Kenwood: Kenwood TM-281 and PulseLarsen glass mount, motorhome, your thoughts?

[FIREUP]

Gang,
HRO and I think one other seller is on its last day of a sale for various products. And, I'm thinking of purchasing the Kenwood TM-281 single band 2M mobile for the motor home. At present, I'm not looking for a ton of bells and whistles. I'd just like alternate forms of communications when traveling. I spoke with one of the lead people at HRO on this radio and, for the most part, he claims is a seriously rugged radio for race people, off roaders etc. As stated, it's the last day of the sale and it's going for $137.00. Now, as for a possible antenna. So far, I'm thinking of this:

PulseLarsen KG-144-UDPL Antenna Mobile Single 2M, KG144UDPL

I'm not one that gets squirmish about drilling holes in bodies of cars/trucks/motorhomes etc. for antenna leads and other stuff. Not a big deal. But, based on logistics, I have a stationary window, that's above my drivers side slider. The upper, front corner is about 18"-20" below the roof line. If I were to mount that Larsen glass mount at that upper corner, that 47" element would be, for the first 18"-20", parallel to the motorhome, about 2" or so inches away from it. Then, the remaining part of that antenna would be up in the open air. But, and here's maybe a critical part. If that Larsen is placed in the fashion I'm describing, it will reside approximately 18"-20" away from my C/B antenna which, is almost directly above the driver but forward a bit, mounted on the roof top. So, I know it's really not a good practice to have the two antennas as close as they may end up but, for "decent" performance of that radio, will the antenna situation be Ok or not? I say "decent" because, again, I know the close proximity of the two antennas could and most likely WILL cause poor performance.

This specific antenna is recommended by the knowledgeable person at HRO due to its length, i.e. 1/2 wave. But, again, it's radiance is "partially" obstructed by the side of the coach. So, your thoughts? By the way, I have 'till this evening at about 5:00 P.M. to still purchase this radio on sale.
Scott

 

[cmdrwill]

Kenwood TM-281 IS a great radio. Also check price at Gigaparts.

The antenna you mentioned is way overpriced .You CAN do way better. HRO has a horable markup.

 

[FIREUP]

I thank you for taking the time to reply. I did check on Gigaparts before and, first off, the Kenwood TM-281 is the same exact price in Gigaparts as it is in HRO. And, both establishments are ending their sale today, the 30th. But, the PulseLarsen KG glass mount antenna IS cheaper at Gigaparts but, their cheapest shipping is $20 so, it pops the price right back up to equal with HRO. But, I think the window I'm thinking of mounting that Larsen on is or has, a slight tint. But, if so, it's factory tint, not add-on. But, the manufacturer states this antenna may not work with ANY form of tinting, even factory stuff. Still researching.
Scott

 

[popnokick]

Glass mount antennas and tinting are a "roll the dice" proposition. Some folks have great results with them (I have) but others do not... and much depends on the metallized tinting in the glass (if any). Unfortunately if there are tinting standards it is very hard to determine what specific standard your specific piece of glass is using. What would be a useful invention is a "Glass Tint Tester to Determine if Thru-Glass Antennas Will Work". Seems like it would be possible.

 

[mmckenna]

I think that antenna is going to be a less than ideal performer, as I suspect you may already know.

You're going to have a (or nearly have) a 1/4 wave of aluminum framing/skin right up against the antenna, and that's likely going to create some SWR issues.

If it'll clear, I think you'll be much better off with a 1/4 wave whip mounted on the roof. If the roof skin is aluminum, drilling the hole would be the way to go. If it's not metal, then fabricate a sheet metal mount that you can seal down on the roof. Or, find some other suitable structure to mount it too.

While keeping your feed line runs as short as possible, it's more important to have a good location. You don't want it all the way at the rear, but make sure you've got some good space around the antenna.

Glass mount would probably be pretty low on my list of antenna choices in an install like this.

As for the radio, it's probably a good price and a good radio. Sometimes simple works well.

 

[W5lz]

A 5/8wave antenna just is not that hard to mount on almost any metal 'skinned' vehicle. There are a number of mounts that do not require drilling a hole! A thru-glass mount just is not a very good idea.

 

[cmdrwill]

Need to know more about your vehicle, for a good antenna.

And you will need way more that 18 inches separation, or take the chance of blowing out the receiver.

 

[ramal121]

Hope you grabbed the mobile. Not a bad price.

