Finding Your Best Crystal Radio 'DX Diode' (Part 2)

Readers may recall my summertime blog, "Finding Your Best Crystal Radio ‘DX Diode'". It described a theoretical method I tried in order to see which of several dozen diodes might emerge as the best of the show, or in crystal radio DX circles, the ‘Holy Grail Diode’!

The grading system revolved around the combination of several factors … the diode’s measured forward-voltage (Vf), the weakest signal level detectable from an RF oscillator (whose level could be varied) and the diode's current when detecting a fixed-level signal on 1220 kHz. These values were used to derive a numerical ranking that I called ‘Vdx’, which would hopefully rank the best overall performers!

It’s not unreasonable to think that diodes with a very low forward voltage (Vf) combined with the ability to detect the weakest signal from the signal generator, might likely be the best diodes in the bunch … or are they?

These tests capacitively-coupled the oscillator signal directly into the crystal radio’s antenna tuner, which then coupled them into the detector stage. Using the methodology described in the earlier blog, the 48 diodes under review were narrowed to the ‘top 10’ likeliest best performers.

This time, actual ‘on-the-air’ signals would be used to compare diodes against each other in real time. A closer look at the top candidate diodes was made over several days and evenings as the days grew shorter and darkness arrived earlier.

My DX set has provisions for comparing a current good performing diode against two others.

 

In this arrangement, shown above, the current ‘best diode’ is mounted in the center switch position so that an immediate comparison can be made between it and the other two in real time.

A weak groundwave signal from Seattle, with a slow fade rate, was used initially but nighttime skywave signals were found to be most useful. Several  hours were spent tuned to 2800 watt CKBI in Prince Albert, Saskatchewan on 900 kHz. Their C&W format meant that most of the time they were broadcasting music, which I've found is always much easier for the ear-brain to detect in the noise floor than are spoken voices.

So what did I eventually find out? My original ranking methodology concluded that the best overall diode of the many dozens was the Sylvania JHS 1N3655A, a 40-year old microwave mixer diode.

The observations of the CKBI signal strength were by ear-brain only and no actual levels were measured since signal levels were usually too weak to measure on my detector's micro-ammeter. Measurements may yet be undertaken using an oscilloscope or by using an audio amplified output to compare signal voltage levels.

So … would my diode-ranking order and testing methodology hold up when actually using the diodes in a hi-end, low-loss crystal radio system when connected to an actual antenna?

I started ‘A-B’ comparisons against what has always been a reliably good performer mounted in the center position, a fairly modern twenty-year old  1N34A.

As noted above, the #1 rated diode (with my Vdx rating of 66) was the 1N3655A microwave mixer diode. Although it did not produce the loudest signal (diode current) compared with others, it had an exceptionally low Vf of .18V and its weak-signal detection level was good although not the lowest. Like a few others, it detected the nearby UHF data stream ‘clicks’ from a nearby Wi-Fi modem, often a characteristic of a good performer.

I was somewhat aghast when my #1 ranked 1N3655A was immediately outperformed by the modern 1N34A, ranked 44 out of 49! The 1N3655A was not just poorer than the 1N34A, it was very poor by comparison ... hmm ...was my selection process really that far off?

Diode #2, also with a low Vf of .197V was also poorer than the 1N34A, whose Vf was an unimpressive .375V.

And so it went for the most part, with my top 10 choices! Most of them were equal to the 1N34A but nothing stood out while listening to real on-air signals until I got to the three ‘curiosity’ diodes, originally tested at the very end.

The 38th-ranked Soviet-era D18, a military grade germanium in a glass ‘50s-style' package, was compared next. Earlier testing had shown it to produce a loud signal (higher current) but combined with its high Vf of .366V led to a low overall ranking.

Surprisingly, the D18 produced a noticeably better signal than the 1N34A and was moved into the #1 position.

Next up was the FO-215, often touted as the Holy Grail diode. It compared favorably with the D18 but was no better. Some have found that paralleling two FO-215s produced even better results but I did not find that to be the case.

                                                                                

The third diode was a very old Sylvania 1N34A from the 50s, possibly one of the earliest in production. It had an unimpressive Vf of .335V but did produce a loud signal in earlier testing. It detected the signal from Saskatchewan equal to or perhaps slightly better than the D18 … it was hard to say for sure. It was certainly no worse!

 

These last two were both made in the 50s … was there something different about the way they were made? Was the germanium different back then? How did they perform so well when their Vf was so high? It almost appears the opposite of what might be expected.

