Background
I few months ago, I set out on a quest to put together a mid-power backpack VHF packet station using equipment I already had, but with one catch: I wanted the ability to deploy it with a self supporting vertical antenna for use in situations where suspending antennas from trees or structure was impossible. I knew what type of components were necessary to make this idea work, but I couldn't find the critical piece: the 1/2 wave vertical compact antenna that could handle the 35 watt target power output. So I decided to turn to Microsoft Copilot AI in an attempt to find what I was looking for, but all I got was responses that what I was trying to do was not feasible unless I used some type of Slim Jim antenna or vertical dipole that I could suspend from a tree or something similar. But that didn't suit my use-case: I wanted to be able to deploy it on a picnic bench, or even just sitting on the ground. So I started prompting AI to find half-wave portable vertical 2 meter antennas that could handle the target output power. In many flowery words, AI told me I was a moron.
But I figured it out.
Overview
My compact, backpack and airline‑friendly VHF packet setup is built around the Kenwood TH‑D75, the classic Tokyo Hy-Power HL‑35V 2‑meter amplifier, and a Smiley ½‑wave BNC telescoping antenna mounted directly on the amp via a right‑angle adapter. The goal was simple: create a rugged, minimal‑component chain capable of sending and receiving Winlink or APRs packet messages from anywhere—no mast, no tuner, no bulky battery. On my phone, I would use WoAD for Winlink messaging and APRSDroid for APRS. The surprising part is how well this combination works when assembled correctly. RF behavior, mechanical stability, and thermal performance were all better than expected. This article explains the exact hardware chain, why it works electrically, and why the mechanical layout matters just as much as the RF.
I found the little Tokyo Hy-Power 35 watt VHF amp years ago at a local ham swap. I bought two of them for $60, sold one on eBay and kept the other. There are plenty of amps like these floating around; you just have to look. To connect the radio to the amp, I used a 3 ft Fujikura 1.5D‑GEV coax jumper. This Japanese‑spec miniature 50‑ohm cable is thicker and lower‑loss than RG‑174, but nearly as thin. I believe I picked this jumper up at Ham Radio Outlet years ago, but any quality jumper with a male SMA on one side and PL-259 on the other will work. These are plentiful on Amazon using RG316 coax: https://amzn.to/4d6lszG. For the sake of both portability and to minimize antenna impedance mismatch, I wanted to couple the antenna directly to the back of the amp. To accomplish this, I used a right-angle PL-259 to BNC adapter. Amp power sources tested include the Bioenno BLF‑1203AB (12 V, 3 Ah LiFePO₄) and the Shargeek 170 USB‑C PD battery with a TUFTELN 12 V PD cable, both chosen for airline‑friendly travel.
Choosing the BNC‑terminated version of the Smiley antenna was a deliberate technical decision affecting durability, RF performance, and the long‑term health of the amplifier’s output connector. BNC connectors are mechanically stronger than SMA connectors for whip antennas. SMA connectors, while excellent for RF integrity, have a tiny center pin and a fragile threaded collar, making them vulnerable to bending or snapping under side‑loading from a whip. BNC connectors, by contrast, were designed for field use, frequent connect/disconnect cycles, mechanical load, and ruggedized equipment. The bayonet lock spreads stress across the entire shell rather than concentrating it on a small threaded pin.
In terms of power handling, a typical BNC connector is rated for 100–150 W at VHF, while the HL‑35V outputs 20–35 W depending on supply voltage. During testing, the antenna base and right‑angle BNC adapter stayed cool with no heating due to mismatch observed - exactly what is desired in a portable packet setup.
BNC connectors also maintain a stable connection under movement, which is important for portable setups that get bumped and repositioned frequently. The bayonet lock prevents accidental loosening, maintains a consistent ground path, keeps the radiator vertical, and avoids intermittent contact. This stability is crucial when the antenna is mounted directly to the amplifier.
Physically, Smiley’s BNC base is robust, featuring a thick nickel‑plated brass base, a solid internal radiator connection, and molded strain relief. This is a purpose‑built radiator with a connector designed to support it, unlike flimsy HT duck antennas.
This orientation eliminates torque on the amplifier’s output connector, keeps the radiator vertical for proper polarization, prevents detuning from mechanical stress, and keeps the RF path extremely short. This difference is what makes the setup work reliably rather than just once.