Now my comments. Motorhomes are the worst of the the worst trying to install an add on antenna without having a huge ugly factor. I'm going with your logic here. Glass mount eliminates a penetration for the coax and being a half wave you don't have to worry about a ground plane. Easy peasy. Now the sad part. The above comments are valid. The lower portion of the whip, is it against fiberglass or aluminum? Either will affect the SWR and the radiation pattern. Metal more so. If the SWR is in the 2.0 to 2.5 to 1.0 or better range that is not stupendous for efficiency but should not put too much undo stress on the transmitter if you trust Kenwood to build a robust product. In any case I think it would work with compromises.

Window tint MAY affect the rf transfer from inside to outside. Depends on the metallic content of the film. Aftermarket tints can be cut with a razor and removed before landing the sticky tape. Otherwise you take your chances with what is on the window and trial and error prevails.

18 to 20 inches between antennas is not much and yes transmit power induced into the opposing antenna may certainly cause damage to the other receiver. Your only saving grace is the difference between 27 and 146 MHz and the ability for either tuned front end of the receivers to block or shunt the induced energy from the other band before it hits the first RF amp. It's a crap shoot but I think it will be all right.

There are other suggestions and they are with merit. A unity or gain antenna with a horizontal ground plane underneath on the roof top will certainly give maximum performance but the install complexity has just gone up up several fold. Are you on your last dime and need specific recommendations on whether this will work or are you willing to spin the wheel and experiment with a month's worth of beer money?

Sent from my SM-T560NU using Tapatalk

 

[W5lz]

All antennas require an "other half" to operate. There has to be two "terminals". In the case of a vertical antenna, that other half is a groundplane of some sort, counterpoise, radicals, or maybe the shield of the feed line. 1/2 wave verticals are no exception.
Beauty is in the eye of the beholder. If ugly is a consideration then you WILL end up with less than 'good' performance. (I'll bet money on that!) Hide that air conditioner too... it's ugly!
Fiberglass is easy to make into or modify for providing a "groundplane". Got some aluminum foil and glue? Couple of long flat metal strips And some screws?

 

[cmdrwill]

Your only saving grace is the difference between 27 and 146 MHz and the ability for either tuned front end of the receivers to block or shunt the induced energy from the other band before it hits the first RF amp. It's a crap shoot

Crap shoot for sure. get some separation between antennas, why take a chance?

All antennas require an "other half" to operate.

Correct, but a half wave radiator with a matching transformer, ie 'loading coil', already has 'both half's'. so it does not need a groundplane.
All this was covered in Antenna 102.

 

[W5lz]

cmdrwill-
I thing terminology may be a problem here. A loading coil makes an antenna appear electrically longer. It has nothing to do with this.
An impedance matching coil (base of the antenna) only 'matches' impedance between feed line and the antenna. Still nothing to do with this. Neither provides that "other half" or the second "terminal". That's true for all antenna, half wave included.

 

[cmdrwill]

Mr W, I have to disagree.

I thing terminology may be a problem here.

Probably terminology and or English language not to mention slang..

 

[FIREUP]

Ok Gang,
Well, first off, as you all know, based on my intent, my purchases and my questions, I by far, am nowhere near any form of an expert here. So, hence, that's why I went with some advice from the techs at HRO and, purchased the radio and the glass mount antenna. Now, first, the motorhome in question is our '04 Itasca Horizon, 36GD with the CAT C-7 330HP. It is a full body painted, fiberglass coach, with a totally fiberglass roof. Now, I'm not one of those that's "squeamish" about drilling holes etc. in bodies of cars/motorhomes/boats or anything that such a hole might be needed in, for a given purpose. If it needs a hole, for a realistic purpose, well, in goes the hole, no biggie.

And, if I knew more about antennas, I might have looked at different ones. Here's one major problem. My roof to header clearance is not very much as we drive the coach in and out of it's cave. I've got oh, maybe around 18"-20" inches or so. I have very, very limited access to any of the underside of that roof skin. Motorhomes aren't made to have great access to things like that, once they're all built. So, a glass mount was, at that and this time, about my best choice. We'll see just how well it performs.

Now, as for the close proximity to my C/B antenna, well, I've got a bit of a remedy for that. I "WAS" going to mount the new glass mount antenna at the highest and most forward corner of the upper side glass. And that was going to present that close proximity for the two antennas. But, after a bit of thought, I just decided that, I can move that location to the rear section of that same window. That window is about 30" long so, what that's gonna do for me is, place the distance between the C/B antenna and the HAM antenna, to be about 36" or more, plus or minus. I'll report back when I have more exact figures. Thanks to all who've taken the time to help me here. It's very, very much appreciated.
Scott

 

[W5lz]

It may be that a glass mount is your best bet. Depends on how hard access to the roof would be. And considering clearance, a 1/4 wave probably best for a roof mount.
I have an aversion to glass mount antennas, just seen too many that were done wrong or just junk to start with. But! It's still a concideration.

