FT-7800R low output power

[Heater]

Hello all and I am glad to have found this site.

I have recently acquired a Yaesu FT-7800R dual-band rig that I am using in the shack for now. However, I purchased this radio used and I have a few questions about its power output. The max power on VHF is 50W and for UHF is 40W. I have the rig connected to a Workman SX144/430 SWR meter which is a crosshair meter showing forward and reflected power. I am not all that familiar with these type of meters and I have a couple of questions regarding the results I am seeing:

1. I am not seeing the max power outputs on either band. The highest I have measured is ~30 to 35W on VHF and 20W or so on UHF. On average, I am measuring about half of the rated power for the rig. This happens in each power setting mode, which are
50/20/10/5 for VHF
40/20/10/5 for UHF
2. The SWR readings range from 1.3 to 1.8 in the VHF band and 1.5 to 1.3 on UHF. (sliding up in freq on both bands).

Normally when looking at my plain Jane HF SWR meters and I see 1.3:1 I would go on about my day and not worry all that much about it. However, this being a new rig and a new-style meter for me to work with, I am seeing things I am not understanding.

So, my question boils down to is this radio having some issues or is it related to antenna/swr/coax/mismatch results? I do not have a dummy load to test with at the present time. Does anyone know if the radio output power "falls off" outside of certain frequencies? This radio has the extended MARS mod and I was wondering if maybe that could have any effect.

Thanks for reading this if you made it this far. Any information is appreciated.

 

[Moleculo]

It is possible that the radio is cutting back the power output as it sees a increase in SWR...that would be normal if that's what it is doing. Also, as you get farther outside the radio's designed frequency range, the bandpass filters are going to start cutting back the power output also. For example, if the radio is designed for full output from 144-148MHZ, if you TX on 151Mhz, you should expect to see some power loss. The power loss can be quite a bit. To get an accurate power reading of the radio to see if you have a problem with it, you need to TX into a dummy load. Once you hook up a dummy load, if you still see low output it would be helpful if you could borrow another meter to compare with to see if the problem is the radio or the meter.

 

[SR385]

If you have a buddy with bench equipment, have them do a bias realignment on it. Too many radios come out of the factory pretty far out of alignment.

It seems they load a defacto firmware that will guarantee the radio falls within a safe limit, but it's in no way hand calibrated from piece to piece.

 

[Heater]

Ok, thanks fellars. I have determined that the TX power increases in these two circumstances:

1. If I tune around to find the lowest SWR for my antenna on each band (which happens to be roughly 141.650 and 457.000).
2. Inside the upper parts of the UHF ham band the power seems to become a little more t'wards what I would expect. Same for VHF freq above.

This brings me to here: Either it is a SWR issue on my 1/4 wave ground plane or it is that plus/or a combination of where the TX freq. is located. I hope it is the antenna as I would expect this radio to not be notched so to speak. I am working on the dummy load and finding another antenna for further testing.

I have read the alignment procedures and found all the equipment I could but it is older and is too low in freq. to be useful for what I would need to do and I don't really want to go that route just yet. Odd thing is there are many hams licensed around here but I cannot find where they hang out on the radio!. I know a very good 11m/HF technician but I don't know if he is set up for VHF/UHF either. I know he can fix an HR2510 though.

I am mostly listening right now (as I have been for many years with me scanner) but I like home brews the best. I may have to break down and get me a good dual-band antenna (any suggestions?) before I burn something up. I need something with a good bandwidth as I'm going to need Ham + MURS and 440 + GMRS).

Thanks again.