4. Power Behavior Is Ideal for Packet
The Bioenno 12 V 3 Ah LiFePO₄ battery provides about 36 Wh capacity. The HL‑35V input power on transmit is approximately 42–45 W, with an average of 21–23 W at about 50% duty cycle for packet, resulting in a runtime of roughly 1.6 hours. The Bioenno is rated for 12v, but at full charge, I measure around 13.8-14v.
I carry a Shargeek 170 USB‑C PD battery around to power my notebook PC and phone, so I decided to try it with a TUFTELN 12 V PD cable to provide 12v to the amp through a USB-C port. This idea was a bust and didn't work. While the cable successfully delivered 12v to the amp to turn it on, the combination of the PD cable and battery couldn't respond to the instant wattage demand when the amp was transmitting. The Shargeek immediately went into overload protection when transmitting. Oh well, it was worth a try.
Field Results
In my initial test, I was travelling, staying in La Quinta, CA near the base of the San Jacinto Mountains and tried to get into a Winlink station in Cathedral City with two sets of hills in the way. This is about 14 miles direct but the hills made it impossible with just the barefoot HT - even with the Smiley antenna on the HT. With the amp in-line, I was able to connect and pass messages reliably. Later when I got home, I tried the setup from my back yard to an RMS station 27 miles away(!), which worked perfect. The entire chain behaved like a miniature fixed station rather than a fragile portable lash‑up.
The entire setup can fit into a pouch in my backpack - It's perfect.
And AI said it couldn't be done.
I few months ago, I set out on a quest to put together a mid-power backpack VHF packet station using equipment I already had, but with one catch: I wanted the ability to deploy it with a self supporting vertical antenna for use in situations where suspending antennas from trees or structure was impossible. I knew what type of components were necessary to make this idea work, but I couldn't find the critical piece: the 1/2 wave vertical compact antenna that could handle the 35 watt target power output. So I decided to turn to Microsoft Copilot AI in an attempt to find what I was looking for, but all I got was responses that what I was trying to do was not feasible unless I used some type of Slim Jim antenna or vertical dipole that I could suspend from a tree or something similar. But that didn't suit my use-case: I wanted to be able to deploy it on a picnic bench, or even just sitting on the ground. So I started prompting AI to find half-wave portable vertical 2 meter antennas that could handle the target output power. In many flowery words, AI told me I was a moron.
But I figured it out.
Overview
My compact, backpack and airline‑friendly VHF packet setup is built around the Kenwood TH‑D75, the classic Tokyo Hy-Power HL‑35V 2‑meter amplifier, and a Smiley ½‑wave BNC telescoping antenna mounted directly on the amp via a right‑angle adapter. The goal was simple: create a rugged, minimal‑component chain capable of sending and receiving Winlink or APRs packet messages from anywhere—no mast, no tuner, no bulky battery. On my phone, I would use WoAD for Winlink messaging and APRSDroid for APRS. The surprising part is how well this combination works when assembled correctly. RF behavior, mechanical stability, and thermal performance were all better than expected. This article explains the exact hardware chain, why it works electrically, and why the mechanical layout matters just as much as the RF.
I found the little Tokyo Hy-Power 35 watt VHF amp years ago at a local ham swap. I bought two of them for $60, sold one on eBay and kept the other. There are plenty of amps like these floating around; you just have to look. To connect the radio to the amp, I used a 3 ft Fujikura 1.5D‑GEV coax jumper. This Japanese‑spec miniature 50‑ohm cable is thicker and lower‑loss than RG‑174, but nearly as thin. I believe I picked this jumper up at Ham Radio Outlet years ago, but any quality jumper with a male SMA on one side and PL-259 on the other will work. These are plentiful on Amazon using RG316 coax: https://amzn.to/4d6lszG. For the sake of both portability and to minimize antenna impedance mismatch, I wanted to couple the antenna directly to the back of the amp. To accomplish this, I used a right-angle PL-259 to BNC adapter. Amp power sources tested include the Bioenno BLF‑1203AB (12 V, 3 Ah LiFePO₄) and the Shargeek 170 USB‑C PD battery with a TUFTELN 12 V PD cable, both chosen for airline‑friendly travel.
