Contents :

A collection of thoughts, and my notes about experiments and ideas, technical or otherwise, connected to Amateur Radio, Satellite working and monitoring and other electronics.

Saturday, November 20, 2010

Thor's Hammer stuck

I have noticed that Thor's Hammer has stopped uploading. Reason unknown, but could be the Inet connection has been lost, or the PC has been rebooted due to a power outage. I will have to wait and see.

Since I cannot just go there and back again in a day It will have to wait till I can go there for it to be updated

Tuesday, October 26, 2010

New kits arrived

It took a while, but I now have "a few" kits to build.

Some SoftRock II kits, different bands, each can be made directly for 160,80,40,30 or 20m, all components in the kit. Some SMD soldering necessary, but should be possible, even with my eyes.

Some "Funkamateur" single frequency kits, among those a 10.7MHz kit to connect to my VHF-UHF RX (R7000, possibly AR-8600).
Two kits for 9MHz, one will be modified for use on 10MHz

the other 9MHz might be made "wideband", so a multitude of LO signals could be used, possibly a Si570 synthesizer or the DDS60 kit

Two lower band kits, to be decided

The FA wideband SDR TRX, will need a PA and a programmable LO, not yet ordered. Covering 1.7 - 30 MHz with preselection, so seems quite usable.

The "standard" 1W PA could probably easily be replaced by a home made solution, but I will see if I do not get to order the standard one at some stage. The local oscillator, the so-called FA-SY may be the way to go for full band coverage. A housing is also available, I may order that one, too.

Update :
The FA-SY oscillator has been ordered, along with a housing fit for the FA-SDR TRX
More Update :
The FA-SY kit and the housing have arrived

Lots of kits to build, not too much time, so let us see what comes up here.

The intention is to use some of the fixed frequency stuff for simultaneous WSPR and QRSS monitoring.

Tuesday, October 12, 2010

600m WSPR at "Thor's Hammer"

Since I visited the QTH of OZ9QV last month I have been monitoring the WSPR reception there.

The WSPR receiver is of course the same as the one for QRSS, with WSPR running concurrently on the PC.

With the tiny indoor tuned multi turn loop (diameter 22cm) the following stations have now been received successfully on 600m .

PA0A, PA0O, G3XIZ, PE1GRL and EI0CF being 1225km from there.

For such a simple setup I am quite happy with the results, even though I know that improvements are certainly possible.

Saturday, September 25, 2010

Grabber : "Thor's Hammer" at OZ9QV : updates

During a holiday (and being there for other reasons) in Denmark I have made an update to the "Thor's Hammer" QRSS grabber. More will happen later at another visit.

The grabber can, as usual be found at :
Thor's Hammer

The grabber now works on two bands, a more stable receiver (old TRX with defective TX) has been installed for 10 MHz and the viewable frequency range reduced. Still using an older low powered PC

10 MHz Grabber :
RX range : 10139.880 - 10140.120 kHz
SpectrumLab set for display of 3 stripes of consecutive periods
Antenna : indoor dipole

500kHz Grabber :
RX range : 502.700 - 505.500 kHz - some noticeable frequency drift, but acceptable
SpectrumLab set for 3 strips as above
Antenna : indoor multi turn tuned loop

The 500kHz RX seems to have some problems with receiving WSPR, only once or twice the WSPR signals from PA0A and PA0O have been received.
The signal from (I think) G3XIZ was visible, but no decodes.

All in all I am fine with the improvements, but more is needed. I would like to add more bands, e.g 80m, 40 and 20m, possibly 136kHz but things do take time to get running, and new antennas will be necessary.

I may experiment with a wide band active loop antenna (H-probe) or an E-probe (short active whip).

Sunday, August 29, 2010

Simple 80m Grabber Receiver Ready

Next time I will visit the OZ9QV grabber "Thor's Hammer" there will be another band active in grabbing : 80m

I have finished encasing a modified RockMite 80 (RX only)

Frequency drift is acceptable :
10 deg C : 3499.955
23 deg C : 3499.915

Yes - negative temp coefficient.

