NMO mount antennas

[W8HDU]

Is there a recommended spring that can be used with the Larson NMO30 and the 64" whip?

As someone who works in the woods, where the antenna takes a beating on limbs, I would highly recommend a spring. I use both the Larsen NMO150B, and the NMO27B, with the Larsen p/n: SPRINGB spring. Keep in mind, when you add the spring, you must subtract from the whip length to get a proper match! Keep the length long, and then start cutting back in small increments.

 

[K6GBW]

This post reminded me I needed to get my NMO mount onto my Subaru Crosstrek. Went pretty quick.

 

[smittie]

Laird or Tram/Browning, anyone have a preference between those two? I know that Pulse/Larson is the brand of choice here.

I apparently have a Laird C27 that has gone bad. I was trying to tune using my new NanoVNA but could not get any response on SWR or Reflected loss. Out of frustration I switched the coil to a Tram equivalent that I thought was bad. Immediately got the kind of readings indicated in the various YouTube how-to videos I have watched.

Still not convinced that this would all get much easier if I knew what to sacrifice and to which gods.

 

[prcguy]

Laird or Tram/Browning, anyone have a preference between those two? I know that Pulse/Larson is the brand of choice here.

I apparently have a Laird C27 that has gone bad. I was trying to tune using my new NanoVNA but could not get any response on SWR or Reflected loss. Out of frustration I switched the coil to a Tram equivalent that I thought was bad. Immediately got the kind of readings indicated in the various YouTube how-to videos I have watched.

Still not convinced that this would all get much easier if I knew what to sacrifice and to which gods.

Both Laird and Larsen are respected commercial brands. Tram/Browning, not so much.

 

[W8HDU]

Laird or Tram/Browning, anyone have a preference between those two? I know that Pulse/Larson is the brand of choice here.

I apparently have a Laird C27 that has gone bad. I was trying to tune using my new NanoVNA but could not get any response on SWR or Reflected loss. Out of frustration I switched the coil to a Tram equivalent that I thought was bad. Immediately got the kind of readings indicated in the various YouTube how-to videos I have watched.

Still not convinced that this would all get much easier if I knew what to sacrifice and to which gods.

I can only speak for Larsen, because we ran another manufacturer's antennas for a while, and switching to Larsen was a marked improvement. Greg Makar, in their Customer Service dept was also helpful in application. I run both 29, and 151/154 radios. As for you antenna change, one thing to check is the brass piece in the antenna coil assy is fully contacted with the NMO center conductor. Not only did I have one which did not make good contact, but the metal was correoded because the prior tech installed it without the rubber O-ring. (He didn't think it was needed). It was able to be cleaned, O-rings are $2, and the contact was cleaned with Coolamp so should be fine. The only other antennas we've run are the old 99" whips on a spring, but I've had too many complaints of vehicles beating up a drive-thru.

 

[W8HDU]

Tram is what failed for us.

 

[mmckenna]

Laird or Tram/Browning, anyone have a preference between those two? I know that Pulse/Larson is the brand of choice here.

50 years ago Tram and Browning made high quality CB radio equipment.
Then they disappeared.

A while back, suddenly the Tram and Browning names were back on antennas. Doing some digging, Tram/Browning brand names were bought out by someone since they had some left over brand recognition. It's a small shop somewhere in the middle of the country, I forget where.
They sell Chinese knockoff antennas. Many of their antennas are copies of other brands. They look like well known antennas, but their quality is questionable, as noted by others above. They showed up at one of the big trade shows many years ago. The guy there didn't seem to want to talk to people about their antennas.

So, Cheap Chinese Antennas sold with an American brand name on them.

You decide….

I apparently have a Laird C27 that has gone bad. I was trying to tune using my new NanoVNA but could not get any response on SWR or Reflected loss. Out of frustration I switched the coil to a Tram equivalent that I thought was bad. Immediately got the kind of readings indicated in the various YouTube how-to videos I have watched.

