Category: Antennas

The radio amateur SV2CZF makes some very interesting antennas and sells them on his website for a small fee: https://www.sv2czf.com

For a long time I had been tempted by the MWA30 (https://www.sv2czf.com/mwa30.html), which is a very small portable mini-whip that runs on battery power. Unfortunately, mini-whips must be well grounded, so I decided to use his latest antenna, the SAR32M. This one works even without good grounding and you can connect an antenna via a whip antenna like a telescopic or a loop.

Features

• Reception from 50 KHz to 175 MHz
• Built-in rechargeable battery which can be charged via Micro USB port (approx. 10 hours battery power)
• A normal whip antenna, like a telescopic antenna, can be connected
• A loop can be connected
• A loop and a telescopic antenna can be connected in parallel
• Impedance adjustment for shortwave
• Built-in Pre Amp for amplification
• Only suitable for receiving, when transmitting the SAR32M will be damaged directly

How to order

The SARM32M is already shown on the homepage, but cannot be ordered through it yet.

• Write a e mail in english to this adress: info@sv2czf.com
• By default, the SARM32M is delivered with BNC connectors. But you can also ask SV2CZF to install SMA connectors
• Antenna 94,99 € and shipping 6,99 €. The antenna is shipped in a bubble envelope and passed customs without any problems for me
• The shipping took for me from Greece to Germany only 5 days.

Experience in practice

I use the SAR32M mainly with my Malahit DSP2. Here, the SMA32M with the same 70 cm telescopic antenna, depending on the frequency range, can get out again about the 3 S-stages (for example, in the 40 m band). Unfortunately, the reception breaks in from about 50 MHz, so that e.g. 2 m works better without the SAR32M in between.

On the other hand, if you connect a loop, the SAR32M shows its potential. You can compare it well with the MLA 30 +, which also provides very good reception results. The loop made of wire, which is supplied with the MLA 30 +, also fits optimally to the SAR32M. However, any piece of wire or cable can also be used.

The battery life is about 3 times longer than the Malahits DSP2 with a 3400 mah cell. The great thing is that this makes the SAR32M perfect for portable use.

Here are two examples on the 40m band, received with the SARM32M and a 70 cm telescopic antenna. First CW:

Again with SSB with only a 70 cm telescopic antenna:

The performance is very very good.

From inside

On Facebook I found the following picture of the inside view. The legs are firmly glued and usually break off when you try to open the lid (yes, I tried 😉 )

In China you can get a kit for an antenna tuner for about 10 €, which I once assembled for fun. Here is the link to buy it: Manuel Antenna Tuner DIY Kit 1-3 0 MHz

The build was a little tricky because there wasn’t much room in the case. In addition to the parts included in the kit, I added two banana sockets. This is what my finished kit looks like.

Matching the antennas actually works quite well: tested from 160m to 12m.

DL4ZAO has further developed and modified the circuit of the Mini-Whip antenna and published a number of variants. Here you can find the website of DL4ZAO: dl4zao.de

DL4ZAO BlueWhip MegaWhip

I have rebuilt the MegaWhip from DL4ZAO. The reception is much less sensitive to interference compared to the Mini-Whip from pa0rdt. Link to the building instruction: https://www.dl4zao.de/_downloads/Megawhip.pdf

Features of the BlueWhip MegaWhip

• It is an active receiving antenna that cannot transmit
• The antenna is very broadband and you can easily overlook several mHz with the SDR
• By jumper you can add a FM band stop

DL4ZAO BiasTee Basic

I have also rebuilt the BiasTee. On the same website you can find a building instruction for a BiasTee. Link to the building instruction: https://www.dl4zao.de/_downloads/Bias-Tee-Basic_100.pdf

Since I live in the middle of Berlin and am surrounded by 6-story apartment buildings, my reception conditions are very poor. The sources of interference are extremely diverse. In addition, there is an LED street light directly in front of my balcony.

I have provisionally set up the MLA 30 Plus on the balcony on the second floor, on a two-meter high bar, which points diagonally to the street. I have noticed that the further the antenna is from the apartment, the better the reception.

