6700 killer on 160m!

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I spent a few hours operating CW in the mini-Stew Perry Contest  last night on 160m.

I had spent part of yesterday installing a PixelLoop receive antenna and was eager to see how it compared against my 55' top loaded vertical.

With the 6700 and two SCU's I was able to compare both antennas in real time as well as in diversity.

For diversity, I fed one SCU from the loop via RXB and the other SCU via ANT1 (also used for transmit).  Diversity worked fine but the difference in noise levels between the two antennas was sufficient to make it a distraction.  Diversity really works well when you have two comparable antennas separated by some reasonable distance (reasonable is a combo of "eye of the beholder", available space and wavelength ;-).

Comparing the two antennas was done by using two pandaptors - one fed from ANT1, the other from RXB - then aligning the two manually and putting a slice in each.  Using the K6TU Control iPad let me very quickly switch from one to the other without having to change window focus with the mouse.

The Pixel Loop has its own pre-amp (27 dB) but a typical small loop is around -45 dBi - as a result, the signals from it were weaker but with much better signal to noise.  The loop background noise was a little under S1, the vertical about S5 where I live here in Woodside - no close neighbors or industrial noise).

Part way through the comparison I thought about adding additional gain using the pre-amps in the 6700 so tried 10, 20 and 30 dB of additional gain.  What a killer combination!  This really helped bring the signals up and then there was never a case where the vertical was better copy than the loop.

This despite the loop being fixed in one direction - I hadn't time yesterday to complete the remote WiFi controlled rotor that is destined for the loop.

Total killer good fun!

Running the 6700 in QSK with 1.5 Kw from the amp was a lot of fun - with receive signals much (MUCH) easier to copy on the loop with pre-amp support from the 6700.

Stu K6TU
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Stu Phillips - K6TU, Elmer

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Posted 4 years ago

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KM4CQG

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Stu I was just looking at this loop at HRO wondering how it compared wellbrook?
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Stu Phillips - K6TU, Elmer

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No clue on the Wellbrook.  I had a home built K9AY loop some years ago and was never happy with it - likely a combination of good ground and a not so good preamp.

Using the preamp on the 6700 worked very well - the signals were significantly amplified over the noise - I didn't think of Chris' recommendation to up the AGC-T - that would also have helped!

A contest - even a small one like the Mini-Stew is not a place for much experimentation!

Stu K6TU
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K6OZY, Elmer

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I own two of these loops.  One is one my 6700 and it works wonders on MARS. 

Stu, I also have the lower audio in my Loop but I equalize it  by increasing AGC-T slider on the bottom of the slice volume widget until they are about the same.   I tried using the 6700 preamp on upper bands like on 10M and saw no appreciable difference.   I never tried adding gain down on the lower bands.      Normally on these radios, we know if a preamp was needed if when we turn on the preamp the noise floor drops.   This doesn't seem to happen on the Pixel Loop.   I add 10, 20, or 30dB preAmp and the noise floor is unchanged.  I figured it was simply because there was already a preAmp at the loop and it wasn't doing any good.   How did you measure an improvement?   Did the signal strength increase without a  corresponding noise floor increase?

I love Diversity!
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Stu Phillips - K6TU, Elmer

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Chris,

I purchased the Pixel Loop solely for use on 160 and 80 to help on receive.  I was pretty happy with the first performance last night...

Now to add the rotor!

Try gain as well on the lower bands - the loop gain is a function of cross-sectional area AND frequency... as you go lower, the gain plummets...

Stu K6TU
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W5XZ - dan

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sure glad to see somebody else say pre-amps ARE useful on 160m!! (with compact, very low gain, but directional receiving antennas.)

tnx, Stu

73, w5xz, dan
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Stu Phillips - K6TU, Elmer

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Dan,

Absolutely! Low band receiving antennas almost always benefit from a pre-amp!

Stu K6TU
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k0eoo

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Thanks Stu for the detailed report.  Your comments come as I'm in the middle of building several RX loops for 160/80m.   So, would you wrap some numbers around how much better the SNR was on the loop vs. the Vertical?  Thanks in advance for all you do....  Dennis, k0eoo
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Stu Phillips - K6TU, Elmer

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Ken,

I have built several loops this way using the feed arrangement described by Rick N6RK - google for it and you will find it.

Its a high impedance transformer that presents minimal load to the tuned circuit of the loop and varactor diodes - then steps the impedance down to 50 ohms for the receiver.

The loop will still benefit from using the preamps in the 6000 however.

Stu K6TU
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k0eoo

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Stu, How did the N6RK loop compare to the Pixelloop?
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Stu Phillips - K6TU, Elmer

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The Pixel Loop isn't tuned while a typical magnetic loop is... as a result, the higher frequency limit of the tuned loop is limited by the combination of the distributed capacitance of the coax plus the inductance of the loop.  For a loop that is 8 feet on a side, this places a maximum limit of about 4MHz on the tuned loop.

