The Rochester VHF Group

Transcription

1 The Rochester VHF Group The VHF Journal Winter 2018 Volume 71, Edition 2 In this issue The Chairman Speaks Microwave Sprint db Article Fall Workshop Pictures Treasurer s Report Shack/Equipment Pictures Calendar of Events The K290R Project Article The Chairman Speaks by Jarred Jackson KF2MR Welcome to Winter! The recent deep freeze has reminded me of just how lucky we have been with warm-ish weather for the last two January contests. As I write, the long range forecast has come out for the start of the contest and it looks like we could be above freezing. I look forward to the January contest starting on January 20th and hope to hear all of you on the air. As you may have heard, the W2UTH callsign will be used by Ev, W2EV. Ev s goal is to put the club callsign in the record books, so lets do everything we can to help him with this plan. See the article later in the newsletter for more information on January contest plans. Most of the work from the Board of Directors since the last newsletter has been focused on getting ready for the Fall Workshop, getting our new PayPal account properly setup and discussing some activities for Spring. The workshop was well attended and feedback was positive. Check out the article in this newsletter to see some of the pictures from the event. Jim, WB2YJH did a great job with the new bank account and PayPal account and Bill, K2TER updated the website. By clicking on the Join Now button you can join or renew with a 1-year or 3-year option. The BOD will meet again in February to plan out the rest of the season. In terms of activities, we will be setting up a site visit to the K2LIM contest site this spring. If you have never been to the site, I strongly encourage you to check it out. It is located about 15 minutes south-west of Watkins Glen. Through a lot of planning and work, the group has created a very effective multi-operator site that consistently performs at the top of the national rankings. More details on this trip will be available in early March. 1

2 Fall Microwave Sprint by Jarred Jackson KF2MR A Microwave sprint is different than other sprints in that the points you earn are composed of the cumulative number of kilometers added up for all your contacts. To calculate the distance, you use software or online tools to determine the distance between the center of the six-digit grid squares. RVHFG member Bill VE3CRU, let me know well in advance that he intended to go out for the event rain or shine. Most of my contacts came from Bill as we had six different grid combinations across Lake Ontario and even squeaked out one contact in an obstructed seventh grid combination. Best DX on came from another northern RVHFG member, Dana VE3DS. Frequency QSOs Best DX - km G 0 0 For setup I had antennas and radios for 432 5G. Unfortunately, I was not able to make any attempts on 5G. I was surprised to hear from W2EV. Ev was able to use his 900 MHz HTs to help with some local activity (Thanks Ev!). Total score for this event was 4,485 points which is by far my best yet for a Microwave Sprint. db by Tom Jennings KV2X Introduction. A decibel or db is used to specify ratios of powers and voltages in a logarithmic fashion and are commonly used for gain and loss calculations in electronic systems. In view of its logarithmic scale the decibel is a convenient representation of very large ratios in terms of manageable numbers as well as providing the ability to carry out multiplication of ratios by simple addition and subtraction. In ham radio, the gain of amplifiers is specified by decibels. Attenuators use the db to indicate how much loss they introduce. Decibels are also used to represent absolute values by providing a reference. For example, dbm is used as a common power reference. One milliwatt is defined as 0 dbm. Antenna manufacturers use the dbd as a measure of an antenna directivity and gain. History. The decibel unit was originally invented by Bell Telephone Labs as the Bel and given its name after Alexander Graham Bell. The Bel unit was defined as a ratio of power levels of 10 to 1 for most measurements. The decibel is one tenth of the original Bel unit. In Telephones, amplifiers are driving speakers and doing so over long lines. To drive speakers there needs to be a power transfer. If you are in the business of driving speakers, you will analyze how much power there is available and how much power was lost in getting the signal to the speaker. (Cont d on page 3) 2