Seeing the above behaviour, I couldn’t pass up the chance of testing the 48th ranking diode, a beautiful black NOS Rogers 1N34A, probably another product of the 50s. Its Vf was truly discouraging, at .401V and the reason I had mostly ignored it in the past. It was put up against the D18.

 

I was astounded to find that not only was the vintage black beauty better than the D18, it was a LOT better! The ‘just barely’ detectable CKBI signal popped out of the noise to become one that was easy to hear! I had to rock the ‘A-B’ switch back and forth many times just to enjoy the big difference!

Out of curiosity, I tested the last-ranking diode (Vf of .444V) and it truly was deaf, with not even a sound emitting from the phones … so at least I got that one right!

What is obvious now is that the method I used to rank the diodes was flawed. These results have brought up several questions for me that I had never considered previously … far more questions than answers!

Takeaways? I've found that there's a lot about diodes that I don't know and need to learn about! I’ve learned that a diode’s Vf value is not an indicator of its weak-signal detection capability in crystal detectors (in spite of what some You Tube videos might try to convey). I've learned that when detecting a weak signal, the diode is operating below its Vf value which helps explain why a high Vf value does not mean a poor detector or a low Vf does not mean a good detector. Low Vf values were a well considered number when ranking my diodes … an apparent mistake.

Further to this, the diode is operating within its ‘square law region’ when detecting the weak signals we seek. When operating in this region, it means that increasing the input signal by 5 times (for example) will increase its output by 25 times. Similarly, decreasing the input level by 5 times will result in a 25 times drop in output. The importance of reducing as many losses as possible in the antenna tuning stage along with the detector stage itself can certainly pay fast dividends when it comes to weak signal detection. Conversely, ignoring system losses will very quickly reduce performance.

Also ignored in my system was diode capacitance, diode operating impedance, reverse leakage and no doubt some characteristics I'm not even aware of. Diodes with lower C will have fewer losses than those that are higher. I wonder how much of a factor was this in my overall unexpected results! The diode’s internal resistance when detecting a signal is a factor that I did not consider. The method of determining this value is complex but it may explain some of what I noticed.

There appears to be something different with older diodes that makes them great performers … larger junction? Germanium quality?

A final take away ... with enough knowledge, one can measure every tiny detail about a given diode without actually using it. No doubt a ranking list of diodes going through such rigorous scrutiny could zero-in on the top few. What's the BEST diode to use? It's probably the one that seems to work the best in your particular detector, until a better one comes along ... but it appears you can't go too far wrong with a very good 1N34A ... even in 2024!

 

The George Batterson 1935 QSO Party

VE3AWA - TPTG 210s

After the most recent running of the AWA’s Bruce Kelley 1929 QSO Party, a group of dedicated ‘29 enthusiasts and builders were hoping to see a second Spring edition to provide another opportunity to use these wonderful vintage designs on the air. They might sound pretty awful by today’s standards but for the average ham, these were considered state-of-art in 1929.

We approached the AWA regarding a second BK, but for a number of reasons, were turned down. All was not lost however, when Contest Coordinator, Joe Fell (W3GMS), suggested that we pursue a slightly different angle … something that would honor the third original AWA founder that had yet to have his memory honored in the form of a contest … the late George Batterson, W2GB

 

The three of us, Lou (VE3AWA), Gary (W8PU) and myself (VE7SL), immediately took Joe’s suggestion to heart and got busy building a contest!

 

The final details for the spring running of the George Batterson 1935 QSO Party can be found in the link below. It is an event similar to the BK but with a couple of exciting new opportunities … any tubes that were available before (and including) 1935 may now be used. 

 

53 / 6A6

Any commercial transmitters for the same time period may also be utilized. And unlike the BK, crystal controlled transmitters may also be used, something that was very popular in the 30’s.

1935 Style  53 20/15/10m Harmonic Power Oscillator

It is hoped as well, that the QSO Party will catch on quickly and encourage some new homebrewing activity among AWA members and others. With the flood of new tubes and circuit designs, the 30s was an exciting time to be a radio amateur!

The 1935 Radio Amateur's Handbook

For contest dates, rules, logsheets and other helpful links, CLICK HERE.

Please pass the word out (or the link to this blog) to fellow hams that might be interested ... start searching designs, warm-up those soldering irons and hit the workbench!

 

Hope to see you all in the “GB”.

