Monday, 2 January 2017

AGC for Digital Ops: Friend or Foe?

Contributed by Brian Waterworth, VE3IBW.

I belong to the Elecraft reflector discussion group.  While I joined to learn more about my rig (KX3/PX3), I have found a wealth of amateur radio knowledge on various topics.  This group often has side conversations about everything Ham radio; sometimes Elecraft gear isn’t even mentioned.

One such tangent conversation centred around the use of AGC (Automatic Gain Control) for digital modes.  Being that I predominantly use digital for my HF operations, I was very interested in this topic.  The reflector elmers recommended turning off AGC when using digital modes.   

My research, prior to joining the Elecraft reflector, seemed to suggest that AGC should be on.  For digital modes, use the fast setting and for voice modes use the slow setting.  This seemed to work for me.  But I don’t think I really had a good grasp of what AGC was doing at that time.  A few years of operating PSK31, RTTY, and JT-modes revealed something that I unconsciously did not make a connection to AGC (fast or slow).  This reflector side conversation opened my eyes to AGC and its effect on my weak signal digital QSOs.

AGC, as many reading this article might know, is the ability of a transceiver to dynamically reduce RF gain when too much radio frequency energy is present in the passband.  The idea behind these adjustments is to avoid saturating downstream transceiver components (local oscillator, audio amp, your ear drums).  

I glibly referenced ear drums in the last paragraph because the reflector discussion turned to why AGC is nice to have when a strong signal enters the passband.  But, how many of us actually listen during digital operations?  I used to, but at a very low audio volume.  Beeps, twerps, blips, and clicks are a little fatiguing after a while.  For my current digital operations, I rarely have the speaker enabled and never listen through headphones.  All the information I need to operate digital is via a digital-mode program’s waterfall.

Narrow digital modes, such as PSK31 and JTx, enjoy many potential QSOs within a typical receiver passband.  A voice mode QSO, by contrast, occupies the entire passband.  During Field Day operations, PSK31 can have 20+ active QSOs in progress too.  If one of these QSOs happens to be a very strong signal, AGC will reduce the RF gain.  This doesn’t sound so bad.  However, in one passband (say 14.076MHz), you might have 20-30 active JTx QSOs and one of these might be yours with a weak station.

I use FLDigi to work PSK31 and RTTY during Field Day.  To compensate for strong signals in the passband, I created macros to reduce the receive filter bandwidth around a signal I was interested in trying to establish a QSO.  This worked great to filter out stronger adjacent signals in the passband.  But, was it necessary?  I am beginning to think it wasn’t.

Let’s look at an example using WSJT-X.  It doesn’t have the convenience of macros to adjust and re-instate filter settings like FLDigi does.  

I got interested in JT modes over the past two years as I wanted to work QRP and be able to make contacts around the world with very little power (5 watts or less).  I also wanted to do this in a portable fashion (on a sailboat, in a park, on an island, in my backyard on a nice day).  JTx modes seemed like the best candidate.  There are some JT-mode operators that use 30+ watts.  There are also band conditions that will present a low power signal as 0db or more above the noise floor; i.e. a strong JTx signal.  With AGC enabled, these stronger signals will reduce the RF gain.  Weak signals will become weaker.

Each trace, (JT65 between 0-2,500hz and JT9 above 2,500hz) in figure 1, is a CQ or an active QSO within one passband.  The darker red and deeper yellow colours represent stronger signals.  You can see there are some very weak signals where there is no red at all (usually between -15db and -25db below the noise floor).

Figure 1: Typical WSJT-X waterfall with AGC turned off, Preamp off

Imagine you are halfway through a JT9 QSO, which takes about six minutes to complete, and a strong signal comes through for some other QSO or a CQ call; could even be at the opposite end of the passband.  Your transceiver’s AGC will reduce the RF gain and your weaker signal QSO may be artificially reduced beyond the JT decoder’s capability.  At this point, you may or may not be able to complete the QSO.  

Figure 2: WSJT-X waterfall with AGC-F and Preamp off

From figure 2, the darker bands through time slot 14:38 is the effect of the AGC reducing the RF gain in the presence of the strong signal at about 1,375Hz.  To level set, blue is the typical WSJT-X waterfall colour displayed when there is enough audio drive from the rig, through the computer’s sound card, to the WSJT-X program.  Black indicates not enough audio drive.  From the above diagram, you can see that some of the weaker JT9 signals (> 2,500hz) are obliterated on the WSJT-X waterfall.  The JT modes are fairly robust, but a strong signal in the passband may be enough to disrupt a QSO when AGC is turned on.

