Category Archives: Uncategorized

More 122GHz Chaparral® Style feedhorns

I made up another batch of my variant of the VK3CV model choked Chaparral®-style feedhorns. Chokes are 7mm diameter, bore is 2mm, Body is 30.75 x 15mm, with an adjustable 4mm diameter coupling cavity. These are made from brass.

Grooves are 0.5mm wide by 0.75mm deep, made with a toolpost spindle at 14,000 rpm using a two-flute carbide end mill in the lathe at 8rpm

First of the batch fresh from machining.
Batch of completed feedhorns ready to debur and finish.
Locknuts
Microscope view of the 0.5mm grooves
Part-machined battels and coupler bodies
M8 x 0.5mm mandrel to machine locknuts to thickness
Spacer and part-machined locknut on the mandrel ready to machine to thickness
Toolpost spindle drive made to fit my Aloris-style toolpost. 600W, 48V variable speed motor

24GHz Round Flange Coupler

I was asked to make up some quick-detach coupling tubes to allow two 24GHz round flanges to be clamped together. I made a tube with a 22mm x 0.75mm thread outside and broached a keyway slot, then made a brass key to fit and fixed it with Loctite. So far I’ve only made up one of the clamp rings, I’m waiting for a real example to turn up so I can get the tolerances exactly right. All its fine so far though.

The coupling ring with key and one of the locking nuts
Pair of round flanges inside the coupling ring
Locking nut fitted to one side

HB9PZK POTY Lenses for 10GHz QO-100 downlink

Willi HB9PZK modelled a Rexolite lens for a “POTY” dual-band patch antenna to use on the 10GHz downlink from the QO-100 amateur satellite. https://rfantennas.wordpress.com/author/hb9pzk/

The design is a joy to make when compared with the dual-taper versions. I have some one-inch Rexolite 1422 round bar, so I’ve been making a few of these lenses to replace the lossy Nylon versions that some folks are using. Rexolite is a cross-linked polystyrene, which machines rather like plexiglas. It has a tan-delta around 0.0004 and almost zero water absorption.

Willi’s design has a stepped transition to the read. This latest batch is to fit UK 22mm plumbing pipe with a nominal wall thickness of 0.9mm and an inside bore of 20.2mm instead of the standard 20.0 bore.

Two Rexolite HB9PZK-designed lenses for 20.2mm ID waveguide
One of the lenses fitted to a POTY

W6PQL 23cm 600W PA Heatspreaders

Nice simple job squaring, facing, drilling, tapping and slotting some free-machining C111 copper for an oversized heatspreader for a W6PQL MRF3750 600W PA board. 4 x 5 x 0.5 inch thick. I have quite a number of these to machine up now. C111 is such a contrast from horribly gummy C101

Meinberg NTP configuration

Here is a basic setup for Meinberg NTP which is suitable for Windows 7 onwards. The download link for the latest version is at https://www.meinbergglobal.com/english/sw/ntp.htm#ntp_stable

When you install it, you will be asaked about creating a specific user to run the service. Up to a point this is a good idea, as it reduces the risk of security compromise, but you must ensure that the password you create for it will never expire. If you are not concerned about the small risk of compromise, you can use the SYSTEM account. Don’t user your own account though.

It will ask about which servers to use. A really simple solution is just to pick the UK pool from the drop-down list. You need to select four or more servers to ensure that the system will ignore any insane outliers.

When you complete the config, it will ask if you want to view the configuration file. Do that and it should contain things similar to this:

restrict default noquery nopeer nomodify notrap
restrict -6 default noquery nopeer nomodify notrap
restrict 127.0.0.1
restrict -6 ::1
driftfile "C:\Program Files (x86)\NTP\etc\ntp.drift"
server 0.uk.pool.ntp.org iburst minpoll 6 maxpoll 7
server 1.uk.pool.ntp.org iburst minpoll 6 maxpoll 7
server 2.uk.pool.ntp.org iburst minpoll 6 maxpoll 7
server 0.nl.pool.ntp.org iburst minpoll 6 maxpoll 7
server 1.nl.pool.ntp.org iburst minpoll 6 maxpoll 7

# these are default settings, it does no harm to put them in the config file anyway

maxpoll 10
minpoll 6

The NTP recommendations say this:

Forcing a poll interval that is more frequent than what NTP would normally select on its own, hurts accuracy and stability of time on the local system.

NTP polling does not directly synchronize the local system clock to the server clock; rather, a complex algorithm calculates an adjustment value for each tick of the local system clock

Shorter polling intervals cause NTP to make large but less accurate calculations that never stabilize, causing the local system clock to wander. They are also useful if you want to make sure that your NTP daemon will detect an outage of the NTP peers in less time.

Longer polling intervals allow NTP to calculate smaller tick adjustments that stabilizes to a more accurate value, reducing wander in the local system clock.

If you do mane any changes to the config file, you need to restart the ntpd service, either using the services.msc GUI, or go via control panel/admin tools to services, or if you are command-line oriented, just type:

sc stop ntpd
sc start ntpd

You can monitor status using

ntpq
> peers

You can also run the w32tm Stripchart to check against another NTP server:

w32tm /stripchart /computer:fr.pool.ntp.org

Press control-c to stop the stripchart.

There is a neat GUI program on the Meinberg site at https://www.meinbergglobal.com/english/sw/ntp-server-monitor.htm

Note that it is fairly old and says it is for ancient Windows versions, but it works fine on W10

RSGB Convention Talk 2019

I presented this talk at the 2019 RSGB convention on 13th October 2019 at Milton Keynes. It is more of a polemic and call-to-arms to work on ways to push the limits of VHF/UHF/SHF weak-signal communications in the way the LF enthusiasts have, working with Eb/N0 very VERY close the the theoretical limit, but we are up against stochastic processes which spread troposcatter and other DX propagation modes on the sub-metre wavelengths and make the LF approaches less than useful.

I am calling for the implementation of an adaptive feedback channel using perhaps 146 or 71MHz datacomms, perhaps New Packet Radio or something dedicated, to give us a way to close the loop and modify transmit parameters on the fly. This is not going to be easy, but it could be a nice challenge. It also might fit the Ofcom criterion of “Not just more of the same” on the new allocations.

This is a Microsoft Powerpoint pptx file. Please don’t copy it to other websites, just create a link pointing the this page.