Midland MXT-400 Transmit Question

[garbon2535]

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[Jones]

Do you have another radio to try? That would verify if the meter is good. If the meter is good, then the radio is bad. Can't be the antenna if the meter is showing zero reflected power across the band.

 

You could also try another antenna, such as a mobile mag-mount on top of your washer or refrigerator, or a dummy load if you have one.

[berkinet]

...Can't be the antenna if the meter is showing zero reflected power across the band. ...

If the cable or connectors between the radio and the meter are defective, that might account for the problem.  How does the radio work on receive?

[AdmiralCochrane]

I used an old piece of RG8 between my 400 and my swr/power meter and it ate up 45% of the power output. Changed to direct connection at the back of the radio and now measure 40 watts.  UHF is very easy to leak out of coax and any bad or weak connectors are signal killers

[GuySagi]

Almost half your power Admiral? Wow, that might explain a frustration I've been having with the Btech-50X1 I'm running for a base. SWR is 1.3 with two feet of RG-8 to a Daiwa meter, followed by LMR400 for 50 feet to the roof. I've never seen the power get into the 40-watt range on the meter even when the radio is set to high on the proper channels and its meter says its pushing out more. 

[jec6613]

Have fun everybody ... https://www.timesmicrowave.com/calculator/

 

Also, there's insertion loss on each connector, which you can find in the spec sheet, not to mention any losses with poor assembly.

 

Oh, and if you're using UHF connectors like virtually all of the radios are, try re-seating the connector, because SO239/PL259 can't mate with enough consistency once you get to even VHF.  They're called UHF connectors because when they were invented, UHF was 3-30 MHz.

[garbon2535]

Thanks for all the replies. This information is very helpful; however, I have not solved my problem.

 

The radio seems to receive OK. I can pick up a repeater 35-40 miles away with no problem. I can pick up handhelds 1.5 to 3 miles away around my neighborhood.

 

I am using LMR-400 cable. I have a 50 foot run from my radio to a PolyPhaser DC block lightning protector and then 25 feet of cable to the antenna. I am using PL-259 connectors because my radio has SO-239 on the back.

 

With the SWR meter, I use a 3 foot jumper of LMR-400.

 

Today I tried connected a mobile mag antenna connected to SWR meter the with a 3 foot jumper to the radio, all with RG-8 coax. I had the same results with the exception that my SWR reading was 1.5 instead of nearly 0.

[mbrun]

I agree that your numbers do not sound right.

 

When troubleshooting, it is always best to eliminate as many variables as you can.    Every piece of equipment, cable, connector, adapter and the environment are candidates for affecting results.

 

Anyway you can hook your meter up to the back of the radio directly (i.e. M-M UHF adapter) plus a dummy load screwed directly to the meter output?   This should show you a 1:1 SWR and the actual output power of the radio.   

 

Can you can get your hands on a different meter so you can contrast readings between the two?  When readings are not as expected, it is nice to contrast two pieces of measurement equipment to just to provide confidence.

 

Check specs on your meter. What is the minimum power level the meter requires to function accurately.  If the radio is indeed outputting low, the meter may give you bad readings.   Case and point, the manufacturer of my SWR meter advises the meter must receive at least .5 watts for meter to perform accurately.

 

Michael

WRHS965

KE8PLM

[Lscott]

Have fun everybody ... https://www.timesmicrowave.com/calculator/

 

Also, there's insertion loss on each connector, which you can find in the spec sheet, not to mention any losses with poor assembly.

 

Oh, and if you're using UHF connectors like virtually all of the radios are, try re-seating the connector, because SO239/PL259 can't mate with enough consistency once you get to even VHF.  They're called UHF connectors because when they were invented, UHF was 3-30 MHz.

Normally the power loss in a good quality RF connector is rather small, a few tenth's of a db. What you do have more of a problem with is with the impedance of the connector. The common PL-259/SO-239  are noway even close to 50 ohms. At UHF this impedance mismatch can cause elevated SWR, more reflected power. The general advice is to use constant impedance type RF connectors. For GMRS the typical one recommended is the "N" type. There are other common constant impedance connectors you will likely encounter, SMA and BNC.

 

You do have to watch which impedance the connector is designed for. They are commonly available in either 50 ohm or 75 ohm versions. For GMRS and the usual 50 ohm coax you need the 50 ohm version of the connectors. You can't simply look at them to tell the difference, the physical dimensions are similar. 

 

If anybody is interested in the whole issue of coax cables, matching, RF connectors etc. the following guide has a lot of useful info.

 

https://www.fclane.com/sites/default/files/rfguideen.pdf