Feb 16, 2013
The following was shown at my NCDXF Beacon Monitor at my home:
The above "silence gap" exists from 12:00 -13:15 UTC
Checking other monitoring stations shows there is no proof for any correlation with the meteor hit. There must have been a different reason, perhaps local disturbance?
Feb 7, 2013
Weak Signal Audio 160m, a new projectWhen searching for progression, sometimes there is a need to look at matters from a totally different perspective.
Why discuss the use of headphones?
List of headphones under test
Comparison test conditions
The listening test
- Weak signal alone in the band noise
- Weak signal close to a loud signal
- How easy/difficult is it to pick and decode a weak CW signal?
- Which is offering you a better reading resolution while tuning the band?
- What other audible effects, good or bad are noticed?
Noise cancellation headphones
And some final remarks
Feb 29, 2012
The ability, to delete all directions but one, is put in two figures of merit; MDF and RDF(refer ON4UN’s book). In short, a kind of horsepower if you will, to distinguish the good from the better receiving antennas. And just because humanoids simply must quantify everything.
I refuse to go in detail about RDF and MDF, because they represent computer models from antenna modeling programs, which by principle, cannot handle close to ground antennas, or more specifically, cannot handle real ground at all. Until someone takes a helicopter and runs zillions of circles at different heights around a lowband receiving antenna, measuring its pattern, I rather use my ears instead.
And then again; what elevation angle is required at which moment? Too many parameters. Better have a few antennas more at your hand!
|Setting up station @PI4TUE|
The lowband receiving antenna is a whole lot different from multi-element VHF yagis, where forward gain is simply the most important figure of merit.
But, there is also a common factor between them; the “better” the antenna, the smaller the forward lobe in degrees azimuth/elevation. Where “better” has a total different interpretation; the VHF yagi needs the small lobe to collect all tiny weak signal particles from the dx and to a lesser extent, avoid signals from the side and rear. Lowband receiving antennas mainly concentrate on deleting signals from all unwanted directions and to a lesser extent collect the weak signal from that direction which remains.
Antenna computer models?
I shit on virtual, calculated dB’s.
In the end it all boils down to achieve a S/N ratio where you can make the QSO yes or no.
There’s no free lunch.
A decent lowband receiving antenna (like multi phase staggered beverages) requires real estate and/or extensive hardware and trimming (6-9 Circle). A physical shortcut like Flag/Pennants/K9AY/EWE, or even the BOG is a choice mainly based on the will to put up any RX antenna to receive at least something. Some work better than others, depending on the environment. And then there is man made noise for which vertical polarized antennas seem more sensitive. Or is it not?
You need to experiment and find what works best for you.
On a site note; even a short vertical, suppresses high angle signals thanks to its theoretical doughnut shaped pattern And being less susceptible to local noise because of its short length, this IS a valid dx receiving antenna. The total opposite is a short backyard NVIS covering high angles only. Here you have it; two RX antennas which fit even the smallest gardens!
Need proof? Find my result in 2012 CQ160 CW Low Power
During last week’s ARRL DX CW contest weekend at our PI4TUE club-station, we (again) were in desperate need of a working RX antenna and had little time to install it in the usual public space.
The PI4TUE station is located in a building at the Eindhoven University of Technology.
It’s nice to have antennas at 70m above street level, but the local noise level is very high. Let me emphasize that again; for the lowbands extremely high!
Both on the roof and on ground level (up to a distance of 150m from the buildings), we have experimented for some 10 years with the following receiving antennas: K9AY, KAZ Delta RX(only on roof), magnetic loop (s), short tuned verticals ... etc. All including extensive common mode filtering.
Nothing ever offered any S/N advantage compared to the available TX antennas; full size 40m dipole and vertical @65m, full wave 80m loop @73m and two full size 160m 0.25 slopers @63m.
Because of limited available real estate, beverages have not been tried thus far. Also, there are some large rusted fences along the property perimeters.
