Diplexer split between commercial FM broadcast and 2m amateur

[KD7RJC]

I'm trying to find a diplexer type component to allow me to receive commercial FM broadcast 88-108MHz into the factory car stereo and 144MHz+ on an amateur radio, using the same antenna for both. Does anyone know of such a beast? I've found a few examples out of Europe that claim some finer discrimination between frequencies, but their amateur bands are narrower than American bands and their components claim 144-146MHz, not up to 148MHz.

I suppose ideally I'd want a triplexer that could do commercial FM broadcast out one port, 2m and 70cm amateur out another port, and GMRS 462-468MHz out a third port, but I am aware that this is asking for a unicorn.

 

[prcguy]

There were some couplers used on old VHF disguise antennas that would tap off to the AM/FM car radio. Do you want to use the stock AM/FM antenna for everything or use a 2m amateur antenna for AM/FM? Here is a coupler that would use the 2M amateur antenna for AM/FM and its cheap because there is little use for one today.

NOS NIB Vintage Antenna Specialists ASPS619 VHF HI Band AM/FM Coupler | eBay

Find many great new & used options and get the best deals for NOS NIB Vintage Antenna Specialists ASPS619 VHF HI Band AM/FM Coupler at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[KD7RJC]

Thanks, that's enough of what I've been looking for I'm likely going to buy a few. Given that most of my radios are closer to the ages of these devices than to being new, technology-wise this looks like a good match if they're functional at all.

The mobile installs could go into a Nissan Frontier, a Jeep Renegade, a '95 Chevy Impala, or a small metal-walled travel trailer. The Frontier is my daily, the Renegade my wife's. I'm inclined to replace factory antennas, but it'll depend on the nature of the antennas I find and how effectively they would work given the factory antenna mounts on the various vehicles.

For the Frontier, the factory mount is on the cowl, passenger's side, just aft of the hood. There's a post on a forum where someone retrofitted this position for a CB. I don't think that SWR was measured for 11m, but I'm curious if one of these 5/8 over 5/8 70ish cm antennas replacing the factory antenna in this spot might work, it doesn't require a ground plane and the length would put the center of the antenna roughly in line with the truck's metal roofline. I would not be ideal-ideal, but it might be good enough for either 70cm ham or for CBRS.

For the Renegade, I'd have to see what my wife is willing to put up with, up to and including if she chooses to take the test for Technician. Like me, she's not really inclined to drive around in a cybernetic porcupine, so any changes would need to be subtle. If I were to replace the factory antenna on her jeep, I'd have to make sure that the result still looks good and works properly with the factory stereo. That may mean having to figure out a separate satellite receiver for XM, even though she doesn't use XM, and I'd probably need to make whatever I do be reversible.

The Impala is least likely to have an antenna permanently mounted. Most likely mag-mount only and since I just spent a lot of money repairing the factory power antenna assembly, it's unlikely that I'll replace it with a ham radio antenna. I guess I could test SWR, see if it's anywhere close to OK for an amateur band or CBRS, but I would be surprised if it is.

The travel trailer would have the least need for limiting to one antenna, but I still might want to use the factory-installed broadcast radio with a ham radio or GMRS antenna, if only because there's no point in adding unnecessary holes when water intrusion is the biggest killer of travel trailer.

I'm also looking at the Compactenna, but I'm annoyed that I can't find any planar plots of the radiation pattern of the various Compactennas. I get that it's 1) expensive to perform that sort of testing, and 2) the plots don't necessarily reflect real-world performance, but they're expensive enough that I would like to know. I may end up putting one of those on my truck for amateur 2m/70cm, I'm considering putting it under the tall fiberglass canopy (purple on diagram, with pink for the shelf):



downside is that I would have to devise a different mount if the shell comes off, which sometimes it does.

So we'll see.

 

[mmckenna]

Thanks to the brainiacs at the FCC, there's two definitions for CBRS.

Citizens Broadband Radio Service, 3.5-3.7GHz Federal Register :: Request Access
Citizens Band Radio Service, 27MHz.

I'm assuming you are talking about Citizens Band Radio Service?


I'd be interested in seeing the SWR curve for a 5/8 over 5/8 UHF antenna on Citizens Band.

I'm a bit confused about what you are looking for. Are you wanting to transmit on 2 meter band as well as listen to FM broadcast? Or just listen on both?