YADD - Maritime HF Activity Revisited

Before the HF maritime CW bands were closed back in the ‘90s, I spent many enjoyable hours listening to ships and maritime coastal stations all over the world while they exchanged CW messages or sent position and weather reports using the old AMVER system. It was a constant delight to hear various ship Radio Officers (ROs) using their keyers, bugs and good old hand keys to demonstrate their unique fists to the world, especially when using the latter two! Fists ranged from simply superb to downright awful, making one wonder if the ship’s oiler had been enlisted to send the nightly traffic! It was particularly interesting to plot their positions, as many of the vessels eventually showed up in the Port of Vancouver, an easy drive to where I was living at the time.

 

I often mailed reception reports to ship ROs and had a few invitational ship tours when they arrived in town. I was always impressed with the ship’s radio shack as well as the vessel's onboard cleanliness. Most were truly spotless!

 

Several years ago I wrote a blog describing my use of YADD, [Yet Another DSC Decoder] a brilliant piece free software written by the late Dirk Classsens. At the time I had been unaware that there was still a huge amount of HF maritime activity and that every large commercial vessel involved in deep sea travel was still on the air after all these years!

 

A look back at the earlier blog will explain many of the important things you might want to know about YADD and how to use it.

 

I recently fired YADD up again last week to see what was being heard and what I might be missing during these high sunspot days of Solar Cycle 25.

 

Some of the interesting catches, to me at least, began with a 2135Z decode of ‘CQ2283’ the bulk carrier AGIOS GEORGIOS S calling another vessel on 12577.0 kHz.

 

At 41,000 tons and 225m, she's a big ship, earlier named the ICARUS

Flying under the flag of Portugal, she was bound for Kakinada, India, and almost at the antipode from my location

The AGIOS GEORGIOS S nears Kakinada, India, in the Bay of Bengal

Next was the container ship MOL CHARISMA, C6WN8, calling RCC Australia (Canberra), also on 12577.0 kHz.

 

MOL CHARISMA - 21,000 tons and 316m long

Registered in the Bahamas, the MOL CHARISMA was in the Aleutian Island chain
near Dutch Harbor, Alaska, bound for Prince Rupert, BC.

 

The general cargo vessel MAHO CORAL, 3FEP4 (Panamanian registry) was heard twice, calling the nearby oil tanker, ORIENT CHALLENGE, 9V5083 (Singapore registry) on 12577.0 kHz. A response was heard eight seconds after the second call.

 

The MAHO CORAL - 127m

The ORIENT CHALLENGE - 183m

I was surprised and delighted to see that the ship being called was right behind her and both were just around the corner from me in Boundary Pass, heading for Vancouver!

 

About to enter BC's Gulf Islands enroute Vancouver

It was great to see the pair from my window about an hour later as they passed the Roberts Bank coal and container port. 

A switch to 16804.5 kHz found the CMA CGM MAUI calling the coastal station in Valencia, Spain.

 

 

CMA CGM MAUI, a true leviathan - 154,000 tons 366m length

At the time of my intercept, the French-registered CGM MAUI (FMYR) was off the southern tip of Italy, anchored at Valletta, Malta, in the Mediterranean Sea.

Next was the crude oil tanker YANNIS P, calling Guam Radio on 16MHz. After transiting the Suez Canal, she was in the Red Sea, bound for Singapore.

 

 

YANNIS P - 81,000 tons, 274m

Registered in the Marshall Islands (radio call V7A2246), the YANNIS P was hauling Russian oil from Ust-Luga to Singapore, a very long voyage! Her 0019Z transmission on 16804.5 kHz was made at 0319 local time in the Red Sea, demonstrating the great HF propagation to be had during these solar-peak years.

 

Shortly before my local sunset, I decided to drop down to the MF range for the evening and listen on 2187.5 kHz, not really expecting to hear too much. I was surprised to immediately see a decode from the BBC XINGANG (V2GC3), a 125m long general cargo ship registered in Barbados.

 

The BBC XINGANG was at anchor in the St. Lawrence River, not far from Montreal ... a surprising catch for 2 MHz as the sky was still bright here on the west coast.

An all-night listen produced several hundred ships, mostly calling each other, in all likelihood to comply with their mandatory daily DSC system test. Ship positions ranged from the US east coast, to the Gulf of Mexico and west into the Pacific. Only one coastal station of note was heard, that being the one on Kamchatka Island, Russia. As conditions improve, I plan to do more overnight listening on this frequency as there are numerous coastals in the Far East that make for challenging DX targets.

