Power and Frequency Tuning for a TK-880H

[jgillaspy]

So, I have my TK-880H running now, connected to a Nagoya VHF/UHF antenna and was using my Surecomm SW-102 to check things and I noticed the reported power was off. Now I have read through other threads here and I know this meter isn't really measuring power, but voltages, but the 880H is supposed to output 45W and I'm not getting anything close to that (26.2W). 

 

Is there a way to "tune" the power (High/Low)? The low power is too high for GMRS01-07, so I'd love to fix that w/o lowering the high power output.

 

Also, how does one lower the band range w/o a ton of equipment? I now have passed the Technician ham test and am waiting on my new call sign, so I'd love to use this radio for both GMRS and 70cm ham.

 

Any help will be greatly appreciated. I do have the service manual, but I'm not finding much. I found on another site there there are physical adjustments w/in the radio, but w/o proper test equipment the changes are highly NOT recommended.

 

JG

[jgillaspy]

Hey All,

 

Thanks again for the info. According to Alex's post I'm really not very far off with my cheap meter, so maybe I'll just not use the first 14 channels (bummer). As far as tuning the split I've sent emails to a couple of radio shop here in SATX and I'll see what they offer. One place I found online wanted $250/hr )more than I paid for the radio), so maybe I'm better off just letting it be.

 

JG

[WRAK968]

Fair bit of questions here.

 

Tuning is done through the KPG software for the radio, HOWEVER, I would not attempt to retune a radio without the proper meters and equipment and a surecom 102 isn't the best to meter for perfection. One thing I do question is, have you tested the meter against a known source? I do use a surecom meter myself for quick checks, and I recall that I had to tune the meter before I could use it. It took a few trys however I did get it to be close enough for what I do. IF you choose to do this yourself with cheap equipment, I am not to be responsible for damage or rule violations.

 

You will need a length of coax about 1.5 times the frequency wavelength, (9 or 18 inches should work) the meter, a 50 ohm 100W dummy load able to support the frequency you are tuning for, radio, power supply, programming cable and computer with KPG49D software.

Set up the radio and power supply, connect the coax from the radios antenna port to the "Input" side of the meter, and connect the dummy load to the "Output" side. Connect the programming cable, and turn the radio and computer on.

Open the 49D software and do a read from the radio.

Click "Edit>Test frequency"

 

Enter in several frequency sets, You should have the lowest frequency you plan to transmit on, the highest frequency, and a frequency somewhere close to middle between your high and low frequencys.

 

Save the file, and write to the radio. Once written, click "Program>Test Mode"

 

Select the center frequency (likely to give you the best results for your usage "band")

 

Double click "RF High Power"

 

Take a note of the current value, Just in case you make a mistake, you're able to return to this number and start again.

 

Use the left and right arrow to adjust the value in the new window. Make small adjustments and click "TX" Get a reading and click "TX" again to stop transmitting. Keep making adjustments until you reach about 40W (This unit is rated at 40W output to my knowledge) You can run slightly low, however to protect the radio, I wouldn't tune above 40W.

Once complete click "OK" to exit to the test mode window.

Select the lower frequency and go back into RF High Power, DO NOT MAKE CHANGES, Simple click TX and take a reading, and do the same for the High frequency. Note, Both frequencies will be BELOW the 40W output. This is NORMAL as long as they aren't super low.

 

When complete, click "Close" in the test mode window, and your radio should reboot.

 

For low power, I don't believe that radio can go much further than 20W low power without causing damage to the radio, and for frequency alignment and getting into the 70CM band you would likely do better taking the radio to a shop and having a pro do it for $50. This will void the part 95 certification, however at least there is less risk of transmitting way off frequency by accident. I would also advise against any physical adjustments on the radios boards as a 1/4 turn on the wrong pot will fry your radio, your station, or worse, could cause a fire. Again, most shops can preform this service at a reasonable price for you.

[jgillaspy]

Hey WRAK968,

 

Thanks for the info. I have not tuned the meter, but I was using a 50ohm, 100W-capable dummy load. I was actually wanting to lower the low power setting to ~5 watts so I can use the first 7 channels. Current reading are a little shy of 10 watts. I'll see if I can find a radio shop here in San Antonio to make the changes for me.

 

JG

[axorlov]

TK-880H supposed to produce 40W, not 45. All three of 880Hs I own show 30W on the power meter I trust (Diamond SX600) into the 200W dummy load.

[JohnE]

you can turn them up but be aware that a lot of the used radios can be a little "soft" after yrs of service already.

the pins on the brick sometimes need to be "touched up" w/an iron as they get heat fatigued.

just an FYI

[WRAK968]

Hey WRAK968,

 

Thanks for the info. I have not tuned the meter, but I was using a 50ohm, 100W-capable dummy load. I was actually wanting to lower the low power setting to ~5 watts so I can use the first 7 channels. Current reading are a little shy of 10 watts. I'll see if I can find a radio shop here in San Antonio to make the changes for me.

 

JG

Dropping to 5 watts on a high power radio will cause damage, I honestly wouldn't even let it run at 10W as low power is rated at 25W. If you want the lower power, you may wish to get the standard 880, (Non-H version) which can handle 5W low power with little issue.

 

The problem is that reducing the power output beyond specifications causes heat to build up in the radio, the more heat, the more likely you could burn up the finals, and yes, it can even happen with extremely low power being used. I'm not exactly sure why this happens or the science behind it, so perhaps one of the better knowledge folks could explain it for me

[tweiss3]

Yea, like most radios, you can only set the power according to the factory pre-sets (H/L/EL/etc...). 

[Lscott]

Dropping to 5 watts on a high power radio will cause damage, I honestly wouldn't even let it run at 10W as low power is rated at 25W. If you want the lower power, you may wish to get the standard 880, (Non-H version) which can handle 5W low power with little issue.

 

The problem is that reducing the power output beyond specifications causes heat to build up in the radio, the more heat, the more likely you could burn up the finals, and yes, it can even happen with extremely low power being used. I'm not exactly sure why this happens or the science behind it, so perhaps one of the better knowledge folks could explain it for me

You have any links to information on this? I find it hard to believe this can happen unless who ever tweaked the radio down some how botched the internal settings.

 

The power brick spec sheets I've looked at show a bias pin that controls the power output. I a few of the Kenwood HT designs there is a feedback loop that measures the current through a set of low resistance resistors. The voltage developed goes into the feedback loop to adjust the bias pin voltage to keep the power output on the module constant. At least that's how it looks to me in the service manuals.

 

Some of the power modules are static sensitive and you can blow them if you're not careful. There is also a warning about getting the pins too hot while soldering which can also bugger up the module.

[WRAK968]

You have any links to information on this? I find it hard to believe this can happen unless who ever tweaked the radio down some how botched the internal settings.

 

The power brick spec sheets I've looked at show a bias pin that controls the power output. I a few of the Kenwood HT designs there is a feedback loop that measures the current through a set of low resistance resistors. The voltage developed goes into the feedback loop to adjust the bias pin voltage to keep the power output on the module constant. At least that's how it looks to me in the service manuals.

 

Some of the power modules are static sensitive and you can blow them if you're not careful. There is also a warning about getting the pins too hot while soldering which can also bugger up the module.

I just know what I've been told in the past. First, I do not do anything inside of the radio, instead I use the software to make changes to the radios power output. The TK880 uses digital tuning to make said changes. However, I've found that going more than 5-10W below what the radio is rated for can cause heat buildup in the radio, limiting your TX time and risking damage to the radio. Its why I don't recommend dropping that low without a service shop doing it as they can make physical changes to the radios internals that would prevent this.