Stico makes antennas that will work as both AM/FM broadcast as well as LMR band. Expensive, but an option if you need the looks. STI-CO® | Mission Critical Antenna Solutions

 

[KD7RJC]

Thanks to the brainiacs at the FCC, there's two definitions for CBRS.

Citizens Broadband Radio Service, 3.5-3.7GHz Federal Register :: Request Access
Citizens Band Radio Service, 27MHz.

I'm assuming you are talking about Citizens Band Radio Service?


I'd be interested in seeing the SWR curve for a 5/8 over 5/8 UHF antenna on Citizens Band.

I'm a bit confused about what you are looking for. Are you wanting to transmit on 2 meter band as well as listen to FM broadcast? Or just listen on both?

Stico makes antennas that will work as both AM/FM broadcast as well as LMR band. Expensive, but an option if you need the looks. STI-CO® | Mission Critical Antenna Solutions

My brain was playing acronym soup, and I mis-typed, I work with CBRS professionally, purely on the networking side. I meant GMRS.

 

[mmckenna]

Most of the ham oriented duplexers are not designed for splitting FM broadcast from 2 meters. On the commercial side, there's no reason to have such a thing.
You might be able to roll your own.

Maybe if you share exactly which bands you want to use, we may know of a suitable solution. There are antennas that will provide pretty good performance on 2 meters, 70 centimeters and GMRS, if that is what you are looking for.

 

[KD7RJC]

Citizens Broadband Radio Service, 3.5-3.7GHz

My brain was playing acronym soup, and I mis-typed, I work with CBRS professionally, purely on the networking side. I meant GMRS.

And to further clarify this is what I meant in trying to clarify what CBRS I was referring to in the clarification, whih was to clarify that the clarification was for GMRS that was mistyped.

Clear?

*grin*

Most of the ham oriented duplexers are not designed for splitting FM broadcast from 2 meters. On the commercial side, there's no reason to have such a thing.
You might be able to roll your own.

Maybe if you share exactly which bands you want to use, we may know of a suitable solution. There are antennas that will provide pretty good performance on 2 meters, 70 centimeters and GMRS, if that is what you are looking for.

For the near term I have a 45W mobile 2m and a supposedly 5W GMRS HT. Long term I'm likely going to end up installing a modern remote-head 2m/70cm (and possibly more) mobile and a GMRS mobile.

Since GMRS is limited to a single band, likely the GMRS antenna would be used to bring in broadcast FM to the factory car stereo. I've found that factory car stereos are not especially sensitive to antenna quality, probably due to how much power radiates from those transmitters. If the antenna isn't pefect for 88-108 MHz it'll still be good enough.

Since amateur is more likely to have multiple bands on a single radio, I would use a dediated antenna for that. Would make it easier if nothing else. I actually picked up one of those Compactennas today, been experimenting with where to place it and how to mount it. Since I have a tall fiberglass camper shell on my truck I may build a metal shelf that's at the same height as the cab roof just behind the cab under the fiberglass, and install it there where that metal shelf acts as the ground plane. That way the ground plane is electrically separate from the rest of the truck but still connected to the outer part of the NMO mount.

 

[mmckenna]

OK, makes sense.

So, what is the goal with the antennas? Are you trying to limit the number of antenna?

I've always found that dedicated antennas will work better.
I leave my AM/FM antenna alone. Utilizing that, or replacing it, so I can run a two way radio on it will result in less than ideal performance. Having the antenna shifted off to one side of the vehicle results in a lopsided ground plane, which will make the antenna directional.

Only time I've used a disguise type AM/FM antenna was for a PD vehicle that needed to be low profile. It worked, but not as well as one would hope.

A GMRS antenna can be small and work well. Years ago I was quite active on GMRS as well as having my ham ticket. I played around with a lot of antennas. Permanent mount NMO base on the roof of a full size pickup, and I'd swap out various antennas depending on what I wanted to play with. After trying everything from a 1/4 wave UHF antenna all the way up to the co-linear types, I finally found that in my application, the 1/4 wave UHF worked fine and would easily give me 20+ miles range simplex. There was no noticeable difference when trying 5/8th's wave, 1/2 wave, or co-linear antenna designs. The longer length just added to the risk from low branches/parking garages.
Nice thing about it was that a 1/4 wave UHF antenna (for GMRS or 70cm band) is about 6 inches tall and really is not something that stands out. On top of a full sized truck, it disappeared and wasn't really visible unless you were specifically looking for it.

