Re: HF Amplifier

Dave Kjellquist, WB5NHL


Are you still using the Comet CHA-250B    Carl and Kevan are absolutely right as to where to spent your efforts.  An antenna other than the CHA-250B aka "antenna dummy load" would do wonders.  Even Comet, in there advertise, recognizes the CHA as mostly a radiating dummy load.

"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."

The way they are able to create a broadband vertical is with a lossy transformer. In their "matching transformer" a very wide range impedance on the secondary is NOT accurately transformed to the primary thus maintaining the 50 ohm load.

One possible solution would be a Hustler 6BTV vertical. At Schofield middle school for SCR we used a Huster 6BTV with good success. Even with a very modest temporary ground system it did well. As a single aluminum pole the visual impact is minimal.  If necessary the Hustler can tilt mounted to hide it when not operating.  DX Engineering sells the 6BTV for $242.   

On 6/30/2021 7:19 AM, Kevan Nason wrote:
You likely have a good reason for wanting 250 watts maximum, but I'm having a hard time understanding why you are willing to spend so much money for such little power increase.  That is assuming you are using 100 watts now. Carl's suggestion of improving your antena seems a much better route -- whether it is to get a hex beam OR improving your vertical's performance. Especially since a hex beam would give you improvements on both transmit AND receive.

At the risk of stating the obvious... Going from 100 watts to 250 watts is basically a 3 dB improvement in your transmitted signal. That helps, but mostly only if you are chasing weaker signals like the DXers and Contesters do. Many newer rigs have S meter calibrations of 3 dB per S unit. Older rigs have 6 dB per S unit. Your desired amp will only give a 1/2 to 1 S unit increase in signal for the other guy. You won't make a lot more contacts with that little of an increase. Think of how little difference you see when someone calls you with an S5 signal and while they are talking you see the meter "jump" all the way up to S6. It just doesn't make much of a difference. Is that worth the money?  Not for me. And it's my experience from attending dozens of Field Days that most people just skip over those very weak signals where that one S unit improvement would make the difference. They just don't want to make the effort to dig the other station out of the noise. I'm not an FT8 guy, but I doubt it will mean a ton more contacts in that mode either.  You'd likely get much better performance from a Hex due to its directionality. True, a Hex doesn't do 40 or 80 meters, but the high bands are rapidly coming back. If you're looking at 40/80 then I would focus more on better low band antennas. In fact, that is the route I took here at my own station. By improving my 40/80/160 meter antennas I've seen a dramatic improvement in my ability to work stations -- without buying an amplifier.

Kevan N4XL

Dave, WB5NHL
8BDXCC, 314 countries confirmed (mixed current)
Hamshack Hotline x5555

Dave,  WB5NHL
Treasurer,  NABRC

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