But Topbanders never give up. So this year it was time to try a BOG.
On a piece of lawn, facing the USA, 8 plastic fence posts were put in the grass. A 70mtr (max available space) long 0.5mm dia insulated stranded copper wire was linked on the bottom of the posts. At both sides a copper pipe was hammered 1 m deep into the ground, hoping NOT to meet any local wiring. KFC! From our shack at the 13th floor, 150m 75Ohm SAT coax + another 50m RG58, across several roofs, cross-overs between buildings (which required informing security, asking them NOT to shoot us from the roof) was used to connect to our BOG through a 1:4 transformer on a BN73-202 binocular. There were no 50/75 transformers installed. This was never tried before, not permanent and we had about 3 hours available.
On average, the antenna wire was at a height of 3 to 12 cm across the lawn.
Why not directly on the ground? Well, according to theory, directly on the ground should have an electrical "lengthening" effect (which is wanted). But on higher bands (40m) such can introduce a direction reversing effect (not wanted). Also, flat on the ground the signal is supposed to drop several dozen of dB’s. Well, theory is one thing, and often ensures that we hopelessly remain staring at computer models.
Instead of debating, better start building the darn thing!
Since we really needed *any working* receiving antenna on 160/80/40 and there was no time for experimenting anyhow, the wire was deliberately hung 2 inches directly above the ground.
Termination at start was 390 ohms, and later changed to 195 until the analyzer measured a flat SWR curve up to 10 MHz.
At the TRX end a HD version common mode filter was connected: 17 turns of RG174 on a #77 ring core, followed by a galvanic separation using 2x2 turns on two BN73-202 binoculars, with the secondary separately routed in Teflon tubes. Over the top? Yes, maybe, but since all our previous effort only offered noise and I use this kind of filter successfully at home.
On Friday afternoon, around 17UTC a quick check at BCB frequencies well known to us (1584, 4015, 6995 etc) all clearly showed F/B and F/S performance, which was promising!
|"You sure you don't hit anything ??"|
|Blue wire near ground IS our BOG|
Those of you who participated, know this was a weekend with some of the worst lowband condx for years. Even more reason to have any decent RX antenna available.
In the contest, our antenna was a success!
None of the 20 worked USA mults on 160m, delivered by the BOG, could be heard on the full size TX sloper antenna. On 80m this was the best receiving antenna ever. From a quiet S1 background noise, stations appeared out of nowhere with S1 - S5. Again, most of them were no QSO or just not there on the TX full wave 80m horizontal loop @73mtr AGL. On 40m about 30% was better than the quarter wave TX vertical at 65m height. In most cases the S/N was better not only because of the lack of constant cracking noise from the TX vertical.
Why did we succeed this time? Because the BOG is only active in the horizontal plane, the local man made noise is perhaps largely ignored? That is supposed to be a myth. So I rather stick to the remaining fact that on a specific lawn on which several other types of RX antennas have been tried, this one did work FB.
We do have experience with different kinds of 200-300m phase staggered Beverage antennas on (large) outdoor terrain for many years. Any kind of BOG is a poor performer in comparison.
But this thing sure has potential at (small) residential areas.
No hallelujah yet. We will soon make some additional attempts out on the free field, before moving it along the property of our neighbors.
The internet offers very little data on the BOG.
73 Mark, PA5MW (PI4TUE)
Mar 11, 2011
After having moved, a couple of years ago, I wanted to launch my 160m activities at this new QTH. But the list of opportunities was quickly overtaken by the local challenges. The few attempts were marred either by public exposure (neighbors included), safety issues (see nov 1 2009)and lack of real estate. Next, work and other activities shifted priorities such that I kept stuck at the stage of computer aided antenna modeling.
I had to lower my ambitions as advancing plans to the next season again and again, did not get me anywhere and certainly not the pleasure of simply making QSO's on Topband.
The stealth Topband Antenna
An unobtrusive wire up in the air as high as possible, plus a few radials on the ground resembling some sort of basic Groundplane Antenna are my major goals.
