630 Meters for 2020

Project 3 of 7 for 2020

Upgrading from last year’s 630 meter station is underway. The antenna will be reused. A new station transceiver was added during the year and can provide the 630m signals on the XVTR port. The biggest addition will be a linear amplifier to improve the transmitted signal. Actually, it’s a non-linear amplifier because the WSJT-X digital modes do not require the amp to be linear. A non-linear amp is just fine. The amp decided on is the K5DNL. http://k5dnl.com/sale_amp200.htm

Two Hundred Watts? Yes, it’s legal because with a 2.5% efficient antenna the radiated power is a perfectly legal 5 watts.

On 630 meters, or 474.2 KHz, the antenna’s phase is very important. The rf current and voltage need to be in the same phase for the best radiation. An oscilloscope is used to make the phase measurement, with current on one channel and voltage on the other. When the sine waves line up the phase is perfect. K5DNL has available the hardware to sample the current and voltage to feed to the scope. Ken calls it the Scopematch. One was obtained along with the amplifier for this project. The scope in the shack here is the Hantek DSO5102P dual channel oscilloscope.

A big jump ahead happened when the decision was made to reconfigure batteries and build a 24 volt system temporarily. The amp runs on 24 volts. The main batteries for the permanent 24v system are on order but are still off shore.

Status: A temporary 24 volt supply has been set up and the project is awaiting time to complete it.

630 Meters

Antenna

Joy came today when the first contact was made on 630m.  In fact five contacts were made on JT9.  On WSPR, spots were posted from all over the United States.

Last month a vertical antenna tuned up on 474 kHz.  The matching network had taken several tries but today it seemed to come together. The ground screen is made up of four radials, two 100 feet long and two 50 feet long rolls of welded wire fencing laid flat. The vertical radiator is 36 feet in height.  Two horizontal 50 ft wires connected to the top of the radiator make up  a “tee” top hat.  The loading coil enclosure and one of the radials look like this:

The matching network (loading coil) is inside the enclosure.  It consists of 100 turns of 16 gauge wire wound on a piece of plastic pipe.  The top of the coil connects to the vertical radiator and the bottom connects to the ground screen.  Upon close examination one can see a ferrite rod attached inside the coil form.  The rod is the secret to easy tuning.  By moving it up and down the resonant frequency can be dipped, a lot like tuning an i.f. transformer on a receiver.

The coax is tapped onto the coil at the 50 ohm location.  Once it proves to be stable the clip will be removed and the wire soldered right to the coil. Holes in the coil form make it easy to clip onto the coil windings.

A snapshot of the antenna analyzer shows the resonant frequency and swr, both excellent at 474 kHz and 1.1.

Extrapolating from the above screen it can be seen that the 2:1 bandwidth is approximately 3.7 kHz.  The antenna is theoretically usable from 472.15 kHz to 475.85 kHz.   Extremely narrow bandwidth which could be problematic with shifts in temperature or wind.

Hitting the button to show the rest of the numbers reveals an almost perfect match of 53 ohms and almost zero reactance.

The antenna is ready to attach to a 630 meter transceiver.

Retuning on October 30 produced the following analyzer pattern:   (Very nice) Notice the new frequency of 475 kHz which is up one kilohertz from before.  The reasoning is when a 1 kHz tone is transmitted with the dial at 474.2 we are actually transmitting at 475.2.

Rig

Within the last few months information has been released on how to modify the Icom IC-7300 to transmit on 630 meters.  The IC-7300 already receives on 630 out of the box.  The “wide band transmit” modification consists of removing two surface mount diodes.  HRO will perform the mod at a charge of $40 and that is the method we chose.  This solution eliminates the need for a downconverter.  Output is 30 watts.

Stay tuned for the first tests.  See top of page.

The saga continues.  After a day of use the IC-7300 failed.  It refuses to put out power due to infinite swr activating the protection circuit.  At first a rig failure was suspected but swapping out the 7300 with a new one produced the exact same result.  A failure in the antenna was suspected.   Meanwhile, Googling the problem produced a possible explanation.  The IC-7300 was not designed to transmit on such a low frequency.  It has no low pass filters below it’s design frequencies therefore the output has harmonics.   The harmonics are reflecting back from the antenna and causing the swr meter to read high, which in turn triggers the protection circuit and shuts down the output.   Why did it work the first day before failing?   Hard to say.  Solution is to insert an external low pass filter.  A search is underway for one that can handle the 30 watts output of the IC-7300.  On the bright side neither the radio nor the antenna seems to be faulty.

The only filters that could be found are for qrp.  A higher power design was discovered at this web site:    http://njdtechnologies.net/630-meter-low-pass-filter-values-from-wa3etd/

Using junk box parts resulted in homebrewing a filter that could handle 30 watts and perhaps much more, shown below. The toroids are T200-2  powdered iron (red). The cores are wrapped with white Scotch fiberglass tape. The calculator available at the njd site above yielded 33 turns for this toroid.  One turn was removed after it was wound to obtain the 14.5 uH needed.  The capacitors are 1000V mica.

