Kenwood TM741A Transmit problem

[Don]

My radio does not seem to transmitt.I am new to this. I have checked,coaxil,that is fine antennae is fine(Diamond x50na).I can here a lot of differant repeaters and some link systems .Power supply seems fine(12.9) What am I doing wrong? Don

[K7KBN]

Measure the output of the rig into a dummy load through an external wattmeter (don't rely on the built-in metering). See if you actually have any RF out.

If you do, check the repeater splits and PL tones. For the splits, you'll have to check the repeater directory or contact the owner/operator of the particular repeater. The manual will have the information on the tones.

[Don]

Measure the output of the rig into a dummy load through an external wattmeter (don't rely on the built-in metering). See if you actually have any RF out.

If you do, check the repeater splits and PL tones. For the splits, you'll have to check the repeater directory or contact the owner/operator of the particular repeater. The manual will have the information on the tones.

I wanted to thank you for getting me some thoughts. I am disabled and it will take me some time to aquire a swr/power meter. Qestion .Is the power meter the same as a watt meter? I also will need to aquire a dummy looad. I kind of live out in the middle of nowhere and being I can"t get a hold of a local ham for help Its going to take a while . Thank you for respondind.

[5B4AJB]

Hi Don
yes, a power meter is a wattmeter.

I was going to advise you to build a dummy load, but I think your radio is 50W output.
You could still do it, but a commercial one would probably allow you to transmit into it for longer.

I wrote a simple program for parallel resistances, for using resistors from the junk box to make a dummy load. Traditionally, these are filled with mineral oil to allow longer transmit times.
(can't find the program right now, sorry)

http://s100.photobucket.com/albums/m23/ ... myLoad.flv" onclick="window.open(this.href);return false;

This one uses ten, 500 Ohm resistors, connected in parallel. It should be man enough to check your output, provided you only key the radio for 10 seconds or so...

[edit] you can use a lightbulb as a dummy load, see if you can procure a car bulb rated at 50W.
Solder a plug to a few inches of coax, and split the end, solder to the bulb, instant dummyload!

[Don]

Hi Don
yes, a power meter is a wattmeter.

I was going to advise you to build a dummy load, but I think your radio is 50W output.
You could still do it, but a commercial one would probably allow you to transmit into it for longer.

I wrote a simple program for parallel resistances, for using resistors from the junk box to make a dummy load. Traditionally, these are filled with mineral oil to allow longer transmit times.
(can't find the program right now, sorry)

http://s100.photobucket.com/albums/m23/ ... myLoad.flv" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

This one uses ten, 500 Ohm resistors, connected in parallel. It should be man enough to check your output, provided you only key the radio for 10 seconds or so...

[edit] you can use a lightbulb as a dummy load, see if you can procure a car bulb rated at 50W.
Solder a plug to a few inches of coax, and split the end, solder to the bulb, instant dummyload!

I have procured a 50 watt car lamp, I want to makemsure I have this right.Take coaxil with the proper end to plug antenne from radio into then solder center core to center of lamp and the cable outer shield to outer bulb base. If correct (please excuss me ) what am I looking for. Thank you

[5B4AJB]

Yes, that's fine. It's worth insulating because RF burns can be painful

This trick is OK for solid-state transmitters, but not so good for valves...

[Don]

Yes, that's fine. It's worth insulating because RF burns can be painful

This trick is OK for solid-state transmitters, but not so good for valves...

My wife took me to town yesterday and a friend bouht me a swr power meter. I hooked it up and heres where I am. All tests done on low power. SWR is a little over 3. Power apears to be about 1000 watts.This reading I think is good. But what do I do with my x50na vertical 2meter /70cm antennae to lower the high SWR? Thank you again for helping a newbie get going. Don

[K7KBN]

Yes, that's fine. It's worth insulating because RF burns can be painful

This trick is OK for solid-state transmitters, but not so good for valves...

Demetrius - I think you have that backwards.

With my old tube transmitters, a light bulb "worked" OK as a dummy load because the pi-net output circuitry could adjust the final for the mismatch. A solid state transmitter will simply cut back power until there's no power out to protect itself.

An automotive lightbulb with a 12V 50 watt rating will not have an impedance anywhere near 50 ohms. Cold, it'll be very low, probably less than half an ohm. Drawing 50 watts at 12 volts, Ohm's Law predicts about 2.8 ohms. Not a good value for a dummy load.

[5B4AJB]

Yeah, I realise a solid-state jobby will reduce it's output, but I read in my mate's FT101 manual NOT to use a bulb for tuning. Never owned a valve set myself...


Don, you can't re-tune the X50, it's either your coax or the position of the antenna making a high VSWR.

Set the meter to FWD and transmit.
Adjust the meter so the needle is at 100%

Now set the meter to REF and transmit.
This should show your true VSWR.

There's probably another switch for power, independant of the meter sensitivity.

[K7KBN]

Don -

1000 watts??? :shock: I hope that was a typo, unless I missed something.

I also hope the SWR meter you got is one that works reliably on VHF and above. Many of the cheaper ones get pretty bad above HF (30 MHz) because of the lead length and overall layout inside the case. Lead length becomes increasingly critical as frequency increases.
What brand/model of meter did you end up getting?