Since the temperature is expected to be within that range (most likely 15 - 25 for the majority of the time, and I expect to put the RX and PC into a cupboard, I would expect the local oscillator to stay within 3499.925 +/- 10 Hz for most of the time, quite acceptable.

The addition of another band to the grabber is worth it alone, I think.
New antenna needed as well.

I know that more activity is on 40m by now, but the winter should be good for 80m experiments.

The grabber is expected to run with an older, low powered PC, together with the 10 MHz grabber.

The new grabber receivers should be installed before the end of the year.

I am playing with an idea for a more stable grabber receiver for 3500/7000/14000 kHz, more on that later.
It will be a bit more complicated to build, so I will be taking my time.

Monday, August 23, 2010

Thor's Hammer again

Yet another alignment,

The receiver is drifting quite a bit, so the 'window' has been widened to 550 Hz, at least some signals are visible.

Further improvements to the grabber will happen later.

Saturday, July 31, 2010

Thor's Hammer with frequency drift

The receiver has a considerable frequency drift, even more than I expected.

When I visit next time I may have a better RX at hand. - if there is enough time to ge one going.

Monday, July 26, 2010

Thor's Hammer Realigned

I was visiting the house of OZ9QV and got the 10 MHz grabber realigned.

I broadened the viewing frequency window, since the receiver has some temperature drift. In any case, QRSS signals are now visible again on the grabber.

Thor's Hammer, by OZ9QV :

QTH JO65cp
Frequency 10.140 MHz
Cheap transistor synthesized receiver
Older low spec PC


Thursday, July 15, 2010

Update IC-703 500kHz

After having made a study of the IC-703 manual I see that there is a high pass filter in the TX path , cutting off at 1.6 MHz.
This is most probably for avoiding the IF frequency (455kHz) reaching the TX output.

A switch - switching in a 500kHz bandpass filter (alt 136kHz filter for LW) or bypassing the filter - would probably be possible, but the *tiny* SMD components at this place in the radio makes me think twice about making the attempt.

It *may* be possible to tap the signal out to an external amplifier, but then there is still 30mW out of the TX at 500kHz, so that could as easily be used.

Conclusion : 500kHz looks possible with the 703, but I doubt the internal filter mod is worth the risk of ruining a perfectly good TRX.

Sunday, July 11, 2010

Modifying the IC-703 - - and 500kHz

Ham radio manufacturers are funny (funny-strange, I mean).

They make 100 W radios needing lots of cooling, yet the PA's work through.

On the other hand, making QRP radios, PA transistors go KAPUT, drivers go KAPUT (FT-817 and IC-703 respectively)

SInce I have a FT-817 with a PA that died, I know it is just a matter of time before it happens again, unless the correct mods are made.

This week end ( with temperatures up around 30 C) I got to do the necessary mods for the IC-703

1) Driver modification. This one is not too bad, a matter of cutting a single PCB track and rerouting a piece of wire on the accessible side of the PCB, no need to remove the PCB. When at it, I adjusted the bias to the driver down to the recommended .5V, so the driver should be safe even with high temperatures now. In the original IC-703 the driver is connected directly to the full supply voltage, now it is connected to the 8V supply line.

2) CW Keyer input. For some obscure reason the keyer jack is grounded through a choke, giving rise to RF making it impossible to release the TX key. The solution, connecting the keyer jack ground directly to RF ground can be made provisionally outside the radio, but the more elegant solution requires the main board PCB to be lifted from the housing. Not too tricky, but beware of the flat cables (connectors).

3) 500 kHz TX option. This one required moving a *tiny* SMD diode. I managed to do it with a "normal" small solder tip, but the result is not that pretty.
The mod does open for TX on 500 kHz, but max output is about 40mW, and it looks like something is heating up, because the output reduces a bit after key-up, then stabilizes. I would probably not try to use the max output, but reduce it a bit, them make a power amp.

All in all not too bad for a hot summer's week end.

Tuesday, July 6, 2010

New Toy, Heavy Stuff

Just picked up a Maritime transceiver, the IC-M710.
The station operational from 1.6 to 30MHz, so TX on all bands 160 - 10m.

