20-10-2021, 05:26 PM
(This post was last modified: 20-10-2021, 05:40 PM by Murphyv310.)
Hi.
I've been testing various ways of coupling this circuit to an external antenna. the original lash up had no tuning and produced harmonics. The third harmonic was hard to pick up and there after I couldn't detect it with my SDR Play.
I've attached the circuit so far, It is virtually the same as the the old one with a 1ZH42A. On this setup though I tried a few ideas one is as marked as "A" in the circuit, it is a transistor radio ferrite rod, coil and a tuning cap, this just about fills the shed on its own when tuned. The low impedance winding can be grounded on one side and the other to a 6 foot "long" wire and this easily fills the shed and gives reasonable results in the garden up to the house. I also tried a TOKO oscillator coil wired the same as "A" and it works well with a little more range but it is sharper to tune and the length of the antenna needs retuning if the length is altered. "B" is a Pi tank circuit and this gives the greatest range. This also filters out harmonics as does "A" with 72v HT its actually a bit more than Pantry, reducing the HT tames the output and less drive is required, T1 is a valve output TX in reverse, the low impedance side goes to the headphone socket output from an MP3, DAB radio etc, it can easily overdrive the transmitter.
Personally I dont really think the harmonics are an issue without tuning, the level is low and there is more hash from SMPS, wall warts and Powerline adaptors than a small pantry TX. I did a comparison with my Minimod and I feel it is noisy in comparison.
Tomorrow I'll do the tests with the scope looking at the waveforms and post up the results. Next will be to build it properly and into a box.
PS Tuning caps used were 5-150pf I also decoupled the HT with 100nf
I've been testing various ways of coupling this circuit to an external antenna. the original lash up had no tuning and produced harmonics. The third harmonic was hard to pick up and there after I couldn't detect it with my SDR Play.
I've attached the circuit so far, It is virtually the same as the the old one with a 1ZH42A. On this setup though I tried a few ideas one is as marked as "A" in the circuit, it is a transistor radio ferrite rod, coil and a tuning cap, this just about fills the shed on its own when tuned. The low impedance winding can be grounded on one side and the other to a 6 foot "long" wire and this easily fills the shed and gives reasonable results in the garden up to the house. I also tried a TOKO oscillator coil wired the same as "A" and it works well with a little more range but it is sharper to tune and the length of the antenna needs retuning if the length is altered. "B" is a Pi tank circuit and this gives the greatest range. This also filters out harmonics as does "A" with 72v HT its actually a bit more than Pantry, reducing the HT tames the output and less drive is required, T1 is a valve output TX in reverse, the low impedance side goes to the headphone socket output from an MP3, DAB radio etc, it can easily overdrive the transmitter.
Personally I dont really think the harmonics are an issue without tuning, the level is low and there is more hash from SMPS, wall warts and Powerline adaptors than a small pantry TX. I did a comparison with my Minimod and I feel it is noisy in comparison.
Tomorrow I'll do the tests with the scope looking at the waveforms and post up the results. Next will be to build it properly and into a box.
PS Tuning caps used were 5-150pf I also decoupled the HT with 100nf
