Curious Antenna Test

[n3pi]

Hi Folks,

First let me apologize if this subject has been discussed before, but I did not have the time to do an extensive search on the matter. I have often wondered why Motorola opted to change the thread-antenna pattern on the XPR7500 series radio, if already the standard female SMA has been proven effective for many years. Don't get me wrong, I own both the standard and stubby and to my amazement, the shorter one works better, in my opinion.

Being on the LMR business for 30+ years, I know and understand antenna physics so please this is just experimentation...

Out of curiosity I measured the radio antenna port and actual factory antennas and they seemed extremely close to the 1/4-32 stud found on the old MX/Gemini radio series, so I found an "old school" from my old collection and I got this:



To my surprise it works better than the current OEM on analog and DMR repeaters. I guess it will be a conversation piece from the few of us that used to work on HT210/220/MT500/MX300's.

AP

 

[PRC148]

If it works it aint dumb.

 

[Alpha]

I am not completely surprised. Back in the old days they actually took antennas out to a triangulation test range with a turntable (I've been there and seen it) to map the performance of an antenna, mounted to vehicle or on an HT. The real, actual performance was measured in the real world, not estimated by a computer program that simulates reality. Somehow these days, I tend to think a lot of new stuff lacks that real world testing and proving element of the manufacture process.

The fact that I'm not amazed having been said, I had wondered how the old MX-stud antennas would work. I have a nice yellow stubby from Dayton to put on mine!

 

[N4KVE]

I too use the stubby UHF antennas on my 7550, & 3500 with great results, but the XPR7550IS sold only in Canada does use a SMA antenna. I wonder why? GARY

 

[Alpha]

The fact that they are intrinsically safe would be my guess. With the stud type antennas you can see down into the radio body - although there is some kind of plastic plug there, it must not seal well. With the SMA, they can seal the chassis there around the connector.

 

[com501]

Digging out the box of old antennas tonight....

 

[PossumCop]

Perhaps it's just my slightly darker view of reality, but I tend to believe that the antenna change isn't so much driven by engineering to make a better radio than it is part of a larger scheme by Motorola marketing to force customers to buy the newest and latest (and at a significantly increased cost, I might add) to keep up-to-date. It wouldn't surprise me at all to find that there was a decision to go to the “new” antenna thread pattern just so they could sell more units. It also didn't surprise me to learn that the Canadian 7550 still uses the SMA because that market doesn't impact a much larger US market for essentially the same radio.

I am dating myself here, but I recall MANY years ago when the HT-440 came out our Motorola rep was telling us just how much better it would be than the 220s we had in the field at the time. I have to admit that the change to the BNC was a plus, but the 440s really just sucked otherwise.

What really burned me was the fact that Motorola more than doubled the price of commonly broken or lost parts (knobs, cases, and battery covers) for the 220s while the RF boards and other internal components that were in most cases identical to the 220s remained at the same price. At the same time, the plug-in ear piece connection changed just enough so that any 220 ear piece would no longer fit a 440. To me, the SMA to thread change looks like another pothole on the same road.

(Sorry for the long rant...it's been a difficult week.)

 

[JMINN699]

Then Motorola replaced the HT440 with the HT50 and went back to a stud mount. At least in UHF the HT440 would talk rings around the HT50.

 

[rescue161]

I looked for one in my box of junk, but all I found was a Saber antenna. Threads match, but I'd have to cut a bunch of material off of the antenna for it to fit down into the radio. Sucks too as the Saber antenna is much more flexible. I wish I still had an old MX antenna as they were very flexible.