Gary @N8DMT
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n8dmt.mastodon.radio.ap.brid.gy
Gary @N8DMT
@n8dmt.mastodon.radio.ap.brid.gy
33 followers 1 following 400 posts
Amateur Radio Extra, Maker, Product developer, Wireless/RF/Antenna guru / electronics consultant, LabVIEW, RTL-SDR, ADALM Pluto, GNU Radio, FCC testing. Location […]

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n8dmt.mastodon.radio.ap.brid.gy
US Coast Guard aircraft executing a search just south of Key West Florida. Additional assets joining in now.
Screen capture from adsbexchange showing a grid search pattern.
December 6, 2025 at 1:22 PM
n8dmt.mastodon.radio.ap.brid.gy
Found another ZFL-2000 amp in the lab stock - but this one is tagged as “BAD”. Will retest and if actually defective, will set aside for disassembly during next snow day. Curious to see if there is a part number / label on the back side of that 12-pin circular Mod-Amp case. #rfamplifier #smokeletout
Photo of a Mini-Circuits ZFL-2000 modular RF amplifier with a "BAD" label attached. Is it really bad (or just faking it)? Time will tell. If bad, will disassemble to see what RF amplifier module is used within.
December 5, 2025 at 3:33 PM
n8dmt.mastodon.radio.ap.brid.gy
What is inside a Mini-Circuits ZFL-2000 RF Amplifier? Had a few minutes to take a quick look inside one of these RF Amps. Didn’t learn much, and was surprised to see a fully-cased (pins) amplifier module inside. Would take a lot more effort to disassemble […]

[Original post on mastodon.radio]
Photo of a Mini-Circuits ZFL-2000 RF amplifier module with SMA female connectors on each side. Power and GND pins are on the side adjacent to the RF connectors. Photo inside of the RF Amp, showing a small printed wiring board connecting the SMA jacks and power/GND pins to the module within. Disassembly would require removing the SMA jacks, unsoldering the center pins, removing the four screws and extracting the module/PWB from the case. Too much work just to see what module is used...
December 5, 2025 at 1:59 PM
n8dmt.mastodon.radio.ap.brid.gy
Completed a few tests on the 2.4 GHz RF Equipment (RFE) components for the single-band Pluto transceivers. TLDR: All looks good and ready to continue evaluating controller software. Details at the qsl.net blog. #hamradio #sdr
https://qsl.net/n8dmt/24-ghz-pluto-rf-equipment/index.html
VSWR for the TECOM 2.4 GHz antennas showing under 1.5:1 over the 2.39 to 2.45 GHz band. Photo of the UTE Microwave RF circulator being tested for forward insertion loss and frequency coverage. This unit covers 2-4 GHz and provides more than 20 dB of reverse isolation. SATSAGEN measurement for the UTE Microwave circulator showing forward passband of 2 to 4 GHz. SATSAGEN measurement of UTE Microwave circulator showing greater than 20 dB of isolation in the reverse path.
November 26, 2025 at 9:21 PM
n8dmt.mastodon.radio.ap.brid.gy
RF equipment setup complete for first low-power 2.4 GHz test using Remote SDR and Pluto SDR. Waiting for the afternoon to find/retrieve the second RaspberryPi-5 computer needed for the second transceiver controller. (Have moved multiple times with re-boxing […]

[Original post on mastodon.radio]
Photo showing two Pluto SDR connected to UTC Microwave circulators and Tacoma 2.4 GHz collinear antennas. This supports simple half-duplex low-power tests of the RemoteSDR controller software.
November 23, 2025 at 3:01 PM
n8dmt.mastodon.radio.ap.brid.gy
Here is the system drawing showing the local laptop PC with headset and the remote computer & RF equipment group (Raspberry Pi 5, Pluto SDR, and transmit/receive amplifiers and filters leading to the antenna). Ideally, the remote equipment is located VERY […]

[Original post on mastodon.radio]
System drawing for the PlutoX transceiver showing local laptop PC & headset, connecting via Ethernet to the remote equipment group (Raspberry Pi 5, Pluto SDR, TX/RX amplifiers, filters and antennas).
November 21, 2025 at 9:50 PM
n8dmt.mastodon.radio.ap.brid.gy
Slow Work Day: Let’s sort ferrite! Made a quick ferrite material sorter using NanoVNA-H4 and a two-turn test loop. Ended up finding at least four material types. Now labeled in separate bags and ready for (easier) future use!
#hamradio #emiemc #sortalltheparts
Close up of the two-turn test loop attached to the NanoVNA-H4 analyzer measuring S21. Normalized this as my calibration reference. Desktop photo showing many ferrite clamp-on parts ready for test. Some are labeled with part numbers (and material types), others are not marked in any way... Example for testing a type 31 core. Blue curve is the DUT trace. Red is a previously stored trace using a type 43 core. Phot showing ferrite sorted into three major piles. Not precise, but better than I had before. The rectangular clamp on in the upper left (from Radio Shack long ago) was the worst of those tested today. Would need many turns through it to attenuate common mode signals. Ugh!
November 17, 2025 at 8:50 PM
n8dmt.mastodon.radio.ap.brid.gy
Have you seen video on the DIY capacity hat for a vertical antenna whip? Link below for one ham’s approach. Have purchased some 24” zip ties and found the lab stock of copper tape. Interested to see how this works on my 17’ SS-17 whip antenna!

