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

Sun Mar 22 17:24:42 EDT 2026

Kihwal,

Nice work! Do you remember how you coupled the nanoVNA ports to the VFO 
buffer coupling transformer? I'd be interested to know, if you do.

73,
-Larry/NE1S

On 3/22/26 3:21 PM, Kihwal Lee wrote:
> Larry,
>
> I did sweep the 600L couplers. The input impedance is 3900 ohms, iirc. 
>  A 49:1 broadband transformer won’t be a good fit.  The impedance 
> ratio needs to be close to 78:1.  I had the same idea and even 
> inquired Danny (E73M) at myantennas.com about it.  His main concern 
> was the high voltage.
>
> My 600L had faulty 15 and 10m couplers. You can see my old sweep using 
> a Hermes VNA from here:
> https://k9sul.fayoly.net/projects/ce600l/ce600l_fix1.html
>
> I used a nanovna while repairing my 200V.  I think this was the VFO 
> buffer bandpass, before and after the adjustment.
>
>
>
>
>
>
> For other parts, I injected 5-6MHz sweep signal from nanovna to the 
> VFO port and watched the resulting response with a spectrum analyzer.
>
> This is the 20m output. The output varied about 1dB over the 1MHz 
> range. Much less across the 350kHz band range.
>
>
> 73
> Kihwal
> K9SUL
>
>
> Sent from Yahoo Mail for iPhone 
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>
> On Sunday, March 22, 2026, 10:35, Laurence M. Szendrei via 
> Central-Electronics <central-electronics at mailman.qth.net> wrote:
>
>     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
>     >
>     > Sent from AT&T Yahoo Mail on Android
>     >
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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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