Modifications to the Chinese Forty er kit

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  • #11490 Reply

    Apparently I'm wrong here, so I open the discussion on the above topic. The scheme is here:

    I made modifications to the band 80 60m, it works fine, it is possible to make connections with RW.

    I read from the manual, that I will have h21e around 130 and PA around 200.

    It happens to me sometimes, that it doesn't work at all, or it has less power. Last time I tried the PA data with your amplifier (because those of 200 I missed them) however, the performance was minimal, but the consumption was 360mA, and with this consumption, the fan cooler may not be enough in the case of use 3866.

    I mostly use a transistor 1969, in which the output is approx. 2W and consumption approx. 250mA.

    I added one more instance of the LP filter to the output.

    Can anyone advise?, how “tune in” execution and collection? Mam len mostikovy PSV meter, however, with the factory PSV/power meter, I can estimate the power to the antenna quite well.

    Takze tolko na uvod.

    I welcome all comments from experienced designers. This is a great kit, da sa povedat, that it is the kit of my life. And I'm a married man.

    I would also be interested in why the 100mH choke is there at the input 386, in the last kits, what i ordered, I add 100uH there. Ja tam stale davam 100mH.

    Miesto drivera 8050 there I go 9018 s ft tusim 800MHz.

    I would also be interested in why the diode is there in the base of the PA, something is limiting there, or what?

    I'm actually interested in all the comments of an experienced designer about this kit, whatever it is. What is the connection of the oscillator to the output B and E from the NE602? The kit could be further minimized? Atd, etc. The floor is yours.

    #15002 Reply

    If this scheme current, the answers are as follows:

    A. Behind the output stage transistor Q5 is a Pi cell formed by C17, L4, Q18, which matches the impedance of the output stage to the impedance of the antenna. Its tuning is as follows:
    1. I will place a mA meter in the upper end of L3.
    2. I lock and slightly change the capacity of C18 (upwards, or down) to the minimum current to the collector of transistor Q5. At the same time, I measure the output power to the antenna. It should be the largest at the minimum current.
    3. I will slightly change the capacity of C17, e.g.. upwards. It increases the current to the collector of Q5 and the output power drops. I change the capacity of C18 like this, to find the minimum current to the collector of Q5 again. If, after setting the minimum, the power to the antenna is lower than it was at the point 2, I will change the capacity of C17 in the opposite direction, that is, to a lower one and I repeat the fine-tuning to the minimum current with C18. This is how I continue by gradually changing the capacity of C17 in the right direction and fine-tuning C18 to the minimum current, which correspondingly increases the power to the antenna. I will finish setting up the Pi article, when I reach the limit current of the output transistor Q5 (maximum permissible with regard to the current cooling and transistor parameters), which should correspond to the maximum possible power to the antenna. It roughly applies to this connection of the final stage, that the transmitted power to the antenna is about 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. An inductance of 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 connection operates in class C and the negative voltage on the base transition – the emitter could break it.

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

    I wish you success in experimenting.

    73, Stano OM8AQ

    #15003 Reply

    Thank you for the useful information.
    I had no idea, that the LPs are tuned like this, I always only measured the L and C values ​​of the article in advance, to be as close as possible to paper.
    The Chinese recently add 100uH instead of 100mH to that kit, and dam gives 100mH, ktore som zakupil separe. They probably have excess stocks of those with a value of 100uH.

    #15004 Reply

    One more clarification – in this connection, an important property of the Pi cell is used, and it is, that acts as an impedance transformer. Therefore, it is necessary to tune it using the above procedure for each individual implementation (antenna). For more operative tuning, it is advisable to use rotary tuning capacitors at positions C17 and C18.

    The pi element also fulfills the function of low frequency pass (LP filter), but only secondarily, with little efficiency. This is due to the low Q factor of the L4 coil.

    Stano OM8AQ

    #15005 Reply

    Noro look here, maybe something will appeal to you

    #15006 Reply

    Thanks AQ for the clarification. I have two instances of that filter in a row, one creation gate after another.
    In the 80m band, I looked at the SDR receiver, the harmonic level decreased quite a bit after the addition of the second instance.

    I also built this kit on the 60m band:

    There is a 1A@11V outlet and the performance is only slightly higher than the 49er.
    I already burnt one transistor D882 and replaced it 1969, I point out, that with a connected load in the form of a bridge PSV metro.
    The cores of the LPF filter are getting a little hot, so it's probably not 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 flat and put some in there
    miniaturne kondiky with transistors on a separate pcb, as AQ says.

    #15007 Reply

    Norbert, my answers and questions are:
    1. It makes no sense to put two Pi cells in series. I don't understand the information: “In the 80m band, I looked at the SDR receiver, the harmonic level decreased quite a bit after the addition of the second instance.” Which harmonic is it? ? If it is basic, i.e. the first at 80m, no wonder. It is much more interesting to measure the level of the second and other harmonics, whether the higher amateur radio bands are not disturbed by unwanted radiation.
    2. Please explain in a sentence “There is a 1A@11V outlet and the output is only slightly higher than the 49er.” which means “49is” ?.
    3. Bridge PSV meter for QRP is fine, but cannot measure output power.
    4. If the core of the coil in the Pi cell is heated, it is clear, that either the impedance of the final stage is not matched to the impedance of the antenna and a substantial part of the radiated power is converted to 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 KV – has too high magnetization losses at the operating frequency.

    Stano OM8AQ

    #15008 Reply

    I don't post articles in a series, but for myself, jeden za druhym.

    I was looking at a kind of accordion, here I have to suppress the PI article.

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

    With this bridge PSV meter, I can estimate the performance. When I can't even set the full deflection with the potentiometer, is performed small. If it works for me “around the corner”, so i know, that the performance is significantly greater. So it's not exactly a measurement, but it will help.
    These QRP devices cannot wake up my cheaper factory PSV meter, which also measures performance.
    I read somewhere on the web, that the Chinese toroids are not of very good quality.

    #15009 Reply

    To: Norbertx: What is the difference …individual articles and series?

    #15010 Reply

    So cascading, If you want….

    It seems to me, that the double pi article is actually two connected one behind the other. I guess based on that, that the average capacity is usually double compared to a simple pi element.

    Na vystupe PA su az tri prisposobenia, one thing is the special transformer with connected primary and secondary, then there is a pi article, which AQ is talking about, that it also transforms the impedance and finally there is one or another antenna tuner….to je dost prisposobeni v kaskade.

    #15011 Reply

    So I tried “doladovat” however, the performance changed only to a small extent with these five articles. Island or kit, where the performance was obviously small, less than 1W.
    Then I tried different end transistors, I just plugged them into the PCB and measured the performance. 5109 he left immediately. The D882 works well and performance increased significantly with L and C flood ratings, so it wasn't the low pass filter. With a transistor 1969 it had little effect, with D882 the power is also 3W, I managed HB right away.

    I feel, that beta and ft play an important role here…?? S9018 is used as a driver, which has beta 200 a ide do 800MHz.

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

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