With the cooler […]

[Original post on mastodon.radio]
Photo of some 24" zip ties and multiple rolls of adhesive-backed copper tape. Planning to build a DIY capacity hat for a 17' telescoping whip antenna system.
November 14, 2025 at 9:19 PM
n8dmt.mastodon.radio.ap.brid.gy
The 3/8-24 antenna ground-isolator/connector test box is completed. This simply connects or disconnects the lower ground stake connection to the upper counterpoise / coax-feed and vertical whip assembly. It’s easy to have the ground stake connected with the […]

[Original post on mastodon.radio]
Photo of the antenna ground isolator / connector box parts (plastic electrical box, wire, 3/8-24 bolts and nuts, SPST switch). Photo of the interior wiring of the test box showing SPST switch in the middle and wires leading up and down to 3/8-24 bolts. This is intended to attach to a ground spike on the lower side and radials/coax-feed/whip on the top side. Photo of the outside of the box (up is to the left in this photo) showing counterpoise/coax-feed/whip attachment to the left 3/8-24 socket and the connection to the ground spike (bolt connection) on the right.
November 14, 2025 at 8:58 PM
n8dmt.mastodon.radio.ap.brid.gy
I’m sure there is a project in here somewhere: Parts for an experimental ground isolator for a 3/8-24” vertical antenna mounting system. The box goes in between the ground spike and radials/coax-feed/vertical-whip. The switch will open or close the ground […]

[Original post on mastodon.radio]
Photo of a 1 gang 18" Nail on PVC box, two 3/8-24 nut, two 3/8-24 bolt, a SPDT switch, a hunk of yellow wire, a lock washer and an elongated nut fitting 3/8-24 hardware. Not shown are two 3/8" wire terminals to connect the antenna mounts to the switch. Will it make any difference?
November 12, 2025 at 8:44 PM
n8dmt.mastodon.radio.ap.brid.gy
A follow up post on the DIY RF Comb Generator. TLDR: It works even better when mounted to a small board with SMA jacks! Nice quality combs up to over 1 GHz! Details over at the qsl.net blog. #hamradio #testequipment
https://qsl.net/n8dmt/diy-rf-comb-gen-test/index.html
Desktop photo of the SATSAGEN / UNO / EtherKit SI5351A / comb-generator-board / TinySA-Ultra showing a nice series of RF combs up to 800 MHz. Close up photo of the comb generator with the RF input SMA jack on the left, a 15 nF series capacitor leading to the shunt small-signal diode and the output SMA jack on the right. Board is soldered and tested but not yet cleaned after being soldered together. It works!
November 11, 2025 at 1:25 AM
n8dmt.mastodon.radio.ap.brid.gy
DIY RF Comb Generator for less than $1.00? After evaluating the mil-spec Herotek comb generator module and Pluto SDR clock source combination, decided to try out a low cost alternative for generating combs. With an on-hand SI5351A clock source, added two […]

[Original post on mastodon.radio]
Desktop photo of the comb generator setup. SATSAGEN controlled Arduino UNO controlling EtherKit SI5351A clock source, with CLK0 feeding series capacitor on proto board to shunt signal diode with clip leads attached leading to TinySA-Ultra spectrum analyzer. A large number of comb signals are displayed on the TinySA. Close up photo of the protoboard showing a single blue capacitor in series from the CLK0 output (right) to shunt signal diode and output to spectrum monitor at left side of the blue capacitor. (Not worried about parasitics for this test.) Close up photo of the TinySA-Ultra display showing comb pickets extending up to 500 MHz.
November 10, 2025 at 3:32 PM
n8dmt.mastodon.radio.ap.brid.gy
Finished up testing of what looked like an RF amplifier module but was really a comb generator. TLDR: It works! Now have picket-fence RF signals! Details in two posts over at the qsl.net blog site. #hamradio #testequipment […]

[Original post on mastodon.radio]
Photo showing Pluto SDR with HP and LP filters around 640 MHz, HP8447 RF amplifier, Herotek GCA640 comb generator with heatsink, and a TinySA-Ultra spectrum analyzer displaying a series of RF combs (pickets). A well-used HP transistorized power supply is feeding 5 VDC to the comb module. It works!
November 8, 2025 at 4:06 PM
n8dmt.mastodon.radio.ap.brid.gy
Getting the lab organized a-bit more: Printed out a data sheet for a pair of Narda RF couplers. Have both couplers back in the same storage package again. What is the RF Geek equivalent of the old hammer-nail saying?

