Why is the SSDR RF meter so low?

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  • Updated 3 months ago
Currently I run barefoot on 6 meters. I set the power to 100. The radio is putting out just a bit short of 100 watts which I confirmed with two separate LDG 600 Pro II tuners with two separate M-600 meters.

All is good except that the SSDR RF meter shows only about 75 watts.

Why is the SSDR meter so low? SWR in SSDR shows about 1.1

Has anyone else seen a lower than expected RF reading in SSDR?

Flex 6700 SSDR v2.3.9 Windows 8.1
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Pat N6PAT

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Posted 3 months ago

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AA0KM

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Pat N6PAT

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Thanks but that doesn't explain why the SSDR meter says 75 watts but two different external meters both state just short of 100. Clearly the rig is sending out full power as expected but the SSDR meter does not show that.
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Greg - N8GD

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Since the power reading of 75 watts is coming from inside the radio, I would propose that it is correct and your external 100 watt measurements are not. Let me explain:

First of all, you need to make sure you have a minimum of 13.8 VDC at the power pole connector on the radio - 14.0 VDC would be better.  Also, make sure the power pole metal slide connectors are clean (a little DeoxIT might help), tight, and have good tension. Poor voltage can cause low output on Flex radios. This may be the root cause of your 75 watt reading.

Second, don't measure your output into an antenna. Yes, it measures 1:1.1 SWR, but is that a pure resistive component? You don't know without a good antenna analyzer. Inductive or capacitive reactance can greatly affect power measurements. You should be measuring into a known good 50 ohm dummy load (not 45 or 55 ohms, but 50 ohms - they do drift with age and poor connections). Gerald covered this in the posted link.

Third, if you want to properly measure the radio's output properly, you really need to put your wattmeter as close to the radio antenna connector as possible - a double ended PL-259 barrel connector would be best, but may not be practical. Coax jumpers can place the power measuring device at an SWR peak or valley along the cable and not be producing a true indication of power that the internal SWR bridge in the radio sees.  Jumper length is even more critical on 6 meters because of its shorter wavelength.

Take a look at the above items and see if you don't find the error is much smaller, or even non-existent.
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Pat N6PAT

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Installed DDUTIL. It says 13.8 at the rig but I do see it drop a bit to 13.2 when transmitting.

The PS is a 32 amp Alinco  DM 330MV.  I'll try a different PS later and see if I get the same results.
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Tom N5MOA

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My power supply, Astron 35, is set to 14.2 (Fluke meter/DDUTIL agree) at the radio, drops to 13.9 on transmit (Fluke/DDUTIL).

I also replace the original pwr supply cable with a me-built cable, using silver plated 45amp power pole conectors. Whether that made a difference, not sure but couldn't hurt.

Setting my power slider to 100w, DDUTIL reads 101-110w (on SSDR meter and OM 2000+ meter) across all bands into a dummy load on my 6500.
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Tom N5MOA

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My power supply, Astron 35, is set to 14.2 (Fluke meter/DDUTIL agree) at the radio, drops to 13.9 on transmit (Fluke/DDUTIL).

I also replace the original pwr supply cable with a me-built cable, using silver plated 45amp power pole conectors. Whether that made a difference, not sure but couldn't hurt.

Setting my power slider to 100w, DDUTIL reads 101-110w (on SSDR meter and OM 2000+ meter) across all bands into a dummy load on my 6500.
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WQ2H - Jim Poulette

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Just an FYI, given that there a a lot of variables here, this is what I have seen:

I dedicated a Yaesu FP-1030A linear supply to the 6600M. I like these because they are economical, whisper quiet, and specifically state +13.8Vdc min @ 25A continuous. With a static 1A draw V=+14.3Vdc, I usually use between 30-35W to drive the amp and the power supply V never drops below +14.0Vdc. A test using the 6600M alone on 10m @ 100W, the V dropped slightly to +13.9Vdc - but it indicated between 100-110W out on the SmartSDR meter, and an MJF-828.

I use home made 8 AWG "soft" stranded cables (fused) that are about 20" long with soldered ring terminals on the power supply side and 3 wraps on a 43 torroid.

Good luck !
73
Jim, WQ2H
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Pat N6PAT

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I just checked it setting the power to 50 watts.  DDUtil shows 13.8v before transmit and 13.6v during transmit.

SSDR meter says output just over 40. Both LDG meters read exactly 50 watts which is what I would expect.

I'm not going to mess with this anymore. I'll just go by the external meters as they seem to be in agreement. The SSDR meter just seems to read a bit lower output than it really is.

Thanks for the advice

Have a Flexcellent day!