Now I need to learn to operate the thing, it is not quite the same as a normal HAM transceiver, but there will be time for playing, the set tunes in 100Hz steps, but with a clarifier.

Capable of running 150W out continuously (I have heard), the radio can be used for heavy duty operation

Now for some playing...

Saturday, June 19, 2010

Crystals and oscillators . . .

For some time I just had a few boxes full of crystals and oscillators- some found at ebay, others at rallys etc - not very practical when trying to find a particular one, or know which ones I have.

So the last week I have sorted out a bit, so that crystals with standard values (and in large quantity) have been separated into their own drawers. Others have been grouped in similar frequencies. some are still left unsorted, but that will have to wait.

Now to make a list of what I really have.

The idea is to write a small program for calculating possible uses of the crystals I have - for simple single frequency (or vxo controlled) receiver or transmitter circuits. After all, not all TX/RXs need to be DDS controlled. Yes - I know that there are lists out there with frequency combinations from standard crystals, but I have some additional frequencies in my stock, so will have to figure those out myself.

At least I got a *little* bit more order in my very messy shack ;) - even if I could use some more sorting out - that will have to wait.

DDS-60 has arrived

Just received a DDS-60 "daughter-board".

Now will be the time to look into getting the DDS programmed, there is no controller yet.

For very simple stuff a PIC or PICAXE processor programmed in BASIC will probably do. For more functionality (and more memories) I should probably go for a more advanced processor. IFor that I consider the Arduino project, using AVR ATMEGA processors. It uses a variation of C (with a limited functionality and special commands for controlling I/O pins), something I have not yet done anything with, but is it ever too late to learn ?

Arduino is an open source project, so even the bootloader can be loaded on to a processor without one, unlike the PICAXE bootloader which is proprietary. I now have an Arduino board and a few processors on the way.

More to think about, more to try out ...

This summer I also have a large reading project going on, so a bit less radio building activity is expected.

Sunday, June 13, 2010

Enter the DDS

Just received a kit, the DDS-2 from N3ZI.

The kit contains all parts, including a simple display, for making a functional DDS.

The kit is relatively easy to assemble, all parts were present. The SMD integrated DDS chip is somewhat more tricky to solder without creating solder bridges. I think the pads are a bit wider than the pads for the NE612 SMD mixer on the Rockmite/Warbler kits from Small Wonder Labs.

First the bad news : Tuning the DDS-2, as it is, is an exercise in patience. it is slow, when trying to use the fast function (turning the knob faster), the tuning becomes erratic. The lack of a keyboard entry function is serious with such a slow tuning.

It looks like a modification of the firmware should be attempted. Quite a daunting task, given that (as far as I know) the source code is not available, and my programming skills are not that good.

The good news is that the temperature stability looks fine. the crude "switching on and off the fan" method revealed about 20 - 25Hz drift on 10 MHz, of course relatively less on lower frequencies. For a non- temperature compensated clock oscillator this feels quite good, and I would expect better stability when the DDS is boxed.

Other good new on the DDS-2 : even if tuning is a bit of a pain, there are two redeeming qualities :

- the standard firmware has 10 "memories", acting like the "Band stacking" feature of many modern transceivers. so a multi frequency MEPT with 10 (11) pre-programmed frequencies is quite doable

- the application of the RIT should be quite useful for generating FSK easily, eg for a relatively frequency agile MEPT.

However, for more experiments I did order a DDS60 daughterboard that should be programmable from a PC or an external (PIC, PICAXE etc) microprocessor board.

Sunday, June 6, 2010

More RM30 info

The RM30 was tested a bit this week end before the shack update, and the results look encouraging and disappointing.

The sensitivity of the RM30 looks really good, noise increases more than 30dB when a piece ow wire (in the shack) is connected, indicating sufficient gain for a grabber.

The frequency response shows the unmodified RM30 to have a slightly too low peak frequency, about 1kHz, so next test will be a (variable) capacitor in series with the input crystal, the main problem is mounting it on the PCB.

