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Re: sBitx antenna-first warning

Jack, W8TEE
 

We went through that same questioning process. Someone dinged us a few days ago because we're using the IRF510's. Out answer may be different because we are aiming the T41 at experimenters who may well blow a few while they're experimenting. Since we bought a bunch several years ago and still have some left, that's what we went with. If enough people are upset about the power drop above 20M, I'm sure someone will replace the PA board. Also, we felt a lot of experimenters have experience with the 510's and probably have some spares. Also, they're still easy to find (Mouser have 27000+!).

Your situation is different in that changing the PA would be a little harder. Also, assuming they have spares is, perhaps, less likely. Also, I searched for the RD16HHF1 at Mouser and Digikey...nada.

Jack, W8TEE

On Wednesday, August 3, 2022 at 11:59:04 AM EDT, Ashhar Farhan <farhanbox@...> wrote:


I guess the best way out is to use a robust transistor pair like the RD16HHF1 which can withstand infinite SWR, match the antenna regardless of the impedance at either end with an inline swr meter.
Remember the ol' 807 transmitters with a Pi network? You just did a dip and load until you came up to the full power.
The design question is, should we go for more expensive and difficult to get RF transistors or just use inexpensive IRF series and keep many spares?
- f

On Wed, Aug 3, 2022, 8:33 PM Jerry Gaffke via <jgaffke=[email protected]> wrote:
Not sure which statement that would be.
I've been making lots of them.

A resistive SWR meter assumes that the transmitter wants to see a 50 ohm resistive load,
but the transmitter will not necessarily work best at exactly 50 ohms.
For example, assume we are operating at 30mhz and there is a long trace to the antenna connector.
The antenna system would want to have a little bit of capactive reactance to counter the inductance of that trace.

Not much point to worry about such minor issues.
We just need a reasonably good match between transmitter and the antenna system,
doesn't have to be perfect.? You could spend a career trying to understand everything
that could go slightly wrong here, many people do.

Jerry, KE7ER


On Wed, Aug 3, 2022 at 07:45 AM, Evan Hand wrote:
Jerry,

A resistive bridge SWR meter should not work if this statement is true.

Am I missing something here?
73
Evan
AC9TU

--
Jack, W8TEE
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