3 Definition. The fundamental definition of the decibel (db) is in terms of a power ratio. Two powers, P1 and P2, can be related in db by A(dB) = 10 log(p2/p1) where log indicates the base 10 logarithm. The subscript (db) is used to indicate that the numerical result is in decibels. As shown P2 is expressed relative to P1. Reversing P1 and P2 changes the sign of the result. If the powers P1 and P2 are the results of a pair of voltages across a pair of resistors then A(dB) = 10 log(v2 2 /R2)/(V1 2 /R1) A(dB) = 10 log(v2/v1) log(r1/r2) A(dB) = 20 log(v2/v1) + 10 log(r1/r2) The first term is the voltage form of the decibel equation and the second term accounts for the differences in the two resistances. If the two resistances are equal, this equation can be further simplified to A(dB) = 20 log(v2/v1) This last equation as taken on a life of its own and is often used as the defining equation of the decibel. If the resistance associated with each of the powers are equal, then the power equations and the voltage equation are consistent. If the voltage equation is used when the resistance are not equal, incorrect results will occur. The voltage form of the decibel equation can be used successfully if power gain is not inferred from it. Absolute db Values. As discussed above, the db represents ratios of two values in db form. By providing a reference values decibels can be used to refer to an absolute value. In the case of power P(dB) = 10 log(p/pref) One of the most common power reference is 1 mw which is the basis of the dbm. Then P(dBm) = 10 log(p/0.001) Here is a table of Watts to dbm copied from an Excel spreadsheet using the above formula: Watts dbm Watts dbm Amplifier Gain. The power gain of an amplifier, G, is the ratio of its output power to its input power, Pout / Pin. The power gain expressed in db use this formula: G(dB) = 10 log(pout/pin) So, a power amplifier s gain would be if the input power or drive is 10 Watts and if the output power is 80 Watts, plugging values into the power gain formula above: G(dB) = 10 log (80/10) G(dB) = 10 log (8) G(dB) = 10 (0.9) G(dB) = 9 db 3

4 db article continues Loss. If Pin is greater than Pout, then the radio Pout/Pin will be less than 1 indicating a loss. Expressed in decibels as a negative number. For example, if power in is 10 W and power out is 5 W then G(dB) = 10 log (5/10) G(dB) = 10 log (0.5) G(dB) = 10 (-0.3) G(dB) = -3 db Note that if Pout and Pin are equal then then the gain will be 1, and 10 log(1) = 0 db. Cascade. Decibels are used to simplify gain calculations when multiple circuits are cascaded. For example, if 3 amplifiers are cascaded together, then the power gain of all three would be GT(dB) = Pout/Pin = G1 G2 G3 GT(dB) = 10 log (G1 G2 G3) GT(dB) = 10 log (G1) + 10 log (G2) + 10 log (G3) GT(dB) = G1(dB) + G2(dB) + G3(dB) When using decibels for gain calculations, multiplications are transformed into additions. The output power may be expressed in dbm. For example if you had a system where the input power is 100 µwatts with a 3 db attenuator followed by a 20 db amplifier followed by a 5 db amplifier the total system gain is calculated by GT(dB) = -3 db + 20 db + 5 db = 22 db With the 100 µwatts or -10 dbm input power then the output power would be Pout(dB) = -10 dbm + 22 db = 12 dbm The above example shows how the db is used to simplify potentially complicated calculations to just additions and subtractions. References. Witte, Robert A. (2014) Spectrum and Network Measurements, Second Edition. Edison, NJ: SciTech Publishing, an imprint of the IET GT = Pout/Pin GT(dB) = Pout(dB) - Pin(dB) Pout(dB) = GT(dB) + Pin(dB) Expanding the total gain into its individual components, Pout(dB) = G1(dB) + G2(dB) + G3(dB) + Pin(dB) 4

5 Fall Workshop-Nov. 11 Tower near the Irondequoit Library KF2MR with his Ft-817 driven 8 band transverter system AE2DM s presentation on repurposing electronics for ham radio N2OA s presentation on using WSJT-X and FT8 during the Sept. VHF contest 5