In figure 3, I turned off the AGC prior to operation.  I received an answer to my CQ from a station in Spain.  I received this station’s hail at -27db below the noise floor.  The diagram shows a very faint trace at about 2,550Hz.  

Figure 3: WSJT-X waterfall, active JT9 QSO with a Spanish station at -27db; preamp off
The presence of the strong signal at approximately 2,200hz in the passband may have caused the AGC to reduce RF Gain to a point where WSJT-X would not have been able to decode this very weak signal.  Fortunately, the AGC was turned off and other strong signals did not affect the RF Gain setting.

By switching off AGC, I have been able to successfully complete QSOs with very weak stations in the presence of stronger stations in the passband.  If not for the Elecraft reflector elmers, I would have likely continued operating digital with AGC turned on.

Sunday, 1 January 2017

Minutes: Board of Directors 2016-10-18

Meeting held in the Magna Centre, Multipurpose Room 1. Called to Order at 19:00 by Chris VE3NRT. Board members attending: Chris VE3NRT Pres, John VA3JI Treasurer, Geoff VA3GS, Barry VA3LLT, Eric VE3EB, Steve VE3UT, David VA3DCY Secty, Doug VE3ATP, Rick VA3VO, Absent: John VE3IPS V. Pres. Others attending: None
  1. Approval of agenda and declaration of conflict of interest: Chris VE3NRT
    • Additions: 6 Correction to August BoD minutes and 7 Winter Field day.
    • Motion to amend the agenda, moved Steve VE3UT, seconded Barry VA3LLT. Carried
    • Motion to adopt the agenda, moved Geoff VA3GS, seconded Rick VA3VO. Carried.
  2. Minutes: David VA3DCY. Moved by John VA3JI, seconded by Doug VE3ATP to adopt minutes of the Board Meeting 2016/09/20. Carried.
  3. Trailer: Barry VA3LLT. There is an 8” crack in the Hilomast, lower portion of the top section. Costs to repair options from the manufacturer: $250US plus brokerage fees (1 way) if shipped via UPS from Canada, $125US (1 way) if shipped from within the USA (Buffalo), $250US forrepair including parts and labour. If the mast was delivered to the factory (in Florida) the repair time would be approximately 2 hours. Other options suggested were to attempt to repair the mast section locally, pick up a replacement section in the spring and place a sleeve around the crack as a temporary fix. The agreed plan is to 1/ get a manual, 2/ order parts and ship if feasible and 3/ Chris or another club member could take the mast to Florida in the spring for repairs.
  4. Hamfest: Geoff VA3GS. At the moment 80 tables (including 5 courtesy tables), have been sold out of 100. Setup will be at 13:00 Friday November 4. We will only be bringing the EmComm trailer, not the tower trailer to the hamfest. Don VE3IXJ will have a static display outside the trailer. We hope to have 'QSL' cards with club information available as a handout.
  5. Meetings: Geoff VA3GS. There will be a silent auction at the November meeting with items from a donation to the club. Rick VA3VO will set the reserve bid prices. The January meeting could either be a 'junk-in-the-trunk' with mini presentations or, a Saturday visit to the Hammond Museum instead of the Tuesday meeting. The February meeting is undecided, March a talk from Mike VE3MKX, and the April and May meetings would be talks from Bob VE3WY and Dr Paul Delaney (dates to be determined).
  6. Treasurer's Report: John VA3JI
    • Opening Balance 2016/10/01 [Available to members on request to secretary]
    • Income: Hamfest vendors: $422.00; Dues: $185.00; Donation: $7.02; Total:$614.02
    • Expenditures: Repeater: $75.00
    • Closing Balance 2016/10/18 [Available to members on request to secretary]
    • Hamfest Income: Tables: $588.00 (to date); Admissions: $210.00; Grand prize: $60.00; Total: $858.00
    • Moved by John VA3JI, seconded by Geoff VA3GS to adopt the treasurer's report. Carried.
  7. Repeaters: Steve VE3UT.
    • Steve asked a question from Grant VE3ATV, do we want to promote an ATV repeater? It was decided to ask the club if there is any interest, and if there is to ask Grant to talk to the club members.
    • Motion 2016-10-18-4d to approve $75.00 for a mast section and cables used at the MacKenzie Richmond Hill Hospital when installing the link antenna for VE3YRA. Material supplied at cost by Rick VA3VO. Moved Steve VE3UT, seconded by Geoff VA3GS. Rick VA3VO abstained from voting. Carried.
  8. Public Service: Eric VE3EB
    • The last events were 2 weddings at the Sharon Temple on Saturday October 1, and the Run for the Cure on Sunday October 2. There was a good turnout for the event, with 11 hams and 1 student participating.
    • Eric proposed getting QSL cards for public service events and hamfests, and 10 to 20 lightweight club jackets, instead of vests, which would be owned by the club.
    • We should set up a Trillium committee for funding these and other projects.
  9. York Region Astronomy Association (YRAA): Chris VE3NRT. The YRAA is responsible for operation and maintenance of the equipment at the David Dunlap Observatory and also provides education to youth groups, schools and adults. In addition to optical astronomy, YRAA wants to incorporate radio astronomy into their offerings, and would welcome collaboration from YRARC. Chris will send a letter of YRARC support, to YRAA.
  10. Correction of August BoD Minutes: David VA3DCY. The motion number for item 5b to purchase plaques for the Harvey Bell Award and the Melted Coffee Pot Award, was incorrectly published as “motion 2016-07-19-5b”. The correct motion number is 2016-08-16-5b. Motion 2016-10-18-6, moved by David VA3DCY, seconded by Geoff VA3GS that the minutes be corrected. Carried.
  11. Winter Field Day: Steve VE3UT. We need to investigate the source of the noise at the Sharon Temple / Temperance Hall location, and we should ask Steve VE3EZ for assistance. 10 people attending a WFD event would be considered a success. WFD this year is on January 28 and 29.
  12. Brad VE3HII noted that that VE3YRA was not listed in the AMSAT report for Summer Field Day.
Meeting adjourned at 20:50. Moved Rick VA3VO, seconded Geoff VA3GS. Carried

