Yesterday I got a notification to pick up a parcel at the local supermarket. Yes, supermarket, the post office was closed and "out sourced" to my local grocery. Actually, this even has an advantage to me, opening hours are much more convenient.
So, today it was pickup time for a parcel from Thailand. In the parcel, a "Super Radio SS-301" handheld transceiver. You may not have heard about this brand nor the model... it is a clone of the Albrecht AE2990AFS, aka Magnum 1012, aka Dragon SS301. Imagine, the radio incl. shipping set me back not even €170.- (check ebay for the present conditions).
A guide for frequency coverage modification was provided inside the box. However, other than this single sheet of paper, the radio, a battery case, and wrist strap and a rubber duck aerial, the box did not contain anything in addition. I guess, I will have to hunt down a manual on the internet (probably not the most difficult task ever).
The actual modification itself, from whatever mode to 12m/10m operation, was done in not time at all. Contrary to the guide, two solder bridges had to be removed (Soder Wick) first. Temporary shorten terminals 1 and 2 whilst switching on the radio is a bit tricky, not difficult however. Having selected the correct code, for hams "0" would be ideal, the two solder bridges 2-3 and 4-5, have to be put in place again.
The radio is a bit annoying what beeping is concerned. Julian G4ILO describes how to solve is issue.
Listening to my 10m MEPT (A1A), which happen to run today, I noticed a slight jitter in the PLL. I am not yet sure what this means and what causes it, I hope that this could be solved in the same way the PLL-jitter in the Target HF-3 was removed, by retuning individual sections of the frequency synthesis.
The radio employs the following modes of operation: FM, AM, USB and LSB. There is no CW. I noticed that between USB and LSB pure noise sounds very differently. Another indication that factory tuning may not be ideal.
The transceiver is provided with microphone and external speaker jacks. Digital modes, provided the jitter is gone, should therefore not be a problem.
The lack of CW, although kinda natural to a HT, kinda sucks. As soon as the bands are open again, I will use a keyed sine generator for transmitting CW using the side-band modes via the microphone jack. Due to the low locking speed of the PLL, QSK is no option... so what! Audio keying a transceiver has got an added bonus: power regulation can be done by audio level control.
Can't wait until CONDX provide us with open high bands, so I can have DX-QSOs whilst walking to work.
Thursday, April 28, 2011
Thursday, April 21, 2011
Day to Night Transition
Just a spectrum I would like to share. It nicely shows the transition from day time propagation to night time propagation.
Tuesday, April 19, 2011
Skanti Marinetta TRP 1
I got lucky! Ever since I made my GMDSS-GOC, I wanted one of those:
In the Scheepvaart en Transport College Rotterdam, where I studied for the GMDSS-GOC, those units are on display. You can only guess how happy I am to finally got one into my collection of marine radios. The best thing on this purchase, the set is complete with all standard accessories.
I would like to thank Willy PA0WMR for keeping this rig in near original state. Willy also stated that the transmitter delivers about 5W on 600m.
What is all the fuss about a yellow box anyways you may ask. And the question is well justified. First of all, the box, with the lid closed, swims ;-) It is yellow! (That would be a reference to Douglas Adam's Hitchhiker's Guide to the Galaxy).
OK, lets be serious, why am I so happy to finally posses one?
Having a look at the manual/schematics we see that the rig
500kHz, 2182kHz and 8364kHz are (former) distress frequencies and must not be use by ham- radio operators!
Where is the hamradio use of these units? Well, we all hope for the 600m band. The 500kHz signal is created by a 2.000MHz gate-XO and digital dividers. Depending on what band we will finally get, this crystal can simply be replaced by a fitting one. However, since it is a digital XO, on simply could remove the crystal and feed a DDS generated signal into the digital gates.
According to the schematics, the transmitter's 8364kHz crystal can easily be replaced by a 40m crystal. However, the receiver employs some resonant LC-stuff with varactor tuning, which should not pose a major problem to modify to 40m, e.g. 7030kHz.
The receiver uses a 2682kHz crystal oscillator to the 2182kHz emergency frequency. The transmitter employs a 2182kHz digital gate oscillator. We got two options for ham-bands here, 160m or 80m. Both have pros and cons. 2182kHz originally is an A3 frequency. The wiring inside the TRP 1 is providing AM modulation accordingly.
On the 80m band, AM is used in places, hence, that would be a nice possibility to join the action. However, filters will have to be modified.