The lower frequency response of the magnetic loop depends on how much capacitance you add and at some point the Q will become very poor.

The Pixel loop is untuned and uses a pre-amp to offset the lower gain of a smaller loop - the smaller loop is also a mobius loop which has a better signal capture than a untuned shielded loop OF THE SAME SIZE.  It also should be quieter again for the same size loop.

The Pixel Loop hears well down into VLF - I wanted something that would cover a broader range than a single tuned loop.


Stu K6TU
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k0eoo

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Thanks Stu, I should have been more specific in my question; above you mentioned you had had a N6RK loop and now the Pixelloop, so, I wondered if you could put some SNR numbers for 160m or 80m between the two receiving antennas?  I'm thinking of building the N6RK loop which  is why I'm asking....
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Stu Phillips - K6TU, Elmer

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Dennis,

I don't have my 160m shielded loop up at present so sorry but I'm not able to make a comparison.  

Stu K6TU
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Ernest - W4EG

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Stu,

When I worked you on 160 last night; I gave diversity a try, but I was not setup as elaborate as you. I was going to ask you for a comparison, but I felt you were into the contest and I did not want to take your time. 

I used a Hy-Gain Hy-Tower 18HT with the 160 top loaded coil and a full wave 160 meter OCFD. The result was fabulous with no pre-amp needed.  The east coast as yo may have noted was very easy to work with very nice signal reports.

Thanks for the QSO and maybe one of these days we could try diversity.

F-6.7K

Ps. Any thing yet for Microsoft Surface tablets remote control?

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Stu Phillips - K6TU, Elmer

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Ernest,

I can only speak for my own development efforts - I don't intend to develop anything for either the Microsoft surface or Android products.  Unfortunately the environments are different enough that its design once, write multiple times and I don't have the motivation or time to do more than iOS.

Maybe someone else will focus on these - the API's are freely available.

Unfortunately, until users get used to paying for software, there isn't much (any?) incentive for a developer to commit the effort.

Stu K6TU
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KY6LA - Howard, Elmer

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Come On Stu

You know Hams expect software and infinite updates to be free
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KM4CQG

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Stu & Howard

I purchased the 6700 today should be here tomorrow afternoon. I am going to try this dual antenna diversity test as I am finding working these faint island DX signals fun.

Do you guys think I can get by with just a dedicated Magnetic loop receiver antenna and then use my Hex and other antennas as the 2nd and Transmit antennas?

Whats the minimum spacing I should plan on between antennas?

Thanks
Ian
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Stu Phillips - K6TU, Elmer

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Ian,

If the loop has a pre-amp (like the Pixel Loop does), then it will work.  I have been very surprised how well it works even without a rotor.  In my case, probably 600 feet between the antennas.

The important thing is to remove correlation between the signals at each antenna - at least 0.5 to 0.75 wavelengths is the figure I've seen as the minimum to do this.

You can also use polarization difference (ie vertical and horizontal) as a another way to de-correlate the incoming signals.

One thing I have done is to use two panadaptors and three slices...  one pan with the pair of slices in DIV mode, the second pan adaptor to control the 6700 pre-amp gain for the SCU with the second antenna as the input.  This also helps equalize the incoming signal levels so that the audio level is easier to match.

It takes a little experimentation to find the right audio pan for each signal plus the right audio level to get the best effect in your head.  So worth spending some time altering the controls to see whats best for you.

I think you will enjoy this!
Stu K6TU
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Tim - W4TME, Customer Experience Manager

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"Do you guys think I can get by with just a dedicated Magnetic loop receiver antenna and then use my Hex and other antennas as the 2nd and Transmit antennas?"

Yes.  And it will be better than just getting by ;-)

"Whats the minimum spacing I should plan on between antennas?"

The rule of thumb is as far a part as possible for two reasons.  Wavelength diversity do that you can overcome selective fading and to get the receiving antenna outside of the transmitting antenna's near field so that you don't overload/damage the loop's preamp or overload the ADC in the 6000.
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K1UO - Larry

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Hmmm...  when I try adding the 20db preamp on the F6300 to the Pixel Loop the f6300 ATTN (attenuator) indicator immediately comes on?   Does the user have any control over the Preamp or Attenuator on a 6300?    I may have been absent that class.  sorry.
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Tim - W4TME, Customer Experience Manager

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The RF preamp in the 6300 is not designed to operate on the low bands which is why you cannot enable it.
(Edited)
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K1UO - Larry

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Tim,

Is that something that can be reprogrammed in the 6300 for us that are in quiet locations or with quiet RX antennas and would benefit from that preamp?