On my wife's sedan, I put a small glass mount antenna on it since we were not hanging on to it much longer. Not ideal, but surprisingly worked well on GMRS and 70cm.


As for the 2 meter/70 centimeter antennas, there are some good options out there. Ultimately I settled on a few that I'd use depending on the installation:
Larsen NMO-2/70sh This is a 19" tall dual band antenna with a spring at the base. Worked very well for my application.
Simple 1/4 wave VHF antenna, since I spent most time on VHF, UHF wasn't a high priority. However, a 1/4 wave VHF whip is 3/4 wave on UHF and actually worked very well in my situation. SWR was nice and low. The radiation pattern launches a bit high, but that worked fine since just about everything I did on UHF was via repeaters.

I did try some higher gain dual band antennas, but never liked the taller profile. And again, never really could hear the difference in performance.


Using a co-linear UHF antenna for GMRS and a dual band diplexer would probably work well enough for GMRS and AM/FM broadcast. Unless you get really out in the boonies, most FM broadcast stations will work just fine, as you noticed. My wife's truck has a very small FM radio whip on the roof that works surprisingly well.

 

[KD7RJC]

I roughed-in the under-canopy mount and ground-plane today.


Before I had this truck, I had a '95 Nissan Hardbody, and I'd had both a fiberglass camper shell and a metal headache rack for that truck. When I sold the truck to my parents when my wife and I had our kid and I needed a crew-cab truck, he's usually kept the fiberglass canopy mounted, and has never installed the headache rack.

Did some measuring and it turns out that with only a little modification I was able to fit it inside of the canopy on this truck, and cutting off the upper corner extensions I was able to re-weld them on to support some mounting ears for these shelves for 19" racks.




It looks like I'll have plenty of space for a COMPACTenna:


Coincidentally I had my new-to-me Radio Shack HTX-242 powered up today as I was driving home from picking up the headache rack from my parents', and being Field Day today, I made QSL with the Compactenna mag-mounted on the roof near the 3rd brake light. Normally this would be unremarkable but I was in north-central Phoenix and the contact was near Flagstaff. The signal was poor, but it was enough to have a brief conversation even the better part of 140 miles apart. I assume he was using a highly directional antenna on a mast.

So I will end up testing the Compactenna on these shelves, plus I need to fix the power to the radio, right now I'm powering it off of a cigaraette lighter socket, which is of course not so good when it comes to interference from the vehicle's own electrical system.

 

[mmckenna]

That is an ingenious solution. I like it.

 

[KD7RJC]

That is an ingenious solution. I like it.

Thanks! Now I have to determine if it actually works.

With UHF I am unconcerned, the rack shelves are each larger than what the references I found for ground plane size indicate. For VHF I'm not as sure. I'm hoping that whatever creativity went into the COMPACTenna resonates well (said literally for once) with these shelves. I could attempt to go larger, possibly installing something like an oil drip pan for a garage floor that would be both wider and longer than these, but without more overhead clearance I doubt that an inexpensive monopole whip would work.

I need to devise a way to test for the COMPACTenna as well. The mag-mount won't bond to the shelves identically to a through-hole mount, and I had bought a Tram 5.5" diameter one. I may have to fudge my own sheet metal bracket that has no magnet for a sheet NMO mount I bought to see how the antenna performs at various places on the shelf. I want to get it right before I drill.

Also I need to improve the power to the radio. Right now I'm using a cigarette lighter socket so the vehicle electrical system is in play, using the second cigarette lighter socket to charge the phone plays havoc on the HTX-242. Clearly I will need to resolve that before I make any firm conclusions on antenna mounting, since I suspect the complicated radio power-ground is not helping with antenna-ground in addition to issues with vehicle electrical noise.

 

[KD7RJC]

This is how the HTX-242 is currently installed:


It's just sitting there. I haven't drilled any holes.

Larger view of the center stack:


I don't want to put anything in that slot next to the 4x4 knob and stability control button. Nissan made alterate center stack lower bezels, including ones with four or five switch positions. I want to swap for one of those, so if I put lockers, lights, or even controls for powering the radios in, there's somewhere factory-ish to place them.

