More PS considerations for Acom amps/tuners

K8EZB
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More PS considerations for Acom amps/tuners

Postby K8EZB » Sat Apr 16, 2022 10:59 pm

I have PS implemented and apparently working well currently with favorable signal reports. However, my setup may not be optimum. I am using an Acom 1200S amp and companion 04AT tuner with my 7000DLE. So far, I have had the PS coupler/sampler (TelePost LPC-501 with 50dB sampler port plus additional 6 dB attenuator external to TP coupler) installed at the output of the tuner, not at the output of the amp. I have made this choice because the coax between the amp and tuner, in addition to carrying the RF output of the amp, also carries 26VDC @1 amp for tuner power, and control signals for the tuner logic said to be some kind of FSK signaling. For this reason, I thought it best not to place the coupler/sampler on the amp output as I could not be sure that the low level DC and signaling voltages reaching the 7000DLE would not cause problems with the operation of the 7000DLE. Some have suggested that the optimum placement of the coupler/sampler for PS operation is at the output of the amp. Perhaps those here with more relevant experience with the 7000DLE can comment as to tradeoffs and other issues.

Thanks,
Rick
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Re: More PS considerations

Postby w-u-2-o » Sun Apr 17, 2022 12:51 am

If the coupler truly has 50dB coupling factor then you probably don't need the 6dB pad. You can determine this from the step attenuator value during transmit. If it really is a 50dB coupler, then plus the 6dB pad you should be seeing a step attenuator value of approx. 16dB at 1200W. Removing the 6dB pad will jump that up to 22dB attenuation, which is fine. See this topic: viewtopic.php?f=20&t=2384

Keeping the feedback signal on the high side (without exceeding the safety limits described in the link above) keeps feedback SNR high, and assists in achieving reasonable feedback signals when operating below maximum power levels.

As for putting the coupler after the tuner, that is unusual, but there is no reason it shouldn't work. Perform testing with the built-in two-tone signal generator and post some screen shots of with and without PureSignal active. If the third order intermodulation products are -55dBc or better that's pretty good.
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w9ac
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Re: More PS considerations

Postby w9ac » Sun Apr 17, 2022 2:55 am

K8EZB wrote:So far, I have had the PS coupler/sampler (TelePost LPC-501 with 50dB sampler port plus additional 6 dB attenuator external to TP coupler) installed at the output of the tuner, not at the output of the amp.
Thanks,
Rick
K8EZB

Rick,

Can you confirm that you're using the LPC-501 coupler and not the LPC1 directional coupler? Unless you have a non-standard version of the LPC-501, its sampling output is on a RJ-45 jack with CAT 5/6 cabling.

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Re: More PS considerations

Postby W9EZ » Sun Apr 17, 2022 11:19 am

Paul,
I also run the LPC-501 with the 50bd PS tap with no additional attenuator. They can be ordered that way. And Also Scott is correct with his figuring as my S-att is at 22 at 1k-1.2k. Works fantastic.

Todd
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Re: More PS considerations

Postby NJ2US » Sun Apr 17, 2022 11:55 am

Only thoughts I have to offer, is that the O4AT (automatic transmatch/"tuner") should be considered as part of the Load(Antenna), and therefore the Coupler should be placed between the Amplifier output and the "Tuner". The coupler placed at the Tuner output will indicate incorrect Power levels depending on the impedance mismatch. With regard to the injected voltage, the PS tap is inductive, and as such will not carry any DC voltage to the Bypass port of the Apache transceiver. I agree that it wont matter where the coupler is with respect to Pure Signal performance, but you will not measure the true power output of the amp (including the ability to see its gain on the telepost) with the coupler on the output of the tuner. Also agree that the additional 6db pad is not needed, and only adds another plumbing point of failure.
73,
Jeff
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w9ac
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Re: More PS considerations

Postby w9ac » Sun Apr 17, 2022 12:05 pm

W9EZ wrote:Paul,
I also run the LPC-501 with the 50bd PS tap with no additional attenuator. They can be ordered that way. And Also Scott is correct with his figuring as my S-att is at 22 at 1k-1.2k. Works fantastic.

Todd

Thanks for confirming. The reason for asking is that the standard LPC-500 series couplers have RJ-45 connectors for use with CAT 5/6 cabling. More to my concern, the Telepost LPC1 couplers (used with the LP-100A wattmeter) cannot be used in Rick's bias-T configuration between the amp and tuner. The LPC1 coupler uses a Tandem Match (aka "Sontheimer Bridge") design where the inner thru-line conductor between the RF IN and OUT connectors have a DC short to chassis ground through a toroid. That would cause a ground-short to the +26V bias-T voltage that's sourced by the ACOM amp.

