Fwd: NanoVNA and dummy loads

[Rod Johnson]

My first impression as a result of the appearance of the printing on these loads, was that they did not look to be of  very good quality.  ( Just a first impression, but they looked more like they had been rubber stamped).   They also were not labeled with the same designations as the ones in the E-bay listing.

  I cobbled together a short coax to one and hung it on the Nano VNA. (see photos)

  The sweep is from 500 to 1500 MHz. The marker is at 1290 MHz.  The indicated SWR is 2.29:1

   The SWR seem to climb pretty steadily from 500 MHz to about 900, then drops off.

  If I am interpreting these Nano VNA results correctly, I do not think these particularly good loads at these frequencies.

  It would be interesting to see what they look like on a more professional instrument, just for comparison. 

 It will also be interesting to see what comes in the other order, which was for two of the 150 watt versions.  I expect them to arrive in the next few days.

  Tomorrow, I will look at these to see what they look like for the lower bands.  They might make decent loads to bolt to a small heat sink with a computer fan, for use on HF or even the VHF frequencies.  They were only about one dollar each.

  

 Rod J

[Pete Mahowald]

Hi Rod,

    I remeasured my dummy load, which was meant to be a dual (for HF SO2R) and outfitted with PL-259's.  It's on a 3"x8" heat sink with thermal grease etc.

The 150W has a 2" (!) cable to a PL-259.  The 100W has a 4' RG-58 to a PL-259.  The short cable is marked with an "S" and the long with an "L".  The cable strain reliefs are aluminum flashing, screw holes are tapped 4-40.

Here's what the NanoVNA says for the 150W with the short cable.

The horizontal frequency axis is 50 kHz to 1300 MHz.  The vertical axis is in SWR, with 1.0 being the bottom line and each line 0.2 higher than that (at the upper left, it says "200 m/"?).  At 1.3 GHz it has 2.3 : 1 SWR.

Here's the 100W with the longer cable (same axes).  The marker is at 1287 and says 1.81 : 1 SWR.

The longer cable may contribute to the lower SWR (and enough cable may be enough to make them useable at 1.3 GHz ha ha).  PL-259's I'm sure don't help.  A stub or some tuning may bring tune them at 1.3 GHz.

So I'm getting about the same as you.

Let me know if you see this on the reflector, I'm not seeing my echo.

--Pete

--
You received this message because you are subscribed to the Google Groups "PNW Microwave" group.
To unsubscribe from this group and stop receiving emails from it, send an email to PNW-Microwav...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/PNW-Microwave/260885830.59812.1615533805975%40mail.yahoo.com.

[Mike Lewis]

Text and pictures made it all through.

 

An improvement would be to use end launch or chassis mount with 4 hole bulkhead flange and use 2 holes to bolt to side of heat sink.   The connector center pin can be just above the heat sink or maybe create a small trough for clearance if needed. Position the resistor lead right at the connector center pin.

 

Mike

K7MDL  EL87sm & CN88sf

To view this discussion on the web visit https://groups.google.com/d/msgid/PNW-Microwave/fdb7c32a-ab51-b8bc-695f-f95f5fae2d7c%40gmail.com.