All of the signals logged to date have been heard on my Yaesu FT-1000mp and simple half-sloper wire antennas. Listening has been from the east shore of Mayne Island, BC, midway between Vancouver and Vancouver Island in the Strait of Georgia.

My home on Mayne is a wonderful location for radio as it is extremely quiet and located right on the ocean. My best direction favors the east while my poorest is to the west, due to Vancouver Island. The path to Asia has a good saltwater start but eventually runs into Vancouver Island and parts of the BC mainland before reaching the open ocean. 

As good as this spot is, it truly pales in comparison to that of fellow DXer, Walter Salmaniw, from Victoria. Walt also has a home in Haida Gwaii (Queen Charlotte Islands) located at the northern tip of the island.

Dream location!

From here, Walt has recently been listening on the DSC frequencies as well, using a 450' N-S unterminated (bi-directional) Beverage antenna next to the ocean. With nothing but saltwater for hundreds of miles, Walt's reception on all bands is truly mind-boggling. His 2 MHz overnight run, netted dozens of ships in Asia as well as coastals from the Far East! On 16 MHz, for every single ship that I was able to decode over-the-pole from the middle east, Walt would log a half dozen or more. When not in Haida Gwaii, Walt can listen remotely from his home in Victoria ... truly the best of both worlds! 

As mentioned earlier, some of my fondest radio memories were those times spent listening to HF maritime CW activity. Many 'prepared form cards' or PFCs were sent to the ships or coastal stations heard, with an amazingly high return rate. These prepared QSL cards left blank spots for the recipient (Radio Officer) to fill in. They were often returned along with several pages of handwritten letters.

The 'lakers' were very reliable QSLers

Laker STEWART J CORT

If you miss the maritime HF activity or want to collect some new maritime QSLs, the opportunity still exists ... but instead of sending a reception report in care of the ship's Radio Officer, it will now need to go to the ship's Electronics Officer (ETO) or to the Captain. Reports can be sent to the ship's company who will then forward them to an upcoming port of call.

There is an an active group of DSC maritime DXers in Groups.io DSC-List, where loggings are posted daily. The group also has several helpful files and guides that will be of interest to those getting started. 

One of the group members, GM4SLV, has set up a wonderful website called YaDDNet devoted to collecting and posting listener's decoded loggings in realtime. One of YADD's features is the ability to automatically upload decoded signals, similar to PSK Reporter. It's an easy 30-second job to configure YADD to upload your spots to the net. His site also contains the latest MMSI look-up file used by YADD which is updated in real time from the latest log postings ... presently at 72,626 vessels!

Clicking on any of the uploaded ship names displayed in the real time YaDDNet log, automatically takes you to an online vessel-tracking site which usually has a picture of the ship along with all of its information, including its present position.

If you set up YADD to do some listening, I'd strongly urge you to also set it up so that your decoded spots are uploaded to the YaDDNet page in real time. Your latest logs will also keep the MMSI database up-to-date for all YADD users worldwide.

Good luck with your maritime listening or QSLing. Who says there's nothing interesting to be found on shortwave radio anymore!

Finding Your Best Crystal Radio 'DX Diode' (Part 1)

Over the past few weeks I’ve had time to examine many dozens of diodes, mostly germanium, in my crystal radio diode collection. Many of them were removed from equipment built in the '50s and '60s (old diode matrix boards), some are vintage NIB 1N34As while others are modern SMD Schottky style diodes.

 

There are numerous excellent websites such as this one by Dick Kleijer or  SV3ORA's site  ... all describing elaborate ways to determine which diode is ‘the best one’ (the holy grail diode!) for crystal radio work. Most methods use a vigorous, somewhat complex test procedure plus a lot of math, most of which is well beyond my old brain, in attempts to flesh out each diode’s inherent characteristics ... as the sites referenced above illustrate, the simple appearance of a crystal diode belies its complexity and determining  diode behaviours can be more challenging than one might suspect.

My testing procedures were much more basic, and in the end, may hopefully reveal the best diode in my collection. I think one needs to undertake this with the understanding that there really is no overall ‘best' crystal radio diode but rather, only a diode that is best for your particular system and what works best in my system may not necessarily be the best one in yours.

 

My plan was to measure a few diode behaviors, shrink the list of candidates and then compare them against each other in my system's high-Q tank circuit.

 

My first step was to measure Vf or the forward voltage needed to ‘turn the diode on’. This can usually be determined to reasonable accuracy by using the diode test function on most digital multimeters. I’ve always supposed that the diode with the lowest Vf  turn-on threshold would probably be the most sensitive, but is it the only factor? Hopefully my tests would indicate if anything else is in play.