Last night, I measured the DC resistance on my LPC-501 coupler and it does show an infinite DC resistance between the inner thru-line conductor and the chassis. So, glad to hear the LPC-501 works in this application.

To Rick's question, if the LPC-501 is placed after the 04AT tuner, a combination of high SWR and high power can present a large reflected wave with substantial high voltage at the output port of the LPC-501. It's not so much of a concern if transmission line SWR isn't excessive. The line SWR on my home center-fed Zepp with open feeders is as much as 80:1 on some bands and creates some very high voltage at points along the line. As such, I would move the LPC-501 coupler between the amp and tuner.

I'm not sure if anyone's conducted a meaningful sensitivity analysis that measures PureSignal's ability to linearize as a function of varying line SWR at the sampling coupler. It would be an interesting measurement.

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Re: More PS considerations

Postby w-u-2-o » Sun Apr 17, 2022 1:23 pm

Those are some great points, Paul. Some definite potential for damage (ha, a pun!).

With regard to the impedance issues: that's why I'm curious to see some screen shots from the OP.
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Re: More PS considerations

Postby K8EZB » Sun Apr 17, 2022 8:04 pm

Thanks to all for taking time to respond. Some clarifications/additional info:

1. Yes, I understand that the optimum placement for the coupler is at the amp output and before the tuner. But, as I explained in my op, the coax between the amp and tuner also carries DC power to the tuner and signaling to the tuner logic. Not sure how this might affect the 7000DLE at the Rx Bypass input, even if substantially attenuated, both electrically and in terms of PS operation.
2. Without the external 6 dB pad I see an S-ATT value of 25 when running about 500 watts on 40 m. In a previous post I inquired about the possibility of exceeding the max input level to the 7000DLE and Scott advised adding some additional attenuation “to be safe.” Added the 6dB pad as a result.
3. Not sure what Jeff means by “the PS tap is inductive.” This would not be the case for the LPC501 attenuator which is a simple resistive divider. And, in any event, there is more going on than just DC voltage (see 1 above).
4. So far, the highest SWR I am seeing at the ant feedline (output of the tuner) on the freqs on which I use the amp is under 2:1. The highest I see is on 17m at about 3.9:1, but I don’t use the amp on this band.
5. In getting some screen shots per Scott’s suggestion, I have encountered a problem I don’t yet understand. With the amp in BYPASS, and 2-tone turned on I see RF at both the 7K output and the amp output of about equal magnitude, which is what I would expect. When I put the amp in OPERATE mode and turn on 2-tone, I see RF drive output from the 7K but no amp output. The status indicator on the amp indicates that the amp is keyed, but no power out. This all works as expected when driving the amp with a voice modulated signal, but not in 2-tone test mode. I have been looking at various 7K settings but not seeing anything obvious. Pilot error is the most likely explanation, but not yet seeing the error.
6. With my amp/tuner combo I am not sure there is the option to use any sampler (not limited to the LPC501) between the amp and tuner for the reasons outlined above. Any sampler would see the amp RF, the DC power to the tuner, and the tuner control signals, and likely present these at an attenuated level to the 7K input. (The amp-tuner is designed to allow mounting the tuner remotely from the amp near the ant feed point, and this is why all this is on the same coax with the amp RF.)

RB
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Re: More PS considerations

Postby w-u-2-o » Sun Apr 17, 2022 8:33 pm

K8EZB wrote:2. Without the external 6 dB pad I see an S-ATT value of 25 when running about 500 watts on 40 m. In a previous post I inquired about the possibility of exceeding the max input level to the 7000DLE and Scott advised adding some additional attenuation “to be safe.” Added the 6dB pad as a result.
This indicates that the coupling factor provided by Telepost in your coupler is NOT 50dB as claimed, but instead approx. 43dB. By all means use the 6dB pad!!!

4. So far, the highest SWR I am seeing at the ant feedline (output of the tuner) on the freqs on which I use the amp is under 2:1. The highest I see is on 17m at about 3.9:1, but I don’t use the amp on this band.
That seems relatively safe, but use at your own risk ;)

5. In getting some screen shots per Scott’s suggestion, I have encountered a problem I don’t yet understand. With the amp in BYPASS, and 2-tone turned on I see RF at both the 7K output and the amp output of about equal magnitude, which is what I would expect. When I put the amp in OPERATE mode and turn on 2-tone, I see RF drive output from the 7K but no amp output. The status indicator on the amp indicates that the amp is keyed, but no power out. This all works as expected when driving the amp with a voice modulated signal, but not in 2-tone test mode. I have been looking at various 7K settings but not seeing anything obvious. Pilot error is the most likely explanation, but not yet seeing the error.
It's not you, it's the amp!