The frequency stability, however is not nearly as good as I would want. I may have to get some of the clip-on heaters that DB6NT has for sale, but initially the RM30 will be boxed and thermally insulated.

Update :

47pF in series with the input filter crystal brings the peak (rather broad) up to 10140.5 , this is quite acceptable since the bandwidth of the filter is about 1 kHz in the RM-30 setup.

Shack update

Some time ago I moved the shack from the "attic" position, especially because it gets extremely hot up the in the summer and very cold in the winter. Also the mess there is "rather visible".

Today I was digging out some of the test equipment from upstairs, so the shack downstairs is now sort of usable. The soldering iron was , of course there already, but now I added my Lab power supply, oscilloscope, frequency counter is now set up, as weel as an old "Bolometer" for RF power measurements. oh yes, a step attenuator from 1 - 110dB is not bad to have in the shack - and an ancient AF signal generator. An old digital multimeter running off mains seems to be out of service at the moment, but a portable one will have to do for now.

The RF signal generator, running from 10 - 500 MHz is not that good for SSB/CW measurements, but will have to do for now. It seems I should build a DDS or synthesized RF generator and just use the external attenuator.

And finally the heavy equipment : a spectrum analyzer, yes old surplus, but looks like in working order still, all will now have to be powered up some time every day to make sure it does not burn out.

Monday, May 31, 2010

WSPR BFO offset test

Tried the BFO offset function on the WSPR2 program.

Using the FRoG receiver I set the USB frequency to 10137.490, same in the WSPR settings, and set the BFO offset to 1710Hz in place of 1500.

Spots are coming in nicely on 10MHz with just a piece of random wire indoors.

Later : tests with the RM30 grabber rx input filter, and see if sensitivity is sufficient - then some compact antenna.

Sunday, May 30, 2010

RockMite 30/80 Update

I have run a simple test of temperature drift of the two RockMites :

Using a fan blowing on the PCBs lying on the desk the RM80 drifts less than 10Hz when the fan comes on or off for about 5 minutes, that is quite acceptable, given that the RMs will be boxed, and likely I will use some insulating Styrofoam.

The RM30 is a bit more tricky. I tried to lower the frequency with a choke in series with the tuning trimmer capacitor I mounted, and the drift with fan was about 50Hz at on/off.

It turns out that grounding one side of the crystal resulted in a frequency of 10138.490. Not ideal for WSPR, but should be useable with WSPR2 and "BFO offset". Not tested yet, but will be in the near future. Temperature drift at the fan on/off is now 20Hz, and with a bit of insulation that should result in an acceptable temperature stability.

It looks like the drift is more due to the capacitors in the oscillator than the crystal in itself.

Oh, and I am a bit disappointed that the RMs have several zener diodes, but the oscillator itself runs from the raw supply voltage. Where did that idea come from ? I find it surprising that there is not more stability problems with the LO in the RMs

Next step with the RockMites : input crystal filter tuning - if necessary.

Sunday, May 23, 2010

RockMite 30 Experiments

In addition to mounting all but the inductors and transformers for 80m the Warbler and a few more components for the 40m WSPR Warbler I have built a RockMite 30, for use as a Grabber RX only for 30m.

The evening welt with getting the Local oscillator (10.140MHz Xtal) down to 10.138.700. This is done by bypassing the frequency switching, using a simple serial connection of a 10uH inductor and a variable capacitance ( 12 - 30pF ).

The input Xtal filter will be added later, after stability test of the local oscillator, and will probably be a simple SIngle Xtal tunable filter.

Tomorrow will be busy with some non radio activities, so progress will be much slower than it has been this week end.

Warblers update

I have made myself busy today, mounting the vast majority of resistors and capacitors on my two Warbler kit PCBs.

Tomorrow I should be able to get at least one of them in good receiving order, I will try to make that the 40m WSPR one.

We will see how things go.

Wednesday, May 19, 2010

Sporadic E Season and 10m

At the start of the sporadic E season I have retuned my main grabber to 28.321/28.322MHz , still retaining the secondary image for 500kHz.

The 28MHz grabber is using a FT-817 and the 500kHz grabber is still using the ATS909.