Minutes: General Meeting 2016-11-01

Meeting held in the Sharon Temperance Hall. Called to Order at 19:30 by Chris VE3NRT. Total members and guests attending: 35 including 1 guest and 3 new members.
  1. Welcome & Introductions – Chris VE3NRT
  2. Adoption of Minutes from 2016/10/04 general meeting. Moved by Doug VE3VS, seconded by John VA3JI. Carried.
  3. Announcements: Setup for the hamfest starts at 13:00 Friday Nov 4. We received a cheque for $175 from the Central Ontario ARC for our participation in a recent COARC event.
  4. Treasurer’s Report – John VA3JI
    • Opening Balance 2016/10/01 [Available to members on request to secretary]
    • Income: Hamfest vendor fees: $1230.00; Membership dues: $185.00; Donations (US currency conversion): $7.02; Total:$1422.02
    • Expenditures: Hamfest - prizes: $171.50; Hamfest - Markham Fair Grounds: $4329.60; Hamfest – float: $750.00; Repeater $75.00; Bank charges for PayPal $7.74; Total Expenditures: $5333.84
    • Closing Balance 2016/11/01 [Available to members on request to secretary]
    • Additional income to be deposited: Hamfest vendor fees: $40.00; Membership dues: $155.00; Membership dues:$35.00; Donation $5.00; Bank Fees: -$1.57
    • It was suggested from the floor that we charge extra when payments are made by PayPal. No action to be taken at this time.
    • Moved the treasurer's report be adopted, by John VA3JI, seconded Bill VA3QB. Carried
  5. Repeater Report – Steve VE3UT
    • We need to check on the noise source at the Sharon Temperance Hall before winter field day.
    • We spent $75 on a link antenna at the MacKenzie Health Unit (to link the VE3YRA site with the hospital site).
    • The Field Day announcement, which has been running in error, has been turned off.
    • This morning it was discovered that that the link transmitter at the VE3YRC-V site has failed. The VE3YRC-V repeater (147.225 MHz) is now running in stand-alone mode.
  6. EmComm Report – Robert VA3BXG, John VE3IPS
    • At the recent GTA set, we had limited participation, and did a test call-out. The next EmComm meeting will be on November 10, at the Newmarket Community Centre.
    • The Fox Hunt, with help from Brian VE3IBW, will likely be held on November 19. Planning will be done at the next EmComm meeting.
  7. Other Business
    • Barry VA3LLT's wife is in hospital, in serious condition. Move by Steve VE3UT and seconded by Eric VE3EB, that we send flowers to Barry's wife. Carried.
    • Doug VE3VS is preparing name tags for those wishing tags.
    • Next year, CLARA will be holding its 50th birthday and preparation for the event is underway.

