Out of Band Antenna Tuning

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Add the ability to manually adjust the internal tuner, a slider for inductance, and a slider for capacitance, to tune for best signal when monitoring outside of the ham bands.

This would be ideal for folks who want to listen to short-wave while not in proximity to, or without, an outboard tuner.
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Mystery Ham

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Posted 2 years ago

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Bill -VA3WTB

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Is that normally found on Ham gear? I have not had a newer radio in some time, just wondering if they offer that now on most radios.
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Mystery Ham

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Many newer radios have "general receive" capability that allows for monitoring the multitude of shortwave broadcast bands.
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Bill -VA3WTB

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Yes I know about general coverage, what I am asking is,,,do most radios have  inductance, capacitance adjustments for receive?
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Mystery Ham

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Technically, Yes.  When you tune on the ham bands your receive path will go through the tuner(that's why the band comes alive after tuning) unless you RX on a different antenna. ( in that case you may benefit from manual tuning on the RX antenna)

Prior to the Signature Series Flex, I've only had one radio with an internal tuner, and it disappointed me that it didn't allow manual control.  LDG does have some models of autotuners that do offer manual adjustment that fills just that purpose.
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Chris DL5NAM

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Mister Mystery - how you will tune out of band? How should it work without RF at a SDR? TX out of band ?
Don't know from what country you are.  A real Ham don't do it :-)

73 Chris DL5NAM
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Mystery Ham

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Paul & Ned,

I've never used a noise bridge before, however clearly, based on the various schematics I've seen yesterday and today, a noise bridge does put broadband noise on the antenna. Granted it is less than a mW, but it would seem to be illegal, in most countries, to transmit across the entire HF spectrum at once.

Mystery Ham
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Paul

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That's a fair point MH. On the same basis then, I also wonder whether antenna analysers might not be legal in some juristictions.

In support of the bridge though; the emissions from it should be imperceptible to the outside world if it's designed correctly. Presumably this would be done by keeping the bridge noise temperature (Tn) above that of the detector (Trx) but below that of the antenna (Ta) ie: Satisfy Trx<Tn<Ta

Also, I think it's likely that the power spectral density of the noise generated by the bridge outside it's own environment would be imperceptibly small in the far field due to the relatively narrow receiver bandwidth.

Even if the above conditions were not met, I believe a bridge would still be less antisocial than (say) tuning up by momentarily transmitting a carrier like many amateurs do. I wonder if anyone on here actually knows the FCC, OFCOM, IARU position on this?
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k3Tim

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Having an adjustable L-C to 'pre-tune' the antenna for SWL would be a nice enhancement. 

"Somewhere" out on the web I thought read one could xmit under a certain power level on HF. Recall the BPL (broadband over power lines) used HF frequencies.

If this were not the case, all the VNA/Antenna Analyzers would be illegal. A web search of "DIY Antenna Analyzers" and subsequent schematic research shows they use of a DDS in the design. I stumbled on the web info after looking at some RFI problems I was having that seemed to be strongest at 13.56Mc. A search of "13.56 mhz rfid" was interesting as that is one of the ISM (aka, junk) bands.

Am I correct in assuming a DDC - SDR is the only device that can receive both amateur and SWL bands w/o compromise? The point being, the 6Ks while fine HF amateur xcvrs also excel at double duty of SWL. 

_..--
 Tim  - k3Tim
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Mystery Ham

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From personal experience, most modern amateur gear makes for excellent SWL gear.  Some of the better Amateur products will employ bandpass filters for the operating bands.  The 6700 has them.  However for 60m and outside the radio amateur bands, they are switched out.  Many other products will use low pass filters that switch in and out depending on the band selected.

As far as SWL products that I own, none employed bandpass or lowpass filters.  They also did not employ antenna matching circuits.  However due to their overzealous preamps for small antennas, and weak mixers, I could frequently get interference several MHz away from local AM broadcast (MW) stations.  However, by using an outboard antenna match with adjustable L & C, I could frequently bring the desired signal out of the mud and eliminate the interference.