I already tried getting different wires up a large tree, but the launching velocity power of my legal sling shot wasn't sufficient.
A friend offered help by supplying a special tinned copper wire having teflon isolation. At only 0.2mm diameter this stuff is both unobtrusive and extremely light.
With help of the slingshot it is quickly launched in a large tree using a 40g weight at the end.
It's the white wire, routed along branches of a small dead tree in the back garden. The horizontal wire is a short wideband horizontal antenna.
From here it goes upwards to a large tree some 15m away, ending at a height of >22m and then some length horizontal tangled up in the branches. In total I guess, about 26mtrs. Unimportant really, since there are plenty of opportunities to match it on 160m.
A copper ground rod and some 6 attached radials varying from 6 to 9mtr (20-30ft) in length are covering the west-to-northwest quadrant. Minor detail; since the vertical wire rises up in the southeast direction, none of these few radials cover the area under this sloped GP.
The white box is a True Balance type remote controlled ATU, which was not used for 7 years already. Together with some common mode supressor #31 FT240 ferrite core and already available coax from earlier experiments, I'm connected.
The final picture already shows the current situation where I have added another 10 radials in this small quadrant. The Yagi is my next priority for the summers Es season on 6m. And yes, that door in the upper right does need some maintenance attention.
So how does it play, QSO-wise?
Let's summarize this: a lossy 0.2mm dia wire, an even less-than-poor man's RF ground, a quick&dirty matching unit and 100W input power for that 'Sloped 160m GP'. Good points: it's at least 1/8 wave up and free in the air.
Within the hour I work stations on Topband within a 2000 km range including an UA2, but some later an Asian UA9.
The next morning at 05:54 UTC I work Dave, W5UN. Wow! Was that perhaps a special moment of extraordinary propagation? Later that evening I meet and work another well known Magic Band operator UK9AA. Two more US stations from PA and TX are worked in the next few days. It's no magic, using only 100W this antenna exceeds my expectations.
In between I have added some 10 more radials in by tiny 8x7m backyard. It requires a different setting on the remote ATU.
Using my short RX vertical I can hear many of the active dx'ers and dx-peditions on 160m. Most have large pile ups and are gone before I can make the contact. That is fully acceptable; this must not be too easy right?
New continents are entered in my log soon; JA7NI and today FM5CD. Both take some time before they are able to dig out my puny Little Pistol signal. Slow speed and perseverance while riding the QSB waves proves successfully.
Now how cool is this ???
In the next weeks I will try to arrange:
- Replace the ATU for a Low loss matching unit using a Heavy Duty Coil
- Detune the TX antenna to lower (induced noise) coupling to my RX antennas
- Add a PTT controlled RX antenna sequencing
- Make more QSO's, have fun operating Topband
Sep 19, 2010
This model has just a few basic functions like 20 memories, a red emergency number button, an LCD showing the dialed number (no call ID recognition) and 3 selectable true analog ring-tones.
Installation process takes 1 single non-dramatic step: connecting your RJ11 cable. No batteries to install and charge 24hrs, no firmware upgrade, no operating system settings, no help desk and no on-line manual.
That long greyish thing on the left is your handset(wired connection!). As soon as you pick it up from the hook-switch you hear the analog line buzz. Not that digital created artificial sound image from the past, just the real thing.
No answering machine, mailbox, Call ID and/or hide call ID. Just the basics needed for a phone conversation between earthlings.
Feb 24, 2010
Last weekend I participated at our club station PI4TUE.
This is the University of Technology Eindhoven's contest call.
Class: M/S HP
Operators: ON9CC, PC5A, PE2HD, PA5MW
Band QSOs Mults
160: 83 29
80: 261 42
40: 866 55
20: 999 59
15: 933 58
Total: 3142 243 Total Score = 2,290,518
Club affiliation: Bavarian Contest Club
Antennas: 160m sloper@220ft (RX: 5ft vertical@200ft), 80m full size horizontal
loop@220ft, 40m 1/4 GP @200ft, 20-10m 3el SteppIR
Rig: Ten-Tec ORION
Power: 400w from Acom 1000
Wow! This was big fun. Some of us love this contest even more than CQWW.
