Monday, November 30, 2009

Ten Tec kit 1340 mod

Having built the first (essential) stages, it's now time to decide on further deviations of the circuit and the way it is most intelligent to construct.

Remember, the idea is to use as much as possible from the kit to build a 40m QRSS transceiver.

First consideration, phase 1 completes the keying and rx/tx-switching. We need that, phase 1 should be built w/o any alterations.

Phase 2: this is the VFO & buffer, well, we don't want a VFO, we want an (TC)XO instead, hence, I propose to postpone any construction to a later stage. If you really want to do some soldering in that stage, that's seems reasonable to do: Q18, C33, C83, C84, R55-R59, L16. This is the last buffer stage with a low-pass. At the other C33 we will couple in the XO.

Phase 3: TX mixer. I believe, the transmit mixer should be postponed. Really. Let's first the the receiver operational and take care about the transmitter later.

Phase 4: RX front-end and filter. The front-end we really need, I suggest to build everything but the filter. Since the bandwidth we are interested in is just 100Hz, the idea is not to use all four crystals for the filter, but just a single one. Here, some experimentation from my side is still required.

Phase 5: BFO, RX mixer, audio. BFO and RX mixer we obviously need... What audio is concerned, the preamp-stage seem reasonable to build, up to C12. R6 could be replaced by a trimmer and the a.f. final skipped totally, finally we want to feed the signal to the computer.
My preliminary opinion on the AGC is not to include it. It could be turned into a manual gain control (using R6 feeding bias to Q7's base) or made switchable.


UPDATE: All those considerations brought me to a point where so few is left of the original kit, that it would be the best to start from scratch, w/o a kit, with a given bonus.
Considering the reverse, i.e. the intermediate frequency being 4MHz, and the L.O. being 11.0592MHz, one could actually see the rig serving both the traditional and the new QRSS frequency. And yes, I have to admit, I did see it in the first place, that the TT1340 would be serving the traditional frequency out of the box.

HENCE: For myself, I decided to build the TT1340 as intended by the designers, and home-brew a QRSS transceiver with the 4MHz I.F. approach.... In fact, this will be more like a superhet receiver and a MEPT, both having switchable TCVXOs (11.0000 vs 10.0592). Added value here, the MEPT could be FSKed at the 4MHz oscillator, allowing for better set control for the TX QRG.

Sunday, November 29, 2009

30m as my DC-RX sees it

A busy 30m band, and that's what the two diodes listen to. Sometimes other modes occur, but that's usual mix, PSK31, WSPR, QRSS and RTTY. Unknown noise band just across the qrss-section, does anyone have an idea what that could possibly be?
If you wonder why the spectrum is brighter at about 10.140MHz, I am using a single 10.140MHz crystal as front-end filter, tuned to the qrss-section.

receiver comparison

Short test this morning, all about receivers again. Usually, if there is no special experiment going on, I have my little diodes doing the receiving for my grabber. And so did those during the night, when we stopped the experiment on 20m.
Due to the 20m experiment, the AOR AR3030 (with Collins filters) still is close to the grabber computer. Thus, a quick look to compare the homebrew direct-conversion receiver to the commercial product. Same antenna (G5RV-jr), same matching, just another receiver.
Here's the result:

Some short explanation, around 0745z I decided to have a look on the grabber to see if something is dripping in. I reckoned that the brightness setting for the spectrum was a little on the darker side and therefore adjusted to the level I usually use. Around 0806z the receivers were exchanged, and sensitivity levels needed adjustment. Since both receivers deliver quite different a.f. levels, the spectrum on the d.c.-RX is essentially black at 0805z, this is due to the working of spectrumlab, whenever you used this software before, you will know what I am writing about.
The AR-3030 show a slight warming up curve, fair enough, I was off all night.
As for sensitivity and noise, I don't see much difference...
To me this is a very satisfactory result, given the d.c.-rx cost a fraction of the commercial receiver equipped with the finest of filters'.
I could, and probably will, give the FRG-100 a shot, however, the FRoG is not equipped with a narrow bandwidth filter.

Saturday, November 28, 2009

YES! (AT-120)

For some reason, life meant it good with me and let me obtain an article I long thought lost. An ICOM AT-120 :-))
The tuner suits my two marine radios, aka SSB radio telephones, IC-M700D and IC-M700TY perfectly. Could well be that the tuner will join one of the radios on board Pandia for /mm operations on 14.313MHz or PSKMAIL frequencies.
Most likely, the AT-120 will match Pandia's backstay, other configurations are thinkable however....