On the 160m band one may want to aim for A1 operation. A 1.843MHz crystal would do the trick here... However, the wiring will have to be changed to engage the BFO in the "2182kHz" labeled switch position.
What is the prospect for the future use of the rig?
I believe it would provide endless fun during field day operations. In particular when operated from cranks, independently from any power supplies.
The (yellow) box contains everything needed for QRP-ops, including a telescopic vertical antenna and a "long(er) wire" aerial.
I figure it could be reasonable to replace the TBA570 receiver with a NE612 superhet design for side-band use.
The XOs could be replaced by either a DDS or some synthesizers for enhanced flexibility.
Some PIC controls seem obvious, the automatic SOS-TXing is inadequate, obviously.
It all comes down to how much modification is actually wanted. Maybe the greatest fun can be obtained when staying as close as possible to the original functionality, i.e. AM on 80m, CW on 40m and 600m.
Other than that, it is an extremely nice addition to my marine radio collection.
 |
| Skanti Marinetta TRP 1 portable survival radio |
I would like to thank Willy PA0WMR for keeping this rig in near original state. Willy also stated that the transmitter delivers about 5W on 600m.
What is all the fuss about a yellow box anyways you may ask. And the question is well justified. First of all, the box, with the lid closed, swims ;-) It is yellow! (That would be a reference to Douglas Adam's Hitchhiker's Guide to the Galaxy).
OK, lets be serious, why am I so happy to finally posses one?
Having a look at the manual/schematics we see that the rig
- has a modern (digital) design
- operates on 500kHz, 2182kHz and 8364kHz
- is crystal controlled
- allows for CW and AM
- has a built in dummy load
- employs an antenna current meter
- contains an ATU
- can create its own energy (by means of cranks)
- can be energized by an external source
500kHz, 2182kHz and 8364kHz are (former) distress frequencies and must not be use by ham- radio operators!
Where is the hamradio use of these units? Well, we all hope for the 600m band. The 500kHz signal is created by a 2.000MHz gate-XO and digital dividers. Depending on what band we will finally get, this crystal can simply be replaced by a fitting one. However, since it is a digital XO, on simply could remove the crystal and feed a DDS generated signal into the digital gates.
According to the schematics, the transmitter's 8364kHz crystal can easily be replaced by a 40m crystal. However, the receiver employs some resonant LC-stuff with varactor tuning, which should not pose a major problem to modify to 40m, e.g. 7030kHz.
The receiver uses a 2682kHz crystal oscillator to the 2182kHz emergency frequency. The transmitter employs a 2182kHz digital gate oscillator. We got two options for ham-bands here, 160m or 80m. Both have pros and cons. 2182kHz originally is an A3 frequency. The wiring inside the TRP 1 is providing AM modulation accordingly.
On the 80m band, AM is used in places, hence, that would be a nice possibility to join the action. However, filters will have to be modified.
On the 160m band one may want to aim for A1 operation. A 1.843MHz crystal would do the trick here... However, the wiring will have to be changed to engage the BFO in the "2182kHz" labeled switch position.
What is the prospect for the future use of the rig?
I believe it would provide endless fun during field day operations. In particular when operated from cranks, independently from any power supplies.
The (yellow) box contains everything needed for QRP-ops, including a telescopic vertical antenna and a "long(er) wire" aerial.
I figure it could be reasonable to replace the TBA570 receiver with a NE612 superhet design for side-band use.
The XOs could be replaced by either a DDS or some synthesizers for enhanced flexibility.
Some PIC controls seem obvious, the automatic SOS-TXing is inadequate, obviously.
It all comes down to how much modification is actually wanted. Maybe the greatest fun can be obtained when staying as close as possible to the original functionality, i.e. AM on 80m, CW on 40m and 600m.
Other than that, it is an extremely nice addition to my marine radio collection.
Thursday, April 14, 2011
Magnetic Loop Antenna Idea
Had an idea... again, I have not tried this yet.
A magnetic loop antenna, as we all know, are relatively narrowband. For mono-band QRSS, WSPR or WSJT activity this is not a problem at all. But what if one would like to receive (well, let's start looking at RX only at this point) on an additional frequency at the same band or maybe even in another band, such a simple magnetic loop antenna would not be so ideal.
Now that the problem is defined, let's have a look at possible solutions. The basic idea is to build two loops sharing one coupling loop by using heavy gauge speaker twin lead.