Not much to go bad. I agree, check and make sure the center tab/pins are actually making contact. Laird has seen some of their base coils crack, so look closely at it.
Larsen NMO-27 is an excellent replacement. Mine is probably 30 years old. I got my money out of that sucker...

Still not convinced that this would all get much easier if I knew what to sacrifice and to which gods.

My grandfather taught me a lot when I was younger. He suggested that antennas were 50% science and 50% witchcraft. I know a lot more now, but I still believe there is some percentage of voodoo in antennas. It's best to tread carefully.

 

[smittie]

@mmckenna, based on what I have learned here I am probably going to get the NMO30 and a 65" whip. I have three Laird C27s (don't ask) so I may work on dialing in one of the Lairds and use the Cobra 25 on the Laird. I have a Galaxy 959 on a 108" whip antenna in another vehicle. I think I am going to use that rig and learn something about SSB. I may decide to pay a SSB capable radio in the Jeep.

Smittie

 

[smittie]

I have been able to confirm that the Laird C27 base I was trying to tune is bad. A second unit worked as advised.

This is something that would have been a lot harder to determine using only an SWR meter.

Thanks to everyone for my continuing education.

 

[W8HDU]

Not much to go bad. I agree, check and make sure the center tab/pins are actually making contact. Laird has seen some of their base coils crack, so look closely at it. Larsen NMO-27 is an excellent replacement. Mine is probably 30 years old. I got my money out of that sucker...

Good catch on the cracking issue. The plastic does have a life span. I've not had any of ours crack, (usually at the bottom where they thread onto the NMO mount), but with white vehicles and cooler climate, I don't think that black coil gets too much solar absorption. A fellow I know down in Scottsdale AZ has white trucks, but he paints his coils white, which does not affect the antenna as long as you don't get crazy with the sprayer.

My grandfather taught me a lot when I was younger. He suggested that antennas were 50% science and 50% witchcraft. I know a lot more now, but I still believe there is some percentage of voodoo in antennas. It's best to tread carefully.

I'm well into my senior years, and I can safely say that what you state is 100% correct. All the measurements and theory gets you close but not perfect. The key is to understand how things play together, and expect to tune an antenna. I've never found a "plug and play" antenna. Too many people try P&P. And it becomes a chess game when you have 4 frequencies in the 150 band, and you're trying to find that match which is acceptable to all of them with 80 watts power.

 

[W8HDU]

@mmckenna, based on what I have learned here I am probably going to get the NMO30 and a 65" whip. I have three Laird C27s (don't ask) so I may work on dialing in one of the Lairds and use the Cobra 25 on the Laird. I have a Galaxy 959 on a 108" whip antenna in another vehicle. I think I am going to use that rig and learn something about SSB. I may decide to pay a SSB capable radio in the Jeep.

Smittie

Just curious, when you're installing the antenna, have you checked from the coax shield to the body of the vehicle, and is it lower than 1-ohm?

Something else, if you're matching over a band of frequencies, for example CB channels 1 to 40, the antenna will tend to match better if you take half and then a little less, such as channel 17 or 18. The following is what their tech support told me about matching our three channels, 29.7300, 29.7500, and 29.7700.

"Hi Frederick, our cut chart is in reference to the end of the whip, that is it should be measured from the center of the ball on the end of the whip (or the top of the ball, the small size of the ball makes it fairly insignificant). So, prior to insertion. Of course we always recommend first cutting to a longer length and shortening to improve VSWR as the proper length can be different depending on ground plane and other factors. I would recommend cutting to slightly lower frequency than center if you want to get equal VSWR on .73 and .77, perhaps to 29.745 MHz, though that is just an educated guess. VSWR tends to get worse more quickly as you decrease rather than increase frequency." - G. Makar (Yageo) 8/21/2022, 12:33

This assumes that the mount is at the same ground potential as the radio and coax shield at the radio end.

 

[mmckenna]

All the measurements and theory gets you close but not perfect.

Pretty much exactly what my grandfather said.
"You can sit there all day with your slide rule figuring out the 'exact' length, but you'll still end up trimming."