Finally we made some substantial progress compared to our past entries; at 1000 QSO's extra this year we have moved from the back end to the middle(ish). Watch out for us next year !
What went very well?
This time I'm well prepared by taking a few days off before and after the contest. Being well rested and refraining from doing the *last minute job* I am fully motivated.
Looking fresh during the final hours...... :)))
The new 3el SteppIR is a big improvement over the 15yrs old 3el compromise trapped(read: noisy) yagi. Next the 80m dipole at 220ft was replaced by a full size 80m horizontal loop at 200ft along the roof perimeter of the building (thanks to PA3DSC, PA0IB, PE2HD and PA3FGA).
But there is room for improvement for the RX antennas on 40-160m.
The HF2V mainly used for 40m
80m horizontal loop along the top perimeter. SteppIR 3el yagi. 160m sloper at the right end-corner
The ORION's user ergonomics offered its merits to all operators. Especially the setup for audio (main=both ears, sub RX =right only) and the volume knobs (toggle for audio on/off) was much appreciated for operating RUN/S&P between main and sub receiver with help of N1MM contesting software; Single Band SO2R in one box so to speak.
The station has no true SO2R capabilities. Another challenge for the future.
Second operator position....... not really.
All operators were sharp from start till end. We strained for the best (band) strategy and our senior contest op successfully taught us additional tricks on the fly.
Operator Aurelio, PC5A looking sharp during sunday afternoon
Food, coffee, sleep, etc.
There was plenty of it all and the couches in the 'lounge' were comfortable for a quick nap.
What went not so well?
Pin 1 issues
We use some 5 pc's, various audio routing, external equipment and zillion connections for different set-ups in the shack. During the contest our headphones showed all kinds of strange varying noises, rattles and hum. The room houses another 30-40 pcs, several HF/VHF/UHF transceivers and other equipment. Definitely a challenge for the future.
Very likely related to the above; WinKey locked up the N1MM program.
The ORION needed 4 power cycles (3 for no RX and 1 for no TX).
All in all a very memorable contest.
Thanks to Martin PA3DSC and Steef PA0IB for maintaining a great club station.
See you in the phone contest.
73 Mark, PA5MW
Feb 20, 2010
I recently ordered this from Cross Country Wireless and received this the other day.
There is a couple of reasons in no particular order:
- Release any front-end(pre-amp) from strong out of band signals, thereby avoiding possible IM from local FM broadcast etc.
- Avoid total blocking of 144Mhz while transmitting on 50Mhz
The Cross Country Wireless offers bandpass filters for 50, 70 and 144 Mhz. They handle 100W RF power and contain a built-in lightning surge arrestor as well. High voltage spike protection too; nice !
The bandpass filter comes with a filter test certificate, detailing RF and VSWR performance.
Final question: "will it result in more QSO's yes/no?"
Let's evaluate that in a few months.
For now I have to catch my next shift in the ARRL DX CW contest at our clubstation PI4TUE.
Have fun guys!
Feb 10, 2010
Feb 2, 2010
My favourite contest.
These last few years I have hardly had time to participate seriously from anywhere.
There's never been any time to prepare myself correctly (make that: I never took the opportunity..etc). Haven't built any decent station after my move to this new QTH. Not even the smallest 160m TX antenna. Not even a low dipole.
I do argue with others about which rig to buy or how to optimize for best performance on 160m, but have not made a single 160 QSO from this city lot yet. Go figure.
Last year there was this great QST article on the 160m No excuses homebrew vertical from John Miller, K6MM. I tried to build my version of a backyard vertical, but the neighbours strongly opposed to its physical exposure. And so it ended.
