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K3 with 2m tvtr - power control feature request

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Graham Kimbell

K3 with 2m tvtr - power control feature request

I have a K3 (old style) with internal 2m transverter that I want to use
to drive a microwave transverter. There are a few issues with the
output power -

* the max output is supposed to be 10W, but measures 7W even after
calibration - seems wrong but I can cope with this
* the minimum power is 5W but should be down 10dB on the max, ie
0.7W. This is a problem because I need about 1W to drive the
microwave tvtr.
* the XV config that allows setting the 28MHz input to the tvtr has
been checked and is exactly the 1mW (0dBm) default. With the
power control set to minimum it measured -7dBm.

So it appears that the internal 2m xvtr has too much gain, and there
does not appear to be any way to reduce the power output below 5W. Is
there any chance of making this possible?

I have a friend with a K3S with the same difficulty, so it seems to be a
common feature.

Graham
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Don Wilhelm

Re: K3 with 2m tvtr - power control feature request

Graham,

You say you have measured the input power to the K144XV and it is a max
of 0dBm and a minimum of -7dBm. If that is incorrect, then my
conclusion (following) is wrong.

A difference of 7dB should produce 1/20 of the power developed at 0dBm -
based on 10 watts output, you should obtain 0.5 watts output with the
-7dBm input.

So my conclusion is that the K3 is "doing the right thing", but your
K144XV is not. Perhaps there is some sort of oscillation in the K144XV
that is causing your problem.

We obviously don't have all the answers here, so I recommend you contact
K3support because they have access to the designers and production test
folks to seek out an answer for you.

Do you have any way of determining the output frequency on 2 meters?
That may be helpful information for support.

73,
Don W3FPR

On 7/6/2017 10:13 AM, Graham Kimbell wrote:

>
> * the max output is supposed to be 10W, but measures 7W even after
> calibration - seems wrong but I can cope with this
> * the minimum power is 5W but should be down 10dB on the max, ie
> 0.7W. This is a problem because I need about 1W to drive the
> microwave tvtr.
> * the XV config that allows setting the 28MHz input to the tvtr has
> been checked and is exactly the 1mW (0dBm) default. With the
> power control set to minimum it measured -7dBm.
>
> So it appears that the internal 2m xvtr has too much gain, and there
> does not appear to be any way to reduce the power output below 5W. Is
> there any chance of making this possible?

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Dave Sublette

Re: K3 with 2m tvtr - power control feature request

Graham,

You didn’t say which microwave transverter you are using. Perhaps the transverter input requirement can be adjusted to accept the 7W vs 5W. Many of us who drive transverters at reduced levels find that the driving rigs often have full power spikes for just a few milliseconds when keyed, even if the power control has been adjusted down. I don’t know if the K3 does this or not. But my point is, you might be better off adjusting the microwave transverter to accept the full 7 W (or 10W) to avoid the power spike problem.

73,

Dave, K4TO

> On Jul 6, 2017, at 10:49 AM, Don Wilhelm <[hidden email]> wrote:
>
> Graham,
>
> You say you have measured the input power to the K144XV and it is a max of 0dBm and a minimum of -7dBm. If that is incorrect, then my conclusion (following) is wrong.
>
> A difference of 7dB should produce 1/20 of the power developed at 0dBm - based on 10 watts output, you should obtain 0.5 watts output with the -7dBm input.
>
> So my conclusion is that the K3 is "doing the right thing", but your K144XV is not. Perhaps there is some sort of oscillation in the K144XV that is causing your problem.
>
> We obviously don't have all the answers here, so I recommend you contact K3support because they have access to the designers and production test folks to seek out an answer for you.
>
> Do you have any way of determining the output frequency on 2 meters? That may be helpful information for support.
>
> 73,
> Don W3FPR
>
> On 7/6/2017 10:13 AM, Graham Kimbell wrote:
>> * the max output is supposed to be 10W, but measures 7W even after
>> calibration - seems wrong but I can cope with this
>> * the minimum power is 5W but should be down 10dB on the max, ie
>> 0.7W. This is a problem because I need about 1W to drive the
>> microwave tvtr.
>> * the XV config that allows setting the 28MHz input to the tvtr has
>> been checked and is exactly the 1mW (0dBm) default. With the
>> power control set to minimum it measured -7dBm.
>> So it appears that the internal 2m xvtr has too much gain, and there does not appear to be any way to reduce the power output below 5W. Is there any chance of making this possible?
> ______________________________________________________________
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Dave Sublette