See this topic: https://apache-labs.com/community/viewtopic.php?f=15&t=2593

Acom has, somehow, programmed their amp's to not operate when they detect a two tone signal input. It makes one wonder what they are afraid of, like perhaps someone demonstrating the poor linearity of their amp's???

Assuming you are running one of the latest versions of Thetis (2.9.0.x) you can use the special Acom-work-around feature in Setup > Tests > Two Tone Test > F#2 Delay. Per the above referenced topic a delay of 200ms should do the trick.

6. With my amp/tuner combo I am not sure there is the option to use any sampler (not limited to the LPC501) between the amp and tuner for the reasons outlined above. Any sampler would see the amp RF, the DC power to the tuner, and the tuner control signals, and likely present these at an attenuated level to the 7K input. (The amp-tuner is designed to allow mounting the tuner remotely from the amp near the ant feed point, and this is why all this is on the same coax with the amp RF.)
Yeah, unfortunately you are between a rock and a hard place. Acom's elegant engineering has, unfortunately, created a significant lack of flexibility. No once can easily place any instrumentation in between their amp and tuner.

Eager to see your screenshots...
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w9ac
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Re: More PS considerations

Postby w9ac » Sun Apr 17, 2022 8:47 pm

K8EZB wrote:Thanks to all for taking time to respond. Some clarifications/additional info:

I understand that the optimum placement for the coupler is at the amp output and before the tuner. But, as I explained in my op, the coax between the amp and tuner also carries DC power to the tuner and signaling to the tuner logic. Not sure how this might affect the 7000DLE at the Rx Bypass input, even if substantially attenuated, both electrically and in terms of PS operation.

I think most of us here are aware of the bias-T limitation. For that reason, some couplers like the Telepost LPC1 cannot be used between the ACOM amp and your ACOM tuner with bias-T power injection. You have an LPC-501 coupler that's not subject to the bias-T limitation; it's fine if placed between the ACOM amp and ACOM tuner.
And, in any event, there is more going on than just DC voltage (see 1 above).

Right, there's a 60 kHz control signal on the bias-T. What effect does it have on PureSignal's ability to linearize? I've no idea especially without the 60 kHz magnitude spec, Other folks may know if PureSignal is selectively immune from such a low frequency form of interference on the transmission line. But, it sounds like it's ripe for experimentation.

With my amp/tuner combo I am not sure there is the option to use any sampler (not limited to the LPC501) between the amp and tuner for the reasons outlined above. Any sampler would see the amp RF, the DC power to the tuner, and the tuner control signals, and likely present these at an attenuated level to the 7K input.

The only troubling aspect is the 60 kHz multiplexed control signal on the transmission line. Many couplers are otherwise fine for use with a DC bias-T arrangement like yours. On my QRZ page are shown capacitive-divider and a toroid samplers that are compatible with bias-T systems.

One further discovery this afternoon: The popular XTRONIC XDC1 coupler uses either a Tandem Match or a close variant. I just measured a DC short across the inner conductor and case at both the SOURCE and LOAD SO-239 ports. It CANNOT be used in a bias-T configuration between an ACOM amp and ACOM auto tuner.

Paul, W9AC
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Re: More PS considerations

Postby K8EZB » Sun Apr 17, 2022 9:37 pm

It's not you, it's the amp!

See this topic: viewtopic.php?f=15&t=2593


Thanks for this. Saves me a great deal of time. My first reaction on reading this was (pardon my directness): WTF?!

I have tried various tone freqs and delays for the second tone but with no change in results. Perhaps Acom has been more clever about defeating 2-tone tests than we realize.

I'll do some more experimenting but I am not optimistic.

RB
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Re: More PS considerations

Postby K8EZB » Sun Apr 17, 2022 9:40 pm

It CANNOT be used in a bias-T configuration between an ACOM amp and ACOM auto tuner.


Thanks for this. I was wondering if this might be an option.

RB
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Re: More PS considerations

Postby Chipp » Sun Apr 17, 2022 9:47 pm

I understand the best placement of the coupler is between the amp and tuner. Are there any considerations or recommendations for amplifiers with a builtin tuner when using non resonant antennas requiring tuner assistance. Amp is an RFkit-2K+.

