MicroMobile SWR Readings?

[racecargo]

Guys,

I'm wondering if anyone knows if the SWR range readings should change when switching from simplex to repeater channels.

 

I have a new install of a Midland MXT275 coupled to their MXTA26 (6dB whip antenna).

These are supposedly "factory tuned", but since I was uncertain about the grounding of my truck's headache rack (where I attached the antenna), or the vertical install that close to the cab, I thought I'd throw an SWR Meter on it.

 

Channel 1 & 22 initially showing roughly 2:1.

Added a 10ga ground wire from the antenna bracket to the truck frame; now getting roughly 1.4:1 on both ends.

(analog gauge with poorly incremented dial is why I'm saying roughly)

 

For grins, I went up the the rP channels, recalibrated, & tried 19rp....meter jumped "into the red" at about 6:1.

 

 

Question is....

Should I be seeing similar SWR on the 467MHz as the 462HMz frequencies? ...or is something terribly wrong with my set-up?

 

FYI....I using a "cheap" Workman 104 meter, supposedly rated for 120 - 505 Mhz.

[marcspaz]

If you are going to be doing your own work, I would recommend getting a quality SWR meter.  I have found that many of the inexpensive meters are only accurate for a very small amount of the "advertised" frequency range, and the higher the SWR, the less accurate they are.

 

I started off with a MXTA26 on all 3 vehicles.  Turned out to be a terrible idea.  on the 467 MHz channels, the SWR was way too high.  I ended up using some small Browning and Tram antennas that are good from 450 MHz to 470 MHz.  One of my trucks has a Comet CSB-790A.  It is three 5/8 waves long, in phase at 62 inches long.  Its rated at 7.7dBi gain and cost about $100. 

 

I get a near perfect SWR of 1.1:1 on all GMRS channels.  Yesterday I was talking to a friend of mine, mobile to mobile about 9 miles apart, using just 2 watts.  It work fantastic... but its a lot of antenna.  Most people don't like the size, because its so tall, but I love it.

[racecargo]

Thanks for the reply.

I assumed going from 462 MHz to 467 MHz shouldn't have a large affect to SWR, so this let's me know something is actually wrong.

 

I plan to take it by a shop this week (if they're open), to compare readings against a "better' meter; but sounds like I should research some antennas also.

 

I'm not looking to put a 62" antenna on this vehicle; are your good Tram/Brownings in the 3ft range?

 

Thanks again.

[marcspaz]

are your good Tram/Brownings in the 3ft range?

 

Thanks again.

Actually, they are a shade more than 6 inches high. Very small and work fairly well.

[racecargo]

Just a follow-up for anyone searching forums with a similar issue........

 

After verifying my meter capability, and a lengthy discussion with Midland's product engineer, we decided to move the antenna around and test multiple locations with just a c-clamp & magnet.

 

Similar crappy readings almost anywhere on the headache rack or near the back glass, with slight improvements with elevation, but still not acceptable (still >3:1 swr, but down from 6:1).

Moving rearward, to the toolbox showed huge improvements and eventually got everything <1.4:1.

(still no idea why 462 & 467 would read so extremely different; I'd think they should have both been right or somewhat equally off)

 

So not discounting marcspaz's comments, as I still don't know how long the antenna will work; but for now "location, location" seems to be the key with the MXTA26.

 

-I'll try to edit this if/when marcspaz's prediction comes to fruition & it dies on me...and fyi: I already have a Tram on order.

[wayoverthere]

so..for a little anecdotal data..

 

my "base" setup at the moment (haven't really decided on a setup yet, so it changes...) is the midland mag mount on a piece of sheet steel in the attic, with midland's now-discontinued 3db whip (~12" long), fed by a BTech GMRS 50x1.  i have one of the surecom sw33 meters, and decided to see what my numbers look like. results are 1.05 on ch 22, 1.06 on ch 1, and 1.2 on Repeater 22.

 

given that 1 and simplex 22 are both in the 462.xxx range, and repeater 22 transmits in the 467.xxx, a bit of variation isn't a surprise, but it seems like whatever is off with your setup is amplifying the variation.