Pushing a few watts through the filter to a dummy load and varying the frequency resulted in a roll off around 700 kHz.   Ideal.  The filter was connected between the IC-7300 and the antenna coax.  SWR now reads 1.7:1 at 475 kHz.  Why not 1.0:1?   Hmmm.

A possibility has been offered by Larry, K0NA:  We need a diplexer.  The harmonics which are filtered need someplace to go and this filter does not provide it.  Otherwise the harmonics are reflected back to the transmitter, much attenuated, but still are registering on the swr meter.  Inserting a diplexer would route the filtered harmonics to ground.  As long as the swr is below the protection cutoff level we won’t worry about it.

Meanwhile the antenna was upgraded by replacing the vertical wire with aluminum tubing.  It still has a 100 ft “tee” top wire horizontally even though it’s invisible in the picture.

Interestingly, bandwidth has gone up to 66 kHz.  This will eliminate worries about mechanical changes shifting the resonance and producing an unusable swr.  Without retuning after adding the tubing the system resonants at 500kHz with a swr of 1.0:1 (note: if we added length the resonance should have gone down, not up).  Tuning the resonance down to 475 kHz does not result in the swr dipping to 1.0:1, however.  Why?  The swr at 10 watts output is 1.3:1 but at 25 watts out the swr jumps to 3.0:1.  Work remains to be done.

The coil has been stabilized with silicon caulk, the clip soldered for permanence, and a porcelain insulator has been installed for the antenna pass through.  Still up in the air on the next step to correct the swr. The basic question still looms; is it the antenna or is it the transceiver and the low pass filter?  Is this a faulty antenna or is the rig responding erratically on this non-standard band?

Results are still irratic.  Next we’ll try the good ole variometer wound on a 5 gallon plastic bucket.  Maybe.

2019 Follow Up:  For the 2019 season the original downconverter was revisited using the IC-7300 for a 80 meter signal.  The downconverter puts out about 10 watts.  The antenna seems to be stable this season with no changes other than dipping it to resonance with the ferrite rod.

The confirmed state count as of Spring 2020 is up to 19 now.   WAS is a long haul project on 630 meters.

-0-

630 Meters

Authorization Letter

October 23, 2017

 

Dear Mark Edwards (W0QL),

We apologize for the delay, this notice is being provided to approve your proposed amateur radio station in the 472.0 – 479.0 band(s) at the following coordinates:  .   UTC has determined that your proposed amateur radio station would not operate within a horizontal distance of one kilometer from a transmission line that conducts a power line carrier (PLC) signal in the 472.0 – 479.0 bands. 

Please direct any questions to the undersigned.

Mike Etzel

Mike.Etzel@utc.org

202-833-6839

End of Letter

630 meters (and it’s partner, 2200 meters) were given official permission by the F.C.C. to operate as of October 16, 2017.  I hope to operate 630 meters with JT9 and WSPR (and maybe even FT8).  A process to register a station has been implemented to notify power companies of amateur operation.  Of course, W0QL filed an application immediately.  The FCC notice started off a long list of action items to get done before we can get on the air.  We made some quick decisions.

• Antenna:  Possibility one – The existing 6 meter antenna is mounted on a 39 foot aluminum mast.  That mast could be pressed into service right where it is as the vertical portion of an inverted L antenna.  The plan is to lay radials around the base of the vertical after cutting the weeds to make room.  A thin wire will run from the top of the mast over to the top of the 20 meter tower about 200 feet away.  Plans came from this article: http://www.wd8das.net/630mPractical.pdf
• Possibility 2 – There is an unused ground screen in place we could erect a vertical over.  It was used unsuccessfully for the 6BTV vertical.
• Possibility 3 – Use existing big vertical with a relay to switch from current operation to 630 meters.
• A variometer will be built to resonate and match.  The variometer is under construction using scrap pvc pipe.  Plans for the variometer came from http://www.g0mrf.com/variometer.htm.

• 
• Rig:  Possibility 1 – Luckily the existing Kenwood TS-480 receives down to the operating frequency for 630 meters, 474 kHz.  Antenna port 2 can be used leaving antenna port 1 in tact for the existing station.  A 630 meter downconverter has been built that provides 20 watts output from 1 watt input.  The TS-480 minimum power output is 5 watts so we will need an attenuator in the line when transmitting.  With a relay driven by the PTT line the attenuator can be bypassed for receiving.
• Possibility 2 -Also under consideration is the K3 because it can put out 1 watt and wouldn’t need an attenuator.
• Possibility 3 – The Yeasu FT-817 puts out a 1 watt or less signal in the 80 meter band that could drive the downconverter.  This arrangement has been bench tested and the output is 15 watts at 474.2kHz.  Perfect for a 10 per cent efficient antenna.  The FT-817 already has the necessary hardware interface and software running on a Intel Compute Stick from an earlier wspr project.  It can be diverted to 630m use.

In all cases possibility 3 seems most viable.

U.S. Amateurs will be allowed to run a maximum of 5 watts EIRP, which is about 1.6 watts ERP.  The short antenna will be inefficient relative to a full size dipole (991 feet long) and should keep us legal.  Radiation resistance is estimated to be .4 ohms and ground loss 6 ohms.  That gives us efficiency of 6.25 per cent.  Our 20 watt downconverter would radiate 1.375 watts erp and be compliant with the regulations.

