Flex 6K ADC overload prevention?

Steve N4LQ

I could answer that if I were allowed to see the schematic.

Tim - W4TME

Not unless the preselectors are enabled for a 6500 and 6700.  The 6300 does not have preselectors.

Steve N4LQ

So the answer is "yes" since this involved a 6500. I assume the preselectors enable automatically when the receiver is tuned to a ham band.

Tim - W4TME

Depends.  There are certain conditions that have to be met, like the frequency spread of the panadapter(s) associated with the SCU and the frequency of any slice defined in those panadapters must be within the frequency boundary of an established ham band (excluding 60m).  You can tell if the preselector is enabled by the absence of the WIDE indicator on the panadapter(s).

JoeMoffatt

The preselector was on. Is the preselector before the ADC? Is it hardware?

Paul Christensen, W9AC

For the 6500 and 6700, I think it comes down to the bandwidth of the preselector - at least for activities like Field Day operations where antennas are often haphazardly strung close to others.  Contest stations present a more controlled environment since they're mostly permanent installations.  Even for FD, I'm not so sure this is a problem with the Flex 6500 and 6700, but let's say signal levels do exceed +9 dBm. 

Here's an idea:

Flex could offer up a tracking preselector (TP) as either an internal or external option to the 6500 and 6700 models.  A TP is essentially a narrow bandpass filter whose center frequency changes in sync with the rig's operating frequency. When I owned an ADAT-200A, I added the optional TP package.  ADAT's standard preselector module popped out and the tracking module was added in a few minutes.  The TP could be bypassed in the menu. 

For the Flex, the TP would connect in the Rx Loop but that assumes my understanding of the loop placement is correct as I have not seen a schematic, nor detailed block diagram of either Flex model.

For an external TP, it could be a device that communicates to SSDR via the Flex 6500/6700 USB port or over Ethernet.  Probably few owners would need a TP as it would almost always be in bypass to have full pan, but as Elecraft has shown us time and again, we often buy accessories we *think* we need if only to have a warm and fuzzy feeling that we own the best.  I'm guilty of this, as are probably many others here.  I have no doubt that if Flex offered a TP, many would be sold. 

Paul, W9AC

Tim - W4TME

Is the preselector before the ADC? Is it hardware?

Joe - the answers are yes and yes.

Steve N4LQ

I noticed this:
With more than one slice open the preselector is disabled (WIDE). Obviously it has to be that way but good to keep in mind for FD operations.
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This may be a bug..........
If you are on say .... 30 meters then open a slice for 6 meters which has +20 DB preselector engaged then change that same slice to 30 meters, both slices will then have +20 DB engaged. Then close the extra slice and +20 stays on. Doesn't seem right.

Tim - W4TME

Not a bug - this is by design.  All of the frequency changes you described are on one antenna (SCU) and the RF preamp is associated with the SCU, not the slice or the panadapter frequency spread.  The SCU (wide band digitizer) has no knowledge of the construct of a "band" this is defined from using a segment of the digitized spectrum. Therefore once you change the preamp gain for the SCU, it stays in that state regardless of the frequency of the slice or panadapter might be changed to. 

It isn't intuitive because you are probably used to a single narrow band (final IF) receiver radio that has a hard construct of what a band is and changing the preamp gain when a band (frequency segment) change is a monolithic event and doesn't adversely effect other receivers or panadapters since there are none.

Steve N4LQ

Well the preamp came on automatically when I opened the slice set for 6m so I figured it should also go off automatically when I close the same slice. 
Slice turns it on so slice turns it off. So I don't understand the intent. But that's ok...I can **** it manually. 
Anyway I've reread your explanation a few times yet no progress. Sorry.

Tim - W4TME

Band persistence turned it on, not the slice.  persistence is an on state operation, not an off state one.

Al_NN4ZZ

It might be more informative to change the "WIDE" message to say "Preselector ON" or "Preselector OFF-WIDE"    Besides giving a positive indication of both conditions, it provides a more descriptive message.  

If anyone thinks this is worthwhile, I can repost it as an idea and see if it gets any votes.  Sometimes it's the little things that make a difference.   Thoughts?

