HF All Band Antenna for Small Spaces, G7UNF
Do you need a compact, efficient, and inexpensive HF antenna for a small urban lot or for that future POTA/SOTA expedition?
If you do, then this antenna idea from G7UNF is for you.
Views expressed in this Amateur/Ham Radio antenna post are those of the reporters and correspondents.
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Russ Roberts (KH6JRM).
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Discovering the G7UNF: A Compact HF Vertical Antenna for UK Operators
In the world of amateur radio, few challenges test the limits of creativity and engineering more than building a compact yet effective HF vertical antenna. Particularly in the UK, where gardens are small and planning restrictions often limit large aerials, the need for efficient, space-saving designs is essential. The G7UNF 40 & 80m band antenna is a brilliantly simple solution to this problem. Tailored for the UK ham radio operator, it offers a practical, dual-band HF vertical antenna with a small footprint and surprising performance.
Let’s dive deep into this compact marvel, how it works, and why it deserves a place in your HF setup.
In the world of amateur radio, few challenges test the limits of creativity and engineering more than building a compact yet effective HF vertical antenna. Particularly in the UK, where gardens are small and planning restrictions often limit large aerials, the need for efficient, space-saving designs is essential. The G7UNF 40 & 80m band antenna is a brilliantly simple solution to this problem. Tailored for the UK ham radio operator, it offers a practical, dual-band HF vertical antenna with a small footprint and surprising performance.
Let’s dive deep into this compact marvel, how it works, and why it deserves a place in your HF setup.
A Solution Born Out of Necessity
Operating on the 40m and 80m bands is a rewarding experience. These bands support both daytime and nighttime propagation and are home to numerous nets, ragchews, and DX opportunities. However, a full quarter-wave vertical for 80m is around 20 metres tall – completely unrealistic for most back gardens in the UK.
Enter the G7UNF design: a compact, loaded vertical antenna that uses coil inductance to electrically lengthen the radiator, allowing you to work both 40m and 80m without needing tall masts or large areas. Despite being just 2 metres tall at most, this antenna is a competent performer when constructed correctly.
Operating on the 40m and 80m bands is a rewarding experience. These bands support both daytime and nighttime propagation and are home to numerous nets, ragchews, and DX opportunities. However, a full quarter-wave vertical for 80m is around 20 metres tall – completely unrealistic for most back gardens in the UK.
Enter the G7UNF design: a compact, loaded vertical antenna that uses coil inductance to electrically lengthen the radiator, allowing you to work both 40m and 80m without needing tall masts or large areas. Despite being just 2 metres tall at most, this antenna is a competent performer when constructed correctly.
Design and Construction: What Makes It Tick
The G7UNF antenna is a classic example of a base-loaded vertical antenna. In its simplest form, it consists of:
- A short vertical radiator (labelled A)
- A loading coil (L1), with a tap point (L2) for feeding
- A coaxial feed point (using RG58)
- Ground radials or a counterpoise system (not shown but essential)
Here are the detailed dimensions and coil specs for both 40m and 80m operation:
Band A (Vertical Element) L1 (Coil Turns) L2 (Tap Point Turns) Total Height Coil Diameter 40m 85.4 cm 59 turns 16 turns 1.15 m 4 cm 80m 150 cm 98 turns 18 turns 2 m 4 cm
The coil is wound on a 4 cm diameter former, ideally plastic or other non-conductive material. Wire used can be insulated copper, around 1 mm in diameter.
Switching bands involves either changing the length of the vertical element (A) and adjusting the tap on the coil or building a switchable or dual-mode version. In portable or fixed setups, this swap can be done relatively quickly.