6 K2EHF demo of commercial radio programming for ham use WB2BYP s presentation on Thermal Noise and Noise Figure Thanks to Jarred, KF2MR; Dave, AE2DM; Jeff, K2EHF; Dave, N2OA and John, WB2BYP for the great presentations at the 2017 VHF Group Fall Workshop held at the Irondequoit Public Library on Sat. Nov. 11th 6

7 Treasurer s Report Rochester VHF Group Treasurer's Report (1/6/18) PREVIOUS BALANCE $ (received from Freddie Sulyma WB2GFZ July 2017) INCOME (from memberships) $ EXPENSES Check #1001 Picnic $95.00 Check #1002 Contest Plaque $75.00 (check #1002 has NOT cleared as of this date) Check #1003 PO Box Rental $76.00 CURRENT BALANCE M&T Bank $ PayPal $ Petty Cash $ Total $ M&T Bank, non profit, commercial, fee free checking account Submitted by Jim Reilich WB2YJH - Treasurer 7

8 Contest Preparation January VHF W2UTH Activation W2EV plans to activate the club callsign for the January contest. He would like to get the club call in the record books in the FM-Only category. He has made incremental improvements and set new records in the past, but with the full support of the club, perhaps he can achieve 8,000 points or even reach an unheard of 10,000 points in the FMonly category. This is really not that difficult with the right support. What can you do? Find Ev on MHz FM and then work him on as many bands as possible from home and then again on as many bands as possible as a rover. This category operates on the bottom 4 bands and if necessary, Ev has the ability to swap to horizontal polarization on a few of these bands. To make this a little more interesting, we will offer a W2UTH FM Challenge QSL Certificate to any fixed station able to accurately log Ev on all bands or any rover station who can do the same from at least two grids. Cumulative Club Score Our goal for the 2018 January VHF contest is to have 23 logs submitted and 220,000 points. Looking at the table below, this is a realistic and achievable goal. What can you do to help? Year Logs Points 2018 (Goal) , , , , , ,232 Rover Blitz On Sunday January 21 st, you are encouraged to join the group for lunch at Mooney s in Le Roy and participate in the Rover Blitz. Anyone can participate, and no experience is needed. We even have enough spare gear to equip at least three stations on 6 bands. Note the proposed frequency change on 6m this year. If you anticipate any trouble with this change, please let Jarred, KF2MR know as soon as possible. Otherwise setup your memory channels as follows: Your participation in this event can provide a huge benefit to the club score. A typical station can acquire 10,000 points in just 90 minutes. 8

9 Gatherings (Above) Breakfast at Atlantic Diner Oct. 14 (Below) Breakfast Dec 9 at Jim s Restaurant. 9

10 Shack/Equipment Pictures K2OS PA and HVPS. Frank has been active on 222 MHz. Recent DX includes tropo CW contact with K0TPP in Missouri EM58 on Nov 15 th and a SSB meteor scatter contact with KE8FD in Alabama EM64 on Dec. 14th 10

11 KF2TV, Harry s MHz 300 Watt solid state amp that he is building 11

12 KF2TV Amplifier Project Cont d 12

13 KF2TV s Shack - Radios are Kenwood TS 590SG, TS 2000, Oak Hills 20M/40M QRP rig. Amp is an Ameritron AL 572 and Palstar AT2K Tuner 13

14 Len, KC2PCD s shack has capabilities of 160 to 432. SSB and FM available too. Antennas are 160 ft. All bander dipole, 6 meter Omniangle from Par Electronics, 2 meter 13 element and element horizontally polarized for the nets. Also a dual band vertical for 2 and 70 cm. Len is also net control for the 2 meter and 6 meter nets on and MHz USB 14

