[Elecraft] KAT 500 Loses Match

[Fred Jensen]

The military isn't chasing DX or contesting ... They need enough 
radiation for adequate operation in their networks.  In the example, a 
resistor in the folded dipole gives them that, they don't care about the 
3dB, and a much easier radio system to set up.  Little different for us 
"Amateurs."

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

Ken WA8JXM wrote on 1/13/2024 9:16 PM:
> Unless its something like a log periodic, I think anything with those 
> frequency/SWR specs can only do it with high resistive losses.  It 
> reminds me of the HF dipole B&W makes for the military: it is designed 
> to appear to have a low SWR by having 3 db of  resistive losses.  The 
> military considered that an acceptable design.   Remember, antenna 
> losses affect TX and  RX, so that's 6 db system loss.
>
> Ken WA8JXM
>
> On 1/13/2024 2:37 PM, Walter Underwood wrote:
>> The C HA-50HD is rated for 250 W SSB or 75 W for digital modes. It 
>> gets a flat SWR with resistive losses in the transformer. That is why 
>> the transformer has heat sink fins. A KPA500 is almost certainly 
>> overheating the transformer and causing failures. I would back off 
>> the power to match the ratings. For SSB with compression, I would run 
>> less than 250 W, maybe 150 W.
>>
>> It is possible that overheating has caused permanent damage to the 
>> transformer.
>>
>> One detailed set of tests showed at least 75% of transmitter power 
>> being turned into heat in the transformer.
>>
>> Here is what Comet says about that antenna.
>>
>> CHA-250HD (New version of the CHA-250B)
>>
>> The Comet CHA-250HD is the revised CHA-250B.
>>
>> The top section of aluminum has been replaced with a solid whip for 
>> greater flexibility and less strain on the lower sections in high 
>> winds.  A uniquely designed broadband vertical requiring NO GROUND 
>> RADIALS.
>>
>> This is EXTREMELY easy to assemble, requires no tuning or adjustments 
>> and VSWR is under 1.6:1 continuously from 3.5MHz – 57MHz!
>>
>> It is not a 1/4 wave vertical, but an end-fed long wire type antenna 
>> with a matching transformer in a vertical position.
>> Broadband:
>> TX 3.5 – 57MHz
>> RX 2.0 – 90MHz
>> VSWR: 1.6:1 or less
>> Max Power: 250W SSB 75W Digital modes/FT8, etc…
>>
>> CHA-250HD Transformer Section
>>
>> This is a the “magic” behind the CHA-250HD, the transformer matching 
>> section.
>>
>> The transformer on the original CHA-250 had smooth sides.  The 
>> current version has a heat sink to dissipate heat created inside the 
>> transformer.
>>
>> Yes, some of the RF that enters the power feeding section is turned 
>> into heat rather than transmitted as RF, but that is one of the 
>> compromises needed to create a broad-band, low SWR, multi-band HF 
>> antenna with minimal visual impact.
>>
>> https://cometantenna.com/amateur-radio/base-antennas/multi-band-hfvhfuhf-2/ 
>>
>>
>> wunder
>> K6WRU
>> Walter Underwood
>> CM87wj
>> http://observer.wunderwood.org/ (my blog)
>>
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