Even worse preparation for 2010
Now work goes before hobby and you better plan things ahead. Taking some days off is a good start. Arriving home at 01:15 AM after ploughing 150km through heavy snowfall, an earlier delayed flight, on a thursday morning and then try to catch-up the 'normal work' on the two left days of the week, is not a good start.
On saturday morning I awake early and monitor the progress of our club station PI4TUE in the CQWW 160m CW contest. They have a great TX antenna, using full size slopers from some 70mtrs(220ft) AGL. But they totally lack any RX antenna. Local environmental noise is such high that all past field experiments failed. It is frustrating to hear them miss all dx I can easily hear on my backyard small 160m RX reference vertical
I arrive at PI4TUE in the afternoon and take my shift from 15:00 till 18:00 UTC. After that I'm completely exhausted, cannot even stay to support the others and head home for a 12 hour sleep.
Sunday isn't any better so I go out for a 3 hour walk to catch some energy again.
Dink, N7WA offers a great service via the 3830 list and it's great fun to read the sopabox comments.
I'm flabbergasted by some of the low power/long wire entries; one European OM making 512 QSO's, 8 states and 52 countries using 5W and a 42mtr longwire ....
Waiting & debating for the new & better station set-up can be an endless frustration.
Next time I will throw out some wire in a nearby tree, connect a tuner and use 100W, just for the weekend. And operate from my own shack, just having fun.
And have my own decent cappuccino
Dec 30, 2009
All rigs have been tested at 14 and 28.4Mhz and other adjacent frequencies to rule out bandfilter anomalies.
Pre-amps,RF gain, AGC and other possible settings which would affect the results have been optimised every time. During each measurement a verification was done with the reference K2 to rule out potential errors as much as possible. Many measurements, especially the hearing tests, were done by two persons.
The found ENB (Effective Noise Bandwidth, column H) allows for comparing apples to apples when talking filter bandwidth.
The filter curves were taken from the audio output using Spectrogram. The Elecraft Wide Band Noise Generator module was used to create a constant signal of about S2-S4.
Both column N and R are key in the evaluation of the measured results and hearing results on 144MHz.
Note:the measurement in column Q is totally different from the rest, where both the RF generator and transverter are using in- and outdoor-antennas:
As such there is a true radio spectrum in between as media. A real life performance test so to speak. Column Q represents the set RF output of the generator at which the MDS recognition threshold by human ear was found.
As mentioned before; I'm testing 28Mhz weak signal performance on a quiet band using a transverter, that is totally different from lowband and/or contest use
What really matters is about making that extra QSO yes/no.
Frankly this rig was only tested during the preliminary test 'Method 1'; it is currently in use as an NCDXF HF beacon tracking receiver. The 570SG has the Inrad 400Hz CW filter and a temperature stabiliser for the LO crystal. Its internal DSP is an early 16 bit version; OK at 200Hz and above, but heavy ringing below.
28Mhz sensitivity is, next to the icom 7400, tops. However, for serious weak signal reception connected to a VHF transverter, this rig (and another 570DG) showed its weaknesses; the sound is rough, noisy and it just does not bring out the real weak ones. Is this due to its published high phase noise? Can't tell cause I have nothing to prove that. The
This rig also has a 400Hz CW filter from Inrad. It's owner installed Individual Inrad filters for both IF stages, but previous experiences showed there is too much attenuation caused by bad internal gain distribution. Only the 400Hz in the 2nd IF was used as well as the original 2400Hz in the 3rd 455KHz IF stage. The additional AF CW peaking filters do work very well, but so does the free extra AF background noise. On 144 MHz its own internal VHF front end was used. In total it lacked some 5 dB in performance. When owning such a rig I would use an external preamp and bypass the internal.
The '746 Pro version' showed the best sensitivity on 28Mhz. Using its internal VHF front end, it does hold its own listening to carriers down in the noise (test method 1). But when trying to copy real CW signals the DSP offers a very rough sound and is ringing already from 200Hz and lower. I tried getting a better S/N result by adjusting its internal IF gain setting (input to the DSP unit), but apart from the gain difference in AF volume it did not offer any better result in the measurements, nor during the hearing results.