RF-principle: Two parameters determine the resonance of a magnetic loop antenna, the diameter of the loop and the capacitor.
For a second frequency in one band one may consider to shorten one cable of the twin lead by just the right amount. This will certainly result in a second resonance close to the first resonance. Since the two leads are somewhat close, there will certainly be some capacitive coupling, what influence this will have, if at all, will be subject to experimentation. The second consequence of the proximity of the leads would be that the lengths cannot be drastically different, hence, using the same capacitor, the frequency offset would be small.
For dual-band use, the two loops should be resonated by individual capacitors. Here, the capacity between the loops will certainly have a dramatic impact on the resonance frequencies.
There is yet another possibility, probably the most messy one... Connecting the second loop to the resonating capacitor of the first loop symmetrically using identical high(er) value capacitors. This will (slightly) increase the resonance frequency of the second loop. I figure, this third possibility is somewhat impractical.
Whatever option is chosen, the (single) coupling loop will couple both loops equally well, since the size of the coupling loop is defined relative to the size of the main loop(s), i.e. 1/6 to 1/4 depending on the loop's environment.
A magnetic loop antenna, as we all know, are relatively narrowband. For mono-band QRSS, WSPR or WSJT activity this is not a problem at all. But what if one would like to receive (well, let's start looking at RX only at this point) on an additional frequency at the same band or maybe even in another band, such a simple magnetic loop antenna would not be so ideal.
Now that the problem is defined, let's have a look at possible solutions. The basic idea is to build two loops sharing one coupling loop by using heavy gauge speaker twin lead.
RF-principle: Two parameters determine the resonance of a magnetic loop antenna, the diameter of the loop and the capacitor.
For a second frequency in one band one may consider to shorten one cable of the twin lead by just the right amount. This will certainly result in a second resonance close to the first resonance. Since the two leads are somewhat close, there will certainly be some capacitive coupling, what influence this will have, if at all, will be subject to experimentation. The second consequence of the proximity of the leads would be that the lengths cannot be drastically different, hence, using the same capacitor, the frequency offset would be small.
For dual-band use, the two loops should be resonated by individual capacitors. Here, the capacity between the loops will certainly have a dramatic impact on the resonance frequencies.
There is yet another possibility, probably the most messy one... Connecting the second loop to the resonating capacitor of the first loop symmetrically using identical high(er) value capacitors. This will (slightly) increase the resonance frequency of the second loop. I figure, this third possibility is somewhat impractical.
Whatever option is chosen, the (single) coupling loop will couple both loops equally well, since the size of the coupling loop is defined relative to the size of the main loop(s), i.e. 1/6 to 1/4 depending on the loop's environment.
Wednesday, April 6, 2011
17m XTAL Controlled QRSS / WSPR / QRP / SDR
Sorry for having been silent for a while. Some new thought, although not entirely mine, I believe sharing it this way would be more than appropriate.
The idea about the frequency generation is borrowed from DJ1ZB. Ha-Jo uses CB crystals on their fundamental and doubles the result.
Doubling sounds very much like two things I previously disclosed on this blot, namely, the subharmonic direct conversion receiver (e.g. this) and the subharmonic I/Q-SDR (see earlier posts on the SDR and possible frequencies).
Both designs rely on a local oscillator on half the operating frequency.
Concentrating what could be interesting for QRP, QRSS and WSPR, lets have a closer look to the available crystals.
Additionally, 18.090MHz is the quite close to the QRP frequency, a subharmonic direct conversion receiver would be an obvious choice, so would be a transmitter with a doubler...
Very obviously, the other frequencies are directed more to QRSS and WSPR. I am not going into the QRSS feature here, it is kinda trivial (see above).
Remaining topic: WSPR. The frequency produced by the 16T-XTAL is very very close to the WSPR "dial frequency" 18.1046MHz. With a Pierce oscillator the tiny amount of 633Hz upwards pull should not be a big deal; remember, on half the frequency, one only needs to pull half the distance.
RX: subharmonic direct conversion.
TX: subharmonic mixing of the local oscillator with an audio signal should create a DSB signal... that's the theory... I have not yet tried it yet, however, I fail to see any reason why this should not work.
The idea about the frequency generation is borrowed from DJ1ZB. Ha-Jo uses CB crystals on their fundamental and doubles the result.