The 6700 and 6700-R are both very good, no transmit on the R... However, I discovered from reading the hardware manual that, while the 6700-R has no transmit hardware, it apparently has an antenna matching unit (tuner).  That little fact has me wondering if my suggestion wasn't already in the works.

Mystery Ham
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Mystery Ham

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Tim,

I'll just paste this in from another posting a couple of days ago.  The Link is the result of searching for minimum power without requiring a license of some sort.   

I've never heard of an antenna analyzer requiring a call sign to be input so it can ID itself while it's attached to an antenna. Nor have I seen an analyzer limited to the edges of the ham bands. Perhaps there is some room within the law in various countries to allow using a momentary low power signal to provide analysis and automatically match an antenna system on an otherwise receive only device.

This may shed some light... http://transition.fcc.gov/ftp/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf

Now, perhaps, in the case of  radio amateur equipment, a signal cannot be emitted under any circumstance regardless of power due to whatever compliance testing may be required...  But that fcc document  has me wondering about the 6700-R and it's apparently transmitterless AMU.

Mystery Ham
(Edited)
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WA2SQQ

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I might be wrong, but most "auto tuners" use a number of caps and inductors that can be combined in series / parallel combinations using a bank of relays. While this design can simulate an almost infinite combination of inductance and capacitance, it's hardly a "variable" scenario. Since the Flex radios are primarily intended for amateur radio, the development cost and time spent on this feature would not likely do very much to increase the overall sales. The marketing folks might say that "the ROI is very small". Use an outboard tuner - easier and much less expensive. It can be easily connected to the looping connectors. If I had to speculate, this might be something that a user would want if the radio were operated outside the intended amateur bands.
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Mystery Ham

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You are correct, most auto tuners use a finite combination of inductors and capacitors to perform their function.  The idea is to be able to adjust, with slider controls in the software, both capacitance and inductance within the limits of the tuner.   And in the context of the idea, it is for listening outside of the regular ham bands otherwise we could automatically tune.  Given that the 6500and 6700 already have tuners integrated, and that it is an option for the 6300, the development cost is limited to software and firmware, which is an on-going process.  Thus low investment for a feature that might actually be used by folks that enjoy SWL.  Flex has already seen fit to support General Receive in their SDRs. Q.E.D.  The real development question here is whether or not there is a way to address the tuner's L & C switching capabilities from the software interface.   Another question: how many features are in the signature series radios that you never use but were incorporated anyway.  I doubt, I'll ever operate two radio single operator in a contest even though a configuration profile exists. However, I have already been enjoying listening outside of the amateur bands.

Cheers!
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WA2SQQ

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At the risk of having this turn into an ongoing debate, I'll make this my last post. Considering the cost of a Flex 6000 radio, I doubt very many SWL'ers are going to purchase one just to listen.  As an SWL'er of more than 50 years an external tuner is much more versatile, and definitely less expensive. As a ham, such a feature would not in any way entice me to buy the radio (for amateur purposes). As a person who works in the consumer electronics industry, I have an extensive amount of knowledge and respect for allocating development resources to any product. You allocate them where you get the biggest return on the investment (time and money). From that point it becomes an issue for the marketing guys to decide. QED
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Mystery Ham

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WA2SQQ,

You may be right, perhaps SWL'ers may not purchase a flex just to listen, then again, there aren't a lot of  hams that would buy one either even though it's one of the best quality receivers on the market.  The idea of the feature is for those who do pony up the $$$.  I do wonder what Flex marketing was thinking when they told Flex engineers that they had to have a receive only 6700-R for $1100 less than the 6700.  Maybe they do know something we don't...

