What kind of antenna is this???

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bobcrean

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I bought this years ago and can't remember why or what frequencies it was good for. The thing below the coil looks like an aluminum tube, open on the bottom, fixed to the whip on the top, and there is a set screw (tunable?). All the original product markings are weathered off. Any help identifying what it might be ideal for is appreciated.

Total whip length is 48"; From tip to top of coil: 29"; From tip to aluminum tube: 36"; Radials are 18: long.
 

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N9JIG

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That is the base version of the MON-52 by Antenna Specialists. The aluminum tube thing is an 800 MHz. choke. The MON-51 is identical except for the 800 MHz. choke. I think the base version was called the MON-31 that came without the choke and the MON-32 with.

They sold these with 2 versions of the base groundplane. The one you have there is the shorter version, they also made one with much longer radials. That version worked great on low-band, the one you have works well on air and VHF hi-band.
 

bobcrean

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Thank you! My current interest is primarily 144-158 Mhz and 460 Mhz as a secondary need. I was going to just build a 1/4 wave GP for 150 Mhz or so, but then found this thing and thought it might work as well for the VHF; I can always build a separate antenna for UHF if needed.
 

N9JIG

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It does work fine on UHF, I have one in my attic and I used it for the DPS on UHF here and it works great.
 

trp2525

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I bought this years ago and can't remember why or what frequencies it was good for. The thing below the coil looks like an aluminum tube, open on the bottom, fixed to the whip on the top, and there is a set screw (tunable?). All the original product markings are weathered off. Any help identifying what it might be ideal for is appreciated...

What you have there is an Antenna Specialists MON-58 all-band base station monitor antenna which covers 25-1000 MHz. FYI the MON-58 antenna was manufactured and sold circa 1990 per the information contained in the antenna's instruction manual. See attached pictures of the cover sheet of the MON-58 installation/instruction manual and a new-in-package MON-58 antenna.MON-58 Picture 10.jpgMON-58 Zoom.jpg
 
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bobcrean

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I would be interested in the 800 MHz choke tube dimensions.
diameter
outside length
inside length
The tube measures .875" OD and has a wall thickness of .025". It's 3.65" long on the outside. I didn't measure the inside length but can if you need it. The thing was filled with bug nest stuff, which I hoed out; not sure that affects the resonance or whatever the thing does, lol. Does it move up and down to tune to a certain frequency?
 

bobcrean

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What you have there is an Antenna Specialists MON-58 all-band base station monitor antenna which covers 25-1000 MHz. FYI the MON-58 antenna was manufactured and sold circa 1990 per the information contained in the antenna's instruction manual. See attached pictures of the cover sheet of the MON-58 installation/instruction manual and a new-in-package MON-58 antenna.View attachment 82372View attachment 82373
That's cool. You wouldn't be able to post a photograph of the rest of the instructions, would you?
 

prcguy

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The antenna had a few different model numbers over the years, I think mine might have been a 700 series.

What you have there is an Antenna Specialists MON-58 all-band base station monitor antenna which covers 25-1000 MHz. FYI the MON-58 antenna was manufactured and sold circa 1990 per the information contained in the antenna's instruction manual. See attached pictures of the cover sheet of the MON-58 installation/instruction manual and a new-in-package MON-58 antenna.View attachment 82372View attachment 82373
 
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nd5y

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Does it move up and down to tune to a certain frequency?
Is it held in place by set screws? The inside dimensions determine the resonant frequency. Moving it up or down would change where the choking occurs and affect the electrical length of the rod below it at the resonant frequency. I'm not sure what effect that would have in real life on frequencies very far from the resonant frequency.
 

kruser

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Does it move up and down to tune to a certain frequency?

Mine is not adjustable in regards to it's position below the coil from what I recall. I don't recall how it is held in place and I'm sure not going to pull the antenna down to look!
 

trp2525

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The antenna had a few different model numbers over the years, I think min might have been a 700 series.

The Antenna Specialists 700 series base station model number was MON731 (see attached picture) which had a list price of $128.85 in 2003. FYI the MON751 (list price $90.00) was the magnet mount version and the MON752 (list price $108.75) was the trunk-lip mount version. Here's the link to the (discontinued) MON731 base station antenna at Universal Radio which includes all of the details of the antenna: Antenna Specialists MON731 Base Scanner Antenna

Antenna Specialists MON731.jpg
 

prcguy

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The tube is held in place on the whip by 2 set screws and its adjustable. Here are some pictures. I don't think you could add one because it sits in between the coil that is not removable and the bottom threaded thing, which is not removable.

There was a 700 series that was basically the same as the MON-58 but I can't find my paperwork. I have several of these antennas and one was a 700 series.