15 Calendar Around the of Events Web

16 Calendar of Events Winter/Spring 2018 January 12 th Contest Prep Meeting Rochester, NY Rochester Makerspace, 7pm-9pm January ARRL January VHF Contest On-The-Air This is the big one. Plan now to participate. January 21 January Contest Lunch & Rover Blitz LeRoy NY Mooney s Sports Bar and Grill, 12:30-2:30pm Everyone is welcome No experience (or equipment) required February 24 Winter Hamfest: Big Flats American Legion 45 Olcott Rd. S, Big Flats, NY $5 General Admission $ 10 per table - First come, first served Food available ********** 50/50 $100 Grand Prize (must be present to win) Drawing at 12 noon Doors open: Vendors at 6:30 am General public at 8:00 am VE Testing 09:30 am April Eastern VHF Conference April Site Visit K2LIM (More details coming in March) Spring Sprints 144 MHz Monday April 9, PM Local 222 MHz Tuesday April 17, PM Local 432 MHz Wednesday April 25, PM Local Microwave Saturday May 5, AM 0200 PM Local 50 MHz Saturday May 12, Z to Sunday, May 13, Z 16

17 The K290R Project Steve Kavanagh, VE3SMA, December 2017 Background I have been using a pair of Yaesu FT-290R 2m transceivers as IF rigs for microwave transverters for many years. My 2.3, 3.4, 5.7, 10 and 24 GHz transverters have been designed to interface with the FT-290R (operated in low power mode) using a single coaxial cable for transmit/receive IF signals and transmit/receive switching control. The FT-290Rs are set to about 100 mw output and they provide 6.8 V DC (through a large resistance) at the antenna socket in transmit. But the FT-290Rs are showing their age and are becoming unreliable. I purchased the first one in years ago. The purpose of this project was to produce a replacement for the FT-290R as a 2m IF radio. The approach selected was to install a low power 2m transverter inside an Elecraft K2, a QRP HF transceiver which I enjoy operating. This provides a much better receiver than the FT-290R, but does not provide FM capability, which can occasionally be useful. It also does not have internal batteries like the FT-290R. An internal battery is an option for the K2 but the transverter takes up the space which would otherwise be available for the battery. The K2 is bigger than the FT- 290R but not as heavy. Because the modified K2 is emulating an FT-290R, I called it the K290R. This article describes how the modification was accomplished. It is probably difficult to reproduce exactly what I did, as some of the parts have become hard to find. Nevertheless, I hope it will help anyone thinking about microwave IF rig alternatives. 2m Transverter Selection I acquired at a flea market an old used DEMI DC low power transverter board. Or so I thought. It seems, after some headscratching and exchanges about small differences from the published schematic and layout, that it may actually be an unauthorized (and not quite identical) copy of the DEMI board. No matter it does work, though with a bit less output than a real DEMI, and provides the same interfaces. K2 Configuration It was necessary to fit the K2 with the K160M module from Elecraft, which adds the 160 m band and, more importantly for this application, a separate receive-only antenna input. This input is then used for the receive IF at 28 MHz. In the primary menu RANT must be set to ON. The normal QRP antenna jack is used for the transmit 28 MHz IF output from the K2. The lowest power at which I thought the signal quality and output power control would be good is 1

18 watt. I activated one transverter band in the K2 menu, set the IF to 28 MHz and the RF to 144 MHz and set the power limit to 1 watt. If the IF rig is to be devoted to a single band, you can set the K2 MHz readout on a transverter band to whatever you want. If you want to use SSB on the microwave bands, the K2 should also have the Elecraft KSB2 SSB module installed. The basic K2 does not have a PTT output. In order to switch the 2m transverter (and the microwave transverter) between receive and transmit it is necessary to add one. One option is to buy the K60XV module, which provides such an output, for which you need to install an extra jack. This would also provide a receive input, so the K160M would not be needed. But I opted to add a separate simple homebrew PTT output board along with the K160M. Mine is a modified version of the one described on the Elecraft website at which would work just as well, I think. The schematic and a photo of my PTT output board installed are shown below. It plugs into J13 on the RF board. I used one of the transverter in/out jack holes (for the K60XV) to mount the RCA jack to provide this output. The centre pin is switched to ground in transmit mode. In the K2 primary menu, under T-R, you must set 8r hold to avoid too much relay chatter.

