Close Menu
    pondelok, 16 marca
    New topic for the forum Add advertisement

    Modifications of the Chinese kit Forty er

    Posted In: Short waves

    • Visitor
      Anonymous he August 15, 2018 at 15:51 #11490

      I seem to be missing here, so I'm opening a discussion on the above topic. The scheme is here:

      http://prekladatelia.info/chinesekit.jpg

      I made modifications for the 80m and 60m bands, it works nicely and can make connections with RW.

      From the manual, I read that the oscillator should have h21e around 130 and PA around 200.

      Sometimes it happens that it doesn't work at all, or it has lower power. Recently, I tried using a PA with a higher amplification factor (because those from 200 have run out), but the power increased minimally while the current was 360mA, and at this current, the fan cooler may not be sufficient when using 3866.

      In the amplifier, I use transistor 1969, which has a power of about 2W and a current of about 250mA.

      I added another instance of an LP filter to the output.

      Does anyone know how to 'tune' power and current? I only have a bridge PSV meter, but with a factory PSV/power meter, I can estimate the power to the antenna quite well.

      So much for the introduction.

      I welcome all comments from experienced builders. This is a great kit, I can say it is the kit of my life. And I am a married man.

      I would also like to know what the 100mH choke is for at the input of 386, in the last kits I ordered, they include 100uH. I still use 100mH there.

      Instead of driver 8050, I use 9018 with ft probably 800MHz.

      I would also like to know what the diode in the base of the PA is for, does it limit something, or what?

      Actually, I am interested in all comments from experienced builders regarding this kit, whatever it may be. What is the oscillator circuit for the B and E outputs from NE602? Could the kit be minimized even more? Etc., etc. The floor is yours.

      Reply
      Participant
      OM8AQ he August 19, 2018 at 14:36 #15002

      If this is the scheme http://prekladatelia.info/chinesekit.jpg current, the answers are as follows:

      A. Behind the output stage transistor Q5 is a Pi network made up of C17, L4, C18, which matches the output stage impedance to the antenna impedance. Its tuning is as follows:
      1. I will connect a mA meter to the upper end of L3.
      2. I will key and slightly change the capacitance of C18 (upward or downward) to the minimum current into the collector of transistor Q5. At the same time, I measure the output power to the antenna. It should be largest at the minimum current.
      I will slightly change the capacity of C17, for example upwards. The current to collector Q5 will increase and the output power will decrease. I change the capacity of C18 so that I can again find the minimum current to collector Q5. If after setting the minimum the power to the antenna is lower than it was in point 2, I will change the capacity of C17 in the opposite direction, that is, to a lower value and repeat the tuning to the minimum current with C18. I continue this with gradual step changes in the capacity of C17 in the right direction and tuning C18 to the minimum current, which correspondingly increases the power to the antenna. I will finish the setting of the Pi section when I reach the limit currentof the output transistor Q5 (maximum allowable considering the current cooling and parameters of the transistor), which should correspond to the maximum possible power to the antenna. It is generally valid for this output stage configuration that the power delivered to the antenna is approximately half of the current collector loss.

      B. Choke L1 and capacitor C8 form a low-frequency pass. They prevent the penetration of the RF signal into the NF amplifier. Inductance 100mH is fine, 100uH is not enough - probably a printing error.

      C. The diode in the base of the final transistor serves to trim the negative half-wave of the excitation voltage. The output stage in this circuit operates in class C, and a negative voltage on the base-emitter junction could break it.

      D. The oscillator in the NE602 is the classic and popular connection of the Colpitts oscillator.

      I wish you success in experimenting.

      73, Stano OM8AQ

      Reply
      Visitor
      Anonymous he August 20, 2018 at 7:18 #15003

      Thank you for the useful info.
      I didn't know that those LPs are tuned like this, I always measured the values of L and C in the article beforehand to be as close as possible to the paper ones.
      The Chinese recently add 100uH instead of 100mH to the kit, I put 100mH there, which I bought separately. They probably have excess stocks of those with a value of 100uH.

      Reply
      Participant
      OM8AQ he August 20, 2018 at 10:23 #15004

      Further clarification - in this circuit, a significant property of the Pi section is utilized, which is that it acts as an impedance transformer. Therefore, it is necessary to tune it using the aforementioned method for each individual implementation (antenna). For more operational tuning, it is advisable to use variable tuning capacitors at positions C17 and C18.

      The Pi section also serves as a low-frequency filter (LP filter), but only marginally, with low efficiency. This is due to the low Q factor of coil L4.

