[Elecraft] [K3] Issue with HI CUR on 12m

[Bill Coleman]

SWR on the problem antenna is below 1.2:1. It’s a trap dipole - designed for that band.

It is unlikely the balun is “breaking down”. It’s a current balun - #43 ferrite beads on RG-313 coax. It can easily handle a kW or more. 

> On Oct 12, 2020, at 2:12 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:
> 
> Bill,
> 
> I would suggest that you check the SWR on the antenna before concluding it is an RF feedback problem.
> Don't forget that the balun may be breaking down with power and show no problem at lower power (like from an antenna analyzer).
> 
> Don W3FPR
> 
> On 10/11/2020 8:53 PM, Bill Coleman wrote:
>> Don,
>> 
>> I finally got around to running my K3 into a dummy load.
>> 
>> I had no problem running 100w or even 110w with a dummy load. Current draw from the power supply was 22 A and 23 A, respectively, on the K3 display. No HI CUR indications.
>> 
>> External wattmeter validates the output.
>> 
>> I was getting the HI CUR indication on a trap 30/17/12m inverted V. I had to take it down, and now I’m using a trap 80/40/20m dipole through the tuner. No HI CUR indication on that antenna, either.
>> 
>> Even though I have current baluns on both antennas, I’m thinking that my HI CUR problem may be related to RF feedback in the shack.
>> 
>> Do you concur?
>> 
>> I’m in the process of a number of shack improvements, including antenna replacements and grounding and bonding, so that might take care of it.
>> 
>>> On Jan 11, 2020, at 11:29 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:
>>> 
>>> Bill,
>>> 
>>> Is this into a dummy load (bypass the ATU or tune the ATU into the dummy load).
>>> If it is into an antenna, there are a whole lot of guesses about how the antenna behaves with higher power levels than your antenna analyzer shows.  So check it with a dummy load to eliminate the possibility that the problem is in the antenna.
>>> 
>>> Put an external wattmeter in line with the dummy load to eliminate questions about the calibration on the K3 wattmeter.
>>> 
>>> If you can measure the actual current drawn, that would also be helpful.
>>> 
>>> 73,
>>> Don W3FPR
>>> 
>>> On 1/11/2020 11:18 AM, Bill Coleman wrote:
>>>> Back in early December, I installed two KSYN3As in my K3 SN 7071. Sometime after that, I noticed that on 12m, I’m seeing a HI CUR indication when I set the power level to more than about 80-85 watts. The K3 will back off on the power level, then slowly ramp back up until it hits HI CUR again.
>>>> I don’t remember seeing this before. After the KSYNC3A install, I ran the transmit gain calibration at both 5 and 50 watts, as specified in the instructions. Just in case something went awry, I ran it again.
>>>> I’m still seeing this problem. What causes HI CUR at 85 watts? The K3 ought to be able to produce over 110 watts on 12m.
>>>> I’m not seeing this issue on other bands.
>>>> No issues with calibration
>> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
>> Web: http://boringhamradiopart.blogspot.com
>> Quote: "Not within a thousand years will man ever fly!"
>>             -- Wilbur Wright, 1901
>> 
> 

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901