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# Prescaler 144mhz to 14mhz and 144mhz to 7mhz

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#### neazoi

Hi I would like to make a small TX transverter from 144mhz to 14mhz and 7mhz.
Instead of mixing, which requires a stable vhf oscillator, I was thinking of a divider, which divides the stable 144mhz signal to hf.
for 14mhz a mc12080 can do a simple /10 divider but what about 7mhz?
Any other propositions for dividers for 14 and 7mhz would be helpful.
Thank you

A transverter by definition works two ways, you can't do that with a divider!

There are several problems with what you propose, the most obvious being that the output would be at digital levels so AM is out of the question. If you start with a 2m FM transmission and divide it by 10 you also divide the deviation. Doing it the other way around, multiplying 40m/20m by 10 you would have to use a PLL and that might produce a carrier at the right frequency but modulation would for the most part be lost.

I must sort out my antenna here so I can get back on the air - I've got withdrawal symptoms since rebuilding my house and having to take the old antenna down!

Brian.

neazoi

### neazoi

Points: 2
A transverter by definition works two ways, you can't do that with a divider!

There are several problems with what you propose, the most obvious being that the output would be at digital levels so AM is out of the question. If you start with a 2m FM transmission and divide it by 10 you also divide the deviation. Doing it the other way around, multiplying 40m/20m by 10 you would have to use a PLL and that might produce a carrier at the right frequency but modulation would for the most part be lost.

I must sort out my antenna here so I can get back on the air - I've got withdrawal symptoms since rebuilding my house and having to take the old antenna down!

Brian.
Thanks Brian.
Indeed it is a two way. However I am interested only in the transmitter portion. My handheld transceiver has dual receiver and separate TX and RX frequencies. The receiver can do SSB and CW on HF, however not transmitting. To transmit on HF, I was thinking to divide down the 144MHz to 14 or 7MHz and then use a filter and a small amplifier. While I was writing the previous message I saw that with a single mc12080 I can achieve all bands through 20m, by adjusting the division switches.
The division process has the advantage that there are no VHF stable local oscillators required, the frequency is divided down from the stable pll or dds of the radio. The error is divided down too, it should be very stable.

However I have not thought of the modulation yet. The handheld can only do narrow FM in TX, but FM is prohibited for radio amateurs on HF. So I can only do CW, by pressing and releasing the PTT of the transmitter accordingly.

For the amplifiers I could use class-E, which would directly match the digital output from the divider, or alternatively a higher class by including an input BPF.

However it would be nice to be able to do SSB or at least DSB. This can be done using the divided signal as the LO for a balanced modulator, followed by a filter, but you would have to speak through the external modulator microphone, not the transceiver mike.
But there may be a way unknown to me, that one could "transform" a higher frequency FM signal into a lower frequency SSB (or DSB) signal?

I advise you to do so with your antenna, speaking on the air techically, is much more exiting than internet!
I think you are located in UK, hey we might be able to talk live one day! I have much success from Greece to UK with a random wire antenna in the past.

Your idea would work but it would be far more difficult than an XTAL oscillator and mixer. If you shift the frequency by say 130MHz you can still use the existing modulator or add your own and it could be up or down mixed making it suitable for TX or RX.

I haven't done the math but given the relatively close spacing of the HF bands, it may be possible to use a simple PLL and VFO to shift 144MHz up/down to several of the bands with just a few switches but then it wouldn't be much more complicated to build a complete transceiver and forget the 144MHz altogether!

I demolished and rebuilt my house a few months ago, that's when the old antenna had to come down. I was under strict orders from "she who must be obeyed" that the new house must not have any external cables or antennas on it so I installed a 50mm plastic pipe underground in the foundations, one end popping up from the floor in my workshop and the other at the end of the garden. It carries two thick co-axial cables, one for HF and one for VHF plus network cables, an video from a remote security camera and a few multi-core cables for anything else. The indoor end is all connected and the VHF is working but I need to install the automatic ATU and power to it for the HF antenna. It is only a long wire but with the ATU it works reasonably well on 160m - 10m. I'm afraid it's a big job and wasn't placed very high on the priorities list.

Brian. (aka GW6BWX)

neazoi

### neazoi

Points: 2
Your idea would work but it would be far more difficult than an XTAL oscillator and mixer. If you shift the frequency by say 130MHz you can still use the existing modulator or add your own and it could be up or down mixed making it suitable for TX or RX.

I haven't done the math but given the relatively close spacing of the HF bands, it may be possible to use a simple PLL and VFO to shift 144MHz up/down to several of the bands with just a few switches but then it wouldn't be much more complicated to build a complete transceiver and forget the 144MHz altogether!