The magnet wire arrived in the mail today.  This will become the winding for the variometer —  325 feet of 16 awg.

The coils are wound:

UNfortunately, the coil only measures 800 micro henries and we need 1900 according to the online calculator.  The eBay listing said the diameter of the wire is 0.0520″.  Two hundred turns would be about 10.4″. I might try it temporarily on the big vertical in Strasburg.

September 30, 2018 – Moved from the back burner to the front burner after a year hiatus.  A 630 meter antenna is in the air and matching is almost done.  A new rig capable of transceive on 630 meter is being broken in.

The transceiver is the Icom IC-7300 with a wide-band modification which has come out over the past year.

http://radioaficion.com/cms/ic-7300-wide-band-modification/

The mod enables transmitting on 630 meters at a power level of 30 watts.  An antenna with an efficiency of 5 per cent would put out an EIRP of 5 watts.  Five per cent is much easier to achieve than the 10 per cent we had been shooting for with the 15 watt converter.  Also fewer cables and fewer boxes to get working.  HRO offers to do the mod for $40.

Antenna consists of a vertical with a top hat and a loading coil at the base.  The top hat is a tee which is 50 feet long on each side.  The vertical is 36 feet tall.  Two radials are each a 50 feet long welded wired fencing laid on the ground.  Two more radials are 100 feet each. Thin white wire is used for the vertical and is very hard to see in this picture extending vertically from the white box.

The loading coil enclosure, radials, and the first few feet of the vertical can be seen in this pic.

This is the loading coil.  It’s modified from the variometer that was wound a year ago. The black plate holding the coil in place is the lid from a Cisco Kirkland candy container.  It fits the 4.25 ” coil diameter perfectly .

It was found that a ferrite rod inserted into the center of the coil changed the inductance as effectively as the variometer coil.  The rod is much easier mechanically.  It is mounted inside the coil using a P clip.  Tuning is accomplished by sliding the rod up and down, a lot like aligning the i.f. strip on a radio.  It doesn’t need to be centered.  Mounting it on one side of the form worked perfectly.

Measuring with the new RigExpert AA-55 antenna analyzer the rod could be adjusted for perfect resonance.

As one can see the swr is 2.7 which is unacceptable.  Multiple taps were made on the coil when it was wound.  Unfortunately the lowest tap is too high.  It was placed at 4 turns up from the bottom and reads 116 ohms.  Plans are to unwrap some of the turns from the bottom and re-resonate the system once 50 ohms is reached.  That should provide a 1:1 match.

Efficiency

To calculate efficiency the formulas of Phil Salas, AD5X, are used.

Rr = (Actual length ÷ ¼ wave length)squared x 36 ohms

Quarter wave length at 474.2 KHz =    234/.4742   =  493 ft

This vertical is 36 ft tall.

36 ft / 493 ft = .0795

.0795 squared  =  .0053

.0053 X 36 ohms   =  .19 ohms      Radiation resistance, Rr

Efficiency is 100 X Rr  /  (Rr + Rg)    where Rg is total loss in ohms ( mostly ground loss ) Assuming 10 ohms of ground loss:

.19 /  10.19   =  .0188  or approximately 2 per cent efficient.

30 watts in produces .56 watts out, ERP.    This should be well within the legal limits of 1.6 watts maximum, ERP.  We hope the ground loss is less than 10 ohms but we currently have no way to measure it. If we use the 6 ohms mentioned early on this is what we get.

.19/6.19    =   3 per cent        .03 X 30 =  .9 watts     (Still within FCC limits)

Meanwhile the new IC-7300 is burning in as well as a new Intel NUC computer.

Loading Coil update:  Removing some of the turns from the bottom worked but a 50 ohm tap for the coax could not be obtained.  It showed up a new problem.  Now the bottom tap is too low, 9 ohms.  Clipping onto the next tap up produces 160 ohms.  The taps are too far apart.  Restoring some turns to get the bottom tap up to 50 ohms did not work.  Each turn is too far from the 50 ohm sweet spot.  Time for a new plan.

New plan:  A coil form where every lower turn is accessible and can be tapped at quarter turn locations much like a B&W or Airdux coil.  A new form was crafted by drilling four holes near the bottom.  Instead of loops for the tap the holes will allow a clip to connect to the turns after scraping off the varnish insulation.  Here is the old style beside the new coil form, again made using good ole scrap sewer pipe (new, of course).

Fully wound and measured using a Banggood tester.  A Wavetek Meterman was also used to verify the readings.  The range is 390 uH to 470 uH by sliding the ferrite rod up and down.  Notice the rod extending from the top of the form, held by a p-clip.

The holes are visible at the bottom where a tap for the 50 ohm coax will go.

Next task is to put the coil in place at the antenna site and slide the rod to obtain a dip.  Then we’ll hunt for a 50 ohm tap point.

A goal is to get on the air with 630m, even if it’s a year late of the first day of operation, October 16, 2017.