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

KY6LA_Howard

Here are some simplistic calculations. As I do not know ground conditions, relative locations of antennas or types of antennas. And their gains Average Power at the Antenna 1500 watts Antenna Gain in dBi 2.2 dBi. dipole Distance to the Area of Interest 200 feet 60.96 metres Frequency of Operation 14 MHz Are Ground Reflections Calculated? Yes Estimated RF Power Density 0.0137 mW/cm2. Or 137mW/m2 Conversion to dBm. +21.4 /m2 Even withe 10dB attenuation. Overload limit =. +9+19= 19dBm Therefor ADC likely overloaded.

Barry N1EU

IMHO, adding the ADC Overload indicator should be moved up in priority.  Seems like a no-brainer but it obviously isn't.

Stan VA7NF

If this were FD then the power would be 150W max, or there is a letter to write.  On our FD (VE7SAR) we calculated using the side pattern of two tri-banders with 150' separation and the numbers came close to the limit.  This year we ran QRP - No problems with two on one band.

Tim - W4TME

We use a directional RX antenna with 30 dB null we align towards the transmission source. so add 20 more dB of attenuation.  We are close to the overload point but not there.

KY6LA_Howard

With 150w instead of 1500W you would get +11.4 dBm/m2 from a dipole within 200'. Too much for barefoot +9dBm but within limits for -10dB attenuation. Of course these are only theoretical calcs Local conditions will dominate.

Mike - N8MSA

Maximum power varies by class:

http://www.arrl.org/files/file/Field-Day/2015/2015%20Rules.pdf

km9r.mike

This brings up a question that I meant to ask while talking to a sales rep prior to purchase and the question still remains. I understand the key importance of the ADC w/in the flex and also understand that technology advances rapidly but do not understand the impact that can have on the advancement of ADC capabilities. In other words, do we live in an age that tomorrow's ADC will make yesterday's ADC look like a neanderthal and would that require a whole new radio to be designed around the better capabilities of the new ADC or could older radios be upgraded with the newer more capable ADC ? I just do not have a better background of the world of ADC and hence a good understanding of how advances can impact end users of the tech.

W9OY

You can't "calculate a beam pattern" 150' from a yagi antenna on HF  you need to get a dozen wavelengths away from the beam for a pattern to form.  Basically at 150ft on 20m you are in the near field.  

My experience with a 6300 attached to a 43 ft vertical matched matched at the vertical base for RX, and a 1/2 wave 40M vertical 175ft away for TX is I could operate a CW signal up to about 800-900w on the TX vert before I had any interference in the 6300 on 40M with about 200 khz separation in freq.  Transmit phase noise was limiting up to +9 dBm where the ADC began to show signs of deterioration.  Note the 6300 has no pre-selector   The transmitter was a TT Paragon into a Alpha 78.

The question I was asking was how much power does it take to crunch the ADC and are there any HF or MF or BC signals at my QTH that will cause the ADC to overload given my antennas.  The answer is no there are no signals off my property strong enough to crunch my 6300 

73 W9OY

Tim - W4TME

This is a good question.  The leaps and bounds in ADC component performance is not as great as it once was as we are starting to approach the limits of physics is some cases.

Everyday there are advances in chip performance.  However, in order to make a significant engineering change to upgrade to a "better" ADC (greater bit depth or faster sampling rate), the change has to meet two criteria; is it significantly better to provide a tangible performance differentiator and is the component significantly cheaper so that the NRE costs can be recouped quickly with additional sales of the new product. 

Whether or not an upgraded part is "drop in" replaceable or not has a lot to do with the electrical characteristics between the two.  In rare cases, there is a minimal amount re-engineering that has to be done.  In most cases, the effort is significant.  However this is probably not want you want to do because along with one new part upgrade, there are probably additional parts and circuit upgrades that should be done at the same time, so it is actually more cost effective to do a complete redesign than retrofit an older piece of equipment. 

We designed the 6000s to have a long production life span and an even longer operational life span.  I don't think a 6000 is going to be relegated to being classified as a Neanderthal any time soon.

km9r.mike

Yes I did not think neanderthal anytime soon due to it's present ADC capabilities as well but simply did not have the knowledge base about ADC advancement to make a educated guess even. I assumed that there might be compounded issues with drop ins as well but there too that was just assuming on my part. The neanderthal was just a hyper exaggeration wrt to ADCs and was in no way an impression of the very thoughtful work that has gone into the making of this awesome rig. Thanks for the great reply and learning along the way : )