I'm looking at either a Navara overhead center console from ARB, if they're still available:


or modifying my factory overhead console to accommodate one or two detached radio faceplates:




If I go with the ARB setup I could probably put a radio without a remote face into that compartment, but I probably couldn't do two radios in that console.

For the factory overhead console, I could probably go with two radios with remote faceplates, I'll have to modify the compartment for the sunglasses for a radio (so it doesn't block the mirror's view) and on the panel with the mic for the factory stereo, rearrange the mic spot to make room.

I'm looking at either under the front seats, or under the rear seats in the ill-used storage compartments, or behind the rear seats.

A friend of mine has a DC-to-DC battery charge system for a dual-battery setup that he uses in his old Ford F150, I may look at what he's done and see if I can make something similar and power the radio(s) off of this sort of thing. We'll see.

 

[prcguy]

Thanks! Now I have to determine if it actually works.

With UHF I am unconcerned, the rack shelves are each larger than what the references I found for ground plane size indicate. For VHF I'm not as sure. I'm hoping that whatever creativity went into the COMPACTenna resonates well (said literally for once) with these shelves. I could attempt to go larger, possibly installing something like an oil drip pan for a garage floor that would be both wider and longer than these, but without more overhead clearance I doubt that an inexpensive monopole whip would work.

I need to devise a way to test for the COMPACTenna as well. The mag-mount won't bond to the shelves identically to a through-hole mount, and I had bought a Tram 5.5" diameter one. I may have to fudge my own sheet metal bracket that has no magnet for a sheet NMO mount I bought to see how the antenna performs at various places on the shelf. I want to get it right before I drill.

Also I need to improve the power to the radio. Right now I'm using a cigarette lighter socket so the vehicle electrical system is in play, using the second cigarette lighter socket to charge the phone plays havoc on the HTX-242. Clearly I will need to resolve that before I make any firm conclusions on antenna mounting, since I suspect the complicated radio power-ground is not helping with antenna-ground in addition to issues with vehicle electrical noise.

The various VHF/UHF/multiband COMPACtenna's work well with a compromised groundplane on VHF. If you put one in the middle of a large car roof the VSWR at VHF actually gets worse and if you move it to the edge of the roof its much better. UHF and higher seems to be unaffected if the ground plane is 12" diameter or a huge van roof. I think they will work ok on the rack shelves.

 

[KD7RJC]

Continuing to go off-the-rails to the original topic...

I went ahead and installed the COMPACTenna on the driver's side shelf. Took the whole headache rack out, drilled out a 3/4" hole with a step-bit and installed an antenna with RG-58 cable, unterminated on the far end for now.


Couldn't center the hole as well as I wanted, the slope of the fiberglass roof is too low further forward. I can add more material to the shelf if I end up needing it, extend it rearward. Will need to do some testing to see.

I started looking at how to get the cable out of the bed and into the cab. I already knew the locations of the grommets on the front bulkhead of the bed. I also knew that there was a vent on the rear bulkhead of the cab, but I didn't know where exactly. Vehicles have been a hobby as long as ham radio has, but I've been a LOT more active. Ended up pulling the interior plastics and found the cab vent, and luckily enough it's transversely in-line with one of the bed grommets, albeit a bit higher.

So I proceeded with the install. Screwed the antenna onto the shelf, and clamped the rack back down under the shell. Since I use the truck as a truck fairly regularly I slipped some FMC over the coax cable to physically protect it, zip-tied it into place, and punched a hole in the bed grommet to slip it into.




With the cab vent I was able to pull the unterminated cable through. I drilled three holes in the plastic vent frame just barely big enough for RG-58 for this antenna and for possible expansion later. I did not just pull the cable through the vent, because I want the vent to still mostly work properly. Three holes made by a #76 drill bit at 0.200" each won't affect much compared to if the flappers were forced open all the time.





After that I soldered on a PL-259 connector, tested with a meter, failed the test, desoldered it, soldered it on again, still had to remove it again and clean out the tin-whiskers inside that were bridging the pin and shield, and then finally soldered it on to pass a continuity (or rather lack thereof) test.

After that, pulled the cable between the folding rear seats, under the rubber rear floor mat and over to the passenger's side of the center console, and up to the radio at the front up under the dash, then reassembled the rear bulkhead interior plastics.

Antenna as installed:


SWR isn't as good as I'd like, it's closer to 2:1 than 1:1, but some hams I've talked to on forums seem to think this is OK.

