12-11-2017, 02:50 PM
For info about the CHA250B...
I was perusing my HDD archive today and found a Comet folder and it contained a CHA250BX file dated 2009.. The part that was of greatest interest was the frequency coverage graph as attached below.
The lowest useful frequency dip is about 4MHz rather than 3.6, but does show SWR dips around 7 and 10MHz, more-or-less skips 14, then low 20's & low 30's, another dip mid to high 50's. The scaling shows < 2:1 across the spectrum from about 3MHz to 90MHz.
Given that it is basically a vertical radiator < 7M high/long plus the previous comments on the impedance matching UN-UN at the base, it seems hard to figure out how the low SWR is achieved across the bandwidth - unless the UN-UN ferrites are so lossy that they 'swallow up' the RF. Low SWR but poor efficiency if that is the case, both on transmit and receive.
Verticals still require ground planes - even ones like this..
73 Doug
I was perusing my HDD archive today and found a Comet folder and it contained a CHA250BX file dated 2009.. The part that was of greatest interest was the frequency coverage graph as attached below.
The lowest useful frequency dip is about 4MHz rather than 3.6, but does show SWR dips around 7 and 10MHz, more-or-less skips 14, then low 20's & low 30's, another dip mid to high 50's. The scaling shows < 2:1 across the spectrum from about 3MHz to 90MHz.
Given that it is basically a vertical radiator < 7M high/long plus the previous comments on the impedance matching UN-UN at the base, it seems hard to figure out how the low SWR is achieved across the bandwidth - unless the UN-UN ferrites are so lossy that they 'swallow up' the RF. Low SWR but poor efficiency if that is the case, both on transmit and receive.
Verticals still require ground planes - even ones like this..
73 Doug
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
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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.