When all you have are RF couplers […]

[Original post on mastodon.radio]
Photo of two Narda RF couplers, one larger and one smaller, both with red plastic connector covers. The larger coupler covers 0.5 to 2 GHz and the smaller coupler covers 1 to 3.5 GHz. Both provide 20 dB loss on the coupled port. These are useful for return loss measurements in RF systems measurements.
November 6, 2025 at 9:22 PM
n8dmt.mastodon.radio.ap.brid.gy
Random RF Component Find #308: Herotek GCA640-258 RF comb generator. Was stashed in one of the garage lab boxes. Needs cleaning! This appears to be a 640 MHz input comb generator that will output multiples of that frequency up to ~ 18 GHz. Includes a […]

[Original post on mastodon.radio]
Desktop photo of a small packaged RF device with SMA connectors and pins for +5V and GND connections. It is bolted onto a small gold colored metal heatsink. Per the part number, it appears to be a RF Comb Generator. Will be fun to check out and add to the lab stock.
November 4, 2025 at 9:36 PM
n8dmt.mastodon.radio.ap.brid.gy
2M FT8 Monitor: Setup the IC-705 with 16’ of RG400 coax feeding a DIY 2 Meter halo perched on top of the office closet door. Using SDR-Control on the iPad for FT8 decode. Will monitor 144.174 FT-8 to see if I can hear anything (only seeing always-there power […]

[Original post on mastodon.radio]
Photo of a small DIY 2 meter halo antenna constructed using a SO-239 jack and number 14 solid copper wire.
November 2, 2025 at 3:41 PM
n8dmt.mastodon.radio.ap.brid.gy
Testing the new 33 cm Pluto SDR controlling software: Have basic RX/TX working and tested on FM mode using a local (second Pluto) SDR linear translator “repeater” controlled by GRC. Notes on using F1ATB’s Remote SDR SW over on the QSL.net website (3 postings) […]

[Original post on mastodon.radio]
Desktop photo of the Remote SDR Pluto SDR with its Raspberry Pi 5 controller, along with a second Pluto SDR being controlled by GNU Radio Companion running on a laptop. Simple GRC program providing a 33 cm 5 MHz split all-mode repeater on the Pluto SDR. Screen capture of a browser window showing Remote SDR loop back test. Boom headset plugged into laptop: Speak into microphone and hear voice in headset. It works!
November 1, 2025 at 8:05 PM
n8dmt.mastodon.radio.ap.brid.gy
Testing a RF Limiter with a Yaesu VX-8DR HT: Was able to find 4 RF limiter candidates for use in a 902 MHz full duplex transceiver and tested one unit’s limiting function using L2 TX Po at 446 MHz. TL:DR, the tested limiter works as hoped! More information and […]

[Original post on mastodon.radio]
Desktop photo showing the Yaesu VX-8DR with antenna connection leading to RF adapter, 30 dB high power attenuator, RF adapter, 10 dB SMA attenuator, and ZX47-55 RF power sensor attached at end. Wires lead to the Arduino and 2-line display. Desktop photo showing same line up but with the AEL MW16301 RF limiter in line next to the Yaesu radio. The limiter does not allow high power to pass through (and instead reflects it back to the source).
October 23, 2025 at 8:15 PM
n8dmt.mastodon.radio.ap.brid.gy
Thinking about a 902 MHz transceiver based on the ADALM Pluto SDR using a set of printed circuit board filters and a RF circulator to combine the TX and RX paths together at the antenna (supporting full-duplex comms). Measured two sets of 902 MHz circulators […]