 

[mmckenna]

Now, first, the motorhome in question is our '04 Itasca Horizon, 36GD with the CAT C-7 330HP. It is a full body painted, fiberglass coach, with a totally fiberglass roof.

Concern should be that any metallic component of the RV in close proximity of the antenna can cause issues (coupling, detuning, reflections, etc).
Very likely there is an aluminum frame under the fiberglass. If the antenna is too close to a frame member, you may have tuning issues.

As long as the RV glass doesn't have a metallic tinting on it, you are probably OK.

Glass mount wouldn't have been my first choice. 1/4 wave on the roof would have been an option, but like you said, clearance under the roof skin becomes an issue. It's a challenge, that's for sure. I've got a 2019 Sandstorm toyhauler that I'm looking to mount a VHF antenna on. I'm not in a big rush, but still considering all my options.
I've done glass mount UHF antennas on vehicles before. They work OK, not outstanding, but if you want a basic setup with easy install, it's certainly an option. Worked with a guy with a little convertible who had a 1/2 wave VHF glass mount on the front window just above the rear view mirror. Worked fine for what he needed

Given all the challenges involved, you probably have an install that's going to work well enough. It's easy for a bunch of strangers on the internets to tell you what you "should" do, but it's a different thing when it comes to making the decision. In the end, it's up to you. Since the glass mount isn't going to do any damage, it'll be easy to remove it and try something else if you are not happy with the results.

 

[FIREUP]

You guys are GREAT!!! As stated previously, I most certainly appreciate any and all help here. I have a bad habit of getting something in my head and, while I do consider some outcome, issues, potential problems etc., I still have tendency to go with an original thought, even though it might not be the best game plan. And this is what happened with my purchase of the radio and glass mount antenna. I got all of it ordered, BEFORE consulting you folks on here. MISTAKE!! But, the order was being processed and, I'll have to give it to HRO, they do well in getting orders processed and shipped. I ordered the two items and, they arrived the next day!!!

Now, I'd like you all to consider how I came to make my judgement on my decision for the way I went with the motorhome antenna install. If you look at the one or two pics below, what you're looking at is the tail gate etc. of our Jeep. And, you'll see the newly installed NMO mount antenna. I don't have a stand-back full picture of just how much the antenna protrudes ABOVE the roof line of the Jeep. But, the part of the antenna that protrudes above that Jeep roof line is around a foot. And, not only that but, my C/B antenna is in the almost same exact position in terms of mounting, only on the other side of the spare tire. So, that HAM antenna is about 24.5" away from the C/B antenna and, is about 3" or so away from the Jeeps tail gate and or, rear glass.

And so far, with the limited amount of contact I've made with nice HAM folks around here, pinging off local repeaters, THEY say I'm coming in real strong with no background sound or issues. So, so far, the Jeeps system is doing fairly well, based on again, the limited contacts I've done.

Now, this is sort of the "reference" I'm using to create the HAM system in our motorhome but, the prime difference is the glass mount instead of the NMO mount. The length of the antenna on the Jeep is right at 41" or so as directed by the instructions for length, dictated by the antenna brand. The glass mount, at present, is 47" long. There will be a considerable longer section of the element above the roof line on the motorhome, than there is on the Jeep.

Now, does this all justify my decision, nope. It's just my line of thought right now. I will be doing the install of the radio and antenna today. But, I'll have to get the big beast out of its cave to try and test the SWR and, maybe make a contact. Again, I'm new here and learning so, I am sucking up all the knowledge and experience you folks have to offer. I paid quite a bit for that antenna and, it's now in my possession so, based on the logistics of sending it back and, the cost, if it doesn't work very well, well, I'll eat it and, move on to what you folks may help me decide on as a next better approach. Remember, I have limited overhead clearance above the coach roof line as we back in and drive out the motorhome to and from its cave. Thanks again.
Scott

 

[RRR]

I'm pretty sure that a whip, physically connected to your scanner, sitting inside the window, would be more effective than a glass mount antenna,,,,

 

[FIREUP]

I'm pretty sure that a whip, physically connected to your scanner, sitting inside the window, would be more effective than a glass mount antenna,,,,

"Scanner"???
I don't have a "scanner". It's a regular Kenwood TM-281A HAM radio, used for both receiving and transmitting.
Scott

 

[RRR]

Good gracious, that's even worse!

A passive antenna could eventually harm your transmitter as well. Seen it several times

 

[mmckenna]

Good gracious, that's even worse!

A passive antenna could eventually harm your transmitter as well. Seen it several times

"Passive antenna"??

A glass mount 1/2 wave is not a passive antenna. The antenna is capacitivly coupled to the radio through the glass. If SWR is check and it's below what the manufacturer specs' for the radio, it'll be fine.