As per the previous post I am in the slow process of building more (simple) grabber receivers and some WSPR equipment for 500kHz and several HF bands, at least 3.5, 7 and 10 MHz.

I am interested to participate in the 160m WSPR summer project, so looked for a suitable set of Xtal frequencies. It looks like 9MHz, BFO 8999.5 (I have a Xtal filter, or could probably use some 9 (27) MHz Xtals) and 7159kHz, pulled a down about 4kHz, this should work.

I may need to add sound cards to the grabber PC in order to monitor more than two frequencies.

Monday, May 17, 2010

RM80 update

I have been operating the soldering iron and modified the RockMite 80 for 3500kHz.

The kit will be used as receiver only, so I bypassed the crystal tuning, ending up on a LO frequency around 3499.920, nicely suited for a grabber on 3500.800kHz

The receiver is probably not too sensitive, so I intend to test it, first with my 30m tuned loop, then most likely with an active antenna of some variety.

The first test has been monitoring the drift of the LO, it looks fairly stable, so a later test will be the rx sensitivity.

Next on the workbench will be the 80m Warbler, usable for PSK31 (of course) and a grabber on the colour burst frequency. I will be building it exactly as intended in the original design, then later build another for use on 40m WSPR.

Saturday, May 8, 2010

QRSS Grabber in OZ

This week I have been in Denmark on Holidays.

During this I have set up a grabber receiver at the QTH of OZ9QV

The receiver is a simple one running on the 30m band, 10.140.0 - 10.140.1


Antenna : Indoor dipole (I don't want to risk too much in thunderstorms).

The system is running SpectrumLab and ArgoUpload, as well as WSPR in receiving mode

I hope to keep this running 24/7, but no guarantees, Internet may go down, power may be out, etc.

I hope some people will have fun using this grabber, and will try to get a bit more up and running there at a later stage.

Update : the OZ grabber seems to lack sensitivity, but is still operational.

Monday, March 29, 2010

WSPR on the Mac

This past week end I have, among other stuff, made a few attempts to get WSPR running on a Mac running Snow Leopard.

Tried a few "Tips and Tricks", using MacPorts and other stuff but none of the tricks were useful.

I was finally pointed to a HowTo for making the install, and this is what will be going on next in that part of the story.

SpectrumLab seems to be running under Wine for the Mac, so it looks like that part is usable.

Fldigi exists as a package and runs, if a bit touchy in the user interface.

Update :

WSPR installed mostly according to the guide, but only on a pristine installation. Not ideal. Thanks to G4KLA for assistance. Now I need to see if I *can* get it installed on my already installed system.

One problem, however : While the >WSPR program starts and runs, it exits at unexpected times with an input overflow message, so not very useful for long term deployment. Back to using Windows for WSPR. (Or possibly Linux, will have to be tested)

Sunday, March 14, 2010

Active antenna experiment.

Having visitors this week end put a limit to my radio activities, but one thing got done.

I built (did not take that long) a small balanced amplifier with a TL592 IC. The aim is using it with small loops and ferrite antennas.

The amplifier can be found at Low Frequency Antennas , I made it for a bit higher gain and with a manual tuning capacitor in stead of the varicap, but essentially everything is as in the circuit diagram.

Going through resonance on 80m and 160m the noise increases by 20 - 30dB, so the noise figure and amplification looks good. It looks like the amplifier will support even smaller antennas than my 80-160m tunable loop.

Further experiments with the amp. should include smaller loop/frames and ferrite antennas. It could be interesting to see if the small (50 - 60mm long) ferrite antennas from small transistor radios will work in the indoor noisy environment, or even what they will do outdoors in the open (less noise)

Sunday, March 7, 2010

A bit of 500kHz experimentation

The new cardboard box frame antenna with better wire turns out to be a bit better. A few dB increase of S/N has been gained.

The loop was at first connected to the HF-3 receiver, and gave some WSPR spots from local stations like PA0A, PA3EGO (also seen with QRSS) and PA3FNY, with relatively good signals if considerably lower than Joachim gets with his Octaplumb. Also G4JNT during night time and one or two other spots from G stations. All in all not very impressive, but not too bad for an antenna inside the noise field of the apartment. Also every night DI2AM with QRSS, and occasionally a good signal from OK0EMW.