Doubling sounds very much like two things I previously disclosed on this blot, namely, the subharmonic direct conversion receiver (e.g. this) and the subharmonic I/Q-SDR (see earlier posts on the SDR and possible frequencies).
Both designs rely on a local oscillator on half the operating frequency.
Concentrating what could be interesting for QRP, QRSS and WSPR, lets have a closer look to the available crystals.
- 27.105MHz (12T) => 9.035MHz x 2 = 18.070MHz
- 27.135MHz (15T) => 9.045MHz x 2 = 18.090MHz
- 27.155MHz (16T) => 9.051667MHz x 2 = 18.103333MHz
- 27.165MHz (17T) => 9.055MHz x 2 = 18.110MHz
Additionally, 18.090MHz is the quite close to the QRP frequency, a subharmonic direct conversion receiver would be an obvious choice, so would be a transmitter with a doubler...
Very obviously, the other frequencies are directed more to QRSS and WSPR. I am not going into the QRSS feature here, it is kinda trivial (see above).
Remaining topic: WSPR. The frequency produced by the 16T-XTAL is very very close to the WSPR "dial frequency" 18.1046MHz. With a Pierce oscillator the tiny amount of 633Hz upwards pull should not be a big deal; remember, on half the frequency, one only needs to pull half the distance.
RX: subharmonic direct conversion.
TX: subharmonic mixing of the local oscillator with an audio signal should create a DSB signal... that's the theory... I have not yet tried it yet, however, I fail to see any reason why this should not work.
Saturday, March 19, 2011
75Ohms Coax update
Low loss & cheap, that was just one part of the story about RG-6 sat-coax. The other side would be the (cheap) accessories one can get for the 75Ohms F-system. My secondary grabber system (Target HF3 & Yaesu FRT-7700) is hooked up to 75Ohms for a couple of days. Additionally I am using one of those ("Sat-Flex"-adapter):
For the readers who have never seen those before, such devices are use to lead a TV-sat signal from the LNC to the indoors sat-receiver. Those adapters are squeezed between a window and a window frame.
There are other accessories available at very very low prices. Splitters, barrels, splitters, etc.
And even better news. I not buying the cheapest available, one may be lucky and obtain this:
Well, it was slightly more expensive (€8.- for 10m @ HEMA) than the previous example, and it did not come with F-connectors. However, see the air-cells? Next to the Al-foil shield, there is a Cu-braid, the soul is made from Cu too. This cable can be soldered just fine.
Somehow the stuff reminds me of aircom-plus (€3.35 for 1m)... many times cheaper though...
There are other accessories available at very very low prices. Splitters, barrels, splitters, etc.
Somehow the stuff reminds me of aircom-plus (€3.35 for 1m)... many times cheaper though...
Monday, March 14, 2011
75Ohms, why not?!
I have been experimenting a bit with more or less cheap (inexpensive that is) materials lately. Came across something called RG-6, or, in other words, very inexpensive 75Ohms coax-cable for TV-satellite reception.
TV-sat-RX means, that losses at frequencies between 1GHz and 2GHz are acceptable. The cable itself proofs on that point, foam dielectric....
We amateurs are using stuff called RG-58, RG-213 etc. for ages.... This relatively expensive stuff is rated 50 (or 52) Ohms, as most of our transceiver's aerial connectors. Most of the modern times transceivers however still employ so called UHF-connectors... something sooo outdated, you would not believe it! And further, look at the inside of 'm transceivers, there is not 50Ohms match found anywhere.... So, what is that hype about 50Ohms anyway?! I don't know!
And hence, I don't care!
However, nowadays UHF-connector have a thread for the the shield. The soul of the sat-coax is copper and hence can be soldered easily. There is hence an easy way to adapt 50Ohms PL-connectors to 75Ohms F-connectors.
My local hardware store provides me with satellite-grade 75Ohms cable for a price of about €5.- per 10m including two of the so called F-connectors... a price, RG-58 cannot match, not to speak about the (two) UHF-connectors aka PL259.
Let's further search for justification of using more expensive 50Ohms-stuff rather than 75Ohms-mass-ware. A dipole is mentioned to have an impedance of 60Ohms.... OK 50Ohms is marginally closer to that than 75Ohms would be.... but... does that matter? I don't think so!
Let's turn to the connectors for a change. I mentioned UHF-connector (aka PL-connectors) before. To the time these connectors have been invented, names like UHF were justified, I believe. However, in modern times, this merely reflects a relict from the glorious past... UHF connectors are considered good for shortwave and lower frequencies. Connectors considered suitable for UHF as of today would be BNC and N-connectors (both 50Ohms nevertheless).
