Kenwood: Kenwood TM-V708A not Tx @ Full power?!?!

[spdfile1]

So I'll start by listing my equipment involved. Kenwood TM-V708A Mobile Dual-Band (2M/70CM) Radio, which is hooked up via 3' RG-8X coax to an MFJ-817C SWR/Power Meter which then goes to (via another 3' RG-8x Coax) a Diamond CX-210A A/B Antenna Switch. Now the antennas I run with are a Comet CA-2x4SR Dual Band Mag Mount Omni-Directional Antenna (A side of the switch) & an Arrow II Satellite Antenna Model 146/437-10WBP Yagi (B side of the switch) both of which are inside the house in my "Man-Cave" (as I can't place any antennas outside my condo). The Omni is about 4-5 feet from the mobile & the Yagi is maybe 5-6 feet from the mobile. I also purchased a MFJ-261 Dry Dummy Load to test my radio. Everything was purchased new within the past month except the Kenwood Mobile & the Comet Mag-Mount Omni-Directional Antenna which were purchased new back in 2006 & the Arrow Yagi which is about 5 years old (roughly). Now one thing I didn't do was hook up the dummy load directly to the SWR meter (which the write up says to hook it up directly to the radio without coax, but than I can't measure power) and I used the 3' length of RG-8X to connect the radio with the dummy load. Now at low power (5 watts) it puts out that at both 2M & 70CM. At medium power (10W) it shows 10W. However at full power (50W for 2M) & (35W for 70CM) the SWR meter only shows about 25-29 watts. I'm hoping that when I connect the dummy load directly to the antenna side of the swr meter that will change but I doubt it cause I'm never that lucky. Does anyone have any idea other than the obvious what may be causing this?
Problem #2: So having the radio go thru the SWR meter and the AB switch to the mag mount (I haven't tested the yagi yet) I get high swr on 2-meter (haven't tested 440 yet). I tested in 1 MHz increments from 144MHz to 148MHz and I get @ 5W on 144MHZ about 1.8:1 swr and @ 50W about 2.25:1 swr. On 148 MHz I get about 2:1 swr on 5W & 2.5:1 on 50W. Totally unacceptable!!!!! So than I decided to cut the AB switch out and run the Mag Mount coax directly into the swr meter and what a difference.. I had swr down at 144MHZ of almost 1:1 on 5W,1.2:1 on 10W & 1.3:1 on 50W. Up on 148MHZ I think the highest was 1.5:1 on 50W. So yes my new AB switch is for some reason causing high SWR readings. That I understand but does anyone know why this may be happening other than the obvious fact that the AB switch has possibly turned to s&$t?!?!?!?
Boy getting this SWR meter has proved one thing. My equipment has a lot to be desired lol!!!!!!!

 

[AK9R]

Now one thing I didn't do was hook up the dummy load directly to the SWR meter...

RF transmit power measurements into anything but a dummy load are always suspect. Get a dummy load rated for VHF/UHF, connect it to the antenna port of the SWR meter, and then check your power output.

Hobbyist-grade SWR/power meters are also suspect. By comparison, the Kenwood engineers probably used laboratory-grade calibrated power meters. And, a reputable repair shop is probably using a Bird 43 (which is an industry standard, but still has a fair amount of error built-in).

Also, whenever I see people claiming that their radio doesn't put out full power, I question the power supply. That includes the power wiring, connectors, and fuse holders. They can all cause a voltage drop and if the radio isn't getting rated voltage during transmit, it probably won't put out full power.

 

[spdfile1]

That was one piece of info I left out that I should of mentioned W9BU!!! So my Kenwood Mobile has a max transmit current of 11.5 amps or less on VHF & 10.0 amps or less on UHF per the owners manual. My power supply is a Radio Shack Switching Power Supply which says 19 Amp 13.8 VDC on the front. I notice when I transmit at “full power” the power supplies fan kicks on. Could it be that the power supply can’t support full 50 watts on 2-meter and 35 watts on 70 cm? But if it was to much for the power supply wouldn’t it trip the breaker!?!? Actually as I’m looking at the power supply (Radio Shack Catalog #22-508B) there isn’t a breaker switch on the unit.

RF transmit power measurements into anything but a dummy load are always suspect. Get a dummy load rated for VHF/UHF, connect it to the antenna port of the SWR meter, and then check your power output.