 

The next task was to determine the minimum signal level of a 1000 Hz modulated carrier on 1400 kHz that could be detected by each candidate diode. An RF probe was used to measure the level of signal capacitively coupled into my crystal radio’s antenna tuning stage which was then lightly coupled  into the detector stage, using the diode under test. No importance was given to the actual base level of this signal other than to note the level at which it could first be detected by ear (using sound powered phones) and making sure the coupling distance between stages remained the same for all diodes under test. This allowed me to compare weak-signal diode ‘sensitivity’ to the diode’s previously measured turn-on point or Vf value. Would the diode with the lowest Vf also be the most sensitive when used in a detector circuit composed of complex impedance, resistance, reactance and capacitance values that the test diode would be looking into?

 

The RF signal coupling was adjusted so the injected carrier could be varied between 0 and 10mV as measured on the RF probe. For each diode, the signal level was slowly increased from ‘0’ until the 1400kHz tone-modulated AM signal could first be detected.

 

The lowest 'first detected' signal level was .6mV while the highest level required 3.4mV, representing a pretty good range of diode behaviours. There were 49 different diodes in the test pool.

 

Four of the 49 diodes detected the .6mV signal, six detected the signal at .7mV, and nine first detected the signal at .8mV. The remainder required a still higher level of injected signal. The average level of first detection was 1.2 mV.

 

Of the four .6mV ‘best detectors’, their turn-on Vf values ranged from .15V to .38V while the .7mV and .8mV detectors had a Vf between .181V and .40V!

 

It seemed, not surprisingly, that generally the higher the Vf turn-on threshold, the greater was the level of signal injection needed for first detection … but evidently using the Vf value alone to determine the ‘best diode’ was not the hard axiom I had always assumed it to be!

 

Since a low Vf was not necessarily needed for good sensitivity, would there by any other tests that might indicate best performance?

 

The next trial was to measure actual diode currents in my hi-Q detector while receiving a lightly-coupled constant level input signal (1400kHz) to see how this value related to Vf. Measured diode currents (Id) varied from 9uA to 14uA for the same level of input signal, with the diode having the lowest Vf also producing the lowest current level ... hhhm! There was more to this than I expected, but generally, the lower valued Vf diodes tended to produce the most current and consequently the louder headphone signal … but not always! Some diodes with a Vf as high as .46V yielded high currents!

 

This now begged the question, “Does the higher current diode with a higher turn on (Vf) prove to be a better overall performer than the diode that turns-on early but produces a weaker signal?” What is the relationship between diode current and weak signal detection?

 

The next step was to express the relationship mathematically by calculating the ratio between the diode’s Vf and the level of diode current  (Id) measured in the previous test (Id / Vf). Each diode could then be assigned a number (Vdx) that might possibly indicate it’s true performance potential in my own system.

The diodes with the highest Vdx values would then be A-B tested under real receive conditions to see if any (or just one!) particular winner(s) might emerge … and if Vf was as critical as initially believed.

 

The Vdx values proved most interesting and seemed to account for some of the anomalies noted in earlier measurements with some of the higher Vdx values coming from diodes not necessarily with a low Vf. I’m hoping that this sorting concept properly takes into account both turn-on level (Vf) and current level (Id), since a higher level in either number will compensate for a lower level in the other. Vdx values ranged from 23 to 66, with seven diodes in the higher 53-66 range.

Click Image For Larger View

All of the 49 diode's test parameters were put onto a spreadsheet and listed in order of their Vdx value.

Click Image For Diode Spreadsheet Data

The highest Vdx assignment of 66 went to my 40-year junkbox resident, a JHS Sylvania 1N3655A microwave mixer diode. It will be interesting to see if it really is the best of the lot! Although it did not produce the loudest signal (Id) compared with others, its Vf turn-on was an impressive .181V and its weak-signal detection level was good although not the lowest. A couple of the UHF diodes exhibited the interesting behaviour of picking up the UHF data stream 'clicks' from my nearby wifi booster. The 1N3655A was one of them.

 

1N3655A Vf = .181V Id = 12uA Vdx = 66

   

Diode #2, with a Vdx of 62, is a mystery diode with a very low Vf of .197V. It was slightly louder and oddly enough, dug down slightly further than the 1N3655A, which had a slightly lower Vf. Although I don’t recall specifically, I suspect the diode may have been removed from a VCR front end many years ago.

