High quality transverter to 144 MHz from S53WW

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Introduction

Javornik 144/14 MHz is a high - end transverter to 144 MHz optimized for use with FT-1000MP as a station on 14 MHz and power supply loss 0,5 dB between antenna and transverter input (without the use of additional preamplifiers!).

He has dva (synchronous) RX konvertory with enough gain to surpass the noise figure FT-1000MP, which is when IP0 is enabled 18 dB. The FT-1000MP will need to be modified slightly – bring out the rear panel connector with SUB RX so, so as not to disturb the appearance of the device.

Local oscillators (130 MHz) are in Buttler circuit with BFR93a low noise transistors. Two separate oscillator signal paths lead to the RX mixers. The maximum LO power to the mixers is 23 dBm and can be adjusted by attenuators (different types of mixers can be used). If one converter is enough for you, it is not necessary to build a LO pair.

TX converter handles the input level of the driver on 14 MHz in the range -20 dBm up to +20 dBm. The driver with transistor BFG196 works in class A and provides a very clear level signal +15 dBm, which is enough to excite the Mitsubishi M57727 hybrid (20W) or M57713 (10W).

RX converter

RX converter diagram, first part
RX converter diagram, second part

Total noise figure of the report (0,5 dB losses in the power supply + XVRT + IF RIG) is designed to level 2,0 dB (170K), which is better than required for TROPO at 144 MHz. Losses 0,5 dB represents, for example, 33m 7/8″ cable, 18m 1/2″ cable or 11m AircomPlus / H2000. Remember, that investment in good (read: gross) is much better than investing the same amount in a preamplifier under the antenna! In cases, where it is not possible to use a short power supply, the proposed method of connecting the 4xBF998 preamplifier to the antenna connector (is the voltage supplied via RX or RX / TX coaxial cable).

Table 1: technical parameters of the RX part of Javornik 144/14 MHz:

	JAVORNIK-144/14	JAVORNIK-144/14 + FT-1000MP (IPO ON, MAIN RX)
NF	0,9 dB	1,5 dB
G	25,0 dB	–
input IP3	+ 4 dBm	– 2 dBm (@15 kHz, calculated, based on my measurement of IP3 at 14 MHz)

The gain of the transverter is set to a more suitable level when using other types of RIGs (so, to make the overall dynamic range as ideal as possible) using attenuators in front of the mixer. The following table shows the values ​​of the pi-cell resistors (R to ground / serial R) for different noise numbers of RIGs so, so that the total noise figure is 1,5 dB.

Table 2: the values ​​of the pi-cell resistors in front of the mixer to achieve the total noise figure 1,5 dB:

G [dB]	NF [dB]	T [K]	IP3out [dBm]	TO [dB]	PI ATT R values	IF RIG NF [dB]
26,5	0,75	55	30	2,5	330/15	20
26,0	0,8	58	30	3,0	300/18	19
25,5	0,85	63	30	3,5	270/22	18
25,0	0,9	67	29	4,0	240/27	18
24,5	0,95	71	29	4,5	220/30	17
24,0	1,0	75	29	5,0	200/33	16
23,5	1,05	79	29	5,5	180/36	15
23,0	1,1	84	28	6,0	150/39	14
22,5	1,2	92	28	6,5	150/43	13
22,0	1,3	101	28	7,0	135/47	11
21,5	1,35	106	28	7,5	130/51	9
21,0	1,45	115	27	8,0	120/56	5

If the coaxial cable attenuation is greater than 0,5 dB, to recalculate the required XVRT profit at the required NF around 2,0 dB (T=170K) use the following formula:
T_IF/G + T_RX = T
T = 170 – 290*(10^L/10 – 1)
Where T_IF = 290*(10^NF/10 – 1) a T_RX is a function of profit (G) according to Table No.2.

For example: T_IF = 11200 K (16 dB) and L = 0,8 dB ==> T = (170 – 58) = 111 ==> First we try with G = 446 (26,5 dB) and T _RX = 55 K da T = 80 which is primary and so we try another value from the Table 2 and we count until then, until we reach G = 281 (24,5 dB) and T _RX = 71 K, which satisfies both conditions.

Determining the value of the HF RIG noise figure is more difficult than it may seem. Data from G3SJX and ARRL reviews are based on sensitivity, G3SJX at 10 dB (S+N)/N and SSB (BW = 2,4 kHz) a ARRL pri 0 dB S / N and CW (BW = 500 Hz). Provided, that the noise width is the same as the filter width (2400 or 500 Hz) anyone can easily calculate the noise figure (for example, NF = MDS applies to ARRL data – (-174 + 10LOG(BW))). But the bandwidth of the noise is not the same, this fact is also visible when comparing the calculated noise figures according to ARRL and G3SJX data. In the Table 3 there are several calculated values ​​of HF RIGs for comparison. BW noise is clearly affected by the intermediate circuits. I still want to say, that the NFs calculated from the G3SJX data are too optimistic, because AF circuits narrow the BW and so some numbers are not detectable (IC-775, TS-870).