Hobbyist-grade SWR/power meters are also suspect. By comparison, the Kenwood engineers probably used laboratory-grade calibrated power meters. And, a reputable repair shop is probably using a Bird 43 (which is an industry standard, but still has a fair amount of error built-in).

Also, whenever I see people claiming that their radio doesn't put out full power, I question the power supply. That includes the power wiring, connectors, and fuse holders. They can all cause a voltage drop and if the radio isn't getting rated voltage during transmit, it probably won't put out full power.

 

[cmdrwill]

You DID measure the DC voltage at the radio while transmitting at different power levels??

Also KWD fuse holders are suspect for poor connections.

 

[spdfile1]

It turns out it's my new MFJ-817C SWR meter. I took my radio, cables & dummy load over to a friends house and he tested my equipment on both a "Bird" & "Micronta" SWR meter and they both agreed that my mobile was putting out about 47 watts on 2-meter (full power) & about 31 watts on 70cm (full power) and without any SWR. It's listed for 50W full power on 2-meter & 35W full power on 70cm. I called Ham City back about it and left a message and they never called my back and so I called MFJ who sounded less than interested to talk to me. They said to send it back to them (MFJ) with my receipt and description of the problem and they'll check it. So that's what I'm doing. Should I be worried when two people say that MFJ stands for "Mighty Fine Junk"?!?!? I don't know but I probably won't be quick to purchase MFJ equipment anytime soon and probably not thru Ham City either.

 

[spdfile1]

I did check the fuse holders for corrosion but did not measure the DC voltage.

You DID measure the DC voltage at the radio while transmitting at different power levels??

Also KWD fuse holders are suspect for poor connections.

 

[mm]

Remember these 2 old sayings about MIGHTY FINE JUNK AKA MFJ equipment, and you will do fine.

"Friends don't let friends use MFJ"

Also since I wouldn't even let my worst enemy use MFJ,

"Friends don't let enemies use MFJ" is also valid.

Remember these sayings and abide by them and you will not be led down the MFJ path of zero quality control products.

 

[AK9R]

Should I be worried when two people say that MFJ stands for "Mighty Fine Junk"?!?!?

Oh, it's more than just two people who say that. I could tell you stories about what I've found in MFJ equipment, but it would be off-topic for this thread.

 

[FKimble]

I'd be worried about the mag mount antenna only 4-5 feet from the radio and my head.

Frank

 

[cmdrwill]

I'd be worried about the mag mount antenna only 4-5 feet from the radio and my head.

Frank

I would guess that someone did NOT read and understand the part of the ham rules on RF Safety.

 

[AB4BF]

Remember these 2 old sayings about MIGHTY FINE JUNK AKA MFJ equipment, and you will do fine.

"Friends don't let friends use MFJ"

Also since I wouldn't even let my worst enemy use MFJ,

"Friends don't let enemies use MFJ" is also valid.

Remember these sayings and abide by them and you will not be led down the MFJ path of zero quality control products.

MFJ may be terrible with their quality control on some things but so far, I have not experienced that. I have an MFJ-993B tuner and also obtained an MFJ power cable with connector for my TS-430S. I couldn't figure out why the lights dimmed on my radio when I transmitted until I put my hand on the original power cable and burned my fingers. On a whim, beforehand, I had ordered the appropriate cable from R and L and replaced it. No more current loss.

The tuner was purchased as an "open box" item from HRO while my TS-430S was getting new finals installed (right after I got my general). Now, when I transmit on our SC SSB net on 75 meters, the NC Operator will ask me how much power I'm running to break through the QRM and QRN. The tuner will, after programming it once, get the SWR down to 1.2 or even 1.1 verified with my Comet dual needle meters. Of course the antenna has a lot to do with it (Buckmaster 8 band up in the tree at 60 feet).

The only other MFJ item I have is a code practice oscillator that I use during Science Education Day at the local state college. Our club will have a line of them so kids and not so much kids can pound out their names in Morse. We have gotten more than one kid interested enough to obtain their license.

All in all, I can't complain about the Mighty Fine Junk I have...

 

[spdfile1]

I'd be worried about the mag mount antenna only 4-5 feet from the radio and my head.

Frank

I typically transmit at no more than 10 watts usually 5 watts and I do that anyways with an HT much less the mobile w/the mag mount so........
The MPE's are only about a foot and a half from the Omni mag mount in the house & that's at 10 watts on 2 meter & 70 cm.