Receiving on 40m

Receiving on 80m

Reception on 20m with FT8 over 2 hours

Currently I am working on a modification of the MLA 30 Plus: I have a 2m long copper tube, with 6mm diameter bent into a circle and mounted on the antenna. Provisionally, I have insulated the upper end of the stainless steel rod with self-welding tape and attached the MLA 30 Plus, with cable ties to these. This will later become the final mounting on the balcony.

ADS-B for receiving the flight data is on 1090 MHz. So a quarter wavelength is about 6.8 cm. However, I cut my copper wires a little longer so that I can still tune afterwards.

What do you need:

• A socket,perhaps a PL, BNC or SMA
• Rigid copper wire, 5 x 8 cm (I stripped mine from a 3 core power cable).
• optional are cable lugs and screws (instead you can solder the copper wires directly to the socket)

I have decided for the SMA socket, because I want to go later anyway on SMA. Otherwise, I have found four different screws and nuts, in the same diameter.

• Next, I attached the cable lugs to the SMA socket with the screws. Alternatively, you can solder the copper wires directly to the socket.
• Then I stripped 5 chum wires from a power cable and shortened them to 8 cm.

• Then I wetted all the copper wires with tin.

• Next, I soldered four copper wires to the lugs.
• After that I soldered the fifth copper wire to the inner conductor of the SMA socket.

• Finally, I connected the antenna to an analyzer and found that the copper wires were too long.
• I shortened all copper wires to 6.7 cm and had a SWR of 1:21 on 1090 MHz. I measured including the cable lugs.

• The antenna is located in the middle of Berlin on the balcony on the second floor and has a range of about 280 km.

I’ll skip the first steps, because I had already described them in the instructions for the BNC socket. You can read that here: http://mini-whip.de/2021/04/08/mla-30-plus-bnc-buchse/

• I stripped the cable a few cm, almost as long as the SMA socket is.
• Now I have bent the outer conductor backwards.
• Then I soldered the inner conductor.

• Since I decided to use the crimp variant of the SMA socket, I now have to pull the heat shrink tubing and crimp sleeve onto the cable

• Now the inner conductor can be inserted.
• Next, the outer conductor must be bent forward again and the crimp sleeve put on.

• Now the connector can be crimped.

• The whole thing should then look like this.

• Finally, I pulled a heat shrink tube over the connection.

• It should then look like this.

• Finally I glued the bushing and the screws for the loop with epoxy.
• Before that, I roughened the areas with a file so that the epoxy would sit better.

• The last thing to do is to fold the cable and close the lid.
• I left the cable extra longer in case I still want to make adjustments.

Since the cable on the MLA 30 Plus is fixed, quite thin and 5m long, I decided to install a BNC socket. I had these two BNC sockets in stock. I would have liked the larger with the rubber verbau, but the diameter seemed too thick, so I have the left variant use.

• When you open the lid, you will see the cable, which is attached to the housing with hot glue.

• The cable can be pulled 20 cm inwards with a little force and then the cable can be clipped off and the adhesive carefully removed.
• Now the hole can be drilled out. I did this with a hand drill, because otherwise you can hit the coil in the middle very quickly. I have seen some videos where the coil was striped with the drill.
• In my case, the diameter of the smaller BNC socket was 9 mm.

• Then the rubber must be removed a few cm. After that I bent the screen backwards.

• Twist the shield together and tin it.
• Tin inner conductor.
• Install the BNC socket. Depending on how much black epoxy was poured, it may be very tight with the nut. It may be necessary to scrape or file the black epoxy down to the board.
• Solder the sheath and inner conductor to the socket. I left the cable longer on purpose in case I want to make adjustments in the future.
• If you still have a ferrite core / folding ferrite, you can still attach it to the coax cable in the housing.

• It might make sense to adjust the blue potentiometer in the upper left corner. With the included wire loop, you can definitely raise the sensitivity a bit. In my case, I had to turn it counterclockwise.
• If you use a longer or thicker loop, you should reduce the sensitivity, otherwise too much interference will be amplified.