 

[smittie]

@W8HDU
TL;DR
NanoVNA replaces testing multiple frequencies. When using an SWR meter for CB I test 1 and 40. NanoVNA allows me to see where the inflection point is which allows me to move the best performance to the frequency I use most.

I always test cable runs and end to end impedance.

 

[prcguy]

My grandfather taught me a lot when I was younger. He suggested that antennas were 50% science and 50% witchcraft. I know a lot more now, but I still believe there is some percentage of voodoo in antennas. It's best to tread carefully.

Antenna theory and design is a fully understood science. Problem is many mfrs don't employ actual antenna engineers and the resulting product suffers. Or a hamster or CBer with some back woods logic comes up with a wild idea and tries to sell it as science.

 

[W8HDU]

Antenna theory and design is a fully understood science. Problem is many mfrs don't employ actual antenna engineers and the resulting product suffers. Or a hamster or CBer with some back woods logic comes up with a wild idea and tries to sell it as science.

A fellow who I knew at one manufacturing company once said, "we would make the best product, then start seeing how we could make it cheaper, until we got to a point where it was good for a period of time which marketing deemed appropriate. That period of time was determined by when they thought the buyer would need to get another one, but not hold the company in contempt for a bad or defective product."

Most engineers know.

 

[alcahuete]

I'm a huge Larsen and Laird fan. Not sure if it's just certain models or what the deal is, but the Laird BB4502NS I bought last year has a very nice solid metal base. Very nice improvement over the plastic bases.

 

[niceguy71]

On my Jeep I believe I had to go trim down to 45" to get the NMO-27 to match correctly. That antenna has been on there now for 8 years and works for the purpose.

Being such a broad purpose antenna, you really have to tune them.

I know the post is old ... but I thought I'd see where you mounted the NMO on the jeep.... what kind of jeep..... and lastly how does it work? compared to other antenna's you've talked to?

 

[Project25_MASTR]

It's a fender mount on a XJ Cherokee. It works better than those who just throw any CB antenna on and don't bother to tune it. It's not something that is relied on or used often.

 

[W8HDU]

Just tossing this out since I completed a Jeep install last Tuesday. We put one of the short "loaded" antennas, (Brits call them a Stinger), on a Jeep, with the small 3/8-24 spring, ball mount, and then an antenna mount bracket. The bracket is army surplus, which was mounted on the passenger's rear fender. Coax was 9913F, with the ball mount connections sealed with DAP "Ultra Clear". The antenna matched to channel 18 as 1.013 : 1.000. The band edges came up slightly, with channel 40 being the worse, (1.175 : 1.000), but on Channel 4 which is somewhat the accepted Jeep channel, the match was 1.135 : 1.000 which acceptable. He does run a BJ-300 helper amp (optional use). The reason for the additional spring is that it gives the antenna additional flexibility of you are working through wooded terrain or brush. This same "type of" spring can be uses on an NMO antenna. They sell them with the thread to the NMO and top of the spring has a hole for the rod. And you can use the Antenna mount bracket (ANT-4) for an NMO mount as well.

If you use a Stinger antenna, get the stainless version. That colored paint is hard to get off to trim the antenna, and then match the color to make it right again. Compressing the coil will only make the bandwidth of the antennas narrower.

This fellow, and the guys he hangs around with put about 7,000 miles a year on their Jeeps by going to vacation areas using the back roads. This year's challenge is to go from the Eastern UP to the Minnesota border all on back, and logging roads, primitive camping as they go. If you can't find the antenna mount at surplus, a metal shop can bend up a box-piece for you. If you use steel, get it E-Coated or at least primed and powder coated. And don't forget the ground strap from the antenna ground to the Jeep's back fender panel. In fact, we strapped from the fender down to the chassis. Use stainless with internal tooth lock washers to get a bite on the metal.

This may be overkill for what you want, but I've never had a mobile antenna installation fail. And some of the places we go, the antennas get the crap beat out of them.