Having worked in hardware and software development since the late '80s, I've come to learn, in a creative work environment that isn't too topheavy, sometimes a feature gets implemented just because a young engineer or two thought it was a cool idea, saw how to get it done, and he, she or they had nothing better to do for a few hours after work.  I do hope Flex is that type of organization, and that Flex management appreciates employees that are willing to spend extra hours innovating, even if it's not in the production plan.  In my experience, some of the best ideas implemented came from throwing aside the roadmap for a few hours and asking one self, "Let's see if we can do this."

So, you  are correct, marketing may not see value in a feature.  After all, why do you need 8 slice receivers, you've only got one set of ears?  For me, if it can't happen on the 6700, maybe I can trade the 6700 in for a 7700 and get that feature a few years from now.

Hope to see you on some of the other threads.

Cheers,
Mystery Ham
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Rick Hadley - W0FG

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In case you missed it, there are now a pair of 6700-R radios on the ISS. I believe that most of us here on the community are unaware, or forget, that amateur radio isn't the only, or maybe even the most lucrative, business that Flex is engaged in, given the opacity of government contracting. When I first got the full dog & pony show at a ham convention, I immediately recognized that I'd have gladly killed someone to get Flex capability when I was working for folks who shall go unnamed, long ago, in a galaxy far away.
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Mystery Ham

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Kevin K4VD,

Your question about how Flex might handle an antenna match for the 6700-R has me thinking...  It may not be so far fetched if components are modular. The existing board from the 6700 could then be used. However, since transmit power isn't involved, lower cost components that can cover a broader range of mismatches could be used instead...

It appears that the 6000 series already remembers it's prior match settings when switching between bands and locations within a band and puts them into play without transmitting when those frequencies are revisited.  So, once a manual match has been set from the software, things should be in good order as long as the antenna ecosystem doesn't change.

One step farther:

I've never heard of an antenna analyzer requiring a call sign to be input so it can ID itself while it's attached to an antenna. Nor have I seen an analyzer limited to the edges of the ham bands. Perhaps there is some room within the law in various countries to use a momentary low power signal to provide analysis and automatically match an antenna system on an otherwise receive only device.

This may shed some light... http://transition.fcc.gov/ftp/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf

Mystery Ham
(Edited)
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Rory - N6OIL

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I'll add some gas to the fire,most peeps that are using SDR receive only radios aren't using tuners that I know of. I have a PlaySDR that I just hook up to any of my antennas. But now you have me thinking, when I tune my TS-820S I preselect for the greatest noise with the drive control, so when I get chance I'm going to hookup my external tuner AT-200 to my SDRPlay and see what happens.
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Mystery Ham

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Rory,
I'd love to hear your results...
73
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Dan -- KC4GO

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Regarding reasons to purchase. One of my reasons to purchase the 6500 was because it would also let me use it to do utility and shortwave broadcast listening. Many years ago I purchased a Drake TR-7 for the same reason. The whole world of HF doesn't revolve around Ham Radio.  As for Mystery Ham there are a couple things you can do.
1: Purchase an all band antenna like Comet 250B for RX use, or
2: use a small manual antenna match or per-selector and run it into RX-A.  just watch the pan-adapter for the area of interest to peak.  Check MFJ I wouldn't expect Flex to add the manual adjustment to the ATU.
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Mystery Ham

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Dan,

I appreciate your sentiments regarding the HF world not revolving around Ham Radio...  Seems to be an American point of view as most other countries offer shortwave programming along with the ubiquitous possession of shortwave receivers among the citizenry.

From my point of view, part of the beauty of operating a signature series flex is the ability to operate away from the hardware and thus, away from a manual antenna match or pre-selector. Thus the feature request for software based L & C controls when listening out of the Ham Bands.   Call me lazy... 

the comet 250b is interesting but the 15 to 30db hit compared to a tuned dipole or vertical seems a little steep.