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Don Wilhelm

One more reason I forgot to mention. If your power output has to be adjusted every time you switch to the band using the transverter, sooner or later, you will forget. That might be the end of your transverter. That is why I always set my stuff up so I don’t have to make any adjustments when bandswitching. We are all prone to making mistakes. I try to prevent myself from making damage this way whenever possible.

73,

Dave, K4TO

dd0vs

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Graham Kimbell

Hello Graham, dear YLs and OMs,

There is adjustment resistor inside the internal Transverter. Here only you will be able to maintain right power setting. I did this one time for all my transverters. Max power is for me 2,5W. With power (pwr) knob, I can maintain 1 to 2.5 W.

Hope this helps

Vy73
Harald
DD0VS

Von meinem iPhone gesendet

> Am 06.07.2017 um 16:13 schrieb Graham Kimbell <[hidden email]>:
>
> I have a K3 (old style) with internal 2m transverter that I want to use to drive a microwave transverter. There are a few issues with the output power -
>
> * the max output is supposed to be 10W, but measures 7W even after
> calibration - seems wrong but I can cope with this
> * the minimum power is 5W but should be down 10dB on the max, ie
> 0.7W. This is a problem because I need about 1W to drive the
> microwave tvtr.
> * the XV config that allows setting the 28MHz input to the tvtr has
> been checked and is exactly the 1mW (0dBm) default. With the
> power control set to minimum it measured -7dBm.
>
> So it appears that the internal 2m xvtr has too much gain, and there does not appear to be any way to reduce the power output below 5W. Is there any chance of making this possible?
>
> I have a friend with a K3S with the same difficulty, so it seems to be a common feature.
>
> Graham
> ______________________________________________________________
> Elecraft mailing list
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
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Gary Hembree-2

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Graham Kimbell

I have made the same observations with my K3/K144XV, vintage 2010: 8 Watts out at 0dBm in and 4 Watts out at –10dBm in, all power measurements done on calibrated Bird and Boonton meters. The transverter performs very well and gets clean signal reports, so it is not excessively non-linear. The measured spectrum, to more than 1 GHz, is clean with no sign of oscillations.

This behavior must be the result of a transmit AGC circuit in the K144XV. Harald has apparently found its upper limit adjustment potentiometer.

73
Gary, N7IR
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w4sc-2

Re: K3 with 2m tvtr - power control feature request

The PO for xverter bands can be on a per band basis. It is all in the config menus.

XVn PWR:
Sets upper limit on power level for XVTR band n. (Tap 1 – 9 to select band.)
H x.x (High power level) specifies a value in watts, and use of the main antenna
jack(s). This should be used with caution, as you could damage a transverter left
connected to these antenna jacks accidentally. L x.xx (Low power level)
specifies a value in milliwatts, which requires the KXV3 option. L 1.00 is
recommended for the K144XV internal 2-m module. (If CONFIG:PWR SET is
set to PER-BAND, the K3 will save the last-used power setting on each band.
This is especially useful for transverter bands.)

HOWEVER, it appears that 1mw is required for the K144XV. I believe that is so the PO of K144 can be calculated by the K3 FW, as there is no direct measurement of the 144 PO. Once the gain of the K144XV, I believe the calculation will be incorrect for display.

73 de Ben W4SC
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dd0vs

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Gary Hembree-2

dd0vs

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Gary Hembree-2

Hello All,

unless otherwise expected, there is no AGC in the signal path of K144VX.
Therefore the dbm setting is not so accurate on output power as expected.
Furthermore, since there are 2 bandpasses in sequence (28MHz and 144MHz) the ripple of those bandpasses creates frequency dependend output power.