1.JPG2.JPG

Mine is not adjustable in regards to it's position below the coil from what I recall. I don't recall how it is held in place and I'm sure not going to pull the antenna down to look!
 

trp2525

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That's cool. You wouldn't be able to post a photograph of the rest of the instructions, would you?

Here's a picture of page 2 (which is all I have) of the MON-58 instructions showing the detailed parts layout/assembly of the MON-58 antenna. This information may be useful to you if you ever have to repair/service your antenna.

MON-58 Picture 8.jpg
 

N9JIG

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That antenna had more names than the Queen. Each version with different base mounts had at least one model number and then they added the choke, starting up a whole new set of numbers.

IIRC the model numbers for the whip itself was MON-51 without the choke then MON-52 with. I think that came with a mag-mount that had a SO-239 base and a plastic threaded adapter. The base of the antenna itself fit an NMO mount and was straight-thru (no coil). The piece was labeled for UHF ("406 - 494") and was the same as sold with their UHF LMR antenna. There was an identical looking piece labeled for VHF that came with their VHF LMR antennas but I never tested it with that piece. The mag-mount came with a Motorola plug, common in the 70's and 80's during this antenna's heyday.

The antenna itself with the base "coil" would fit on an NMO mount and back in the day I would have 2 of them on the roof of my truck. They worked awesome on VHF Lo-band.

The MON-731 base station version was the same antenna whip and base "coil" and had a small square and flat core with the corners folded and holes threaded. The 4 radials threaded into these holes and were about 18 inches long and of fairly thin construction (1/16 or 3/32 steel wire I think). I would have to go up in the attic to measure them to be exactly sure.

The base unit with the longer radials had a more substantial core and the radials were aluminum but I don't recall if they were solid or folded. They were however about the same length if not longer than the vertical radiator. I never had one, they were hard to find. A friend of mine did though and I helped him install it on his roof. I recall being insanely jealous of how it worked, he used it on his R7000 and PRO2004 back in the late 1980's.
 

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trp2525

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...There was a 700 series that was basically the same as the MON-58...

The difference between the 700 series antennas (circa 2003) and the MON-58 was that NONE of the 700 series antennas contained the 800 MHz choke (see my post #13 above in this thread with MON731 picture and link to Universal Radio). The 700 series of Monitor antennas was based on the company's Mosaic (registered trademark) series of antennas. The only Antenna Specialists MON series antennas that contained the 800 MHz choke were the MON-52 trunk-lid mount, MON-53 deck mount and the MON-58 base station mount.

If you want to have a look at the other two 700 series antennas (both discontinued) to confirm that they did not have the 800 MHz choke, here are the links at Universal Radio:

MON751 Magnet Mount: Antenna Specialists MON751 Mobile Scanner Antenna

MON752 Trunk-Lid Mount: Antenna Specialists MON752 Mobile Scanner Antenna
 

kruser

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The tube is held in place on the whip by 2 set screws and its adjustable. Here are some pictures. I don't think you could add one because it sits in between the coil that is not removable and the bottom threaded thing, which is not removable.

There was a 700 series that was basically the same as the MON-58 but I can't find my paperwork. I have several of these antennas and one was a 700 series.

You are correct. I remember the instruction sheet that came with mine (MON-58) or was it (MONR-58) and it had the same warning about not altering the position of the cylinder (Choke) as is shown in the image scan that @trp2525 posted.
I remember some of AS's MON series had a letter R suffix after the MON letters.
You may have sold me this antenna as NOS prcguy! I've had it quite a while and it still performs very well.
After seeing your picture, I think I do remember the set screws. And yes, adding the cylinder choke would require knocking the threaded part off the bottom of the whip and then figuring out how to reattach it. I suppose one could drill and tap it for small set screws.
I think they pretty much used simple tight slip compression fits for their MON series at least. Probably assembled with a press except for the little ball at the top for the low band adjustment on those models. You could remove and reattach the top ball after cutting the whip for the proper length.
 

trp2525

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...The base unit with the longer radials had a more substantial core and the radials were aluminum but I don't recall if they were solid or folded. They were however about the same length if not longer than the vertical radiator...

That antenna was the Antenna Specialists MONR31 (see attached picture) and here's the link to it at Universal Radio: Antenna Specialists MON-R31 Base Scanner Antenna
Antenna Specialists MONR31.jpg
 

bobcrean

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You guys have a wealth of information! So, the bottom line would be: Is this ancient antenna every good as something I would buy (or build) today, for VHF High and UHF? Should I just put it up again with all new fittings/coax and be done with it? I have no antenna analyzing equipment.
 
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