Been quite busy experimenting with this rf-switch the last couple of days.

There has arrived a lot on and off-list comments regarding rf-switches and I have not had the time to answer all, but thanks.

I am now up in what I call revision 4 switch.

What’s new:
Revised schematics for better RX/bypass-port isolation.
New 10 amps relays.
Have done a lot of λ/4 coax tuning.
TX loss is slightly better.
RX loss is slightly worse.
RX isolation is much better.

What needs to be done:
Switch works but the 75 ohm rg-179 stubs are getting way to hot when passing the Kw level.
Need to find something better.

Revised schematics for better RX/bypass-port isolation.

I have got some questions about the home brew rf-switch or relay in my previous post.
To clarify, I got this idea from Leif, sm5bsz web site.
He has done this with PIN-diodes. I don’t have suitable diodes on stock here so I substituted those with small relays. Problem is that lo-Z current at the relays are way to large, and I got to do something with that. Upgrading to larger relays would only make the Q higher and move the problem over to the coax subs I guess. I think. What is needed, is to lower the Q, maybe by adding a small resistor at the relays, say for example 0.1 ohm. (at the point of writing this, I must emphasize, I have not done the math yet.) But I have a feeling it my work. We will see………  🙂 

UPDATE: I have now done the math, and installing a series resistor at the lo-Z point will not lower the rf-current. It will only increase insertion loss. RF-current is about 4,2 amps, and my small signal relays are rated 2 amps @ 30VDC, Guess I got to find some larger ones.

Simplified schematic

Have been working on my 144 MHz SSPA project since 04:00z this morning.
Now the time is 22:30z and I am tired. Continue tomorrow morning.
Here are some pictures of project status.

Starting point this moring


PT-100 Temperature sensor










More inside


73 All

Probing around for a powerful 48vdc supply solution I landed on a fair priced Eltek Flatpack2 rack unit. I know, it is an overkill for HAM shack use with its 8kw of DC output power. But as Jeremy Clarkson says; quote “Power and speed solves many things”  🙂
Anyways, this really is a part of a telecom UPS system, and telecom 48vdc system has negative distribution with positive common return rail. This is the opposite of what we HAM usual needs, so it has to be rewired, or re-bared rather.
This is a 2U rack module with a smartpack2 controller and 4 x Flatpack2 2000w HE rectifier units. You can run a single rectifier without the controller but it will default to about 53,5 volts. In order to change the operating output voltage, you need the smartpack2 controller.
With the factory access password, you can with the controller permanently write new settings down to the rectifier, and it will default to any valid voltage value. Of course it is possible to hack and reverse engineer the eltek CAN-bus protocol with other tools. I know the e-bike community has done it.

Here are some pix:

Smartpack2 rack without load fuses cover panel.

Smartpack2 rack without load fuses cover panel.

Smartpack2 rack unit

Smartpack2 rack unit

Original common positive (+) return bar.

Original common positive (+) return bar.

Rewired to common (-) negative return bar.

Rewired to common (-) negative return bar.


Load fuses

Complete unit

Complete unit

PowerSuite for M$ windows config and monitoring tool.

PowerSuite for M$ windows config and monitoring tool.

Want one of these; search for “SGVU-L” @ ebay.
I am planning to use this in displaying RF-power measurement, but it needs some modifications. So stay tuned……………

Here is some more info:
I got this of ebay as a kit. PCB’s are very nicely build. Kit comes with LM3916 chips, which is a semi logarithmic VU meter LED driver.
Cascading six of these don’t really make any sense if you want to use it as a meter for readings.
So, I have replaced the LM3916 with one LM3915 logarithmic 3 dB/step driver chip for the ten first LED segments, then five LM3914 linear LED driver follows for the rest of LED segments.
Of course this is for one channel only, so you need 2 x LM3915, and 10 x LM3914 for doing both channels.


Mast head mount of the rtl-dongle gives low transmission line loss


Weather proofing of the receiver. Small plastic bag inside, bag open towards the lower side so any condensation can escape, secured with duct tape. This is going to survive heavy winter storms, no problem. The problem is the radiation of the Sun killing the plastics, so there will be some duct tape maintenance.



Raspberry pi 3


5dBi Antenna erected on the roof where I work.


Receiver range: receiver has not been running for many days yet, but so far It show coverage about expected. Light area: new receiver @ work. Dark area is my first receiver @ home. Rings @ 20 nautical mile.

Receivers are feeding the flightradar24 and planefinder networks. If you know about anyone else interesting in a data feed, please let me know.