      Stano OM8AQ

      Reply
      Participant
      om3cvv he August 21, 2018 at 10:53 #15005

      Noro, look here, maybe something will catch your interest.

      http://ok1if.c-a-v.com/

      Reply
      Visitor
      Anonymous he August 21, 2018 at 11:08 #15006

      Thank you AQ for the clarification. I have two instances of that filter in a row, one four-port after the other.
      In the 80m band, I was looking at the SDR receiver, the level of harmonics dropped significantly after adding the second instance.

      I also built this kit on the 60m band:

      http://ok1if.c-a-v.com/RM80CH/PIC%20version%20of%20China%20KIT.html

      There is a consumption of 1A@11V and it gives a power just slightly greater than 49er.
      I have already burned one D882 transistor and replaced it with 1969, noting that it was with a load in the form of a bridge PSV meter.
      The cores of the LPF filter are heating up a bit, so it probably isn't tuned either.
      He has 281pF and 1.2uH there and I have 560pF and 1.5uH there. HI.
      Maybe it would be better to take the filter completely out of the PCB and put some
      miniature capacitors from the transistor radio on a separate PCB, as AQ says.

      Reply
      Participant
      OM8AQ he August 21, 2018 at 21:04 #15007

      Norbert, my answers and questions are:
      1. It makes no sense to put two Pi sections in series. I don't understand the information: 'In the 80m band, I looked at the SDR receiver, the level of harmonic significantly decreased after adding the second instance.' Which harmonic is being referred to? If it's the fundamental, that is, the first on 80m, there's nothing to be surprised about. It is much more interesting to measure the level of the second and other harmonics to see if they are disturbed by unwanted radiation from higher amateur bands.
      2. Please clarify for me in the sentence 'There is a consumption of 1A@11V and it gives a power just slightly greater than 49er.' what does '49er' mean?
      3. A bridge PSV meter for QRP is nice, but it cannot measure output power.
      4. If the core of the coil in the Pi section is heating up, it is clear that either the impedance of the final stage is not matched to the impedance of the antenna and a significant part of the radiated power is turning into heat in the coil and in the final stage as reflected power, or that the ferromagnetic material of the coil core is not suitable for HF – it has too high magnetization losses at the operating frequency.

      Stano OM8AQ

      Reply
      Visitor
      Anonymous he August 21, 2018 at 21:46 #15008

      I do not put articles in a series but one after another.

      I was looking at the second harmonic, here the PI article has to push it.

      Forty 9er is the first kit whose schematic is in my first post.

      With that bridge PSV meter, I can estimate the power. If I can't set the full deflection with the potentiometer, the power is low. If it goes 'around the corner', then I know the power is significantly larger. So it's not an accurate measurement, but it helps.
      These QRP devices cannot excite my cheaper factory PSV meter, which also measures power.
      Somewhere on the web, I read that those Chinese toroids are not very good quality.

      Reply
      Participant
      OM7AC he August 22, 2018 at 7:42 #15009

      To: Norbertx: What is the difference ... articles one after another and in a series?

      Reply
      Visitor
      Anonymous he August 22, 2018 at 8:43 #15010

      So cascading, if you want....

      It seems to me that the double pi article is actually two connected in series. I deduce this from the fact that the middle capacitance is usually double that of a simple pi article.

      At the output of the PA, there are up to three adaptations, one is that strange transformer with the primary and secondary connected, then there is the pi article, which AQ says also transforms impedance, and finally there is also this or that antenna tuner.... that's quite a bit of adaptation in cascade.

      Reply
      Visitor
      Anonymous he September 5, 2018 at 7:11 #15011

      So I tried to 'tweak' the power with that pi article, but it changed only slightly. It was a kit where the power was obviously low, less than 1W.
      Then I tried various output transistors, I just plugged them into the PCB and measured the power. The 5109 immediately failed. The D882 works well and the power significantly increased with the original values of L and C, so it wasn't the low pass filter. With the 1969 transistor, it had only low power, with the D882 the power is also 3W, I immediately managed to get HB.

      I feel that beta and ft play a significant role here...?? As a driver, the S9018 is used, which has a beta of 200 and goes up to 800MHz.

      D882, on the other hand, is not an HF transistor... and yet it delivers a nice performance.

      Reply
    Showing 11 posts - 1 to 11 (of a total of 11)
    Reply to: Modifications of the Chinese Forty er kit
    Vaše údaje:




    26 + = 29