DSP filter curves at 300Hz and 200Hz settings
Please notice there 'brickstone' sharp shapes.
I have had another 7400 several years ago and used it intensively on 144MHz SSB and CW. The sound was very harsh and annoying over time. Then came the first K2 and a DEM 144/28 transverter; what a sonic relief!
Next, from the AB4OJ's Icom website I tried the following trick: choose a filter setting >500Hz and then reduce the bandwidth by offsetting the twin PBT controls. The final result is a 50Hz filter with a very bad shape factor, totally failing in selectivity but the sound is next to noisy much more mellow.
In practise this 50Hz 'low quality filter' offered the best results for the IC7400. Only feasible on a very quiet band. Maybe this will help me on my 50MHz set-up next season.
This is not your typical rig where you turn the VFO knob and quickly use some dials & knobs to make a QSO. It is more a tool to monitor single frequencies or a whole frequency band and make that visual. But it does this very well. This high potential receiver has many capabilities (visual and audio) and has phase noise at such a low level(-140dBc @ 2KHz, -150dBc@10KHz), only seen at scientific equipment.
It offered the lowest measured result at 28MHz sensitivity. Due to its internal latency, a true S/N measurement using the Marconi analyser was not possible.
Interesting fact is that despite lacking 6dB at the bench test(column P), it does perform well during a real life hearing test, using an outdoor antenna (column Q). Might this be related to its extremely low phase noise?
Perseus at 416Hz and 202Hz settings
From this 141Hz setting and lower the ringing becomes worse; I mean ok for monitor carriers but incapable of decoding weak signal CW transmissions.
Elecraft K3 serial:173
We're in the upper class of this test now and the left differences are only minor. The K3 is third best at the bench test in column N. The final column R shows no result as the K3 was not available at that time. An 8-pole 400Hz roofing filter was installed. Interestingly, using the 250Hz roofer and tightening the DSP filter down from 250 to 50Hz the K3 showed a reverse result (worse S/N ratio) on the Marconi. Several actions have been tried: internal IF gain setting, AGC and finally switching from FIR to IIR at 100Hz and 50HZ. The final one was the only setting to show another single dB improvement, but the ringing is awful and makes a weak signal QSO impossible. The K3 starts with slight ringing from 150Hz and down. From there it becomes worse whatever the settings.
K3 400Hz and 200Hz FIR filters
K3 100Hz FIR and 100Hz IIR, please note that the IIR filter actually is wider.
This was also noted at the chapter FIR versus IIR filters at Clifton Laboratories.
50Hz FIR and 50Hz IIR; being a better 'peaking filter' the latter one did show minor improved measurement results.
Officially, any result difference within 3 dB should be considered "measurement deviations". But the differences are clearly there every day and remain when doing the test at a different QTH. When switching from the Marconi analyser to the hearing test, these last few dB's are still very apparent. Even more the perceived sound quality. This is where the K3 differs from the last 3 below; it sounds to harsh for weak signal. I have put out some questions on mailing lists and contacted different K3 owners; no special setting(s) for weak signal listening on VHF and up were found. Both the original K3 owner and another 6M enthusiast reported the same perceived 'harshness' compared to what they are used to at analogue rigs.
I'm not satisfied yet and convinced that we were not able, to let the K3 show its full merits here. Based on its published specs and current results at major HF contest stations, I trust the K3 will be a killer during 6m/VHF contests. Elecraft is continuously offering substantial firmware upgrades and the K3 shows increasing potential. I still fancy one..
Elecraft K2 serial:3323 original
This is a B version. It is a K2 in original shape and aligned according the written procedure. The internal crystal filters have been set-up for 1000, 700, 400 and 200Hz bandwidth.