Table 3: NF values ​​of different HF RIGs per 14 MHz with AIP on (preamplifier OFF) calculated from G3SJX data and ARRL measurements assuming, that the BW noise and IF filters are identical:

HF RIG	NF [dB] according to G3SJX data (BW = 2,4 kHz)	NF [dB] according to ARRL BW = data 500 Hz)
FT-1000MP	16	19
FT-1000MP MARK-V	17	20
TS-870	18	18
IC-775DSP	12	9
IC-756PRO	12	13
IC-738/736	12	14

Why 14 MHz intermediate frequency and not standard 28 MHz? Because the linearity of HF RIG receivers is optimized for 7 a 14 MHz. In the lower bands, it can be improved by including attenuators while reducing sensitivity. Linearity in the higher bands of some devices is bad (without any good technical explanation). Specifically, the linearity of newer devices on 28 MHz is very bad (with the exception of TS-870). Table 4 gives the answer, such as the IP3 of various HF devices.

Table 4: IP3 values ​​of various HF RIGs per 14 a 28 MHz pri AIP ON (preamplifier OFF) as stated by G3SJX (signal distance 50 kHz):

HF RIG	IP3 [dBm] @ 14 MHz	IP3 [dBm] @ 28 MHz
FT-1000MP	24	6
FT-1000MP MARK-V	24	2
TS-870	17	20
TS-850	25	16
IC-775DSP	12	1
IC-756PRO	13	14
IC-738/736	21	22

Now let's compare the VHF workplace reports with 0,5 decibel loss of coaxial cable, XVRT and HF RIG in use Javornik 144/14 a LT2S. LT2S is recognized as good “standard” transvertor so zsikom 20 dB, noise figure 1,0 dB a IP3out +27 dBm. In the table 5 are data on NF and IP3in using Javornik 144/14 and LT2S with different HF devices (data on NF and IP3 are from table number 3 a 4). Because LT2S has too much gain for some HF devices, the overall sensitivity will be too low (it depends on the noise of the antenna, which varies geographically). The data in parentheses apply to Javornik 144/14 with the profit set to such a value, that the NF is identical to LT2S. Data for Javornik 144/14 are in a separate column. A careful comparison can be seen, that profit and NF XVRT affect the total value of the RX system.

For example, let's take the FT-1000MP with LT2S: it may seem, that the sensitivity will be weak so we would immediately add a preamplifier with a gain 10 dB by antenna. In this case, the linearity deteriorates by 10 dB (IP3in = -23 dBm) although the preamplifier is perfectly linear. Alternatively, turn on the preamplifier on the FT-1000MP (IP0 your OFF) – in that case the IF NF drops from 18 dB na 8 dB and total NF of 3,2 dB na 1,7 dB. But! IP3 also drops from +6 dBm on -1 dBm and the overall linearity drops to roughly the level -20 dBm! Finally it is possible to close, that LT2S can only be used with HF devices, of which NF is 10-14 dB and IP3 values ​​are some +20 dBm (on 28 MHz!!!).

Table 5: NF and IP3 values ​​using Javornik 144/14 on 14 MHz and LT2S and 28 MHz:

HF RIG	JAVORNIK-144/14			LT2S
	NF [dB]	IP3 [dBm]	G [dB]	NF [dB]	IP3 [dBm]
FT-1000MP	2,0 (3,2)	-2 (+2)	25 (21)	3,2	-13
TS-870	2,0 (3,2)	-8 (-4)	25 (21)	3,2	+0
TS-850	2,0 (2,7)	+0 (+2)	24 (21)	2,7	-4
IC-775DSP	2,0 (1,8)	-9 (-10)	22 (23)	1,8	-18
IC-756PRO	2,0 (2,1)	-9 (-9)	22,5 (22)	2,1	-6
IC-738/736	2,0 (2,2)	-2 (-1)	22,5 (21,5)	2,2	+1

When considering the required sensitivity to 144 MHz in contests we must also take into account the thermal noise of the antenna (T_A). In some sources, at least T is given_A on 144 MHz 200K, if the antenna is pointed at a cold area of ​​the sky. But the reality is always a little worse. In the picture you can see T_A at our contest workplace JN75DS, 1269 m asl when measuring 2.7.1999 O 19.00 LT. The lowest measured value was 370K, which is equivalent 3,5 dB NF. The maximum values ​​are in the direction of the town of Postojna (roughly 10 km, 500m asl) 1600K = 8,1 dB a place Cerknica / Ljubljana.

