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 ATU CB master EM27

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karelgol
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karelgol


Call Sign : 19-CT-024
Posts : 87
Times Thanked : 0
Join date : 2020-05-21
QTH or Location : Steenwijk, JO32bs
Equipment Used : Magnum 257HP,President Lincoln I, President Bill Asc, AMP-150, Imax-2000, Emperor LA-50
Age : 63

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PostSubject: ATU CB master EM27   ATU CB master EM27 Icon_minitimeTue Feb 02, 2021 7:15 pm

Does anyone has an manual for this one?  I recently bought one and on the Albrecht site the only instruction for use is something like "fiddle with the knobs". There is a "tune" and a "load" knob on the front. On other similar models i've seen two knobs "capacitive" and "inductive". Would "load" translate into "inductive" and "tune" into "capacitve". or is this too simple thinking?

73
Karel
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Victor
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Victor


Call Sign : 26-CT-3228 Ham M7VIC
Posts : 2486
Times Thanked : 169
Join date : 2019-11-10
QTH or Location : Bedford
Equipment Used : Various

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PostSubject: Re: ATU CB master EM27   ATU CB master EM27 Icon_minitimeTue Feb 02, 2021 9:07 pm

Hi Karel,

This unit is a simple 'Pi-Network' tuner. (ATU or Antenna Tuning Unit.) Both the controls are a variable capacitor, (polyvaricon, usually 365pf or 500pf), and internally there is a coil calculated for the 26-28MHz region.

They are simple to use and hence why they don't usually come with instructions. (The Zetagi MM27 is similar and has no instructions.)

The usual way to hook them up is - CB Transceiver to SWR meter to ATU to Antenna. 

You simply adjust the controls until the SWR reads the lowest. This will depend on your antenna SWR and frequency in use so you will have to basically 'twiddle' Wink

You do get the hang of them quickly and learn to 'drive' it with practice. You will usually also hear a sharp increase in received noise when you achieve 'tuning' also. (Should really be called 'matching' as they actually match the 50 ohms of your rig to the mismatch impedance of the antenna in use.)

They can seem quite sharp or fiddly to use at first but you soon get the hang of it. With the limited frequency range of CB frequencies you will find that once you have found the sweet spot you will hardly have to adjust off from the found settings.

I use a similar, (but multi-coil and bigger capacitors), circuit in a homebrew ATU and find it invaluable.

Some will argue about their use but usually as they have 'learned' the 50 ohms coax SWR method. My antennas are all 'resonant' to the frequency in use but due to their construction present a difference in impedance which the ATU matches for my radio. That's why they're usually called AMU's or Antenna Matching Units.

Be careful in use, they can tune/match in even the most appalling antenna setup which at worst will arc and burn out the capacitors. At best you'll just have a terrible antenna setup but you'll get a low SWR....not the best transmission setup! Wink

The capacitors in them usually can't handle a bad mismatch of 50W or so meaning the typical 100W manufacture claim is widely out.


Some people may suggest 'why bother?'

If you have an alternative antenna setup such as a homemade dipole the impedance will not be 50 ohms and therefore the SWR will read high. You 'tune' the dipole to resonance by getting the SWR as low as you can at the frequency in use and then place the ATU in line further matching the impedance keeping your radio happy to see 50 ohms.
It's also handy to give your antenna a wider range across the frequencies.

Their effectiveness has and always will be argued about but results speak louder than words Smile


Long winded I know but hope that helps you out.


All the best,
Victor
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karelgol
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karelgol


Call Sign : 19-CT-024
Posts : 87
Times Thanked : 0
Join date : 2020-05-21
QTH or Location : Steenwijk, JO32bs
Equipment Used : Magnum 257HP,President Lincoln I, President Bill Asc, AMP-150, Imax-2000, Emperor LA-50
Age : 63

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PostSubject: Re: ATU CB master EM27   ATU CB master EM27 Icon_minitimeTue Feb 02, 2021 9:15 pm

Thanks Victor, as always clearly phrased and reassuring.

I'm still searching for the easiest/best antenna to build for DX on 11m. Now i'm considering a moxon, but i am spoiled by the widebandedness of DEWD antennas. Thought this ATU might just help.

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Victor
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Call Sign : 26-CT-3228 Ham M7VIC
Posts : 2486
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Join date : 2019-11-10
QTH or Location : Bedford
Equipment Used : Various

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PostSubject: Re: ATU CB master EM27   ATU CB master EM27 Icon_minitimeTue Feb 02, 2021 9:48 pm

No worries Karel, I thought a fuller answer would be better than simply 'twiddle it' Wink

For last Summer's seasonal propogation I used a simple Inverted V Dipole and managed a few contacts spanning hundreds of miles on CB frequencies. I also tried out a 'Hentenna' and a simple Horizontal Dipole mounted at the highest point on my roof in the attic/loft each with some success.

I had planned to play with a Moxon reading up somewhat, but unfortunately I don't have any experience with the Dual Element Wideband Dipole.

Since then I took my Ham licence and therefore started playing with antennas for those bands instead. My homebrew ATU/AMU was invaluable as although my antennas are Inverted V's, they zig-zag somewhat to fit the loft space so despite being resonant they have a different impedance to the usual 50 ohms. I had originally matched the impedance through standard coax but have since converted to 600 ohm homemade ladder line with a 1:1 current choke and then RG213 to my matcher.

This now allows me to make contacts several hundred miles and even over a thousand miles on certain bands with just my Foundation licence 10W! Smile


Good luck with your antenna experimentations, I do hope you achieve success. Summer will be upon us soon offering some good 'skip' at those higher frequencies. Looking forward to it myself!


All the best,
Victor
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PostSubject: Re: ATU CB master EM27   ATU CB master EM27 Icon_minitime

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