Still 50Ohms, but why? I believe, we stick to 50Ohms (or 52Ohms) for reasons of tradition. Industry seems to like that, since there still is a reason to produce (and sell) 50Ohms coax like RG-58 and RG-213.
As radio-amateur, or HAM for good measures, you always want to watch your options.
I watched mine, and I came to the conclusion that, where ever I would need coax-cable the cheapest commercial (i.e. mass market) solution available was the best for the purpose. Hence I will use RG-6 or whatever (low loss) will be available for cheap at my local hardware store. Who needs specialized retailers, if a tiny change in the setup will do?
Up to now I was writing about low power and low-noise reception. Let's face the other option for a change... QRO! When facing high power, I would anyway not consider using coax-cables. Those just get hot on losses. For QRO, I personally would/will/do go for open wire feed-lines. If that appears too difficult to do, I still would propose using high ohmic window-line for the purpose.
Conclusion: use cheap satellite-TV-coax and forget about expensive 50Ohms stuff!
73!
TV-sat-RX means, that losses at frequencies between 1GHz and 2GHz are acceptable. The cable itself proofs on that point, foam dielectric....
We amateurs are using stuff called RG-58, RG-213 etc. for ages.... This relatively expensive stuff is rated 50 (or 52) Ohms, as most of our transceiver's aerial connectors. Most of the modern times transceivers however still employ so called UHF-connectors... something sooo outdated, you would not believe it! And further, look at the inside of 'm transceivers, there is not 50Ohms match found anywhere.... So, what is that hype about 50Ohms anyway?! I don't know!
And hence, I don't care!
However, nowadays UHF-connector have a thread for the the shield. The soul of the sat-coax is copper and hence can be soldered easily. There is hence an easy way to adapt 50Ohms PL-connectors to 75Ohms F-connectors.
 |
| F-connector 75Ohms coax and a 50Ohms UHF-connector |
My local hardware store provides me with satellite-grade 75Ohms cable for a price of about €5.- per 10m including two of the so called F-connectors... a price, RG-58 cannot match, not to speak about the (two) UHF-connectors aka PL259.
Let's further search for justification of using more expensive 50Ohms-stuff rather than 75Ohms-mass-ware. A dipole is mentioned to have an impedance of 60Ohms.... OK 50Ohms is marginally closer to that than 75Ohms would be.... but... does that matter? I don't think so!
Let's turn to the connectors for a change. I mentioned UHF-connector (aka PL-connectors) before. To the time these connectors have been invented, names like UHF were justified, I believe. However, in modern times, this merely reflects a relict from the glorious past... UHF connectors are considered good for shortwave and lower frequencies. Connectors considered suitable for UHF as of today would be BNC and N-connectors (both 50Ohms nevertheless).
Still 50Ohms, but why? I believe, we stick to 50Ohms (or 52Ohms) for reasons of tradition. Industry seems to like that, since there still is a reason to produce (and sell) 50Ohms coax like RG-58 and RG-213.
As radio-amateur, or HAM for good measures, you always want to watch your options.
I watched mine, and I came to the conclusion that, where ever I would need coax-cable the cheapest commercial (i.e. mass market) solution available was the best for the purpose. Hence I will use RG-6 or whatever (low loss) will be available for cheap at my local hardware store. Who needs specialized retailers, if a tiny change in the setup will do?
Up to now I was writing about low power and low-noise reception. Let's face the other option for a change... QRO! When facing high power, I would anyway not consider using coax-cables. Those just get hot on losses. For QRO, I personally would/will/do go for open wire feed-lines. If that appears too difficult to do, I still would propose using high ohmic window-line for the purpose.
Conclusion: use cheap satellite-TV-coax and forget about expensive 50Ohms stuff!
73!
Friday, March 4, 2011
6m QRSS
This is an extremely easy one. Most QRSS operators once built a 30m MEPT. There is an easy way to recycle those transmitters for 6m. With a converter circuit running a 40MHz oscillator, a 10.140MHz MEPT would be right away transmitting on 50.140MHz. Not too bad, I figure. A NE612 would probably be the easiest and cheapest way to get there this way.
Alternatively, a subharmonic mixer (two anti-parallel diodes) on a 20MHz oscillator would be even easier to build.
