| Author |
Message |
    
Funtimebob
Intermediate Member
Username: Funtimebob
Post Number: 199
Registered: 5-2002
| | Posted on Thursday, May 11, 2006 - 2:58 am: | 
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Out of curiosity I placed my MFJ HT swr meter between my TR-2500 and my MFJ-1717 antenna and the SWR was between 3:1 and infinity on the swr scale. needless to say I've now stopped transmitting outta fear of blowing the radio up. |
Rldrake
Intermediate Member
Username: Rldrake
Post Number: 128
Registered: 1-2006
| | Posted on Thursday, May 11, 2006 - 2:40 pm: |
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What kind of explosive do you have nearby that is causing your concern ? |
Tech237
Moderator
Username: Tech237
Post Number: 335
Registered: 4-2004
| | Posted on Thursday, May 11, 2006 - 3:28 pm: |
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I suspect that an HT SWR meter maybe designed slightly different from a normal one. I believe this as the HT meter is designed to work on a handheld antenna which has minimal (read almost no groundplane).
Try the experiment again (on low power) only use a 50 ohm dummy load on the output of the meter and see if you get a similar reading. If you do you can stop worry about damaging the radio and if you don't look at the coax and antenna for problems. |
Funtimebob
Intermediate Member
Username: Funtimebob
Post Number: 200
Registered: 5-2002
| | Posted on Thursday, May 11, 2006 - 9:43 pm: |
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237, The meter (mfj-841?) is designed specifically to hook onto the radios antenna jack (no jumper) and the antenna screws directly into the meter on top of the HT. the radio puts out about a 1/4 watt on low and will not calibrae at this low setting. on HIGH power ( 2 1/2 watts) i can calibrate the meter. the meter is designed for 5 watts max. dont have a dummy load yet, maybe I can substitute for one if i stick my tongue in the jack  . seriously though sounds like I need to invest in one. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1570
Registered: 9-2004
| | Posted on Thursday, May 11, 2006 - 11:08 pm: |
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funtimebob, here's a neat little thread that will show you how to build your own.
most people will tell you that you have to use carbon film resistors because they wont radiate a signal like wirewound resistors will.
i used wirewounds and the SWR is 1 to 1. as perfect as ive seen.
maybe it does radiate a little bit, but this has worked to my advantage when testing receivers of other radios.
http://www.copperelectronics.com/cgi-bin/discus4/show.cgi?tpc=34&post=83421#POST83421 |
Tech237
Moderator
Username: Tech237
Post Number: 339
Registered: 4-2004
| | Posted on Friday, May 12, 2006 - 9:00 am: |
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The only thing you have to watch if you use wirewoud resistor is not that they will radiate, any resistor will radiate to some extent, but the fact that being wirewound they will have inductance and at higher frequencieds, and 2m is or can be in that ballpark, that inductance can give you fals readings. To be safe stick with carbon film resistors. PM me and I can give you a link to a place that sells nice high wattage resistors that are just right to make dummy loads from. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1576
Registered: 9-2004
| | Posted on Sunday, May 14, 2006 - 2:31 am: |
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thanks for the lesson 237!
i didnt know that was the case.
cool!
not a problem for me as i find VHF utterly boring.JMHO.
matt |