The G7UNF antenna is a classic example of a base-loaded vertical antenna. In its simplest form, it consists of:
- A short vertical radiator (labelled A)
- A loading coil (L1), with a tap point (L2) for feeding
- A coaxial feed point (using RG58)
- Ground radials or a counterpoise system (not shown but essential)
Here are the detailed dimensions and coil specs for both 40m and 80m operation:
| Band | A (Vertical Element) | L1 (Coil Turns) | L2 (Tap Point Turns) | Total Height | Coil Diameter |
|---|---|---|---|---|---|
| 40m | 85.4 cm | 59 turns | 16 turns | 1.15 m | 4 cm |
| 80m | 150 cm | 98 turns | 18 turns | 2 m | 4 cm |
The coil is wound on a 4 cm diameter former, ideally plastic or other non-conductive material. Wire used can be insulated copper, around 1 mm in diameter.
Switching bands involves either changing the length of the vertical element (A) and adjusting the tap on the coil or building a switchable or dual-mode version. In portable or fixed setups, this swap can be done relatively quickly.
Understanding How It Works
The basic principle behind the G7UNF antenna is inductive loading. Since a full-length vertical for 40m (10m) or 80m (20m) is impractical, inductors (coils) are introduced to make the antenna “electrically longer.”
When current flows through the coil, it creates a magnetic field that contributes to the radiation of the antenna. However, coils introduce losses and reduce bandwidth, so careful tuning is essential.
By feeding the antenna at a lower point on the coil (L2), the impedance is brought to a more suitable level for coaxial feed and matching.
The basic principle behind the G7UNF antenna is inductive loading. Since a full-length vertical for 40m (10m) or 80m (20m) is impractical, inductors (coils) are introduced to make the antenna “electrically longer.”
When current flows through the coil, it creates a magnetic field that contributes to the radiation of the antenna. However, coils introduce losses and reduce bandwidth, so careful tuning is essential.
By feeding the antenna at a lower point on the coil (L2), the impedance is brought to a more suitable level for coaxial feed and matching.
Installation: Grounding and Radials
Like all vertical antennas, the performance of the G7UNF is highly dependent on the ground system. Even the best design won’t radiate well without a decent set of radials or a ground plane.
In the UK context, consider these options:
- Lay out 4 or more quarter-wave radials on the ground (ideally 10m+ for 40m and 20m+ for 80m)
- Use elevated radials (1m above ground), which can improve efficiency when ground mounting isn’t practical
- Use buried radial wire mesh or earth rods if radials are not possible
Adding a choke balun (coiled RG58) at the base can also help prevent unwanted RF on the coax shield.
Like all vertical antennas, the performance of the G7UNF is highly dependent on the ground system. Even the best design won’t radiate well without a decent set of radials or a ground plane.
In the UK context, consider these options:
- Lay out 4 or more quarter-wave radials on the ground (ideally 10m+ for 40m and 20m+ for 80m)
- Use elevated radials (1m above ground), which can improve efficiency when ground mounting isn’t practical
- Use buried radial wire mesh or earth rods if radials are not possible
Adding a choke balun (coiled RG58) at the base can also help prevent unwanted RF on the coax shield.
Real-World Performance
While the G7UNF isn’t a DX powerhouse, its performance is respectable for local and regional contacts. Many UK hams report excellent results on 40m with the short version, especially in NVIS conditions, ideal for inter-G country comms.
On 80m, the increased inductance narrows the bandwidth, meaning tuning is more sensitive. A manual ATU or automatic tuner is strongly recommended to find the sweet spot.
While the G7UNF isn’t a DX powerhouse, its performance is respectable for local and regional contacts. Many UK hams report excellent results on 40m with the short version, especially in NVIS conditions, ideal for inter-G country comms.
On 80m, the increased inductance narrows the bandwidth, meaning tuning is more sensitive. A manual ATU or automatic tuner is strongly recommended to find the sweet spot.