Thursday, November 26, 2009

HF3 clarifier adjustment second option

There are two ways, both not very difficult. Adjusting the clarifier takes some patience however, steady fingers help with an unmodified HF3. For the first option, please see the entry about HF3 grabber setup.

Here a second option that does not require a spectrum display, in this method you will be using your ears instead of your eyes. This is now it works, and also why...
  1. pick a broadcast station or timesignal with proven stable frequency
  2. switch to USB (you should now here a 2kHz tone, that would be the carrier)
  3. set the dial 2kHz above the nominal frequency (this bring you close to zero beat)
  4. adjust the clarifier for zero beat

This is why this works, the HF3 has got a very wide side-band filter, I guess that saves the maker some money. Hence, the filter's passband is broad enough to even pass the carrier and LSB contributions, allowing us to adjust the clarifier w/o any further tricks.

Tuesday, November 24, 2009

XTAL filter for the grabber RX

Here is a spectrum to demonstrate the effectiveness of the single crystal filter employed in the 30m QRSS band d.c.-receiver. The filter is tunable by means of a trimmer capacitor.

30m best of 2009-11-24

The following spectra were taken with an indoors rockloop (magnetic loop made from wire) and my homebrew subharmonic 30m direct conversion receiver (cf. my web-page).

From the awaking of the band to its closing, everything was in, Es short skip, regular skips and even DX (flying W) during daytime, closing finale with grey-line DX.

Three band MEPT, 3.5999MHz QRSS QRG update

Two subjects in one posting...


Here are simple ones, I have not seen before:
  1. 3.6 = 14.000 - 10.400 = 14.000 - 2 * 5.200
  2. 3.6 = 14.400 / 4 = (2 * 5.200 + 4) / 4
  3. 3.6 = 7.200 / 2 = (5.200 + 2)/2
#3 may be tricky in terms of filtering.

Three band MEPT:

#1 of the above combinations has added value, since the 14.000 oscillator could be modulated, providing a 20m MEPT at the same time. At the same time, cf. an earlier post, 14.000 can be down converted to 7.0599MHz by means of a 15m QRP crystal.
  • 80m: 3.5999 = 14.000 - (2 * 5.200)
  • 40m: 7.0599 = 21.060 - 14.000
  • 20m: 14.000
The crystals for 5.2 and 14.0 are easily available, e.g. Conrad, Reichelt, DigiKey...
As for the QRP crystal, know your sources: Box73, ESS, QRP clubs, etc.

Monday, November 23, 2009

30m subharmonic DC-RX improved

Today's grabbing results were OK-ish. Not really good, however, the additional r.f.-stage helped, however, the shift the filter frequency prevented the break through.
The 22pF I experimentally confirmed for the version w/o the additional stage are now shifting the filter response far more upwards than wanted. To be more flexible, I decided to replace the 22pF capacitor by a trimmer capacitor with a maximum capacitance of 18pF. The first results are promising. The filter response is now centered to 10140050Hz, which hopefully provides much better reception than I gained with the last design....
Wish me luck!

3.5999MHz QRSS QRG update

Reaching in my junk box, I could not find a 6.400MHz crystal :-( Yes, they can be ordered... however....

What I found instead is even nicer, a 9.600MHz crystal, together with a 6.000MHz one, even in one bag. The 9.600 xtal looks like I salvaged it once from something. I would not recall what, possibly some obsolete network gear.

I guess, the design of the 80m secondary frequency MEPT is hereby decided. Nice in this is, with actually using the difference, some drift cancels out.

3.5999MHz QRSS frequency

Having had my brains chewing on the problem for a while, the solution is really obvious, sort of.
Remember, the task is to generate a frequency of 3.5999MHz, using cheap and available components.

And here it is:
  1. generate 6.400MHz
  2. generate 8.000MHz
  3. mix! => 14.400MHz & 1.600MHz
  4. filter ...
  5. divide by four (FlipFlops) => 14.400MHz/4=3.600MHz
  6. filter ...
Regular CW could be done by enabling/disabling one of the flipflops.
FSK by pulling on one of the crystals.
In my design, I would probably pull one crystal for modulation and the other for the TX frequency.

Now, that was not that hard, or was it?