Why This Setup Works So Well
1. The ½‑Wave Antenna Is the Secret Weapon
Most handheld transceiver (HT) antennas are quarter‑wave designs that rely heavily on the radio chassis as a counterpoise. When placed on an amplifier, the impedance shifts, the SWR rises, and the connector heats up. In contrast, a half‑wave radiator presents a near‑50‑ohm impedance on its own, does not require a ground plane, is much less sensitive to mounting geometry, and maintains a stable match even on a small metal surface. Without an SWR meter inline, the best way to test if everything is working efficiently is to feel for heat at the base of the antenna (although not during transmitting!) The Smiley whip stayed cool and behaved perfectly every single time.Choosing the BNC‑terminated version of the Smiley antenna was a deliberate technical decision affecting durability, RF performance, and the long‑term health of the amplifier’s output connector. BNC connectors are mechanically stronger than SMA connectors for whip antennas. SMA connectors, while excellent for RF integrity, have a tiny center pin and a fragile threaded collar, making them vulnerable to bending or snapping under side‑loading from a whip. BNC connectors, by contrast, were designed for field use, frequent connect/disconnect cycles, mechanical load, and ruggedized equipment. The bayonet lock spreads stress across the entire shell rather than concentrating it on a small threaded pin.
In terms of power handling, a typical BNC connector is rated for 100–150 W at VHF, while the HL‑35V outputs 20–35 W depending on supply voltage. During testing, the antenna base and right‑angle BNC adapter stayed cool with no heating due to mismatch observed - exactly what is desired in a portable packet setup.
BNC connectors also maintain a stable connection under movement, which is important for portable setups that get bumped and repositioned frequently. The bayonet lock prevents accidental loosening, maintains a consistent ground path, keeps the radiator vertical, and avoids intermittent contact. This stability is crucial when the antenna is mounted directly to the amplifier.
Physically, Smiley’s BNC base is robust, featuring a thick nickel‑plated brass base, a solid internal radiator connection, and molded strain relief. This is a purpose‑built radiator with a connector designed to support it, unlike flimsy HT duck antennas.
2. The Adapter Chain Solves the Mechanical Problems
The corrected adapter chain is important for mechanical and electrical reliability. On the radio side, the TH‑D75’s SMA connector mates to a light, flexible 3' jumper, avoiding heavy adapters hardware hanging off the handheld which would stress the HT connector. The amplifier input uses a PL‑259 that screws directly into the HL‑35V’s SO‑239 input as intended. The amplifier output employs a right‑angle BNC adapter, allowing the amplifier to sit flat while the antenna stands vertical.This orientation eliminates torque on the amplifier’s output connector, keeps the radiator vertical for proper polarization, prevents detuning from mechanical stress, and keeps the RF path extremely short. This difference is what makes the setup work reliably rather than just once.
3. Electrically, the Chain Is Extremely Clean
At 144 MHz, the 3‑foot run of 1.5D‑GEV coax has negligible loss, stable 50‑ohm impedance, and no measurable impact on packet performance. The HL‑35V’s output network is forgiving, and the Smiley’s impedance curve is broad enough to maintain a good match even under amplifier drive.4. Power Behavior Is Ideal for Packet
The Bioenno 12 V 3 Ah LiFePO₄ battery provides about 36 Wh capacity. The HL‑35V input power on transmit is approximately 42–45 W, with an average of 21–23 W at about 50% duty cycle for packet, resulting in a runtime of roughly 1.6 hours. The Bioenno is rated for 12v, but at full charge, I measure around 13.8-14v.
I carry a Shargeek 170 USB‑C PD battery around to power my notebook PC and phone, so I decided to try it with a TUFTELN 12 V PD cable to provide 12v to the amp through a USB-C port. This idea was a bust and didn't work. While the cable successfully delivered 12v to the amp to turn it on, the combination of the PD cable and battery couldn't respond to the instant wattage demand when the amp was transmitting. The Shargeek immediately went into overload protection when transmitting. Oh well, it was worth a try.
Field Results
In my initial test, I was travelling, staying in La Quinta, CA near the base of the San Jacinto Mountains and tried to get into a Winlink station in Cathedral City with two sets of hills in the way. This is about 14 miles direct but the hills made it impossible with just the barefoot HT - even with the Smiley antenna on the HT. With the amp in-line, I was able to connect and pass messages reliably. Later when I got home, I tried the setup from my back yard to an RMS station 27 miles away(!), which worked perfect. The entire chain behaved like a miniature fixed station rather than a fragile portable lash‑up.
The entire setup can fit into a pouch in my backpack - It's perfect.
Conclusion
This combination - TH‑D75, HL‑35V, Smiley ½‑wave (BNC), 3' jumper (SMA at the radio, PL‑259 at the amp), and a small Bioenno LiFePO₄ battery forms a highly effective portable VHF packet station with minimal components and excellent RF behavior. It is a setup anyone can replicate and solves a real problem: reliable Winlink or APRS packet in the field without a mast or a 20‑lb battery.And AI said it couldn't be done.