It also has the additional KAF2 audio peaking filter (270Hz and 100Hz). This reduces the out of band noise:
The second picture shows the wideband performance curve using both the 200Hz crystal filter as well as the AF2 100Hz audio filter switched in. Unfortunately this AF2 100Hz filter introduces slight audible ringing.
The measured reduced sensitivity at 28MHz compared to 14Mhz is a normal behaviour.
The K2 does have a relatively low phase noise but at 7Mhz. But like most contenders, not particular that good at higher frequencies like 28Mhz. Nevertheless its performance is superb; hey we're in analogue heaven now! The noise-free AF section of the K2 makes the volume control even act like an additional RF gain. The sound is sweet and offers plenty of details in the quiet background.
I have often used this rig for performance comparisons during the last 4 years and it has always been a close draw with the finalist below. The ORION had been modified by exchanging the 1000Hz crystal (roofing)filter for an Inrad 4-pole 600Hz. This special filter #762 was initiated on request of Bill Tippet, W4ZV as the original 500 and 300Hz filter upgrades created a worse IMD spec due to a distributed gain issue. This was solved in the later ORION II model.
During the sensitivity measurements it became very apparent that any RF gain setting above 92 was creating extra noise and upsetting the S/N measurement. I believe this is the reason why so many new users confirm so called noisy receiver behaviour. Setting the RF gain to an appropriate level is outside the general consumer perception. The manual does explain proper use of the RF gain, but for weak signal you are used to "dialing it up to the max". Thus I got results which are several dB's better than published elsewhere. But the verdict is in the hearing tests and the perceived audio performance. The ORION does very well in this area, being the best DSP rig in the test.
The above 200Hz and 100Hz DSP filter settings are 227Hz and 155Hz in reality.
Both filter curves represent a more analogue shape. Not the slightest ringing noted. Even the 100Hz DSP filter sounds as clean as possible. Perhaps this is due to different chosen DSP filter algorithms by Ten-Tec designers. It does offer the most analogue sound and shows great receiving performance; signals could still be detected deep down in its calm noise floor. What a relief for your ears.
Do not forget the PLL design offers an extremely low close-in phase noise, not matched by any other but the Perseus.
So far the ORION has offered me the best overall results in 22 years of Hamradio.
Elecraft K2 serial:2036 modified
In terms of options it is similar to the other K2. Several small upgrades have been done for boosting general performance. However the following modifications have been done over the years for optimisation on 28Mhz transverter use:
1. Pre-amp and AGC
The original preamp is a compromise in terms of system noise figure vs IMD performance. Changing its gain boosts its total system noise figure. More preamp gain involves a lower intercept point however.
See the Elecraft application note
2. 28MHz Band Filter
This is now peaked at 28.2 MHz
3. AF filter
The AF2 filter is changed from 100 to 140Hz. This small change reduces ringing completely.
The audio gain was slightly optimised by changing R9 to 12K.
Spectran was used to do the adjustment on the KAF2 board, which now peaked a few dB higher.
400Hz crystal +270 Hz audio filter. And 200Hz crystal +140Hz audio filter.
This modified K2 has proven its superiority during these tests. It also functioned as the reference rig during the tests. Switching back from any set-up to this little analogue wonder always immediately showed its advantage.
Best reception: modified K2
Best overall performer: ORION
Best alternative 'second receiver': Perseus (visual performance)
Great future potential: K3
Analogue beats digital, but only just.
Razor sharp DSP filters offer bad audio for VHF weak signal CW message detection.
K2 and ORION offer sonic details like you are diving into the abyss of the RF noise floor.
What is the true 'supporting performance' of low phase noise?
I wanted to measure the noise figure of my K2 and, in the process decided to do some more testing..
Got a bit carried away.... But then again, I never got to measure known VHF performers like the TS850, FT1000MP etc.. And then there's that superb Javornik transverter. And Down East Microwave is (re-)designing a new transverter.
Oh well... lot's of promises for the future ;)
Wish you all a Happy New Year !!!
73 Mark, PA5MW