Coupler Solutions

W8JJ
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Joined: Wed Dec 16, 2020 3:18 am

Coupler Solutions

Postby W8JJ » Thu Apr 01, 2021 2:01 pm

I'm at the point of my new installation that I'd like to incorporate PureSignal. So, I've been reading threads about couplers and talking to others on the air about this and still have some questions. A very common solutions seems to be the Xtronic XDC-4SO. However, it appears to be out of stock at the moment. I'm also exploring the LPA-100a digital meter with the PureSignal modification upgrade that Larry offers for a nominal fee. This seems like a reasonable choice as I would enjoy the metering capabilities while simultaneously resolving the coupler issue. Here is what Larry (N8LP) sent me when I inquired about the coupler modification:

"It consists of a resistive diver from the output of the coupler to ground, and terminates in a BNC connector. The BNC output is attenuated by 50 dB from the transmitted signal from 160 to 6 meters, and would normally connect to the PS input of your ANAN. When the BNC output is not connected to the ANAN, we provide a 50 ohm termination that can be screwed on instead."

As I understand it, the amount of needed attenuation is based on the amplifier output which make sense. I assume 50 dB is sufficient for 1.5KW and I'm wondering if there is a need to vary the amount of attenuation for lower outputs. For example, I'm using a KPA-500 running between 400-600 watts most of the time and may occasionally operate at the 100 watt level. At lower power, is the fixed 50 dB of attenuation a liability as compared to having variable attenuation?

In sum, I'm leaning toward the LPA100a with the ANAN modification as my coupling/metering solution and I'm seeking input before pulling the trigger. Please share your thoughts, experiences, concerns, and any other product recommendations that you may have.

73 Tim W8JJ
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w-u-2-o
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Joined: Fri Mar 10, 2017 1:47 pm

Re: Coupler Solutions

Postby w-u-2-o » Thu Apr 01, 2021 2:37 pm

Short answer

- maximum PS feedback level is set by the no damage max. input level to the hardware, which is +13dBm.
- minimum PS feedback levels needs to stay above -10dBm, below that PS performance will suffer. However higher input levels will provide better SNR vs. internal crosstalk; this is more of an issue for 200D and older hardware and less of an issue on 7000 and 8000 series hardware.
- a 50dB coupling factor is fine, will net a PS level of +12 at 1500W, +7 at 500W, 0 at 100W, and that is plenty fine for acceptable PS operation over that transmit RF power dynamic range. If you want to really guild the lilly, use a 40dB coupler and a 10dB step attenuator to fine tune for different power levels. Note that some amplifier vendors are offering 60dB coupled outputs and that is too much loss at lower output power levels.

Longer answer

- Read this topic: viewtopic.php?f=20&t=2384
K1LSB
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Joined: Wed Feb 05, 2020 5:25 pm

Re: Coupler Solutions

Postby K1LSB » Thu Apr 01, 2021 5:07 pm

Tim,

I built my own purely resistive non-directional RF sampler using a series/parallel arrangement of 2 watt 12K resistors (three pairs in series) to give me a total of 18K resistance (as an experiment I added another small bridge of three resistors to ground but those can be ignored for our purposes).

Here are some pics:

https://drive.google.com/drive/folders/ ... sp=sharing

NOTE: Disregard the variable pots in the box, those were used only for development and are no longer connected.

That arrangement is sufficient to allow PureSignal to get a solid lock at any power level from 25 watts (at 0 dB S-ATT) to the full 1KW output of my AL-80B (at 16 dB S-ATT), while still leaving plenty of headroom available to go well beyond full legal limit power with the Anan.

Mark
AG5CK
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Re: Coupler Solutions

Postby AG5CK » Fri Apr 02, 2021 1:27 am

How important is it to have a directional coupler like the Xtronic unit? I have used the Xtronic coupler and a Coaxial Dynamics sampler that is adjustable.

http://www.coaxial.com/products/7998_7999.htm
Rig: Anan 7000 DLE MK2, Protocol 2 v2.0b, Thetis 2.8.11.
PC: MSI 970a Sli Krait Edition, AMD FX8350, 16 gb ram, GeForce GTX 1050 graphics card. Windows 10.
W7GES
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Joined: Sat Mar 13, 2021 6:56 pm

Re: Coupler Solutions

Postby W7GES » Tue Apr 06, 2021 12:09 am

I ordered a 7000 MK II Black Box last month. While I’m waiting for it to arrive I’ve been reading this forum and spending more money!

After reading the OP’s post I called Larry N8LP up and wound up ordering the LP-700 with a 50 dB sampler coupler so I will be ready for Pure Signal when the rig arrives.

I had ordered the Xtronic 44 dB Directional Coupler from HRO and it was on back order but it arrived today so there are some getting shipped out.

Not sure if I will sell the XDC-4SO or place it after my backup amplifier.

George / W7GES
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w-u-2-o
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Re: Coupler Solutions

Postby w-u-2-o » Tue Apr 06, 2021 1:41 pm

AG5CK wrote:How important is it to have a directional coupler like the Xtronic unit?

Theoretically a directional coupler will provide better results because there is no reverse power component carried back to the PureSignal receiver. However, I don't know if anyone has ever determined whether or not the difference is noticeable.

One of the advantages of the Xtronic coupler is that it has a very flat response over the entire HF frequency range. This make results consistent and repeatable. Other couplers and samplers may not exhibit the same gain flatness.

Finally, beware of adjustable samplers. On some adjustable samplers it is possible, with only a tiny movement of the adjustment, to greatly exceed the +13dBm feedback no-damage power limit. Careful measurement of output of such samplers and locking down any adjustments is recommended prior to connecting it to any Apache hardware.
AG5CK
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Re: Coupler Solutions

Postby AG5CK » Wed Apr 07, 2021 12:59 am

w-u-2-o wrote:
AG5CK wrote:How important is it to have a directional coupler like the Xtronic unit?

Theoretically a directional coupler will provide better results because there is no reverse power component carried back to the PureSignal receiver. However, I don't know if anyone has ever determined whether or not the difference is noticeable.

One of the advantages of the Xtronic coupler is that it has a very flat response over the entire HF frequency range. This make results consistent and repeatable. Other couplers and samplers may not exhibit the same gain flatness.

Finally, beware of adjustable samplers. On some adjustable samplers it is possible, with only a tiny movement of the adjustment, to greatly exceed the +13dBm feedback no-damage power limit. Careful measurement of output of such samplers and locking down any adjustments is recommended prior to connecting it to any Apache hardware.


I felt like the directional coupler was better for that reason. It may make a noticeable difference with an antenna that that's less than ideal but close enough a tube amp loads up into it.

The other coupler I mentioned definately doesn't have a flat response and you do have to be careful. Now I just use it as a sampler for my oscilloscope.
Rig: Anan 7000 DLE MK2, Protocol 2 v2.0b, Thetis 2.8.11.
PC: MSI 970a Sli Krait Edition, AMD FX8350, 16 gb ram, GeForce GTX 1050 graphics card. Windows 10.

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