posted today, 19.03.2021, 08:00 UTC
posted today, 19.03.2021, 08:00 UTC
So, we have an short antenna, easy to build and install. It was working in WSPR mode more than 3 days. It’s time to find the performances… and to see if our expectations are to big, or what can we improve.
First analyse is a simple one. Just go to VK7JJ site (http://wsprd.vk7jj.com/) and follow the instructions. You can see when you see a lot of useful informations about your antenna, the antenna location and propagation.
It looks fine… it’s only an example of useful info. But is not enough. The chart say you can work from YO stations from VK, JA, North and South America. Yes, using WSPR mode.
What about other modes ?
Let’s go to KP4MD site (https://www.qsl.net/kp4md/wsprmodes.htm#application) and download the mode-comparison excel file.
Using your WSPR data you can find if you can work a specific station in another mode (CW, RTTY, SSB, etc.).
Let start with the bad news…
After you shall download and process the data, you shall find that the probability to work VK7JJ in RTTY or SSB mode is very low to very, very low. Red colour is not good….
Let’s check other DX stations
Sorry, no K1ABK, no JA5NVN.
OK, dont panique, let see what can we work.
TF4X 3927 km
MM7BWK 2544 km
OH3FR 1867 km
So, if you want more, try to find if you can use a higher position or re-locate the position, or improve soil parameters, etc.
For example, my location is very unfriendly regarding the obstructions around me. As you can see in the graphs (from 1st part, VK7JJ site), the existing freeway to 310 degrees azimuth is confirmed by number of spots and the obstruction from 230 degrees (a new big house, etc.) is also confirmed by no data/spots on that direction.
Before starting the construction of this type of antenna, consider the following advantages and disadvantages.
So, let’s find some materiales for the Hairpin antenna made with aluminium tubes. What I found:
I decide to use the folowing parameter: 25 cm spacing and maximum 2.85 m lenght.
Building the top connector. Use metal screws (the black one) to obtain a good electrical connexions between tube and connector.
If you are using separate elements like me (not full tube, 2.85 m one piece) you have to cut a longitudinal space and use againg metal screws to obtain a good electrical connexion between elements.
I am using 2 old double sections variables with mechanical multiplier, modified (less plates) to obtain 2 mm spacing. Minimum capacity 10 pF, maximum 52 pF (each section).
Find a good enclosure and a piece of isolating material, with enough thick (15 mm in my example, I found an old textolit bar painted in blue !) to sustain the tubes. Use some Cu wires with big diametres (2.5 – 4 mm) for electrical connexions. Depending the parameters, it can be possibil to need both sections of variables to be connected (if the capacitance need to be more than 50 pF) or only one.
Find the proper mounting metal flanges. Use a common mode shocke (in my case, 20 turns of RG213 U equivalent on 12 cm diameter (on a piece of water drain pipe). Use an insulated tube for tuning the variable capacitors (the white tube in the photo). Connect the equivalent lenght of coaxial cable (as you are using for the trcvr) and start the tuning. Take care, the proximity of human body can influence the measurement. During the tuning procedure don’t touch antenna or mast. Use an insulated tube for variable capacitor (20-30 cm) to avoid your body influence.
With patience, start the tuning. After you shall obtain the resonance and R=50 ohms at desired frequency (most probably you are climbed on a ladder near the mast), step down and re-check the values at 3-4 meters away from antenna. Check the Bw for your specific needs. Re-tune if you are not satisfied.
Go into the shack and re-check the values obtained. Most probably you shall see some differences. The most important is the resonance frequency to be the same (or with minor differences).
Congratulations, you have an antenna ! But, don’t forget, is a small one, is not a miracle. You can make QSO’s 3000 km around you, more or less, depending the obstructions, depending the soil, etc.
Good luck and 73’s !
24 hours WSPR tests, 1 watt power
(14.03.2021 09:00 UTC – 15.03.2021 09:00 UTC)
Many times, during rtty contests, I have a big problem with qrm. A lot of strong signals in a small bandpass, so, if you reduce the RF Rx gain or connect the 6-12 dB attenuator you shall loose the weak signals. In fact, the receiver (the preamplifier, mixer, etc) have to deal with a lot of unwanted (by the operator) signals, so the transceiver performance will be degradaded. Usualy, the modern transceiver have a quality FEF (Front End Filter) after the 1’st mixer. It’s wonderfull, but still need to reduce the RF Rx gaind during some periods of the contests.
So, last cqwwrttycontest (2020) I tried an old solution, a FEF connected direct between antenna and transceiver, with 5 comutabloe monocrystals (7041, 7045, 7055, 7070 and 7082 kHz.).
FT920 - data conector pinout
SCU-17 conector pinout (As viewed from rear panel, not from cable!)
AFSK mode FT-920 pin 1 Data IN (Audio IN) SCU-17 pin 1 Data OUT (Audio OUT) FT-920 pin 2 GND SCU-17 pin 2 GND FT-920 pin 3 PTT SCU-17 pin 3 PTT FT-920 pin 4 Data OUT (Audio OUT) SCU-17 pin 5 Data IN (Audio IN) FT-920 pin 5 Busy SCU-17 pin 6 SQL IN (Busy)
Pin 1 (AFSK Input): Connect this pin to your TNC’s “AFSK Out” or “Mic Audio” output line. The optimum input level is 30mV rms, and the input impedance is 3 k. Your TNC’s audio output level potentiometer will allow you to set the level to the optimum value. This pinmay be used either for 300 baud SSB-mode digital operation or for 1200-baud FM packet. The bandwidth and frequency response are not, however, suitable for 9600 baud operation. Be sure the AFSK-FSK switch on the rear panel is in the AFSK position. For FSK operation (whereby the TNC closes a line to ground to accomplish teletype keying), set the AFSK-FSK switch to FSK, and connect your TNC’s FSK keying line to Pin 1. Pin 2 (Ground): Connect this to the shield(s) of the cable(s) used for connections between the TNC and the FT-920. Pin 3 (PTT): Connect this pin to the PTT line from the TNC. This pin, when grounded by the TNC, places the FT-920 into the Transmit condition. Pin 4 (Audio Out): Connect this pin to your TNC’s “RX Audio” input line. This is a constant-level (100 mV rms @ 600) audio output line which is not affected by the position of the front-panel AF GAIN control. Pin 5 (BUSY): This is a “Squelch Status” pin not generally required for digital mode operation. This pin is held at +5V when the squelch is open, and is grounded when the receiver is muted by the squelch (“nosignal” condition). FT920 Menu settings (dont forget - USB-DATA mode) Menu # Description Value for WSPR/FT4/FT8/RTTY U-45 Packet Freq. Display Offset 0000 U-46 Packet Subcarrier Frequency 2125U Please note, those values are available for regular rtty tones (2295/2125).