Changing the Power Output from HL2

[Glenn Holt]

Hi Steve,

I want to reduce the RF output level from the HL2 by 3db. The reason for this is that for example on 80Mtrs even with the drive slider on Thetis at min (-7.5db) the output level from my integrated HR50 is too high. 

At the moment the only way i can see to do this is to add R97 and R98 on the balanced Pi attenuator at the input to the PA stage. Is the impedance at this point 50 Ohms? if so i can work out the values of the required resistors.

Is there any other way in the software to reduce this level?

BTW the PA gain in Thetis is set at the minimum level for 80Mtrs.

Regards

Glenn Holt

G8NOF

[Robert Dale]

Why not just use a 3db attenuator on the HR50 input? Kyocera AVX makes very nice tabbed passive attenuators perfectly suited for this purpose. Just mount the very small package to the HR50  heatsink, solder the output from your HL2 to the input, solder the output to your HR50 input and your done. 

https://www.mouser.ca/datasheet/2/40/AVXC_S_A0001241810_1-2538407.pdf

73,

Robert VE7ZN 

[Glenn Holt]

Thanks Robert but doing that would add 3db on the RX side. I want to place the attenuation behind the TX/RX relay of the HL2

Regards

Glenn

[James Ahlstrom]

You could change the resistors in the opamp driver to reduce the gain. I am away skiing at the moment and don't have the schematic in front of me.

Jim

N2ADR

[Steve Haynal]

Hi Glenn,

Please see this post, and search this list for R55. 

https://groups.google.com/g/hermes-lite/c/0eftDlIma-w/m/sIkT9WhrAgAJ

73,

Steve

kf7o

[Robert Dale]

Huh? No it won’t change the RX side at all if you place it in TX path. How could it? 

[Robert Dale]

By “TX path” I mean outside of the HL2 and at the RF input of the amp. That is where the attenuation belongs and it will have zero effect on RX because it isn’t in the RX path. 

On Tuesday, January 25, 2022 at 12:58:29 PM UTC-8 holtg...@gmail.com wrote:

[Glenn Holt]

Hi Steve and Jim,

From the data sheet on the OPA2677 I calculate that the existing gain with R55 (120 ohm) in the HL2 is 6.5 times or 8db power gain, increasing R55 to 220 Ohm should yield a gain of 4 times or 6db in power gain.

I will replace R55 with 220 ohm and let you know the result.

As always thanks for your help.

Regards

Glenn Holt

G8NOF

[Matthew]

Hi Glenn,

I'm not sure I fully understand this.

I have not used Thetis, but with SparkSDR, linHPSDR and piHPSDR, I can change the drive level and with an HL2 + Hardrock 50 amplifier, I can control the overall output to be (well) below 50 W. You mention the output level from your HR50 is too high - what are you trying to achieve? If you are trying to achieve a steady 50 W, it sounds like something software related is wrong?

What range of power output from the HL2 are you seeing using the drive slider?

73 Matthew M5EVT.

[Glenn Holt]

Hi Matthew,

 

Thanks for the reply.

 

I use the output of the HL2+HR50 combination to drive an Acom 1000.

 

On 80mtrs the HL2 drives the HR50 to 74 watts with the drive control in Thetis at Max, with the drive control at Min its 25Watts.

 

The Acom has a gain of 13db (that’s 20 times) in power gain therefor the Min output of the Acom is 500Watts which is over the legal limit.

 

This is why I am looking to reduce the HL2 output on the TX side before the TX/RX relay by about 2 to 3 db.

This will also give me a better range of power control with the Thetis drive slider.

 

Regards

 

Glenn Holt

G8NOF

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[Matthew]

Hi Glenn,

That makes sense. Your integrated setup looks great. 

73 Matthew M5EVT.

["Christoph v. Wüllen"]

Well, some time ago I built into piHPDSR (another SDR)
program to scale the TX IQ samples as to get a smooth variation
of the output power with the drive slider, from 0 to 100%.

I had to revert this since it is not compatible with PURESIGNAL
(you get too week TX feedback) and certainly one wants that.

So we are left with the limitation of the hardware, and have
to solve the problem in hardware.

> Am 26.01.2022 um 00:33 schrieb Robert Dale <rober...@icloud.com>:
>
> Agreed. That is exactly what I did!
>
> 73,
> Robert VE7ZN
>
>> On Jan 25, 2022, at 2:56 PM, DL1YCF <dl1...@darc.de> wrote:
>>
>> PA calibrations settings (in Thetis or whatever other program) have little effect
>> since the drive level circuit can only switch between 0 and -7.5 dB in
>> 0.5 dB steps, and you are already few dB in the negative for having
>> full 5W power out of the HL2, so you can go down to about 2 Watts
>> but not much lower.
>>
>> Hardware attenuation between the driver and the HL2 PA
>> (or between the Hl2 PA and the TRX relay) is indeed the way to go.

["Christoph v. Wüllen"]

Of course one can go there by scaling the TX IQ samples.

However, this makes PURESIGNAL dysfunctional so I cannot
recommend this.

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[Marcos X]

Hello everyone, up to what level could the power of the hermes be increased safely?

Could you recommend me some resistance in substitution of R5

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[James Ahlstrom]

I dont think the power can be increased to any significant extent. I am fairly sure it won't work at 10 watts, and that would only be half an S unit.

Jim

N2ADR

[Glenn Holt]

Hi Steve and Jim,

I can confirm that today i have changed the R55 resistor to 220 Ohm which has reduced the power output of the HL2 by 2.5db.

Regards

Glenn Holt

G8NOF

[Steve Haynal]

Hi Glenn,

Thanks for the update, and glad it worked for you.

73,

Steve

kf7o