Is known, that if the noise of the RX system is the same as the noise of the antenna, then the deterioration of S / N is 3 dB. It is debatable, what S / N deterioration is acceptable for VHF contesting. I think, that T_RX should be 0.6 times the T value_Amin – gives deterioration of S / N o 2 dB. A T_Amin is taken as 300/2 + 200/2 = 250K (half earth noise and half sky noise). In the case of the NF system 2,0 dB (170K) so we have a sufficient reserve for unpredictable losses in the relay, jumpers and the like.

Local oscillators

Oscillator scheme, first part
Oscillator scheme, second part
T / R switching scheme
XVRT interconnection scheme

Local oscillators (130 MHz) are connected according to Buttler with low noise transistors BFR93a. The circuit has two separate oscillators for two RX mixers. The maximum level of excitation from LO should be 23 dBm, which we set by attenuators before the mixers. Different mixers can be used (I recommend TUF-1H). When used 23 dBm mixer (e.g. RAY-1 or SAY-1) it is possible to achieve an increase in IP3 by 1 or 2 dB (own RX converter, because IP3 is determined by IF RIG, that is lower than +25 dBm). However, it is not harmful to use RAY-1 at the same excitation as TUF-1H (+14 dBm) – it is better to use SAY-1 than for +20 dBm P1dB. Anyway, price +23 dBm LO mixer is not worth the improvement of 1-2 dB IP3.
If you are not interested in both RX converters, then you only need to construct one part.

TX converter

TX converter diagram, first part
TX converter diagram, second part
PA TX converter diagram

The TX converter can process the excitation signal 14 MHz in levels from -20 dBm per +20 dBm. For TRX, which has a very low signal level (-10 to -20 dBm) it is possible to include an amplification stage. Behind the low-level mixer is a low-noise broadband amplifier. The driver operates in class A with the BFG196 and provides a very clear level signal +15 dBm (IMD5 is around -60 dBc). For the final stage, it is most efficient to use the seamless hybrid PA from Mitsubishi M57727 (20W) or M57713 (10W). This is not the best technical solution, because the modules are not the most linear, but at 20 / 10W or less it is easy to suppress higher IMD products by more than 120 dB below carrier level (which is enough for that, so as not to confuse nearby stations).

The biggest problem of the whole TX part is broadband noise. There are two sources, involved in its production: XVRT a HF RIG. By measuring Javornik 144/14 MHz at 20W output power, the value was reached -118 dBc / 2.4 kHz and can be further improved by 10-15 dB using a TX mixer with a higher oscillator level (Attention – TX noise will only -108 dBc / 2.4 kHz at 2W output power!). However, the noise spectrum of HF RIG is much worse! Looking at the data from G3SJX (ARRL measures TX noise only at a distance of 20 kHz, which can only be considered as phase noise, no broadband TX noise) it is possible to see, that none of the modern RIGs have broadband TX noise better than -110 dBc / 2.4 kHz in distance 200 kHz from carrier frequency. In a narrower range, it is around 100 dBc/2,4 kHz, which is still not the value of the predominant phase noise. It means, that the S / N ratio of the transmitted signal is only 100 -110 dB!!! Dve 500W VHF stanice so 16 dBi antennas in the distance 100 km (!) with radio visibility they produce a signal of strength -27 dBm – What is 111 dB above the SSB noise level (I take sensitivity -138 dBm). Only by pressing PTT on the device with the transmitted noise level -111 dBc / 2.4 kHz will mean an increase in noise of 3 dB!

Someone might judge, that broadband TX noise is especially a problem during VHF contests in busy areas. For example, v S5 is the average distance between well-equipped stations 50 km and distances of 10-20km are no special feature!

JAVORNIK connection 144/14 a FT-1000MP

Na to, in order to take full advantage of the FT-1000MP's capabilities with two separate RX inputs, we will need a simple circuit, which connects XVRT and IF RIG. The crossover switch on can be considered as a minimum 14 MHz, which connects both RX converters to the MAIN RX input in one position. That's because, that the SUB RX does not have the same quality as the MAIN RX and does not provide DSP. But I guess, that only at 20% I will switch the connection from SUB to MAIN RX.

The interface may also include a circuit, which will allow the S system to work&P to SUB RX with both RX converters independent of the switch with quality NB, crystal filters and the like.

Further development

This is a problem with broadcast broadband noise. It is possible to construct a high quality VFO on 130 MHz (preferably VXO or DDS / PLL) and use HF RIG on a single frequency. In that case, it would be possible to rank at 14 MHz crystal filter between RIG and XVRT. The result would be a better S / N ratio of the transmitted signal and a lower level of IMD products on reception.

Does, S53WW
Slovak translation by Viliam, OM3-0122