Unfortunately I haven't managed to talk to another ham with it yet. It was almost midnight when I finished installing and no one seemed to be on simplex or the repeaters. I did manage to key-up a repeater though and it squawked Morse code back at me that was crystal clear. I think it's good, but I'll need to actually talk with someone to know for sure.

My wife and I tested GMRS today, 5W HTs to antennas on the roof. On her Jeep I went with a Browning 5/8 wave LMR antenna tuned theoretically for 450-470 with some adjustability to shorten it by shoving it down into the mount. On 5W (technically more like 4W, these radios don't perform quite as well as advertised) we managed to go 2 miles in a suburban area. This was far better than what we could get with the rubber duckies.

I'm hoping to test amateur tomorrow or sometime this next week. Hopefully 50W with my mobile rig will work just fine.

 

[prcguy]

This is one of the most unusual installs I've seen but it should work ok. Very well done!

 

[AK9R]

You pulled the antenna coax through metallic flex conduit? Interesting. Don't think I've ever seen that used that use in a mobile install.

Between the NMO mount and the first ty-rap, the conduit is going to flex, vibrate, and slap against your ground plane plate. You'll hear it in the cab. I think I'd find a way to anchor that conduit mid-span or wrap it in something that would dampen the noise.

 

[KD7RJC]

You pulled the antenna coax through metallic flex conduit? Interesting. Don't think I've ever seen that used that use in a mobile install.

Between the NMO mount and the first ty-rap, the conduit is going to flex, vibrate, and slap against your ground plane plate. You'll hear it in the cab. I think I'd find a way to anchor that conduit mid-span or wrap it in something that would dampen the noise.

If it's an issue (or if there's risk of mechanical damage to the solder-joint on the underside of the metal plate) I can use those adhesive-backed 1" squares for zip-tie anchors:

I'd probably need to drill through the metal so I can put an anchor into the center hole, but rather than a protruding nut and bolt I'd probably have to go with a rivet. There are other styles available too:



The latter two might be better for rivets, the flat part of the rivet would be on top, the deformed part on the bottom in the mounting holes.

as for the use of the FMC itself, I'm borderline on hoarding and I happened to have a length of the stuff with three #16 THHN wires in it, I think it was for something like interconnecting fluorescent fixtures that don't need the full 14 gauge or 12 gauge wires. Stripped-out the THHN and the RG-58 slipped in with only a little room to spare, tight enough that the cable won't really rattle around inside. Hopefully the FMC withstands impacts better than the RG-58 would if the FMC wasn't there, but it'll definitely do better on sharp edges.

Since I'll have to make a few more changes before this is finished I might get some heatshrink tubing and wrap the FMC with its own jacket, we'll see. I wanted to see if there would be any undesired characteristics if I left it this way before I put more effort into parts that wouldn't have RF potential.

 

[AK9R]

If it's an issue (or if there's risk of mechanical damage to the solder-joint on the underside of the metal plate) I can use those adhesive-backed 1" squares for zip-tie anchors:

You probably already know this...clean the metal with isopropyl alcohol before you stick those on. And after after a few years and heat cycles, they'll pop off anyway. Might as well drill a hole for a proper saddle.

 

[KD7RJC]

You probably already know this...clean the metal with isopropyl alcohol before you stick those on. And after after a few years and heat cycles, they'll pop off anyway. Might as well drill a hole for a proper saddle.

Yeah, been using them for years and years in telecom equipment rooms, always attached them with mechanical fasteners and not simply adhesive. Though it's easier on TMBB since drywall screws have low-profile and flat heads that don't block the zip tie channels.

 

[KD7RJC]

Still haven't worked on physically securing things down more, but I did have an opportunity to hop on to a local net this morning.

Turns out something in my handmic to radio connection is not quite working right. I suspect that the jack on either the radio or the plug on the end of the handmic cable is bad (or both are) as they reported that my connection was bad initially (I was seated in driver's seat at the time) and when I got back on with them again I was standing at the passenger's side with the door open, leaning in, not putting any strain on the handmic cable.

When I was standing and not putting torque on the cable or the jack I came in loud and clear, when I was seated and pulling on the cable to get the mic up to me they couldn't hear me well. This was at around 20 miles distance to the repeater.

So it looks like I need to either make an extension to take stress off of the handmic cable, or to repair the radio if it's just a mechanically-worn socket.