Hi Input SWR

[Kevin Murphy]

Hello Gang,

I have completed my HR500, it only took two years.  Everything went together according to the manual. My symptom of failure is a high SWR indicated by the rig driving the amp.  So a high input SWR into the amplifier. I am driving it with 5 watts from my FTdx3000, just using the TX Ground output from the Rig into the PTT input on the HR500.  When I key the 3000 I get the TX LED on the display lit up red and show some drive power to the HR500 (>2 W by the meter).  I don't show much if any FWD power output and my 3000 indicates >5:1 SWR, closer to ∞ on its meter (internal tuner off).

 The coax between the rig and the amp checked out fine and has been swapped as well (I swapped it with a known good coax that went from ANT 2 on the rig to the Coax switch).  I am at a loss as to what it could be.  Any help would be greatly appreciated, as I would really like to use this amp.

Thank you for you help,

73 de W8VOS, Kevin

[AC1KM]

What is the SWR when the HR500 is powered down (passthru mode)? Same question,  but powered up in bypass mode?

Patrick AC1KM

[jcve...@gmail.com]

If you switch the amp off and attach a 50 ohm load to ANTENNA 1 and the rig to the RADIO, does the rig see a low SWR?

If not, there's something wrong with the input jack, maybe the center pin is not soldered (it's happened before).

If the SWR is low but only goes high when you key the amp, then the problem is most likely the coax jumper going from the back panel to the LPF board or going from the LPT to the amp deck.

The problem could also be T1 on the amp deck, it the core was backwards you might see high SWR.

Also, be very careful using a 100W radio with this amp. If you inadvertently hit it with more than 25W of RF the protection circuitry can't react fast enough to prevent damage.

73,

Jim WA2EUJ

On Friday, August 5, 2022 at 3:03:18 PM UTC-4 adver...@gmail.com wrote:

[Kevin Murphy]

If I bypass the amp (set mode to off) It works great into my Mosely Mini. If I set the mode to PTT the SWR goes hi.

How would I know if T1 is backwards?

73 de W8VOS, Kevin

[jcve...@gmail.com]

T1 Core – Solder T1’s core to the AN1819 PCB. One side is a solid conductor. The other side is
split into two conductors. Be sure to orient the solid and split sides correctly.

Solid End

Split End

If these are reversed, the amp will have a high input SWR and it won't work.

73,

Jim WA2EUJ

[Geert Jan PE1HZG]

One consideration is that the kit - without the amplifier module itself - can be simply measured with an ohm meter by bridging the input connector to the output connector and see what happens if you key the amplifier.

If you have a way to sweep (spectrumanalyser with tracking generator, or VNA), you can also check the low-pass filters that way. It is what I did before installing the 1819 module.

As Jim said, I would be VERY careful with radios that are capable of providing more than 10W RF drive. You can "turn back the power" - and make sure you don't ever, ever forget!  - however many power regulation circuits need RF power to scale back and it's not unlikely there will be a RF peak, which these LDMOS devices really do not like.

Geert Jan

[Kevin Murphy]

Jim,

Yep, it looks like that.

Kevin

[jcve...@gmail.com]

If you pull off the input coax jumper from the amp deck, the center conductor should conduct with the center pin of the RADIO jack when the amp is keyed. The resistance to ground should be > 500 ohms at all times.

Jim.