Sunday, November 22, 2009

HF3 grabber setup

This is what the present grabber setup looks like. The difficult thing is to adjust the BFO such that it is clear where it is. This receiver will not be modified, however, there is a second of this make on the way into my shack. One of the two will be modified, severely ;-)

The grabber is set to listen to QRSS signals on 3,599,900.0Hz. This may look odd, but, the HF3 is not aimed at radio amateurs, it is aimed at yachtsmen (like me). It particular to receiver TTY weather reports, weather charts via FAX, NAVTEX and occasionally some news on HF-BC using A3E. In marine station listings, the frequency for teletype stations given is the frequency between mark and space. To help the sailors, the processor of the radio sets the radio's PLL to the dial frequency for A3E and 2kHz below for J3E/USB. I have not checked J3E/LSB yet, since it is of no importance to me.
When using the HF3 as a grabber receiver, I thus set the dial to the actual frequency I want to listen on, knowing about the 2kHz difference.
To adjust the clarifier, use a time signal, or a known to be stable BC station, to adjust the carrier such that it precisely results in a 2kHz tone.
I tell spectrumlab the dial-frequency minus 2kHz as offset, in this example, it would be 3,597,000.0Hz.

The FRT-7700 makes a good general purpose tuner. It helps to improve all sorts of mis-matches.

Saturday, November 21, 2009

Icom IC-M700D mod

Despite what is told on the internet, there are version of the Icom IC-M700 which actually block out transmission on frequencies outside the marine bands.

Recently, I obtained one of those, the IC-M700D. This radio has got a "Posthörnchen" on it, meaning that the FTZ (Fernmeldetechnisches Zentralamt) gave its blessings. This however means, the radio does not do what it is not supposed to, i.e. transmit outside the marine bands.
Luckily, there is a service manual for the IC-M700 (no D!) available on the internet.

Browsing through the circuit description reveals that LOGIC CIRCUITS holds on control of the receive and transmit frequencies. The manual further recites that IC1006 outputs signals "mute signals for outside the marine bands to P40&P41. Ah! In the schematics diagram, P40 & P41 (pins 7&8 of IC11006) enable a voltage called "TMU" via transistor Q1003. The schematics diagram further shows a wire bridge W1037 shorting the base of Q1003 to ground. Hmmmmm, with W1037 installed, the transistor is never engaged to release the TMU voltage. Could TMU be an acronym for Transmitter MUte?

Let's have a look:

This is how the LOGIC CIRCUITS section looks in its original state:

Note the cut wire, just above the label Q3. That's the cut W37.

W37 aka W1037 reinstalled here. And yes, the radio now switches to transmit on all frequencies. Hard to find, easy to fix.

I hope this will help amateurs since the IC-M700D presently still is very cheaply available, because it does not transmit on amateur radio frequencies... or does it?!

Despite the above success story, the radio by default only is equipped with USB. Yes, the mode switch does have two J3E-positions, however, they both do the same. I will have a closer look into the circuit if there is an easy way to get the BFO to oscillate for LSB too. For the case there is none, the casing provides enough space to add a pulled CB-crystal to add a BFO for the lower side-band. After all, the I.F. is 9MHz ;-)

Friday, November 20, 2009

E-probe vs TV noise

Seems I found the source of the terrible TV noise of 80m. Looking at the location of my G5RV-jr, it only can be in one of the rooms of my next door neighbors. A few meters off, and about 1m higher, the E-probe is dangling on my house.

Here a spectrum, taken just when I switched from the G5RV-jr (left side) to the E-probe (right side). It is clear, the TV is still on, less prominent. Colin's trace remained about the same...

The decision is thus made, for 80m, I will use the E-probe.

Thursday, November 19, 2009

HF3 the Second

It was a toy in the beginning, the more I use it, the better I like it! Actually, I like it that much that I ordered a second one.

There are plans for this second one. Since there is a lot of space inside its' housing, there is room for modification and experimentation. Many years ago, I heard about a kit that converts a FRG-7700 into a transceiver. Cool, I thought, and forgot about it again. And now, the idea is back, with something that connects in either of the two, the FRG-7700 or the HF3. Both are double conversion superhets, both use a lower intermediate frequency of 455kHz. Using the generated frequencies, one could imagine to convert a single side-band signal all the way back from 455kHz to whatever the receive frequency would be.
I figure, it would be the question of just some NE612 mixers and two crystal filters, one for 455kHz (side-band) and one for the first intermediate frequency.

One further could consider to add some temperature control to the reference oscillator.

And, who knows, maybe this could be an easy way of producing some QRSS-signals too.

Monday, November 16, 2009

Roll your own!

This is about my newest addition to the spectrum grabber installation. The regular reader will know, that I was mainly using my rockloop (see webpage) for the 30m suburban subharmonic grabber. My rockloop is, however, a multiband (15m to 40m) aerial, which provided me with enjoyable QSOs in its' entire bandwidth. OK, I could build another one, but than again, multiband?