Guest Speaker – John VA3KOT

John spoke on outdoor QRP. His interest in QRP started with scanning and listening to satellites, which lead to his interest in amateur radio, especially QRP. His rules for operating QRP include an efficient antenna, elevation, using CW or digital modes instead of phone, endurance, the use of spotting web sites (to give advance notice to listen), and good propagation conditions.

Since he operates in public spaces, health and safety are important considerations. The passing public needs to be kept safe from RF high voltages etc. and 'no trace' operating means leaving the site tidy when finished.

When hiking, he keeps it simple with a Yaesu FT-817 radio, minimal batteries for lighter weight and a choice of several antennae including vertical, end-fed, loop and NVIS antennae.

John can be contacted at va3kot -at- gmail -dot- com for further information.

Minutes: Board of Directors Meeting 2016-11-15

Meeting held in the Magna Centre, multi purpose room. Called to Order at 19:04 by Chris VE3NRT. Board members attending: Chris VE3NRT Pres, John VA3JI Treasurer, John VE3IPS V. Pres., Geoff VA3GS, Barry VA3LLT, Eric VE3EB, Steve VE3UT, Doug VE3ATP, Rick VA3VO, David VA3DCY Secty. Others attending: None
  1. Approval of agenda and declaration of conflict of interest: Chris VE3NRT. Additions: 8 WYNSORC. Motion to adopt the agenda, moved Rick VA3VO, seconded Geoff VA3GS. Carried.
  2. Minutes: David VA3DCY. Moved by John VA3JI, seconded by Eric VE3EB to adopt minutes of the Board Meeting 2016/10/18. Carried.
  3. Hamfest: Geoff VA3GS
    • The non-final results from the hamfest – we made a profit of approximately $2400 plus any possible deposit refund. Geoff thanked all involved for their efforts.
    • The question was asked 'should we consider another venue?' The answer was 'yes' if we can find a suitable location with ample parking.
    • The Lions Club sold out of their food.
    • Renting the third hall costs only $200, and it is good to have a place to keep the attendees out of the rain/cold.
  4. Meetings: Geoff VA3GS
  5. Bring non-perishable food items to the December meeting for the food bank.
  6. There will be no speaker for the January meeting, but there will be time for '5 minute' show and tell presentations.
    • Dr. Delaney will be the guest speaker in February or March.
    • Mike VE3MKX will be the guest speaker in March or February.
    • Cliff VE3KOP will be the guest speaker in April.
    • Bob VE3WY will be the guest speaker in May.
    • The AGM will be in June.
    • Motion 2016-11-15-3b to approve $200.00 (maximum) for food at the December meeting, moved by Rick VA3VO, seconded by Eric VE3EB. Carried.
  7. Treasurer's Report: John VA3JI
    • Opening Balance 2016/10/31 [Available to members on request to secretary]
    • Income: Hamfest tables $1455.00; Dues:$365.00; Auction: $140.25; Donation (COARC): $175.00; Hamfest door: $4614.90; Silent auction (Nov Mtg): $113.00; Total Income: $6863.15
    • Expenditures: Hamfest prizes: $196.00; Bank fees (Pay Pal): $1.03; Repeater (WYNSORC): $10.00: -$207.03
    • Closing Balance 2016/ 11/15 [Available to members on request to secretary]
    • Membership to date: Full voting: 33; Associate: 5; Family:17; Life: 9; Total: 60
    • Moved by John VA3JI, seconded by Geoff VA3GS to adopt the treasurer's report. Carried.
  8. Repeaters: Steve VE3UT
    • The CW identifiers on VE3YRC-V and VE3YRA have been lowered.
    • The Fox Hunt is being announced on the VE3YRC-V and VE3YRA repeaters.
    • The link radio at the Bloomington site is now working, levels have been set up, but may need some final adjustments. We need to return to using the mic input on the link radio for better audio.
  9. John VE3IPS: Members from the DDO will be attending the Fox Hunt. The starting location will be 12916 Yonge St. on November 19.
  10. Public Service: Eric VE3EB
    • There are no public service events at the moment.
    • Eric would welcome suggestions from the membership and the board for the QSL cards.
    • Certificates of recognition will be prepared.
    • Barry VA3LLT: Should we have coffee mugs, either with the club logo only, or logo and the individual member's name and call? He will check prices, in possible lots of 10, 20 and 30, and enquire about interest at the next meeting. Chris will check the Costco prices as well.
  11. Winter Field Day: Steve VE3UT. The David Dunlap Observatory might be a possible site for Winter Field Day. Steve will check to see if it is available, and we could also include the Maker's Group and Astronomy Group in WFD. Paul Mortfield is the astronomy contact.
  12. Summer Field Day: Steve VE3UT. Peter VE3PBT may possibly not be available to cook be due to health concerns, however he may be able to advise and/or assist. Geoff has enquired if the Aurora Lions might be able to provide 3 or 4 meals, and is awaiting a reply.
  13. Hammond Museum: John VE3IPS. At the next general meeting,John will propose a trip to the Hammond Museum.
  14. PACTOR for EmComm: John VE3IPS. John is exploring the cost of PACTOR modems 1, 2 and 3. – Pactor 1 is the least expensive, Pactor 3 is the most expensive. It might be an item for a wish list on a Trillium Grant application, but a good business plan would be needed.
  15. WYNSORC: John VA3JI and Geoff VA3GS. The annual dues of $10.00 are now due. Motion 2016-11-15-8 to approve $10.00 for WYNSORC dues, moved by John VA3JI, seconded by Geoff VA3GS. Carried.
Meeting adjourned at 21:00. Moved Barry VA3LLT, seconded Geoff VA3GS. Carried