My solution for the Kuhne-Microwave transverters is:
1. setting Outputpower on 144.100 MHz to 2,5W, with maximum dBm setting with this R87 TX GAIN potentiometer
2. set the TX GAIN in the Microwave transverter to a value that allows maximum microwave output at 0dBm setting. (measurement)
3. checking frequency dependency and dBm setting dependency of the microwave output and create a graph or table for proper settings (for me during contest)

Yes -10dBm setting will not lead to a 10dB reduction on micowave power side, i measured this only for 13cm, it drops from approx 15W@max down to 6@min.

This allows me to stay in a safe area, which is fully sufficient for me.

Hope i made it understandable.

Good Luck and many DX with Microwaves.

BTW: a feature missing on K3 is to program frequencies above 25GHz :-(

vy73
Harald
DD0VS

Gesendet: Donnerstag, 06. Juli 2017 um 21:06 Uhr
Von: "Gary Hembree" <[hidden email]>
An: [hidden email]
Betreff: Re: [Elecraft] K3 with 2m tvtr - power control feature request
I have made the same observations with my K3/K144XV, vintage 2010: 8 Watts out at 0dBm in and 4 Watts out at –10dBm in, all power measurements done on calibrated Bird and Boonton meters. The transverter performs very well and gets clean signal reports, so it is not excessively non-linear. The measured spectrum, to more than 1 GHz, is clean with no sign of oscillations.

This behavior must be the result of a transmit AGC circuit in the K144XV. Harald has apparently found its upper limit adjustment potentiometer.

73
Gary, N7IR
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Dave-3

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Graham Kimbell

Hi Graham

This issue has been pointed out to Elecraft on more than one occasion over
the last few years.

When using either the internal 2m xverter or the xv output from the back
panel, turning the power knob fully anticlockwise does NOT reduce the output
power to zero like on ALL other bands. On my K3 setup the power range is 1w
to 9w (144.3MHz). On my K3S setup the range is 1.5-10W(144.3MHz). Both my
internal transverters as supplied were peaked at 147.5MHz , they were
adjusted to peak the output in the UK narrowband allocation(as supplied they
produced 7.5W and 6W respectively at 144.3MHz)

If using the 28MHz XVerter output from the radio, with the XV level set to
0dBm in the menu, the range controlled by the power pot is 0dBm to -9dBm on
my K3 and 0dbm to -8dbm on my K3S If I set the XV level to -10dBm I get
-9dBm at 28MHz irrespective of the power pot setting (ie the power pot does
nothing!)

Rerunning the power calibration routines (on more than one occasion) has
made no difference to the K3 or K3S results

The last response I got from Wayne (sept 2015) on the issue was that there
is no software solution to the problem; the suggested "fix" involved
setting TX ALC to OFF

Dave
G4FRE

From: Graham Kimbell <[hidden email]>
To: [hidden email]
Subject: [Elecraft] K3 with 2m tvtr - power control feature request
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I have a K3 (old style) with internal 2m transverter that I want to use
to drive a microwave transverter. There are a few issues with the
output power -

* the max output is supposed to be 10W, but measures 7W even after
calibration - seems wrong but I can cope with thisv
* the minimum power is 5W but should be down 10dB on the max, ie
0.7W. This is a problem because I need about 1W to drive the
microwave tvtr.
* the XV config that allows setting the 28MHz input to the tvtr has
been checked and is exactly the 1mW (0dBm) default. With the
power control set to minimum it measured -7dBm.

So it appears that the internal 2m xvtr has too much gain, and there
does not appear to be any way to reduce the power output below 5W. Is
there any chance of making this possible?

I have a friend with a K3S with the same difficulty, so it seems to be a
common feature.

Graham

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Graham Kimbell

Re: K3 with 2m tvtr - power control feature request

In reply to this post by Don Wilhelm

Thanks to everyone who answered this both private and public. To recap,
I'm using the internal 2m transverter K144XV and trying to reduce the
output on 2m below 1W whilst keeping the max of 10W. I conclude:

* the 2m internal tvtr cannot be adjusted to produce both 10W out
max and 1W out min
* this is a generic issue, not specific to my K3, and not due to
oscillation or other fault
* it would be preferable to integrate the 2m tvtr and control it by
measuring the power out as per other bands but this probably
requires a hardware change
* the issue has been around for a couple of years without resolution
* users will have to find work-arounds, probably in external circuitry

Graham

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