Anyway, on the flex tuner, if it is possible to read and write bytes that turn on and off relays to switch in and out inductors and capacitors so the flex hardware automatically memorizes it's prior tune and goes back to it when I change away to another band, tune, and then return, then just maybe the software can manually operate those relays with 2 sliders with values from 0 to 255.  If it's just feeding the tuning processor a frequency and the tuning processor pulls the value from dedicated memory that is inaccessible to anything else, then all bets are off. ( however, I'd bet the Flex folks are keen on diagnostic data and that the registers controlling the tuning relays can be read and manipulated)

Cheers!

Mystery Ham
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Reg

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Here is a little empirical data on the matter of the role of the tuner regarding received signals.  It was suggested that the tuner will make the signals stronger but it will not improve the signal to noise ratio (SNR).  I performed the following test with my FLEX-6700 using a 160 meter dipole antenna.

1.  I tuned to an inactive portion of the 31 meter band and observed the band noise as -97.1 dBm.

2.  I tuned to a nearby AM broadcast station (6.089,700 MHz) and observed the signal amplitude at -70.1 dBm.

I then switched the antenna output of the FLEX-6700 to a Palstar DL2K dummy load and transmitted with a power of 10 Watts while invoking the internal tuner in the FLEX-6700.*  At this point the FLEX-6700 had performed a "successful" tune at that frequency.

3.  I again measured the inactive portion of the 31 meter band and observed that after "tuning" the band noise was -82.4 dBm.  The noise floor had risen by approximately 8.8 dB.

4.  I tuned to the same nearby AM broadcast station (6.089,700 MHz) and observed the signal amplitude at -61.3 dBm.  The signal strength of the subject broadcast station had increased by 21.1 dB.

Now we do the SNR calculations and we find that they are essentially identical.  It would appear that using a tuner makes the noise floor and the subject signal stronger but the SNR remains about the same.

Reg

* As a MARS member I have an unlocked FLEX-6700 so I can transmit on 6.089,700.  I did not transmit on the air using an antenna.  I transmitted into the above specified dummy load.  Given that I didn't transmit into the receive antenna the match wasn't perfect but it was certainly on frequency.
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Mystery Ham

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Reg,

I appreciate your initiative in actually doing some experimenting!

I have some suggestions that may improve the testing methodology and, perhaps, provide some intriguing results.

I’m going to use a term, receive system, that represents the combination of your radio, coax, antenna any other connected device in the signal chain to hopefully avoid confusion.

Consider the following:

If there is a signal that is 5db above the combination of background and local noise on the band, yet, that signal on a mismatched antenna is lost below the noise floor of the receive system, matching that antenna to your receive system may bring that signal up above the noise floor of the receive system.  Empirically, on occasion due to quiet band conditions, this has been my experience when operating outdoors away from noise sources.  Yes, I could switch in a preamp in this case, but I would be adding in the noise figure of the preamp into the mix and potentially reduce the signal to noise ratio.

Many have accurately observed that matching an antenna increased the background noise equally with the signal and the signal to noise ratio stayed the same.  The only fault in the test was that the background noise was already above the noise floor of the receive system. 

Fortunately, there is a way to simulate quiet band conditions when you don’t have them.  (I repeat... this is only a simulation...)   Requires an attenuator: MFJ makes one with SO-239 adapters that works from 1db to 81db in 1db steps, however you don't want to transmit with it in line.

Start with an antenna that requires matching in a band near a very strong signal. 40m may be ideal for this test because Americans can transmit in the regions otherwise reserved for shortwave broadcasters.  Verify the tuner is in bypass (also verify the preamp is off).  Then add attenuators until the noise floor stops dropping (the receiver's noise floor has been found) then add another 10db to 15db of attenuation.  Take a measurement of the strong signal compared to the noise floor.  Manually tune without transmitting for best signal (or remove attenuators, tune and replace them.)  Now measure again...  What did the signal do compared to the noise?

Some may ask “why not use a preamp then?"  A preamp could be used, and the preamp's noise figure would be added to the receiver's noise figure.  The signal path through the tuner is passive and thus much less noise is added.