Minutes: 2016-12-06 General Meeting

Meeting held in the Sharon Temperance Hall. Called to Order at 19:30 by Chris VE3NRT. Total members and guests attending: 39 including, 1 new member, 1 amateur guest and 2 family guests.
  1. Welcome & Introductions – Chris VE3NRT. Adoption of the Minutes from the 2016/11/01 general meeting was postponed until next January.
  2. Announcements: CLARA will be celebrating its 50 anniversary in 2017. To celebrate, a year long contest will be held. For information, see the CLARA web site:
  3. Fox Hunt – John VE3IPS: The fox hunt was held on November 19, with Ian VE3YRP the winner. More fox hunts will be held in 2017 (and they may get harder).
  4. Hammond Museum – John VE3IPS. A trip to the Hammond Museum could be in the works. Details to follow.
  5. Trillium Grant – Eric VE3EB. Eric is looking for interested members to be part of a committee which will investigate applying for a Trillium Grant.
  6. Repeater Report – Steve VE3UT. Several visits have been made to the VE3YRC-V site as well as a visit to the VE3YRC-U site to make some fine adjustments. All 3 linked repeaters (including the VE3RYA repeater) are working well and sounding good. The D-Star repeaters have had network connectivity problems, but are now working properly.
  7. Winter Field Day – Steve VE3UT. Winter Field Day will be held on January 28 and 29. The first location choice, the David Dunlap Observatory, is not available. The regular Summer Field Day site is the second choice and Steve will be soon be in contact with the owners. There are rule changes this year regarding setup, however it was suggested that we set up just before the contest begins, to simulate setup in a real emergency. We plan to use simple antennae to keep the setup simple and have a maximum of 4 stations. A quick show of hands showed 8 members were interested at the moment.
  8. Treasurer’s Report – John VA3JI
    • Opening Balance 2016/11/01 [Available to members on request to secretary]
    • Income: Hamfest vendor fees: $1455.00; Hamfest admissions: $4614.90; Donations COARC+ Anonymous+REACT: $680.00; Membership dues: $365.00; Auction plus club table $248.25; Hamfest grand prize tickets: $670.00; Total $8,033.15.
    • Expenditures: Hamfest - prizes $196.00; WYNSORC fees: $10.00; Bank charges for PayPal: $1.03; Total expenditures: $207.03
    • Closing Balance 2016/12/06: [Available to members on request to secretary]
    • Additional expenses: December Christmas party - food $158.20
    • Moved the treasurer's report be adopted, by John VA3JI, seconded Rick VA3VO. Carried
  9. EmComm Report – Robert VA3BXG
    • EmComm participated in the recent Municipal Exercises and the York Region Conferences.
    • The next meeting will be on the Thursday December 8, at the Newmarket Community Centre. Planning for next year including more fox hunts will be discussed.
  10. Other Business – Geoff VA3GS. Geoff thanked everyone involved with the hamfest for their help, and noted that at the January meeting we will have short, 5 minute talks, and show and tell sessions.