APRS. On the front right fender is the AM/FM radio antenna, along with my scanner antenna. Everything plays well together and I have not destroyed the receivers. I often use simplex on VHF and this setup gets things done. Thinking about it now I would say I can get about 48-64km (30-40 miles) from my mobile to someone's home system. For car to car it is probably half that. It can be less than that depending on terrain. Honestly I have never really concerned myself if I could do better, as my system worked well enough for my needs.

Does anyone know if NMO mounts on vehicles consistently get 64km (40 miles) or better for simplex, when at similar height ASL? I doubt I would change my setup, but it would be good to know either way for future use.

(Wait, don't answer that. This is off topic.)