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| 28MHz 5/8 wave base 6m a.g. vertical aluminium tube 20mm 2m50 and a fishing rod with shunted 1.5mm2 wire total length 6,4meter = 0.64 x wave |
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| Base of former CB 1/2wave or 5/8wave used with external coil 3 wgd ( 1 wdg in the socket) The original coil is removed ( 5+3 wdg 32mm close wound) 3wdg gave best matching using 2 radial wires 1:1.6 got 1:1.2 when 1 radial hanging vertical down... results are very good in compare with the higher h-dipole although the groundwave of DB0PBS at 50km only is received on the dipole. Other signals over iono Es gave comparable snr sometimes even better |
needed is XL +425j to balance out the capacitive -425
Rothammel say 2.3uH for D/d=4000 the ratio of lenght and conductor diameter does have influence on the inductance the thinner the conductor the higher the inductance
The original coil in the base for 11m is 8 wdg 32mm = 2.8uH The CD 11m vertical matching uses a grounded coil with tap at 3 wdg to the center pin PL259.
This 0.64 wave has uses a series inductance to match not grounded
I could not find a match with a grounded tap that would protect against static discharges.
The best matching found was a 3 wdg 50mm diameter coil of 2.5mm2
Way less then the calculated 2.3uH
according to this calculator only 0.3uH ... more coil gave worse result....
https://m0ukd.com/calculators/air-cored-inductor-calculator/
source https://ham.stackexchange.com/questions/9780/calculating-all-specifics-for-a-5-8-antenna
interesting sources : https://ham.stackexchange.com/questions/3829/coaxial-folded-dipole-antenna-matching-impedance
for dipoles
https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/folded-dipole.php
K3 144 XVTR the UT5JCW did have a IMD problem with a very stong local HAM
I found another XVTR with high dynamic mixer very identical PCB look alike
the TR 2018HD designed by UR3LMZ this one uses the ADE-12 + H-level mixer
the UT5JCW uses a d-gate fet mixer
the 28MHz level needed is a bit higher 5mW for full 10W / 12W the K3 level is max 1.5mW in low power XVTR mode then i got about 4W enough to drive my PA.
I use an extern 116 TCXO l.o. and a switching unit to power 12V at band 144 only
1 issue i had with this TCXO Rojo was high temperature caused by using thin piece coax between TCXO and XVTR the extra capacity loaded the TCXO output driver too much and temp went up to 52C ! i had to change the connection mass at the tcxo side.
The far too strong output of the tcxo must be reduced with 4p7 to the ADE-12
better is maybe a potentiometer direct at the TCXO output pin and then a low C shielded cable to the
input of the ADE-12 to prevent 116MHz leakage signal
This TR2018HD failed the test in the September 144MHz contest helas.
I now use the IC706 and this old but FB ICOM engineered can handle the very strong local 144 MHz signals even with the extra SPF5189z preamp on !
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| TCXO over thin coax to XVTR too much load for the TCXO driver |
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