Years ago, I learned about the DCTL (Distributed Capacitance Twisted Loop) antenna. Actually shortly after its' design has been published. To that time, I cut myself a version for 40m from 300Ohm window-line. This loop actually never worked... well, at least not to that point in time.
Just recently I found the bag in which the DCTL was rolled up for storage. That brought the thought that I may possibly made a mistake when making the loop. And yes, in fact, I made a mistake, I forgot the "twist" in it.
Some months ago, I thus fixed it by soldering the leads together which belong together... and... voila, a working 40m DCTL. So far, so good, rolled it up again a was busy doing other stuff.

And now, just recently, I remembered it again (actually I just wanted something to print, in order to test my print-server setup). Only God know why I was hacking "DCTL antenna" into the average search engine and printed just the first thing that popped up:
Now, that would form a nice and cheap receive loop for the grabber.... And yes, it does!

Here come the dimensions of my 30m DCTL (please refer to the link above to understand what I am writing about)
  • Ll = 347cm
  • Lz = 46cm
  • Lc = none
The 30m version is made from TV twin lead, which is much lighter and easier to roll up for transport as the window-line is.
The lazy dawg I am, I could not be bothered yet to include a balun in the design, I am thus sipping the signals off the loop by means of ordinary RG58 coax. Yes, I do consider using TV twin lead as feedline, however, the stuff is rare nowadays, and I'd therefore probably rather wind a balun.... We'll see....

My 40m version is good for TX, I guess, the 30m version will be as well. I will try to tune (trim/cut) it accordingly and give it a try during my next journey.

Roll it up, roll your own!

Potential QRSS frequencies

Since in the US, only the extra class is allowed to transmit on the first 25kHz of the bands, our present habit of using the lowest edge of the traditional five shortwave bands prevents a majority of American hams to actively participate in very slow activity. This is the present situation, I believe:

For 80m, we could consider 3.5999, the border between narrowband and broadband data. An alternative could be the color burst frequency, 3.579. According to the region 1 band plan, this still is a CW frequency, however, massive PSK31 threat. Further pulling, we could possibly end up at 3.575.

Bands 20m and higher, I would suggest to stay close to the IBP beacons, something like 14.0989, 18.1089, 21.1489, 24.9289. For 10m, we got the nice 28.188 crystals made by Nick, so we should use those, I reckon.

For 160m, I would vote for 1.8432 since we got cheap crystals here, and some are operating MEPTs on that frequency already.

Don't forget, there also is the Italian frequency 28.322. Following this approach, and since it has been done before, we can cover 14.31818 with cheap computer crystals/oscillators.

Oh, I did not mention 30m and 40m ;-)
Well, I think, there's no need to change anything on 30m (10.140).
And as for 40m, an on-air test revealed that 7.0599 seems to be working fine. I will write about this "experiment" in the next few blog entries, stay tuned.

Summarizing, here's a list of suggested (new/additional) QRSS frequencies:
  • 1.8432
  • 3.500, 3.575, 3.579, 3.5999
  • 7.000, 7.0599
  • 10.140
  • 14.000, 14.0989, 14.31818
  • 18.1089
  • 21.000, 21.1489
  • 24.9289
  • 28.000, 28.188, 28.322
Comments are welcome!

Saturday, November 14, 2009

IDEA ALERT (7059kHz & 14000kHz MEPT)

When writing my latest post on the KnightsQRSS-list, an idea shot through my head! Did not even require a lot of thinking :-)
A second, even more obvious, combination of available crystals fell out my fingers into the keyboard. Vy vy vy obvious, I even have both crystals in stock, for QRP and QRSS!
  • 7059 => 21060 - 14000
Yes, there are cheap 14MHz crystals available (check here: and the 15m QRP-crystal should be in any of our parts collection anyway.

Here's, what I see, could be done:
A Pierce oscillator for 14MHz. This pulls the frequency up, so that we get into the 20m QRSS-range. For FSK, the 14MHz oscillator should be modulated. In practice, this is a ordinary 20m MEPT, no strings attached. Usually, one would expect the frequency to be 14000.800kHz
An oscillator with the 15m QRP crystal should be constructed such, that the frequency can be pulled downwards in a stable and controlled way to a frequency 21059.xxkHz. Let's make that 210593.
Now, all we need is a mixer, to subtract the 14MHz signal from the 21.059xMHz signal. Tiny downside here: the FSK will be inverted.

Such a design would provide a dual band MEPT. The thing, equipped with two finals and two filter stages, would even allow for simultaneous transmission on both bands.

A further idea is, to switch between the two bands according to the ambient light. This could be done by either the beacon keyer, a separate micro-controller or some analog contraption using OP-amps or transistors.
My personal favorite is the beacon keyer, since it would be rather simple to revert mark and space according to the band.

Now, where's my soldering iron???