There are canned oscillators for 40MHz and 20MHz available, not to mention those cheap crystals.
Alternatively, a subharmonic mixer (two anti-parallel diodes) on a 20MHz oscillator would be even easier to build.
There are canned oscillators for 40MHz and 20MHz available, not to mention those cheap crystals.
Wednesday, March 2, 2011
2m QRSS
Something I was thinking of occasionally, QRSS on VHF, UHF, SHF and EHF bands.
Lets first start with a band that is accessible to all of us, the 2m band.
A short chat with Dave (G7UVW) brought up two frequencies of interest.
Both QRGs can be reached with CB-TX-crystals on their fundamental frequency and doubling the signals a couple of times. 9.x MHz will have to be multiplied by a factor of 16. With a little pull and the right oscillator circuit, this all should be fairely easy.
144.070 MHz
Channel 5T (27.015MHz) will be, very obviously, be 9.005MHz on the fundamental frequency. The resulting frequency on the 2m would be 144.080MHz. A little harmless down pull to 9.004375MHz on the fundamental will get us to 144.070MHz.
144.4905 MHz (WSPR-QRG)
We got two options here, channels 11T (27.085MHz) and 12T (27.105MHz).
11T would require a Pierce oscillator which oscillates above the series frequency of the crystal. The fundamental of 11T is 9.028333MHz, while the required frequency for the target-frequency would be 9.03065625MHz. The difference of 2.323kHz is not problem to a Pierce oscillator at all.
12T will provide a 9.035MHz signal. The pull of 4.344kHz to 9.03065625MHz is doable, could however result in a less stable oscillator.
Put the design into practice seem not to be a great deal, however, frequency stability is a great deal here. So, I figure, good temperature stabilization is in order. The rest is in fact pretty straight forward. I do have to admit that the first ever ham-radio transmitter I built (age 15, just licensed) was a 144MHz A1A TX, based on a CB crystal and BF199 transistors.
Lets first start with a band that is accessible to all of us, the 2m band.
A short chat with Dave (G7UVW) brought up two frequencies of interest.
- 144.070 MHz
- 144.4905 MHz (WSPR)
Both QRGs can be reached with CB-TX-crystals on their fundamental frequency and doubling the signals a couple of times. 9.x MHz will have to be multiplied by a factor of 16. With a little pull and the right oscillator circuit, this all should be fairely easy.
144.070 MHz
Channel 5T (27.015MHz) will be, very obviously, be 9.005MHz on the fundamental frequency. The resulting frequency on the 2m would be 144.080MHz. A little harmless down pull to 9.004375MHz on the fundamental will get us to 144.070MHz.
144.4905 MHz (WSPR-QRG)
We got two options here, channels 11T (27.085MHz) and 12T (27.105MHz).
11T would require a Pierce oscillator which oscillates above the series frequency of the crystal. The fundamental of 11T is 9.028333MHz, while the required frequency for the target-frequency would be 9.03065625MHz. The difference of 2.323kHz is not problem to a Pierce oscillator at all.
12T will provide a 9.035MHz signal. The pull of 4.344kHz to 9.03065625MHz is doable, could however result in a less stable oscillator.
Put the design into practice seem not to be a great deal, however, frequency stability is a great deal here. So, I figure, good temperature stabilization is in order. The rest is in fact pretty straight forward. I do have to admit that the first ever ham-radio transmitter I built (age 15, just licensed) was a 144MHz A1A TX, based on a CB crystal and BF199 transistors.
Monday, February 28, 2011
The T2SFM Antenna
The T2FD (aka TTFD, Terminated Tilted Folded Dipole) may be know to many of us. No, I am not going to discuss the T2FD here. It is just mentioned since it forms the basis for the following design considerations.
The only thing we should keep in mind, the span of a T2FD is 30% of the lowest wavelength, not 50% as a regular folded dipole would be. The distance of the fold is 1% of the wavelength.
In a country as densely populated as Holland, one needs to think of room saving antenna solutions regularly. The goal of the game is hence to reduce the span of antenna setups.
The aerial I am thinking of needs to the at least the popular QRSS bands 80m - 30m, possibly 160m and 20m.
First design step, the a quarter-wave radiator for 30m and tilt it. The length of such radiator would be 7.6m.
Second step, a trap terminating the 30m radiator. This trap also acts as loading inductor for the lower frequencies. As a fist assumption, I was randomly picking 10µH, the resulting capacitance is 25pF.