19 Transmit IF Interfacing The 28 MHz output power from the K2 is considerably more than the 2m transverter board requires, so an attenuator is needed to dissipate most of the RF. I opted to build the attenuator into the (QRP) top of the K2, with a BNC input jack installed in one of the holes intended for the antenna tuner option. 2m Transverter Configuration The 2m transverter board offered a variety of alternative connections. I arranged it to use separate IF and RF transmit and receive connections and ground-to-transmit PTT, and I wired the spare relay contacts to provide +12 V output when the transverter is switched to transmit mode. This voltage is then used to toggle the RF interface and power amplifier circuitry between receive and transmit. The transverter board is mounted in the K2 top cover, on small standoffs. 144 MHz Medium Power Amplifier The maximum 2 m output power from the transverter board was only about a milliwatt. So an amplifier was needed to get the same 100 mw output as the FT-290R. I selected the MGA MMIC as it had the appropriate gain, excellent advertised DC-to-RF power efficiency and was available from Digi-Key. The amplifier was built on a W1GHZ board, as used for his GVA-84 and ADL5534 amplifiers described at See the schematic and a photo of the amplifier under test, below. The real DEMI output should be closer to 10 mw, I believe, so a lower gain MMIC choice might be preferred if the DEMI 28-to-144 MHz transverter board was used.

20 I measured the basic performance of the amplifier, with the following results, showing good linearity up to 100 mw (20 dbm) RF output power at 144 MHz and pretty flat gain over more than MHz. It looks like a very useful general purpose medium power amplifier. I d suggest substituting a surface mount inductor for the hand-wound coil I used, as I found it was easily knocked out of shape when handling, soldering and installing the board.

21 Power Gain (db) Output Power (dbm) Amplifier Output Power vs. Input Power at 144 MHz Relative Input Power (db) 30.0 Measured Amplifier Gain versus Frequency Frequency (MHz)

22 Control Circuitry The 144 MHz interface to the microwave transverters uses a single coax cable for both transmit and receive signals and also carries a DC control signal to switch the microwave transverter between receive and transmit. The control board schematic below implements these requirements. It is shown including the 2 m power amplifier, since that board was piggybacked on the control board. When the 2m transverter board switches to transmit it provides a +12V power supply to this circuit. That operates the RF relay K1 (Omron G5Y-12), which switches the 144 MHz port from the 2m transverter receive input to the 144 MHz power amplifier output, and provides a positive DC voltage (controlled by Zener diode D2) through R5 to signal the microwave transverter to switch to transmit. Once the K1 has closed in the transmit position, the combination of R1, R2 and R3 provide a suitable voltage to turn on the MOSFET switch Q1 and provide the operating voltage to the 144 MHz amplifier through a 5 V regulator U1. See the following photo of the board, mounted on standoffs in the K2 top cover. It was made using point-to point wiring on the non-foil side of a piece of single-sided PC board with the parts mounted on the foil side. The leads run through holes drilled in the board (and countersunk on the foil side to eliminate shorts, unless the lead is to be grounded). The 144 MHz medium power amplifier board is mounted on top.

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24 Overall Assembly The top level wiring for the parts mounted on the K2 top cover is shown in the following schematic. It was not necessary to make any extra holes in the K2 case for connectors, just a few small holes for board mounting in the top cover. S1 was chosen to fit the existing hole for the battery switch, while J3 is a 9-pin D-connector which fits the existing hole for the computer interface connector. The following photos show the inside of the K2 top cover with the 2m transverter installed, and a view of the rear panel connectors.

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26 Results This IF rig was used on CW and SSB in the 2017 ARRL 10 GHz and Up Contest with a Kuhne 10 GHz transverter and 2 watt amplifier and performed well with no issues or failures. I was always able to hear what others at the same site could hear. Manual T/R switching was used on CW to avoid losing the first dit or two of each transmission due to the delays through the various control relays and the sequencer in the 10 GHz transverter.