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JT65 operation with CS-series or KN-Q7A plus Sandwich?

Adam Rong
 

All,

One of my customers in Japan tried JT65 with our rig KN-Q7A plus Sandwich and he melted his finals. Although I have read a document saying that:

Warning!

JT65 is equivalent to 100% key down carrier for the 47 second TX duration. You can easily overheat your final amplifier if it can not handle this situation for the full duration. If you melt your finals you have only yourself to blame.

Running at full output power is seldom necessary or desirable due to the incredible sensitivity of JT65. Most users find 5 to 10 watts (or less) highly effective and 25 to 30 watts is considered 'high power'. 

I still try to figure out how our kits can survive in such severe situation. My first idea is that the final transformer T3 should be replaced by an FT50-43 toroid to avoid saturation. If you don’t have an FT50-43 toroid, you can use two pieces of FT37-43 in parallel (to make still one hole but thicker). If this modification still cannot fix the problem, you probably need to tune the TX BPF IFT’s to a bit smaller RF output.

Another consideration might be frequency stability (thermal drift). Right now, the Sandwich digital VFO is using a regular crystal which has 30 ppm thermal accuracy in the full operational temperature range (although it should be good enough for SSB operation in normal temperature), but if it is a concern to make it as small as 1 ppm or 2 ppm, a TCXO of 3.3V 27 MHz might be a good choice to upgrade.

Thanks,
Adam

AA7US
 

Hi Adam,

Is the substitution of an FT50-43 toroid for T3 a recommended upgrade for any frequency band of KN-Q7A / CS-series transceiver if we want to try digital modes (long transmission times)?

Thank you,

John
AA7US

---In CHINA_QRP@..., <rongxh@...> wrote :

My first idea is that the final transformer T3 should be replaced by an FT50-43 toroid to avoid saturation.

Adam Rong
 

John,

Yes. It is for all bands. It is a wide band transformer.

Thanks,
Adam

在 2017年8月8日,下午11:13,landrjoh@... [CHINA_QRP] <CHINA_QRP@...> 写道:

 

Hi Adam,


Is the substitution of an FT50-43 toroid for T3 a recommended upgrade for any frequency band of KN-Q7A / CS-series transceiver if we want to try digital modes (long transmission times)?

Thank you,

John
AA7US

---In CHINA_QRP@..., wrote :

My first idea is that the final transformer T3 should be replaced by an FT50-43 toroid to avoid saturation.

qrpjl1kra
 

John,

See the following page. You may need translation site.
An builder in JA modified his KN-Q7A+digital VFO to JT65 machine.
He uses a larger core and cooling fan. Without them he blown MOS-FETs.
Though the KN-Q7A/CS40 are designed as SSB equipment, additional
mods enable it to work digital mode. What a fun !  


Junichi JL1KRA

AA7US
 

THANK YOU Junichi!

Wow!  This is an excellent resource and very informative.

73,

John
AA7US


---In CHINA_QRP@..., <mx6s@...> wrote :

John,

See the following page. You may need translation site.
An builder in JA modified his KN-Q7A+digital VFO to JT65 machine.
He uses a larger core and cooling fan. Without them he blown MOS-FETs.
Though the KN-Q7A/CS40 are designed as SSB equipment, additional
mods enable it to work digital mode. What a fun !  


Junichi JL1KRA