Third, the folding distance is chosen to be 50cm, reflecting an operation wavelength of 50m, which is somewhere between 40m and 80m obviously.
The last and remaining bit would be the second "T" of the name, i.e. the termination. I figured 600Ohms could be a good value to start from. When putting this into reality, one needs to remember that the termination resistor should not be induction and should be rated at least 30% of the power applied to the aerial.
There the MMANA script a hacked in:
80m - 20m T2SFM
*
10.12
***Wires***
4
0.0, 0.0, 0.0, -7.0, 0.0, 3.0, 8.000e-04, -1
-7.0, 0.0, 3.0, -7.0, 0.0, 3.5, 8.000e-04, -1
-7.0, 0.0, 3.5, 0.0, 0.0, 0.5, 8.000e-04, -1
0.0, 0.0, 0.0, 0.0, 0.0, 0.5, 8.000e-04, -1
***Source***
1, 1
w1b, 0.0, 1.0
***Load***
2, 1
w2c, 0, 2.17, 114.0, 0.0
w4c, 1, 600.0, 0.0
***Segmentation***
800, 80, 2.0, 1
***G/H/M/R/AzEl/X***
2, 0.0, 1, 600.0, 120, 60, 0.0
###Comment###
Mod by Joachim, PA1GSJ 2/28/2011 9:55:09 PM
Created by Joachim, PA1GSJ 2/28/2011 9:08:01 PM
The first simulations look promising, still a lot room for optimizations. Would be time to also start putting stuff together and try out if this contraption is any good.
REVISION
Had another thought about the 30m trap. The easiest way to make a trap would be a coax trap. With a diameter of 4cm, a length of 4cm a coax trap would have a self-inductance of 2.17µH and a capacitance of 114pF. Purely mechanical, 117cm of RG58 are required in order to form 8 turns on a 4cm diameter.
The only thing we should keep in mind, the span of a T2FD is 30% of the lowest wavelength, not 50% as a regular folded dipole would be. The distance of the fold is 1% of the wavelength.
In a country as densely populated as Holland, one needs to think of room saving antenna solutions regularly. The goal of the game is hence to reduce the span of antenna setups.
The aerial I am thinking of needs to the at least the popular QRSS bands 80m - 30m, possibly 160m and 20m.
First design step, the a quarter-wave radiator for 30m and tilt it. The length of such radiator would be 7.6m.
Second step, a trap terminating the 30m radiator. This trap also acts as loading inductor for the lower frequencies. As a fist assumption, I was randomly picking 10µH, the resulting capacitance is 25pF.
Third, the folding distance is chosen to be 50cm, reflecting an operation wavelength of 50m, which is somewhere between 40m and 80m obviously.
The last and remaining bit would be the second "T" of the name, i.e. the termination. I figured 600Ohms could be a good value to start from. When putting this into reality, one needs to remember that the termination resistor should not be induction and should be rated at least 30% of the power applied to the aerial.
There the MMANA script a hacked in:
*
10.12
***Wires***
4
0.0, 0.0, 0.0, -7.0, 0.0, 3.0, 8.000e-04, -1
-7.0, 0.0, 3.0, -7.0, 0.0, 3.5, 8.000e-04, -1
-7.0, 0.0, 3.5, 0.0, 0.0, 0.5, 8.000e-04, -1
0.0, 0.0, 0.0, 0.0, 0.0, 0.5, 8.000e-04, -1
***Source***
1, 1
w1b, 0.0, 1.0
***Load***
2, 1
w2c, 0, 2.17, 114.0, 0.0
w4c, 1, 600.0, 0.0
***Segmentation***
800, 80, 2.0, 1
***G/H/M/R/AzEl/X***
2, 0.0, 1, 600.0, 120, 60, 0.0
###Comment###
Mod by Joachim, PA1GSJ 2/28/2011 9:55:09 PM
Created by Joachim, PA1GSJ 2/28/2011 9:08:01 PM
The first simulations look promising, still a lot room for optimizations. Would be time to also start putting stuff together and try out if this contraption is any good.
REVISION
Had another thought about the 30m trap. The easiest way to make a trap would be a coax trap. With a diameter of 4cm, a length of 4cm a coax trap would have a self-inductance of 2.17µH and a capacitance of 114pF. Purely mechanical, 117cm of RG58 are required in order to form 8 turns on a 4cm diameter.
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