I decided that with so little activity on 70cm that I would get more out of the 4m yagi being on the mast rather than sitting behind the shed !. The swap was made but on testing there was no match, so it was down again, the connections all checked, the dipole connecter was removed and dismantled to check the balun etc, all found to be intact and rebuilt to find it working perfectly !. There must have been a small gremlin in there somewhere though.
The owl is still in residence to try and reduce the 'fallout' from roosting starlings and collared doves :-)
Now with the yagi up the 4m Es has all faded out, the only station I worked recently (EA5/G0KSC) was on the 6m collinear with a lousy swr on 4m :-(
The owl is still in residence to try and reduce the 'fallout' from roosting starlings and collared doves :-)
Now with the yagi up the 4m Es has all faded out, the only station I worked recently (EA5/G0KSC) was on the 6m collinear with a lousy swr on 4m :-(
I had an idea for something to build over the weekend to see how it would work, a simple RF bridge which could be driven by a signal generator and displayed on a spectrum analyser. It is extremely simple, 3 resistors and 2 capacitors, I used 47 ohm resistors considered to be near enough to 50 ohm to be of little consequence for the purpose of experiment.
The results are very interesting, aerials on a long cable tend to exhibit wildly varying traces which could be related to mismatch on the cable length connected, but helical aerials plugged directly into the unit produce very clean results.
The results are very interesting, aerials on a long cable tend to exhibit wildly varying traces which could be related to mismatch on the cable length connected, but helical aerials plugged directly into the unit produce very clean results.
This is a trace obtained scanning a low band PMR helical aerial and gives a resonance dip at 76MHz
This is a scan of the 4ele 70mHz yagi from 40MHz - 100MHz showing the wild mismatches either side of resonance, the small variations are centred on 70mhz and when a narrow scan is done equates to the level obtained with a dummy load for reference.
It's certainly cheaper than an antenna analyser but does need serious workshop equipment to provide the signals and display, whether it could be achieved with a Chinese DDS vfo to provide the oscillator signal and cheepo tv dongle to provide sdr display would probably take more brains than me to achieve :-)
It's certainly cheaper than an antenna analyser but does need serious workshop equipment to provide the signals and display, whether it could be achieved with a Chinese DDS vfo to provide the oscillator signal and cheepo tv dongle to provide sdr display would probably take more brains than me to achieve :-)