With the "IC-705 meets KPA-500" configuration from last weekend's DX contest still in place - and the Hardrock-50 in series - I couldn't help but wonder if I could use one amp to drive the other.
A quick check of the Hardrock-50's manual mentions one way of doing it:
In my case, I'm keying the HR-50 with its built-in COR function. The KPA-500 is keyed via a direct PTT cable from the IC-705 and I have a 20mS delay dialed in to the IC-705 to prevent the KPA-500 from being hot-keyed.
It works quite well.
On most bands, 1 watt of drive is required from the IC-705 to produce a 500 watt output. 20 and 30 meters require 2 watts drive.
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Via email, posting here in case others have the same Q:
ReplyDelete"I was reading about your use of two daisy chained amplifiers driven by your 705. I don’t have a 705, but bought a used KX3 last year while we all wait for the K4 to ship. I have an RM Italy 100 watt (maybe more like 85 watt) solid state amp, but want to aim for KW power output on HF+6. I have been concerned about daisy chaining amplifiers to get that kind out output, especially around signal distortion and over driving the KW amp. Did you put your output on a scope to look at clipping or distortion? Any thoughts about the upside vs. downside of using two amps in a row?"
The main problem I faced was in over-driving the KPA-500. On many bands, only 2 watts will drive it to a full 50-watt output and this is too much for the KPA-500. This is not an issue on 20 and 30 meters for my particular HR-50 since those bands require more drive to achieve a full output. On the other bands, 1 watt drives the HR-50 to about 30 watts, sufficiently driving the KPA-500 to full output without over-driving.
I haven't yet looked at the output with a scope but I did listen to my transmitted audio via a few of the many SDR receivers online. It sounded clean and I am confident that the KPA-500 is not over-driven since it is outputting about 500 watts, not the 630 that it's actually capable of.
I'm not sure what the drive characteristics are of the RMI amps or how they're keyed. My main concern was in not hot-keying either amp, especially the KPA-500. This is doubly prevented in my case - first, by the fact that it is directly keyed via a PTT cable - it is keyed well before the HR-50's carrier-operated relay can produced an amplified output. Also, I have a delayed programmed in to the IC-705.
If your RMI's output is too high to drive another amp, you could add a 3- or 6dB (or whatever is required) attenuator between the 705 and the RMI amp. Of course, this would reduce your received sensitivity by the same amount.
73,
John AE5X
Hi John,
ReplyDeleteI am a KX3 user since late 2012. I when the KXPA-100 came out I ordered one. Then by a coincidence in 2015 I stumbled over an newly built KPA-500 (I were looking for a SPE amplifier to be true). They are all in my daisy chain with full QSK as well. I am a user of Tom's (VA2FSQ) software Win4K3 and the software handle all of the equipment (incl. KAT500) in the chain. You can set the drive power per band so you don't overdrive the KPA (or match your preference). I see no problems to use other amplifier in line with that software since the KX3 are adjustble between 0.1-15 watts.
//Mats, SM0FPR
Thanks for the info Mats. I find myself having to be very careful in power selection from the IC-705 if I have the Hardrock online so I normally use the KPA-500 alone if I need more power from the Icom. My only use of the Hardrock lately is in outdoor POTA ops.
DeleteFor those using Elecraft gear, here is a link to the software Mats refers to:
https://va2fsq.com/win4k3suite-for-the-kx3/
73,
John AE5X
500W on 30 Meters?
ReplyDeleteInto Cantenna - just noting the differences compared to other bands, and that it corresponds to the HR-50 alone:
Deletehttp://ae5x.blogspot.com/2018/12/thoughts-on-hardrock-50.html