Thursday, November 12, 2009

40m Novice QRSS QRG

I have not looked into any possible scheme of privileges, this is what I found:
  • U.S. 7.025-7.125
  • The Netherlands 7.050-7.100
  • Germany none
In my view, it would be nice to motivate the novice radio amateur to experiment with low level power as well. This would teach that in fact, one does not necessarily need 100W and more to have fun on shortwave.

There are a couple of obvious candidates for which crystals are available:
  1. 7.100 => which can be generated by a 14.200 crystal (ESS) divided by two
  2. 7.059 => 11.0592 - 4.000
  3. 7.085 => 12.000 - 4.9152
  4. 7.096 => 3.000 + 4.096
My guess is that the band will be less noisy at 7.100, this however is a guess only.

There are a couple of other reasons why I would suggest a frequency between 7.093 and 7.097. First of all, it is very simple to build an oscillator for 14.200 with a single crystal, pull it down a bit and divide the signal using a FlipFlop. The second reason I would see in the possibility to create a very simple superhet-receiver (or transceiver) with the combination found under point 4. This combination could also be used as a simple MEPT, however, drift is more an issue in a design using the sum of two frequencies.
This leads to the obvious advantages of the two combinations using differences. Once again, a superhet is possible and in a difference of two frequencies, drift is less of an issue.

I would go so far to state that there even is a kit for a transceiver, when 7.059 is considered. Well near enough at least. This rig would allow for transmission as well as reception.
The Ten-Tec 1340 is having an intermediate frequency of 11.000MHz. A VFO generates a signal around 3.97MHz.
And here comes the mod to the kit:
  • replacing all 11MHz crystals by 11.0592MHz xtals
  • not building the VFO but an oscillator with a 4MHz xtal including a varactor for FSK
For QRSS I believe one would like to reduce the drive to the PA, since the final produces about 5W rf and would probably become hot in time. Maybe the final (2SC2166) could be left out all together. The driver is indicated to deliver 15dBm.
Further, the audio amplifier (LM386) could be left out in its entirety.

Wednesday, November 11, 2009

xmas today!

Two deliveries dropped in today :-)
  1. the PSK30 kit by K1SWL
  2. a 28.188MHz from VK1AA
My thanks go to both OM for their excellent services!

Tuesday, November 10, 2009

IC-M700TY qrv

Pandia is out of the water... I wanted her to stay in, but... the anti-fouling paint is essentially gone, the painter forgot to apply primer on top of the gel-shield before rolling on the copper-stuff...
No comment... thus, Pandia is out of the water for winter, giving me the chance of doing some work on the hull and on other part otherwise difficult to reach.

All right, now, what's that to with radio? Well... what about installing some aerials in the rigging?

Hard cut here; the exercise motivated me to wire up the recently obtained Icom IC-M700TY for the first time. The radio is superb! Never before I had the privilege to experience a noise blanker that actually works, well, the radio has got one. The squelch (on SSB!) works well, it's just a switch, I will have a look at the schematics, my impression was, the squelch seems to be dynamic, flip the switch and after a certain while the receiver is silent. The AGC is very effective, it cannot be influenced. Therefore I think, the radio is (w/o mod) not really suited for QRSS. The radio is controlled by a "high precision" TCXO, whatever that means. Said TCXO however is about four times the size of a TCXO in an amateur transceiver.

Downside, one needs to know the frequencies one wants to operate on. We amateurs tend to flip over a range of frequencies and see what's on. Well, spinning a knob in order to scan the band is a no no with the IC-M700TY. Actually, scanning is, compared to more modern professional (marine) radios, not an option to this radio. Thus, know what you want and which qrg to want it on.

I assume, the IC-M700 is ideal for modes such as PSK31, Pactor, etc. and further for nets and similar channelized voice operations.

Friday, November 6, 2009


Yes, today it dropped in. The radio is in wonderful condition. I think, it has never seen any ship from the inside.

Wednesday, November 4, 2009

Polyakov I/Q-SDR update

Some success but some fall backs too. The regular reader will know, I was working on a subharmonic SDR design for a while, with decent breaks however.

The design involves a 5.0688MHz canned oscillator, two pairs of anti-parallel diodes and some audio amplification (TL082).
Theoretically there also is a front end with a J310, but, it is not working, God knows why... need to look into this... Not oscillation, no attenuation, no amplification, no nothing....

I/Q works, however, the correct phase-shift adjustment is not easy, three parameters to play with. The sideband suppression (image canceling) is surprisingly good, with the proper phase-shift.

Presently the fun is spoiled by a major 50Hz contribution, I've seen that before, proper tins required ;-)