A test with the ATS909 receiver, using just the built-in ferrite antenna gave surprisingly good results, almost as good as the cardboard loop with the HF-3, with DI2AM in every evening.

Test with the FT-817 gave a marginal improvement over the HF-3, maybe 1 - 2 dB.

Test with a FRG-100 receiver showed that the receiver is considerably more sensitive than the FT-817, but due to "antenna noise" (apartment noise) the improvement was again marginal, 1 - 2 dB.

The antenna has now been moved upstairs, still indoors, and another 1 - 2 dB has been gained. interesting to see how much signals will come from the G stations now.

An improved loop for outdoor mounting, like Joachim's Octaplumb will be built here, and some tests with larger transmit antennas are in the plans. Well, and a TX, too, probably beginning with some 50 - 100 mW, so ERP will be in the microwatt range.

This week I am having a visit from a friend staying over, so not much time for building activities, but after that it should go on.

I still have some experimentation on the Rockmites and a Warbler, so more than enough to do here.

Also some experiments with the TL592 amplifier for active antennas (LF,MF,HF) is in the thoughts here, such as variations on the antenna from this site

Saturday, January 30, 2010

Some experiments on the (V)XO of the RM80

After Joachim's experiments with the RM80 frequencies and MEPT, using the varicap, giving some problems with chirp I decided to try another approach, and we will see what the results are.

In place of the varicap I mounted a trimmer capacitor, in parallel with the R10 (feeding the varicap through I mount a 2.2nF capacitor, so that Q2 creates a RF-short of the trimmer capacitor, giving rise to the lower frequency RX LO of about 3579.350.

Just trying, and as expected the oscillator does not oscillate on the stray capacitance of the circuit without any capacitor in stead of the varicap.

First test was with a 2-10pF trimmer, giving rise to a frequency above 3580 (even with full capacitance), and stopping oscillation at low cap. values. Not good enough.

A 2-18 trimmer with a parallel fixed capacitor of 10pF is better : the (high) frequency range is now about 3579.75 - 3580.10. I noticed that the oscillation on the higher frequency is weaker on the higher frequency by about 10 dB, still the oscillation holds. A lower value coupling capacitor to the buffer, as Joachim indicates, is probably in order.

This makes me think that it should be possible to replace the trimmer with another varicap with lower capacitance than the one supplied., and with a zener stabilized voltage make the tx frequency tunable. A range of about 250 Hz should be attainable with one or two BB105 diodes - and I should have some of those somewhere.

On with the experiments, I will leave the RM80 with the trimmer cap for a while and see if the TX frequency remains stable when transmitting.

Update :

The lower value coupling capacitor to the buffer increases the oscillator frequency by 50 - 100 Hz - the oscillator now tunes down to .830 .
Parallel capacitor changed to 22pF, trimmer still 2-18pF, tunes (upper frequency) about .760 - just above 3580.000. nice range.

Monday, January 25, 2010

Rock-Mite 80 update

A new crystal in the oscillator brought the lower frequency down to 3579.350. That is quite acceptable for a grabber, the audio range for the 3579.500 - 3580 will end up at 150 - 650Hz. Not ideal, but workable.

Here is what it looks like with a few minutes of low - high - low frequency :

Still, with the 5V shift the TX frequency only went up to 3579.500, the shift is just too low at 150 Hz.

Enter the Q2 switch transistor and the 12V pull-up resistor. Voila, the upper frequency is now 3579.850, a 500 Hz difference, bringing the TX frequency just inside the 3579.800 - 3580.000 band.

It looks like it will be a good idea to have more than 2 crystals on 3579 for this construction, so a selection of the most suitable frequency can be made, alternatively find a better suitable varactor diode with more capacitance variation at 0 - 5 V.

The other point, with the current (original) "firmware", the RM starts up at the higher frequency rx local oscillator and will have to be switched manually to the lower lo frequency.