Not everyone has quiet band conditions where they live for working weak signals near the noise floor of their receive system. So, the concept of matching an antenna to improve reception, or using a preamp for that matter, may not apply in their experience and unfortunately may be met with skepticism. 

Given the aforementioned skepticism, the concept of allowing manual adjustments of L & C in the tuner remotely from SmartSDR, may seem just as insane as the concept of adding preamp hardware to a flex radio and having the ability to turn it on and off remotely from SmartSDR.  ;-)

Cheers,
Mystery Ham
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Paul

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Although I don't do any out of band listening any more I can appreciate how the OP and other SWL's could benefit from his idea.

I have a couple of comments based on some of the previous replies:

1) not trying to be pedantic, but the role of the ATU is to match the impedance of the radio to that of the antenna system to maximise the power transfered from or into the radio - it's actually an AMU. It *can* therefore be advantageous on receive as well as transmit.

2) an AMU will try to work regardless of the type of antenna. Eg. I use a full wave topband wire loop (not a pixel or other mag loop). This is resonant on all harmonically related bands from top band to 10m. However, the impedance at resonance is very different on each band. My AT1000 pro ii matches any of these different impedances as close to 50 ohms as possible, after which the system is good on both transmit and receive for that band. Change band and there is a mismatch, the AMU must then be adjusted again - either automatically by transmitting a carrier briefly. Or manually, by altering the controls. Currently you *can't * do the latter if you're not in the shack, hence the OP's suggestion.

3) Transmitting into a dummy load will simply change the AMU settings from wherever they were previously to a position that delivers max power into a purely resitive load. Subsequently carrying out a test with an actual antenna without re-matching is therefore meaningless.

4) obtaining a match will indeed increase the received noise level as well as that of the signal. Eg: a weak signal may not be copiable with or without noise mitigation. Match the antenna system and that same signal may be increased enough for the rx to detect it and then noise mitigation could give a copiable signal.

There is comprehensive treatment of the associated theory at:

https://www.ieee.li/pdf/viewgraphs_mohr_noise.pdf

(Skip to slides 24 and 35 if you want the bottom line)

I think it's unfortunate that this idea seemed to provoke antagonism from some - it's a perfectly reasonable suggestion regardless of whether or not it's implemented.
(Edited)
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Mystery Ham

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Paul,

I had never considered the following quote from slide 24...

"The optimum source impedance for components is not always the same as required for maximum gain, and so there will be an “optimum input mismatch” –In such cases, although the operational available output signal is reduced, the available output noise is reduced proportionally more"

It provides some interesting insight regarding building a receiver, and, If I understand it correctly, a slight mismatch, presumably in the right direction, may help to differentiate signal from noise, though I also understand it to be noise within the receiving hardware itself not the background noise on the band.

But it does bring up a point that I think I have failed to make and of which many people appear to be unaware: Tuning (matching) for receiving will only help if there is a signal near the noise floor of the receiver, not near the background noise. 

Thanks for your thoughts and observations

Cheers,
Mystery Ham
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Rory - N6OIL

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Hi MH,
I just heard Joel Hallas give a good talk at the end of his podcast "The Doctor is In" This episode they talked about SDR's and at the Q/A section someone asked about antennas.
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Mystery Ham

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Thanks for the info...  A internet search a few hours ago took me to the ARRL site, but the podcast hadn't yet been posted.  I'll check later.
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Bob G W1GLV

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Per Part 97 you are not allowed any RF outside the Amateur Radio bands. Manufacturers are disallowed from providing a means to do this.
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Mystery Ham

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Bob and Paul,

That is correct, no transmitting required.  Only manual adjustments of L & C via SmartSDR software.

And I believe only one country has a Part 97 rule (law?)   ;-)   Though, I'm confident many countries have something similar but with a different set of requirements.

Though, let me pose a question...  Does that mean an analyzer cannot legally be used in America because it doesn't automatically turn off when you reach the band edges while it's connected to devices or components such as antennas that are designed for frequencies covered by Part 97?