I demolished and rebuilt my house a few months ago, that's when the old antenna had to come down. I was under strict orders from "she who must be obeyed" that the new house must not have any external cables or antennas on it so I installed a 50mm plastic pipe underground in the foundations, one end popping up from the floor in my workshop and the other at the end of the garden. It carries two thick co-axial cables, one for HF and one for VHF plus network cables, an video from a remote security camera and a few multi-core cables for anything else. The indoor end is all connected and the VHF is working but I need to install the automatic ATU and power to it for the HF antenna. It is only a long wire but with the ATU it works reasonably well on 160m - 10m. I'm afraid it's a big job and wasn't placed very high on the priorities list.

Brian. (aka GW6BWX)

Thanks for the info about the transverter Brian.
About the antennas, as I see, you are one of the many that not only do not have the space for HF antennas but also these antennas must be stealth (hidden). There are a few stealth antennas you can try and each will depend on your space.
1. Big loop, parallel to your roof and close to it, so it cannot be seen.
2. Small loop, out of thick copper plumper's tubes, if a 1m^2 antenna is considered low profile in your place.
3. Vertical long wire. Usually these are hidden inside pvc vertical tubes that serve as flag supports.
All cables can be underground, if you have a small garden.
If you go QRP you could use very small diameter wire, as high as possible, so it cannot be easily seen by neighbours.
If you have an attic, you could also build your big and small loops inside it, completely stealth.
You could always use active whips for RX and small loops for TX if you have a 100W transceiver and you can accept the loop losses.

My call is sv3ora you will find my website on net search.

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You highlight one of the difference between your country and mine. Here, there are very strict regulations about heat insulation so the new roof had to include 4 layers of metalic reflecting foam (175mm total thick!) in it to stop heat loss. The walls are the same, it means the interior is basically a screened box, mobile phones don't work and for the most part domestic radio can't be picked up either. Any indoor antenna would be useless.

I have a fairly large area outside (~0.25 sq Km) but it's a densely wooded hillside. I can hide a long wire easily but being in the trees doesn't help it radiate! There is no open space big enough for a beam or a loop, besides, small loops are notoriously difficult to tune and generate many KV across the tuning capacitors. I did consider a vertical pole but again, it would be parallel to tall trees so most of the signal would be absorbed by them. I also live in a national park where they are very reluctant to allow any tall structures to be erected. So basically, it's a lovely place to live but a dead loss (pun intended) for RF.

Brian.

neazoi

### neazoi

Points: 2
You highlight one of the difference between your country and mine. Here, there are very strict regulations about heat insulation so the new roof had to include 4 layers of metalic reflecting foam (175mm total thick!) in it to stop heat loss. The walls are the same, it means the interior is basically a screened box, mobile phones don't work and for the most part domestic radio can't be picked up either. Any indoor antenna would be useless.

I have a fairly large area outside (~0.25 sq Km) but it's a densely wooded hillside. I can hide a long wire easily but being in the trees doesn't help it radiate! There is no open space big enough for a beam or a loop, besides, small loops are notoriously difficult to tune and generate many KV across the tuning capacitors. I did consider a vertical pole but again, it would be parallel to tall trees so most of the signal would be absorbed by them. I also live in a national park where they are very reluctant to allow any tall structures to be erected. So basically, it's a lovely place to live but a dead loss (pun intended) for RF.

Brian.

Difficult situation indeed...
The best options as far as I can think of would be:

The hidden flag-mast antenna (an antenna hidden inside a small diameter PVC tube that serve as a mast for a UK flag. I do not know how much will this be accepted bu the near by neighbours or the regulations there, but this is trully hidden.

The best option as far as I see is the big loop, at the outside perimeter of your roof, very close to the roof (a few cm) so that it cannot be noticed. Depending on the size of your roof this could be resonant to very low bands. This loop is resinant to the multiples of the L, ie if you make one for 40m, it will be resonant in higher bands as well. This is a really cheap antenna to build as well, comparing to it's size.
The loop can be supported by a few ceramic spacers from the roof. There is no high voltage capacitor required, as the coaxial center conductor is directly connected to one end of the wire, where the other end of the wire is connected to the outer conductor. For best results you will need a 4:1 balun between the coaxial and the loop.
The whole construction will look like these lightning protection systems, so no one will notice the antenna and if he does, you can support that it is a lighting protection for the roof.
If there is a metal plate below the loop, I believe that you will gain from that, increasing the gain (directivity) by 3db? (a guess)

I am planning to do the same antenna (resonant to 20m) for my roof as well, this is a truly stealth antenna.

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