Later the test of the receiver as such, enough done for today.

I am optimistic that this will work as a MEPT tx and Grabber rx, but the rx test will show.

Sunday, January 24, 2010

Rock-Mite 80 Initial Test

The RM-80 is essentially assembled, first test has been done.

As opposed to Joachim I have only 100 Hz shift between the two steps, that is not enough to be useful. This has to be a fault, and I will seek it out later this week.

Saturday, January 23, 2010

Rock-Mite Kits Have Arrived

In the mailbox I found a nice little package today :

Two Rock-Mite kits , one for 80m and one for 30m.

This week end I see soldering in my "crystal ball"

Now which one to begin with ? .... well I started unpacking the 80 kit, so 80m it will be, most likely the color burst frequency around 3579.5 kHz.

Wednesday, January 20, 2010

DI2AM reception on 505 kHz

The 500 kHz grabber is now set to two narrow frequency ranges, the "WSPR segment" and 100Hz around the frequency of DI2AM.

DI2AM reception seems to be there essentially all the time after sunset, albeit with some (expected) QSB, and WSPR signals coming and going.

Nice result with a "cheapo" frame antenna wound on a cardboard box 35x40 cm small.

A new somewhat bigger frame antenna (more than 70x70cm) will be made some time, but that will have to wait.

In the week end the construction of the 500 kHz TX should begin

Tuesday, January 19, 2010

500 kHz transmit permit

Today I received a permit for experimental transmissions on the 500 kHz band, 501.000 - 504.000 kHz.

Now I will need to build a transmitter, I will most probably go the way Joachim proposed, using a 27 MHz crystal on the fundamental frequency (9 MHz), then dividing by 9 with a 4017, then by 2 with a flip-flop, followed by a "buffer amplifier" , and later an IRF510 as power amplifier.

The hard part will be the antenna, it needs to be compact, so a "magnetic loop" is probably the only way to go here.

Rock-mite kits

A discussion with Joachim today made me go buy some more kit stuff.

The Rock-mite kits look very suitable for a simple QRSS modification , as seen on Joachim's blog.

I ordered the 80 and 30m versions, one of each.

The best thing is that it is useful as both a grabber receiver and a QRSS MEPT - and the price of $32 a piece to have it sent here should not discourage anyone from doing QRSS.

The Rock-mite is a simple crystal controlled CW transceiver and can be used as such. It is a single frequency device with a crystal as the input filter and another one as (VXO) local oscillator/TX oscillator.

Monday, January 18, 2010

160m - 80m Experimental Loop

Yet another receive loop is born.

The construction is similar to the first 500 kHz loop, i.e. cardboard box loop, but made with Litz wire and with only 6 turns.

The calculation of resonance frequency found here indicates a frequency range covering the whole of the 160m and 80m band, and this looks like what I have.

The coupling is made with a further full loop, and it looks like that creates a too hard coupling to the antenna (not really unexpected), making the antenna rather broadband.

Later this week some experimentation on the coupling loop size is in the planning.

Sunday, January 17, 2010

Better antennas for LF/MF

In order to make loop/frame antennas with higher Q for the low bands (160m, 600m, 2.2km) I have ordered some Litz Wire from across the "pond".

It will be interesting to see how much improvement I can get from this.

"eBay" , of course. It can be a dangerous place, but it is our last, best hope for strange raw materials.

Saturday, January 16, 2010

TVEPG up and running from The Netherlands

I got the TVEPG set up with the HF-3 and the 500 kHz antenna, you can find it at here

The grabber is running on an Acer Aspire One 110, the old model with 8 GB SSD, under Linux, running SpectrumLab under Wine and an upload shell script originally written by Allan OZ5AR.

The frequency range is set to 503.5 - 505.5 at the moment, but I do have another setting for the 500 kHz WSPR band.

Update :
New setting for the 500 kHz Grabber : split screen with WSPR segment and a wider segment shown together.

Friday, January 15, 2010

500kHz antenna connected to the HF-3

The antenna is now connected to the HF-3 and receiving there. DI2AM is visible, if not too strong. Some WSPR signals are easily visible, with the WSPR program they should decode nicely.

