[Central-Electronics] Aligning broadband couplers in 100V or 200V with NanoVNA?

[Laurence M. Szendrei]

Hi, Jim,

Great to hear from you! I should have suspected you were a member of 
this list.

What I aim to do is to get a 2-port measurement with the VNA for each 
coupler per band per stage in the transmitter.. That will actually 
provide a graph to the signal intensity through the coupler vs. 
frequency, similar to what one would get from a sweep generator,  It 
should be possible as long as I can find a way to load each input/output 
with the correct inpedance. The ports on the VNA are nominally 50 ohms, 
which if connected directly would load down the couplers heavily and 
severely broaden/flatten the response by de-Qing them.

More information in my response to Chris I just posted to the list.

If you ever try a 49:1 balun on the 600L, let me know the results. You 
would still need to switch in a different LPF for each band, so what 
would be the advantage over the stock couplers (one per band)?

73,
-Larry/NE1S

On 3/20/26 3:05 PM, Jim Candela wrote:
> Hi Larry,
>
> Long time! I tried an impedance bridge on a CE 600L amplifier. After 
> adding something like a 2.2k, or 2.7k resistor from the 813 plate to 
> ground, I got a good SWR null in the 80m passband. Not perfect, but 
> usable.
>
> I have since thought that one of those 49:1 baluns meant for an EFHW 
> antenna, followed by a LPF (or BPF) would be workable as a CE broad 
> band output coupler on the 600L. With toroids, it might just fit the 
> available space.
>
> Jim
> Wd5JKO
>
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>     On Fri, Mar 20, 2026 at 1:03 PM, Laurence M. Szendrei via
>     Central-Electronics
>     <central-electronics at mailman.qth.net> wrote:
>     Greetings,
>
>     Has anyone here tried using a nanoVNA to check the alignment of the
>     broadband couplers in a 100V or 200V? The problem to solve is
>     impedance
>     matching, since the nanoVNA ports are 50 ohms. Appropriately-sized
>     series resistors on the input and output? Those will attenuate the
>     signal, which might be acceptable since we are looking for a
>     qualitative
>     response. Of course this would be done with no power applied to the
>     transmitter.
>
>     73,
>     -Larry/NE1S
>
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