Pros and Cons of the G7UNF HF Vertical Antenna UK
Advantages:
- Very compact and practical for UK-sized gardens
- Operates on two of the most popular HF bands
- Easy to build with common materials
- Portable for /P operations
Disadvantages:
- Lower efficiency compared to full-size verticals
- Narrow bandwidth, especially on 80m
- Requires a good ground or radial system to be effective
Advantages:
- Very compact and practical for UK-sized gardens
- Operates on two of the most popular HF bands
- Easy to build with common materials
- Portable for /P operations
Disadvantages:
- Lower efficiency compared to full-size verticals
- Narrow bandwidth, especially on 80m
- Requires a good ground or radial system to be effective
Materials Needed to Build It
You won’t need much to build the G7UNF. Here’s a short shopping list:
- 2 metres of aluminium, copper, or stiff wire for vertical radiator
- Insulated wire for coil (approx. 10 metres)
- 4 cm plastic former (PVC pipe or similar)
- RG58 coax and PL connector
- Terminal lugs or binding posts
- Lightweight mast or support pole
You won’t need much to build the G7UNF. Here’s a short shopping list:
- 2 metres of aluminium, copper, or stiff wire for vertical radiator
- Insulated wire for coil (approx. 10 metres)
- 4 cm plastic former (PVC pipe or similar)
- RG58 coax and PL connector
- Terminal lugs or binding posts
- Lightweight mast or support pole
Enhancing Performance with Simple Tweaks
- Weatherproof the Coil: Use PVC tubing or shrinkwrap to protect the coil from rain and corrosion.
- Try Elevated Mounting: Mount the antenna base on a wooden post or pole for better low-angle radiation.
- Use a Tuner: If your SWR is outside of 1.5:1, a manual or auto tuner will make matching easy.
- Experiment with Tap Points: Slight variations in the L2 tap point can greatly affect impedance and bandwidth.
- Weatherproof the Coil: Use PVC tubing or shrinkwrap to protect the coil from rain and corrosion.
- Try Elevated Mounting: Mount the antenna base on a wooden post or pole for better low-angle radiation.
- Use a Tuner: If your SWR is outside of 1.5:1, a manual or auto tuner will make matching easy.
- Experiment with Tap Points: Slight variations in the L2 tap point can greatly affect impedance and bandwidth.
Where to Buy Vertical Antennas in the UK
If building isn’t your thing or you want a professionally manufactured alternative, there are excellent options available. You can browse high-quality HF vertical antenna UK models here:
https://unicomradio.com/product-category/vertical-antennas/
This resource includes commercial HF verticals for all bands and budgets, suitable for both fixed and portable setups.
If building isn’t your thing or you want a professionally manufactured alternative, there are excellent options available. You can browse high-quality HF vertical antenna UK models here:
https://unicomradio.com/product-category/vertical-antennas/
This resource includes commercial HF verticals for all bands and budgets, suitable for both fixed and portable setups.
Why This Design Still Matters
Despite advances in compact commercial antennas, the G7UNF is a timeless, elegant, and effective antenna for UK operators. It’s a favourite among foundation and intermediate license holders, especially those looking for a practical HF vertical antenna UK design that works without breaking the bank.
Beyond its performance, building the G7UNF offers valuable insight into antenna theory, loading techniques, and RF behaviour — all essential for becoming a well-rounded radio amateur.
Whether you’re operating from a garden shed, a holiday cottage, or a coastal hilltop, this antenna proves that even modest setups can yield real results. Try it yourself, experiment with the dimensions, and enjoy being part of the proud UK tradition of homebrew radio.
Despite advances in compact commercial antennas, the G7UNF is a timeless, elegant, and effective antenna for UK operators. It’s a favourite among foundation and intermediate license holders, especially those looking for a practical HF vertical antenna UK design that works without breaking the bank.
Beyond its performance, building the G7UNF offers valuable insight into antenna theory, loading techniques, and RF behaviour — all essential for becoming a well-rounded radio amateur.
Whether you’re operating from a garden shed, a holiday cottage, or a coastal hilltop, this antenna proves that even modest setups can yield real results. Try it yourself, experiment with the dimensions, and enjoy being part of the proud UK tradition of homebrew radio.
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