Mystery Ham
(Edited)
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G8ZPX

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Bob, There is a whole world beyond the North American border where the FCC has no remit.
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Mystery Ham

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Steve,

There's also a significant portion of North America where the FCC has no remit, to  which I'm sure VE and XE hams will attest.  :-)

73
Mystery Ham
(Edited)
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Bob G W1GLV

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The IARU does come into the picture here also. I'm sure they don't want you to spill RF all over the place to satisfy your listening pleasure. There are rules and there are rule breakers.
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Paul

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Hi Bob, as I understood it, the original idea was to include new controls in SSDR to enable manual adjustment of the ATU. This would provide a means for SWL's to legally match their antennas anywhere without RF being emitted. No doubt Mystery Ham will correct me I'm wrong.
(Edited)
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Bob G W1GLV

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Maybe I misinterpreted the original comment, for that I'm sorry.
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Mystery Ham

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You're certainly not alone in thinking the suggestion meant transmitting out of band, Bob.

Among the interesting things happening on this thread is that hams who have become accustomed to tuning while transmitting are being reminded of the days of first tuning for maximum noise floor to get close and then transmit for final adjustments.

It's that first step that is helpful for listening out of the amateur bands, especially if the band's noise floor is otherwise below the receive system's noise floor.

Cheers
Mystery Ham
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Jay -- N0FB, Elmer

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The solution might be to go out and buy a manual tuner with the ability to bypass the tuning circuit at will.  That way when you do your antenna matching for the wavelength you are listening to without the need for transmitting to gain a match.  

I'm not aware of any current transceiver with an internal tuner which provides manual L & C controls.   Nice idea, but not a priority in my book.
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Mystery Ham

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Jay,

Flex has done an amazing job providing a well thought-out path to allowing separation of the operator from the shack with the Signature Series products. It seems much effort has been taken to do as much processing work as possible in the Flex hardware to minimize network bandwidth requirements to provide the opportunity for the operator to work as many as 8 receivers in the comfy chair across the shack from the radio, in the comfy house across the garden from the shack, as well as in the comfy Tahitian bungalow across the world from the house, (provided 35 or so Mb/s bandwidth, otherwise you may be limited to 4 or 2 receivers)

So, I'm glad that you think the ability to remotely adjust inductance and capacitance in the internal Antenna Match Unit using software sliders from SSDR is a nice idea.  Because this idea allows those folks who, in the addition to the radio amateur bands, monitor the bands in between and have a need or desire to provide a better antenna match to the radio(without transmitting) to attempt get that weak signal another 5 to 10dB above the receive system's, not the frequency band's, noise floor.  And this idea keeps those operators in their comfy chair, comfy house, or comfy Tahitian bungalow, rather than trekking a well-worn path back to the shack. 

Preamp, you say?  Save that for when the signal is 10 to 20dB below the receive systems noise floor.  An LC circuit's noise figure is much lower than a preamp's noise figure.

So, if the S-Meter only sees S0 when the radio is turned off or when the antenna has been disconnected, and if the only place to operate SSDR is within arms reach of an Antenna Match Unit, I fully understand your "not a priority" position... Otherwise, I would be curious to know your thoughts.

73,
Mystery Ham
 
(Edited)
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Walt

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For those worried about radiating energy on other-than the ham bands, you may refer to your 'FCC' regulations, that usually have a 'Part 15' and look up the rules of incidental radiators.

All the signal levels, measurement techniques and allowable permissions are defined with ways to calculate them are there, printed up for everyone to read.

Time to put your ham license to use and get your calculators out to see if that 1 milliwatt (or whatever your noise bridge level is) at the antenna will exceed the rules.  In whatever country your in.

And then decide if you can use the noise device with a clear conscience.

And then have a pint !
(Edited)
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Paul

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Or better still, a few pints first to help put the regulations into perspective. Then continue using the bridge until someone alleges you're causing "undue interference" with it.


Cheers ;)