I have a quantity of 2mm tuning screws salvaged from 23GHz
equipment. They have a locking nut and square section lockwasher.
Let me know if you want any.
On 20/03/2021 11:03, Neil Smith G4DBN
certainly measure return loss up to 10 GHz in coax with a
reasonable degree of precision, using some good SMA directioinal
couplers or waveguide cross-couplers, and on 3.4, my
NanoVNAv2plus4 and PocketVNA work very well and seem to agree with
each other and with measurements using some HP directional
couplers. I've made waveguide couplers up to 47 GHz, it's just
that coax at 24 G is stretching me a bit.
It's simple enough to run a simulation in OpenEMS to find out the
best balance of position, length, diameter and profile of the
probe to get the desired return loss and bandwidth. The bandwidth
does seem to come out right in the real thing, although defining
the exact end of the PTFE insulation where it is trimmed does lead
to a bit of uncertainty about the centre frequency.
I try to avoid tuning screws for aesthetic reasons, but that does
lead to a lot of filing of the probes. I might relent, perhaps
using sapphire rods mounted on screws, or threaded screws made
from Rexolite, so there is no issue with contact corrosion. On
some of the aluminium 3.4 GHz Super-VE4MA horns I made with welded
backplates, I added a threaded tuning rod also made from
aluminium. That seemed a reasonable solution to prevent
Using a fairly fat probe certainly helps to increase the bandwidth
of the transition, at the cost of a lower peak return loss, but I
guess anything over 17 dB or so is good enough?
On 20/03/2021 04:49, Alan Beard via groups.io wrote:
This is why I was looking at broadband waveguide to coax
last year as I wanted a "no tune" design, a 23cm feed horn for
my 2m dish.
Preferably with enough bandwidth to be useful at 13cm.
Also, I don't care which face the coax connector is on.
I ended up with this DUBUS design, which I built.
Also, for 3.4GHz I have a Cross-bar transition (circ 1950). But
I find any design details ie. how broadband is it?
On Fri, 19 Mar 2021 20:09:18 +0000, Neil Smith G4DBN wrote
I'm just embarking on machining some
coax-input feedhorns and
waveguide transitions to use with these Wavelab units on 24
I don't have anything I can use to check the return loss of
transitions or horns. I can make up a 20 dB cross-coupler in
waveguide, but while I can sort-of use that with my spectrum
analyser as detector, assuming my best 50 ohm load looks
resistive at that frequency, I can't think how to check a
Without access to a 24GHz-capable VNA and the right
It is just a question of modelling it to get close and then
for maximum smoke on TX and use cold sky versus moon/sun noise
verify that it is working right? Is there some magic bit
testgear I can make or obtain to get the thing tuned spot on
remove any uncertainty?
I'm thinking of using a 2.92 mm connector with a hermetic seal
feedthru and a solid silver probe, because why not. They seem
3.5mm or high-end SMAs. That much Sterling silver is about
It would be SO much easier with a waveguide launch PA/LNA and
relay, wouldn't it...