[Original post on mastodon.radio]
Desktop photo of the RF circulator test setup, showing ADALM Pluto SDR (controlled by SATSAGEN) connected to a dual RF circulator through path with RF terminations on the third and fourth RF ports. A second dual-circulator is next to the one being tested. A SATSAGEN screen capture showing through path insertion loss from 70 to 3000 MHz. There is a low-loss portion of the curve in the 900 MHz band. The through path for the transmitter also offers harmonic rejection to the second and likely third harmonic signal levels. SATSAGEN screen capture showing reverse isolation of over 60 dB in the 900 MHz band. This offers very good reverse power (failed antenna) protection to the transmitter stage in the proposed 902 MHz transceiver.
October 21, 2025 at 8:34 PM
n8dmt.mastodon.radio.ap.brid.gy
Today’s Music Festival Attire: A green shirt with a T-Rex dinosaur with the statement “Make Billionaires Extinct”. Background is a ringed planet and stars.
#makeastatement
Photo of a green shirt with a T-Rex dinosaur with the statement “Make Billionaires Extinct”. Background is a ringed planet and stars.
October 18, 2025 at 11:17 AM
n8dmt.mastodon.radio.ap.brid.gy
KK7B 144/902 converter LO update: Setup the HP1121A RF probe to walk down the LO lineup and found a gain stage with only +2 dB gain. The resistor to VCC is 560 Ohm instead of 100 Ohms as the other amp stages have installed. Will find a 100 Ohm resistor and […]

[Original post on mastodon.radio]
Modular RF amplifier "schematic" showing RF input on the left and RF output / DC input on the right. Amp needs DC blocking capacitors for both in/out connections. Photo showing test setup for measuring RF signal level through the LO source and multiple / filter chain. HP1121A RF probe is connected to TinySA-Ultra spectrum analyzer through a DC block. Sorta-short ground lead ties probe to circuit ground for measurement. Setup is not too precise, but good for relative measurements. (Does amp have gain, output greater than input?) Photo of KK7B 144/902 converter schematic with mark up for probed RF levels at input and output of RF amplifiers. All amplifiers on board are the same with a capital A marking on them (model # unknown). DC levels are marked on top side of amps on schematic and pointed out difference on amp marked "Mar-6". That feed resistor is 560 Ohm (and not 330 as indicated on schematic). Other modular amps all have 100 Ohm feed.
October 13, 2025 at 5:47 PM
n8dmt.mastodon.radio.ap.brid.gy
A few additional thoughts on the KK7B 144/902 translator boards: 1) Add connectors to the RX and TX filter chains on a bare board and use it as a Pluto SDR front-end on 902 MHz. With pi5 & Langstone SW + RX LNA, TX PA and T/R switch yields low-cost 902 […]

[Original post on mastodon.radio]
Bare circuit board with printed RF Filters for 902 MHz (separate TX and RX paths). Photo of Mini-Circuits RF Mixers showing 4 SBL-1X circuit boards with mounted mixers and a tube of surface mount RMS-25MH mixers (tiny!).
October 12, 2025 at 3:08 PM
n8dmt.mastodon.radio.ap.brid.gy
The converter’s oscillator/multiplier stage basically works (although a-bit low on power level). Board draws ~208 mA at +12V which seems reasonable for the number of active devices installed. Frequency looks good at 758 MHz monitored at the tacked-on BNC jack […]

[Original post on mastodon.radio]
Broad band capture of the local oscillator output spectrum as measured on the TinySA-Ultra. Will be monitoring the spurious output level once the desired 758 MHz output is corrected to be closer to +7 dBm. Closer in spectrum capture for the 758 MHz local oscillator signal. Seems close to be on frequency (and verified that tweaking the trim-cap adjusts the frequency. Will leave frequency set alone for the moment and focus on optimizing 1) LO power level and 2) LO spurious/multiplier quality. Have some work to do on both as next step.
October 11, 2025 at 8:48 PM
n8dmt.mastodon.radio.ap.brid.gy
Ran across an unfinished late-80’s project that would benefit from some time to poke around on: SHF Systems 144/902 MHz linear translator boards (3). Two boards are bare and a third has the oscillator built up that might be checked out with current test gear […]

[Original post on mastodon.radio]
Photo of KK7B 144 to 902 Transporter boards and documentation. Two boards are bare and one has the oscillator section built up. Will it work? Close up photo of the KK7B 144 to 902 MHz transporter oscillator section. Curious to see if this fires up (and if not, how much effort to get this stage working. Need to look for some amps and mixers to fill out the rest of the board's stages.
October 11, 2025 at 6:04 PM
n8dmt.mastodon.radio.ap.brid.gy
Further investigation of the EtherKit Si5351A shows it is a useful (square wave) signal source from 4 Hz up to 200 MHz when controlled by SATSAGEN. This is a versatile clock source that will add value here in the home lab. Monitored source output with the […]

[Original post on mastodon.radio]
Desktop photo showing an Arduino UNO controlling an Etherkit Si5351A clock source with output to a 5 dB pad, a DC block, a 2-way splitter with the RF sensor connected to one port, and the second port leading to a 10.7 dB coupler feeding the TinySA-Ultra spectrum analyzer, and the through line leading to an RTL-SDR USB stick at the top of the image. The RF power meter is reading -5.7 dBm, 26 Deg C.
October 10, 2025 at 8:33 PM