 

Mystery diode  Vf =.197V  Id = 12.2uA Vdx = 62

 

Diode #3 with a Vdx of 61 is a modern SMS7630 Schottky microwave detector diode in an SMD package. Although it did not produce a competitive level of loudness (Id) in the diode current test, its shockingly low Vf turn-on of .147V and weak-signal detection threshold were the best of all diodes tested. Before testing, all SMD diodes were mounted on small PC boards in order to attach leads.

 

SMS7630 Schottky  Vf = .147V  Id = 9uA Vdx = 61

Diode #4 (Vdx of 60) is an ISS98, another modern Schottky microwave detector. I recall seeing this diode recommended for good performance in an FM crystal radio detector. Its sensitivity level was excellent.

 

ISS98 Schottky Vf = .211V  Id = 12.5uA Vdx = 60

Diode #5 (also with a Vdx of 60) appears to be a normal germanium of unknown type. I suspect it was used as an RF mixer since it was found on a small printed circuit board with three others, connected in a diode ring configuration typically seen in balanced RF mixers. It produced high current as well as good weak signal capability. 

 

Mystery diode Vf = .22  Id = 13.2uA Vdx = 60

Diode #6 (Vdx of 55) also looks like a germanium of unknown type with a body striping of gray-white-green-gray. If the last band is ignored, this could be a 1N895, a UHF germanium diode. It shows the typical internal cat-whisker type of junction often seen on the 1N34 germaniums.

 

Mystery diode Vf = .238V  Id = 13uA Vdx = 55

Diode #7 with a Vdx of 53 is marked as a ‘95481’ on a green body. It had excellent sensitivity and produced a strong signal (Id), elevating it to the top tier to be looked at more closely.

'95481'  Vf = .246V  Id = 13uA Vdx = 53

Diode #8, another germanium mystery, earned a Vdx of 49 due to its fairly high Id level.

Black 'T'. Vf = .258V  Id = 12.5uA  Vdx = 49

The rather beat-up looking Diode #9 is marked with what appear to be house numbers, '1846' and '6628'. I believe this was pulled from an old portable radio's FM section many years ago. Interestingly, like some of the UHF mixer diodes, '1846 / 6628' detects my high speed modem data stream clicks. Additionally, this tortured specimen produced the highest level of signal among all 49 diodes, with an Id of 14uA.

Vf = .294V  Vdx = 48 Vdx = 14 (Schottky?)

Diode #10 appears to be the brother of Diode #8 with a Vdx of 48. Although it has a lower turn-on point and was a better weak signal detector, it did not produce as much Id as its sibling, dropping it one notch lower on the list. Like its brother, it also has the mystery 'T' marking. Both are most likely unmarked 1N34As.

Vf = .252V  Id = 12 Vdx = 48

As well, three other diodes garnered my interest. Although they ranked lower than I expected, all had previously been found to be good detectors in my system. Their lower ranking may be a hint that my system of grading is not a valid method of determining best performance. All three will be given a harder look in the upcoming elimination tests.

The first is the germanium FO-215. Often touted as 'the holy grail' crystal radio diode but I have never found it to be particularly outstanding. Maybe my system has a lower Q than it really needs in order to show its stuff. This diode is shown on the bar graph above as #11. During testing, it appeared much less capable of weak signal detection than most others but its low Vf and high Id elevated its overall ranking.

Vf = .272V  Id = 13uA  Vdx = 48

The second diode is the Soviet-era D18, a military-grade germanium in a glass '50s-style package. I have previously found it to be a very good detector but its high turn-on level lowered its ranking. The D18 appears on the bar graph as #12.

Vf = .366V  Id = 12.2uA Vdx = 33

The third diode is a vintage Sylvania 1N34 from the 50s and likely one of the first 1N34s to be manufactured. Although it produces a loud signal, its Vf was higher than expected. As I recall, it was salvaged from an old parted-out Heathkit.  It appears on the bar graph as #13.

Vf = .335V  Id = 13uA  Vdx = 39

As mentioned earlier, one can measure and calculate a large amount of data for crystal diodes while they sit passively on the bench but they really need to be mounted, tested and compared in the actual system in which they will be used. Comparing diodes 'A-B' style in real time with weak signals may be better than any measurements made on a diode being bench-tested. 

Will a new ‘holy-grail’ emerge from the pile? This type of testing requires a lot of careful listening so time will tell. 

Testing will be ongoing over the summer / fall months ... stay tuned for the final results, hopefully in time for the fall DX season!