Harry's 2 metre to 20 metre transverter

Hi Jomac,
That was one of those projects that I built to test the design and theory, but I never actually bothered to box everything up to form a finished projects. So I posted the working building blocks for the project.

For a transverter, the most important thing is to get a high-level mixer/oscillator, which will work in both directions, for TX and RX. I have built several versions of the oscillator, and by far the most easy to construct was the 26MHz crystal oscillator module. Use that to overdrive a transistors and you will have all the harmonics under the sun. With a 26MHz oscillator then the 5th harmonic is 130MHz. Mix that with your 144MHz and the difference is 14MHz. The VHF radio will then tune 14MHz to 16MHz (144MHz to 146MHz).

The dimensions of the resonators will not need to be changed at all for any other bands. Just re-tuned a bit. The local oscillator will always be in the range of 116MHz (to 28MHz to 30MHz), to 141MHz MHz (3MHz to 5Mhz). I just looked in my junk box to see what oscillator modules or crystals I had.

Your VHF radio covers a 2MHz range and the HF bands (except 10m) all have less than 1MHz span, so if your oscillator is 1MHz off then you can have 145MHz for the band-start.

I also used my CMOS synthesizer project with a simple prescaler to generate 1MHz steps, from 116MHz to 141MHz and that also worked fine.

The resonators I used were so designed to have a really High-Q to select only one harmonic I wanted, and there are two resonators to give double-filtering.

Now you have a local oscillators, all you need to do is use a simple mixer. Even an un-tuned mixer (a triflar wound torroid and 2 diodes are all that is needed) and you will have a receive-conver that will work from day-1. You can use it to listen to the HF bands and do any experiments. You can add HF and VHF filters later.

If you have a local oscillator with an output of about +10dBm then you can also use it for transmitting PROVIDING you attenuate the VHF rig (or turn the power down) to about 5mW max. In this event you do not even need a power amplifier or any switching whatsoever. You will also be surprised what you can work with a couple of mW on the HF bands. The mixer is bi-directional.

If you want to transmit a higher power level then you will need some TX/RF switching to put in a power amplifier for HF. the FT-290 has 2.5V-DC from the antenna socket that can be used to turn on a transistor and clank in a relay. The relay can then be used to put in a TX attenuator at VHF to the mixer, and put the power amplifier in circuit. I have published a 10W HF power amplifier on my homepages using CB type transistors, and that will give full output with just a few mW at the input.

COILS
The coils I quoted for 14Mhz you can scale easily. If you look at the calculators on my homepages you can key-in the details of the coils, then work out the impedance. they you can re-calculate the same impedance with different frequencies and also generate new coil-winding data. The on-line formulas I have published are surprisingly accurate.

Has this helped you any?





PS - To make a crude transverter all you need is a mixer and an oscillator - nothing more. That is what my project was all about.

I have a wonderful S/H signal generator that covers 9kHz to 3GHz. The output level is +30dBm (1 Watt). About two months ago I was sick, so I sat in the shack and played about a bit. I just wondered what I can do.

I "knocked up" the ferrite/2-diode mixer, connected my HF antenna and connected in different radios. I wound up the generator to 250mW and was able to run 100mW at HF using my FT-290. Above 250mw the FT-290 started blocking.

I was able to cover all the HF bands. I also converted my IC-7300 up to 145MHz and ran 100mW FM to the local repeater, and used a VHF Baufeng handheld radio for 11m CB on 27.345.

The final experiment was to listen to my local VHF repeater (SK0CT) on a cheap (2$) AM-only radio (550kHz to 1.65MHz) that I bought from a "cheap-shop" when I was in Saudi. That also worked a treat using slope-detection to resolve the NBFM.

In general, and within wide ranges, RF is only a collection of numbers and you can mix then as you like to receive almost anything. A "full-blown transverter" is only the same oscillator/mixer, but with a bit of filtering to be kind to your radio (IF) and other users on the bands.

One little anecdote: When I was in Saudi working for the National Guard on their nationwide communications system, I gave a demo to the Saudi and Philippine technicians in my workshop about "how a superhet receiver" works. I used a generator and (the same) MW radio to listen to the NG frequencies around 68MHz/72MHz. Later that day I found myself marched into the colonels office and had to explain to him why I was showing his technicians "spying techniques"  


BR Harry - SM0VPO

I was searching for a 2 metre down to 10 metre transverter with 2 metres being the IF frequency. The only circuit I found was Harry's 2m to 20m project. In the write up he says it should be easy to convert to other bands by scaling the necessary components etc. I can simply scale the coils by halving the dimensions, but what about the associated components such as caps etc., can I get away with simply halving the values?

I have very little in the way of test and measurement equipment now so I need to be pretty close the first time around, any suggestions and helpful advice?

I recently sold my Yaesu FT817, a great little radio but I simply could not get on with the menu system and structure, in fact this 817 was the third I have owned in 15 years, I got rid of the other two for the same reasons.

With the proceeds of the 817 sale I bought an old favourite of mine, an FT290. I also have several transverters that cover 6 metres, 4 metres and 70 Cms which I would like to use with the 290 hence my interests in the 2m to 10m transverter.

Another query I do have is also scaling Harry's transverter for the lower bands. 90mm for the long section of the coil network is fine, but when you get to 160m its something like 720mm long, would normal wound coils be the answer here?

TIA