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Re: More PS considerations

Postby w-u-2-o » Sun Apr 17, 2022 10:10 pm

Chip,

I thought the RF2K amp came with a built-in coupler that is placed, internally, between the amp and the tuner sections? The photos on their website show a -55dB coupled output port.

For those who have an amp with internal tuner, the choices are as follows:

- Don't use the internal tuner, use an external one
- Modify the amp with an internal coupler
- Take a chance on hurting the coupler and just place it on the output of the tuner
- Use resonant antennas
- Buy a new amp that has an internal coupler (there are many good choices now), sell the old one

I realize those are not all good choices, but physics are physics!

73,

Scott
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Re: More PS considerations

Postby K8EZB » Mon Apr 18, 2022 1:22 am

I posted a question on the Acom groups.io forum re disabled 2-tone test in Acom ss amps. Here is a response I received:

I raised this with Acom for my 700S and was told its intended to avoid a problem the frequency counter in the amp had with the test tones


Don't know with certainty this is the case but it's the response I received.

RB
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Re: More PS considerations

Postby Chipp » Mon Apr 18, 2022 2:19 am

Scott, right you are. Thanks for the reminder. I am awaiting delivery of my 7000 MK II and keeping myself occupied reading all the posts. Hopefully it will shorten my learning curve.

Thanks again.
W6MY - Chip
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Re: More PS considerations

Postby VK3ICM » Mon Apr 18, 2022 3:36 am

K8EZB wrote:I posted a question on the Acom groups.io forum re disabled 2-tone test in Acom ss amps. Here is a response I received:

I raised this with Acom for my 700S and was told its intended to avoid a problem the frequency counter in the amp had with the test tones


Don't know with certainty this is the case but it's the response I received.

RB
K8EZB


That was my response on the Acom list. As for your query as to which frequencies work, I don’t believe there is a magic pair as long as it is not close to the default. Try 70 & 190hz per Scott’s post here: viewtopic.php?f=9&t=3817&p=14701&hilit=Acom+190#p14694
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Re: More PS considerations

Postby w-u-2-o » Mon Apr 18, 2022 10:17 am

Yes, please do try 70 & 190, it would be very interesting to know if that works for you.
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Re: More PS considerations

Postby K8EZB » Mon Apr 18, 2022 8:20 pm

Yes, please do try 70 & 190, it would be very interesting to know if that works for you.


Yes, a quick check shows that 70 & 190 Hz tones work without the need for a delay in introducing the second tone, Thanks to VK3ICM for posting the tone freqs. PS seem to be working, with a large reduction in IMD products at 500 watts when PS is enabled. I need to look at this more carefully and do some screen shots.

Rick
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Re: More PS considerations

Postby w-u-2-o » Mon Apr 18, 2022 9:18 pm

Great progress. 70/190 is not the optimum tone pair for checking IMD, but it provides a reasonable estimation of performance, and will work well for testing drive level, making drive adjustments, and getting an initial PS solution.

In addition to working with "difficult" amp's, 70/190 also has one other advantage: it does not sound like the "Song of Our People" :D I find it much more pleasant.
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Re: More PS considerations

Postby VK3ICM » Mon Apr 18, 2022 11:16 pm

Just for interest, I found Acoms reply when I raised the two tone test issue years ago:

I remember there was such an issue and thought it was fixed many years ago. it was not made intentionally of course. Just the frequency counter software did not manage to read the two tone signal frequency correctly. The amplifier will not switch to TX if the frequency is unknown.
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Re: More PS considerations for Acom amps/tuners

Postby K8EZB » Sun Oct 30, 2022 7:42 pm

In my original post on this topic I indicated that I had placed my Telepost sampler/coupler at the output of my Acom 04AT tuner out of concern for the tuner 26VDC power and 60 Hz FSK signaling which appear on the coax between the amp and tuner having implications for PS as a result of appearing on the RX Bypass input to the AL7K. Scott and others have indicated that optimum placement for the PS sampler is on the output of the amp. not the ouput of the tuner. So, after some further consultation with Scott and Larry Phipps of Telepost, I repositioned the TP sampler/coupler to the amp output and added a Mini Circuits DC-Block in the coax from the sampler to the RX Bypass input of the AL7K. This solution seems to be working well, but with limited testing and OTA experience so far. Larry reports that the sampler port onthe TP coupler is a resistive divider and that the level of DC reaching the RX Bypass input to the AL7K would be about 2mv, so not clear tha the DC-Block is necessary. The 60 Hz signaling has no noticible effect on the radio, and in any event, is only present during an amp TUNE operation which switches PS off early in the TUNE sequence..

Rick
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