BTW:  I noticed that when changing the ANT Tab RF gain to 20db for 160, 80,40 the ATTN indicator comes up on the upper right of the panadapter screen...However, there appears to be a bug that truncates the ATTN indicator to just a few marks on the upper right of the panadapter when adding the 20db "gain" for the 40 and 30 meter Bands.   20 on up changes to a PRE indicator all ok.

Regards

Larry  K1UO


ALSO:

The rf gain 20db setting sounds and appears to be acting like a preaamp with the Pixel used on 30M  and appears/sounds to act like an attenuator with the Pixel on 40M

(Edited)
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Tim - W4TME, Customer Experience Manager

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No, it cannot be reprogrammed.  If you require additional preamplification, you will need to add it externally to the radio.

I have added the issue about the ATTN being truncated to our bug tracker - thanks for the heads up on that.

Too much RF preamplification will degrade the SNR when the bands that are noise limited.  If enabling the RF preamp degrades the SNR (the noise floor rises is one indicator) then turn it off.
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Stu Phillips - K6TU, Elmer

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Larry,

You won't be able to do diversity on the 6300 (or the 6500) as there is only one SCU in the radio.  The pre-amp control is on the antenna tab accessible via the ANT button on the side of the SCU.  I don't know whether that is present on the 6300 or not.

Stu K6TU
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K1UO - Larry

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Stu,  When you get the WIFI  ROTOR CONTROL going for the Pixel could you share how you accomplished that and what components you used please...  That project is what I need to do here somehow.

Regards

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Stu Phillips - K6TU, Elmer

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Sure - I have all the pieces...  Here's the "block diagram"...

I have a cheap TV rotor - it uses three wires for AC to the motor with phase shifted AC (using a non-polarized electrolytic)...  the normal control box uses mechanical switches to determine the direction of rotation and a similar AC motor as the "tracking indicator".  I've thrown the control box away except for the transformer - its nominally 24 volts...

The WiFi controller is an Arduino YUN with a relay shield and a magnetic compass sensor.  The Arduino side of the YUN handles the relay shield and retrieves heading information.

The Linux side of the YUN handles the WiFi and runs a simple web server that shows the current direction of the rotor and allows the rotor to be turned to a set heading. Given the pattern of the loop ( think figure of 8) - the rotor only really needs to be turned 180 degrees for full coverage.

The YUN has an external WiFi antenna option via an MCX connector - in my case, I plug this into a short cable that goes to a N type socket and then uses a 6 dBi outdoor WiFi colinear as the antenna.

All this goes in a plastic Cantex box (really easy to machine) - that includes the YUN and Relay shield in a shielded box, a 5v USB power supply that normally goes into a car DC outlet that powers the YUN via a microUSB cable.

I feed 24v AC into the box for the relay shield to switch - and then also use that source of power via a small converter to run the 5v supply.  Most of the 5v devices designed for in car use will handle 24v DC quite easily.

That's basically it - I do have an external AP made by McroTik that will go outside to provide better coverage to where the antenna is located - the house WiFi is basically too weak to get a reliable link.

When I finish this off, I'll post a detailed description on my own blog.

It's a fun and pretty simple project!
Stu K6TU
(Edited)
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Richard McClelland, AA5S

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I believe I saw a comment on this message board from someone who uses two Pixel loops with their planes oriented perpendicular to each other.  Do you think that any nulls at 45 degrees would be noticeable compared to being able to rotate the loop?  From a distance (I don't own a loop), it seems that being able to switch between two fixed loops would be more convenient than using single loop with a rotor.
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Stu Phillips - K6TU, Elmer

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No clue and to be honest, didn't think about that.  I had all the parts except the YUN and relay shield on hand so less expensive than a second PixelLoop.

Stu K6TU
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Richard McClelland, AA5S

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Well, no worries. One could always put up four Pixel loops and not be concerned about nulls in any direction. But then again, if those cards are on the table, how about two shared apex loop arrays separated by 360 meters? That should be adequate for our spatial diversity requirements. Yet again, if we are going to put forth that amount of effort, why not go for something really outrageous?: http://vk6ysf.com/Radio_Extremes.htm
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KM4CQG

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The 6700 showed up today and one can notice the 30db of gain vs the 20db on very low noise bands.

I am waiting on Loop now thanks Tim and Stu!

Ian
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philip.theis, Elmer

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Let me offer this.  This past weekend I had tremendous success with diversity pulling out numerous weak signal situations both on 160 and 80 CW.
Using a series of Beverage antennas on RXA and either Inverted L (160) or 1/4 wave vertical (80)
No preamps.   It was a killer combination.   Repeatedly able to pick out ultra weak signals.
Future plans include a horizontal loop for close in work, but anxious to see how it works as second antenna for diversity.
Fun Fun Fun
Phil K3TUF