For now I will leave it running, and in the week end the 500 kHz system could come on the TVEPG grabber page. no time now, and tomorrow some non-radio activity.

Still the signals are not all too strong, so a better antenna is required here.

The noise levels, however seem very low here.

"Progress" report 500kHz RX antenna

Well - let us say - the antenna tunes down to 500 kHz, but the output looks lower than I get from the ferrite antenna of the ATS-909. The S/N, however sounds like it is better.

The source of the lower output ? I am not sure, but suspect the small size of the loop contributes, and perhaps the coupling winding is not enough with a single turn. further tests are needed.

OK - this antenna is rather small and uses standard hookup wire, so the highest efficiency is not to be expected. a somewhat larger antenna, say 1x1 m made from Litz wire should provide substantially better results.

The first test was with a "dual gang" variable capacitor, but with only one plate set used. of course the hand capacity detunes the antenna so it is essentially untuneable.

SO the second test was with both plate sets, and now we are getting there. because the hand is at the center of the capacitor, no detuning or hand capacity effect is noticeable.

With the 25 windings, the antenna tunes down to just under 500 kHz, so the antenna is a qualified success.

The ATS 909 seems to have a rather good sensitivity on MW, so it is a bit difficult to fully judge the efficiency and usability of the antenna.

The tuning is not *very* sharp, but with a decent maximum at resonance.

The next test should be connecting the antenna to the HF-3 RX which should have a very high sensitivity on 500 kHz. Oh, now for soldering another connector to the cable and see what it will do.

Another solution to the low output could be to build an amplifier, but that sort of defeats the purpose of a 'simple antenna'.

More room for experimentation.

Tuesday, January 12, 2010

500 kHz Receiving Antenna in the Make.

I have been looking into the options for receiving amateur signals on the 600m band (500 kHz). Since I live in an apartment size does matter, so looking for a small sized antenna I looked around and found this article from VK2ZAY , showing a simple 'frame antenna' made with a cardboard box.

Being close to all kinds of noise sources I think the loop is probably the best option for a receiving antenna on such a low frequency.

Since I intend to use the antenna indoors the support material does not matter much.

The box measures are on the small side - 35x40 cm (14x16 inches if you like) - but as a proof of concept I have put 25 windings with taps at 15 and 20 windings, as well as a single winding coupling loop.

Now I will be looking in my junk box to find a suitable variable capacitor to complete the project (this may take some time).

If this works out to my satisfaction I will try out frame antennas for 80m, 160m and 2.2km as well, at some time.

Since there seems to be an experimental license available here in The Netherlands I may even try to put out a 600m signal, yes, I am considering joining the experimental group. The decision, however, has to be made soon before the opportunity expires.

Saturday, January 9, 2010

Idea Box : Direct Conversion RX for Color Burst Frequency Grabber

Using 3.579 crystals as crystal oscillator and filter for a PSK31 receiver/transceiver is well known. Getting a decent sideband rejection with a simple circuit is not easy with this design.

Here is a thought : One of the reasons for the lower sideband rejection is the proximity of the 'BFO' frequency to the signal frequency. Possibly oscillator phase noise is contributing to the problems. Here is a trick for a simple QRSS receiver for 3579 :

N4ESS has crystals on 3575.6kHz this is quite a bit further from the signal frequency than is easily done with 3579 crystals. OK, the beat (AF/'IF')then is at about 4kHz, but using SpectrumLab that is not really a problem, since it can 'convert' and filter signals. Of course, the input filter as in Joachim's 30 QRSS Grabber RX is necessary to get some unwanted sideband suppression.

This should make for a simple design for a DC RX Grabber for the color burst frequency on 80m.

Edit : I looked in the 'stock' and I have a 3575.6 crystal (and of course 3579.5 as well, so building this rx for color burst rx is possible. Other projects come first, such as finishing the setup of the 80m SDR from Box73.

Note :

The same concept should be usable with a 160 RX at 1843kHz with a 1856kHz Xtal, also available at N4ESS, albeit with a somewhat higher 'IF' of 13 kHz.