04-02-2022, 02:33 PM
Ok, different approach.
Do you have access to a range of RF-style capacitors ?? The aim is to add a fixed capacitance directly at the unbalanced terminal of the tuner output in parallel to 'ground', changing what it sees as the effective impedance (R +- Jx) the antenna represents. That will affect the way the Auto-ATU sets up for minimum SWR, and might change which relays are selected at the time. A value in the range 100pF to maybe 500pF would be effective, but only if available.
The same Z-change effect can be achieved by adding an inductance in series at the tuner out, again changing the complex Z the antenna appears as to the tuner.
Grab a length of PVC tube (eg 40mm, 50mm) maybe 300mm long, using uninsulated copper wire with turns well-spaced apart to create an 'air-wound' inductor. Terminate on the ends of the PVC tube. One end goes to the antenna feed wire and a clip-lead goes from the turns to the tuner output to make a selectable-value inductance. You could try the whole inductor as a starting point and see how it tunes, maybe move the clip lead to 3/4 then 1/2, then 1/4 of the turns while testing in each condition. That is simply making it a slightly-loaded "longwire" but it will present a different Z at the tuner terminal, thus it will alter which internal L's and C's are in use at any given frequency. You can always shift the clip lead to exclude any in-line inductance to go back to 'standard operation condition'.
I'm not sure what the "inflammable tuner" brand and model code is (not stated so far) but that info might be useful to find a schematic and then find those relays you mentioned. Of course it might have already sustained enough damage to be unreliable.
Your thoughts ??
Doug
Do you have access to a range of RF-style capacitors ?? The aim is to add a fixed capacitance directly at the unbalanced terminal of the tuner output in parallel to 'ground', changing what it sees as the effective impedance (R +- Jx) the antenna represents. That will affect the way the Auto-ATU sets up for minimum SWR, and might change which relays are selected at the time. A value in the range 100pF to maybe 500pF would be effective, but only if available.
The same Z-change effect can be achieved by adding an inductance in series at the tuner out, again changing the complex Z the antenna appears as to the tuner.
Grab a length of PVC tube (eg 40mm, 50mm) maybe 300mm long, using uninsulated copper wire with turns well-spaced apart to create an 'air-wound' inductor. Terminate on the ends of the PVC tube. One end goes to the antenna feed wire and a clip-lead goes from the turns to the tuner output to make a selectable-value inductance. You could try the whole inductor as a starting point and see how it tunes, maybe move the clip lead to 3/4 then 1/2, then 1/4 of the turns while testing in each condition. That is simply making it a slightly-loaded "longwire" but it will present a different Z at the tuner terminal, thus it will alter which internal L's and C's are in use at any given frequency. You can always shift the clip lead to exclude any in-line inductance to go back to 'standard operation condition'.
I'm not sure what the "inflammable tuner" brand and model code is (not stated so far) but that info might be useful to find a schematic and then find those relays you mentioned. Of course it might have already sustained enough damage to be unreliable.
Your thoughts ??
Doug
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
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If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.