EM Wave on an antenna analyzer

[nd5y]

Do you know what the whip diameter is? It's not in their spec sheet.

 

[k7ng]

I have been buying the EMWave 1/4 wave wideband antennas for almost a year now. Try as they might, my customers have yet to destroy one. They seem to handle tree branch strikes just above the vehicle roof better than Larsen or Maxrad. A sweep of the wideband Maxrad varies hugely from one antenna to the next and one installation to the next, whereas the EMWave and Larsens are more predictable. I have run into one bad EMWave and one bad Larsen, where they just had a poor swept VSWR response that wasn't installation-specific. I got about 5% bad out of the bag when I was using Maxrads.

I have installed well over 100 wideband VHF mobile antennas at my present job...

 

[mrweather]

What would make a basic 1/4 wave antenna go bad? It's not like there are fancy coils/matching devices.

 

[nd5y]

What would make a basic 1/4 wave antenna go bad? It's not like there are fancy coils/matching devices.

As far as the antenna itself not much can go wrong. Corrosion, electrical contact problems or physical damage is about it.

A lot of other things could make the antenna appear to be bad such as mount problems, coax problems, connector problems, installation problems, mounting location, proximity to other antennas or objects, test equiment used to determine the antenna is "bad", not knowing how to use test equipment, operator error, installer error, probably other things.

 

[mmckenna]

I want to see the dummy load sweep below 25 MHz

My spectrum analyzer goes down below 100KHz, but the tracking generator only goes down to 5MHz:

Load is an old Decibel DB4303B 100 watt 50Ω load. 0-960MHz http://dbspectra.wpengine.com/specifications/Terminations_Loads.pdf

 

[mmckenna]

Do you know what the whip diameter is? It's not in their spec sheet.

0.1000 inches

or,

about 3/32nd's

or,

2.54 millimeters.

 

[KK6ZTE]

0.1000 inches

or,

about 3/32nd's

or,

2.54 millimeters.

Do you have that in toenail thickness? That's my go-to

 

[k7ng]

What would make a basic 1/4 wave antenna go bad? It's not like there are fancy coils/matching devices.

The antennas I use are 'wideband' types that are supposed to work over a wider frequency range (lower VSWR, in other words) and kinda sorta claim to be 'no-tune' antennas. I need 151 - 174 MHz if I can get it. All that type of antenna has a matching network in the base. If the coil gets smacked by a tree branch as the vehicle runs up a trail at 35 mph, they often quit working. And for similar reasons even though there's a spring, the springs have a metal braid thru the center that carries the RF, and that corrodes and or fatigues with enough abuse. Plus, I'm on the Oregon coast and even the rain has salt in it.

My antennas are non in an antenna-friendly environment.

 

[mmckenna]

Do you have that in toenail thickness? That's my go-to

I dunno, let me chew one off and grab my micrometer.

 

[nd5y]

0.1000 inches

I think that's what the Larsen NMOWBQ is.
I have been using a FrankenLarsen for 20 years or so made from a NMOQ base, ferrule/cone from a NMO150 (I think), the 0.1" whip from a NMO220 cut down to 1/4 wave a 146 MHz, and no spring. It dosen't bend like the regular NMOQ 0.049" whip and the bandwidth is a little wider.

 

[mmckenna]

Larsen NMOQ 1.75mm 0.0695 inches 1/16th inch.

Larsen NMOQWB 3.2mm 0.1250 inches 1/8th's inch

 

[12dbsinad]

The antennas I use are 'wideband' types that are supposed to work over a wider frequency range (lower VSWR, in other words) and kinda sorta claim to be 'no-tune' antennas. I need 151 - 174 MHz if I can get it. All that type of antenna has a matching network in the base. If the coil gets smacked by a tree branch as the vehicle runs up a trail at 35 mph, they often quit working. And for similar reasons even though there's a spring, the springs have a metal braid thru the center that carries the RF, and that corrodes and or fatigues with enough abuse. Plus, I'm on the Oregon coast and even the rain has salt in it.

My antennas are non in an antenna-friendly environment.

We use the maxrad wideband as well. MWV1322S and MWU4505S (if my memory serves me correct). We've had problems with the coils breaking were the plastic meets the NMO threaded collar. The black plastic is threaded and they usually apply glue. If hit real hard they break at the threads.

I have some EMwave samples, haven't used them yet but they indeed do seem well built.

 

[kayn1n32008]

What would make a basic 1/4 wave antenna go bad? It's not like there are fancy coils/matching devices.

The wide band EMWave antenna has some magic matching guts in the base, it's not just a straight up 1/4.

 

[kayn1n32008]

We use the maxrad wideband as well. MWV1322S and MWU4505S (if my memory serves me correct). We've had problems with the coils breaking were the plastic meets the NMO threaded collar. The black plastic is threaded and they usually apply glue. If hit real hard they break at the threads.

I have some EMwave samples, haven't used them yet but they indeed do seem well built.

I can't remember where I posted the photos, but I had a 430-450 colinear NGP base from Maxrad that the glue had failed. I took it apart and posted photos of the guts. I want to say it was in 2017 that I posted the photos.

 

[kayn1n32008]

The antennas I use are 'wideband' types that are supposed to work over a wider frequency range (lower VSWR, in other words) and kinda sorta claim to be 'no-tune' antennas. I need 151 - 174 MHz if I can get it. All that type of antenna has a matching network in the base. If the coil gets smacked by a tree branch as the vehicle runs up a trail at 35 mph, they often quit working. And for similar reasons even though there's a spring, the springs have a metal braid thru the center that carries the RF, and that corrodes and or fatigues with enough abuse. Plus, I'm on the Oregon coast and even the rain has salt in it.

My antennas are non in an antenna-friendly environment.

The EMWave wide band 1/4 wave are spec's at less than 1.9:1 over 136-174MHz.

 

[12dbsinad]

I can't remember where I posted the photos, but I had a 430-450 colinear NGP base from Maxrad that the glue had failed. I took it apart and posted photos of the guts. I want to say it was in 2017 that I posted the photos.

Sounds like the same issue as well kayn

 

[kayn1n32008]

Sounds like the same issue as well kayn

Sounds like it. Sad part is that the antenna was used for the data link for a RTK reference station. Never mounted on a vehicle, just a NMO mount that attaches to a survey rod. So it would be set up at the beginning of the day, then taken down at the end, unless a crew was in the same area, and left it until they were done the job. Definitely not abused.

 

[12dbsinad]

Sounds like it. Sad part is that the antenna was used for the data link for RTK reference station

If I remember correctly they have a spring contact tab at this location, and a cap for no GP applications. Certainly the weak spot. The antenna's always tunes well though.

 

[kayn1n32008]

Correct.

Found the thread I created with the coil disassembled.

Maxrad MHB-5800

For those that are interested in the guts in the base of antennas, I found a Maxrad base that has failed. Pretty easy to disassemble once the glue fails.

forums.radioreference.com

 

[12dbsinad]

Correct.

Found the thread I created with the coil disassembled.

Maxrad MHB-5800

For those that are interested in the guts in the base of antennas, I found a Maxrad base that has failed. Pretty easy to disassemble once the glue fails.

forums.radioreference.com

Yep, that's it!