Once in a while a little extra help is needed to obtain a contact with a DX station. That extra help can come in the form of a few more watts. When a difficult DX contact is completed we call that being deserving, as in, “We are among the deserving” (Where Do We Go Next, Martti Laine, OH2BH). Here is a photo of the new amp and my silly grin shows a combination of emotions. Sheepish for adding power to a weak signal mode but thrilled at the same time.
(Actually the emotion is more, “Can I get this damn cell phone to take a selfie”.)
Design contraints of a remote base off grid quickly narrow down the choices of linear amplifiers. The SGC SG-500 was the obvious choice because it changes bands automatically using rf sensing, runs the finals at 12 volts, and has a remote on/off switch ability. Luck was with us when we found this pristine SG-500 at a good price online at QRZ Swapmeet.
The amp can draw up to 90 amps. We rearranged the battery banks to dedicate one bank to the amp. Everything else is on the other bank. Testing showed up no problems except a tired SO239 coax connector. We escaped replacing that by using a PL259 with a slightly longer center pin so it would push against the solder cup at the back. Deferred maintainance. With 10 watts input the output is 150 watts with no complaints from anything else in the station. On to the first on-air test.
Wow, amazing, superlatives are not enough. Noticing a big pileup for a station with the call 3D0AY (Swaziland) I found a clear frequency and clicked the transmit button. Seven others were calling at the same time. With only four calls, on the 4th transmission he came back to me! Here is the proof.
As soon as Swaziland anwered my call another station jumped on our frequency. I found another clear spot and tried to complete the qso with Swaziland. He came back again and we completed the contact. Another station immediately jumped on the new frequency. A difficult qso but my station joined the deserving fraternity, thanks to the new amp. I’m hooked. I’ll be using this whenever a pileup is tough.
Sixty-five foot mast from DXEngineering completed today and looks amazingly vertical. Getting it up was like raising a wet noodle. Here’s what it looks like on the ground.
The secret is to never let the attachment point get below the bow point. Lift the upper sections first and keep them under upward pressure so a downward facing bow never forms.
When it’s all over it looks like the top picture. This will be the south support for a 40 meter dipole and possible for a 630 meter antenna.
Adding a tuner to the 20 meter yagi didn’t work out so well for 15 meters and 17 meters. Next trial is erecting end fed half wave verticals for those two bands today. We are using LNR PAR EF-17 and EF-15 antennas mounted on two fiberglass poles. Below is the 17 meter version.
Preliminary testing has been successful when compared with the yagi/tuner combination. We attempted to answer cq’s from Japan with the yagi on 17 meters to no avail. Switching to the end fed half wave produced an immediate qso with JN8QNF.
By adding a tuner to the 20 meter antenna system it is now possible to operate on 15 meters, 17 meters, and 30 meters in addition to 20 meters. The 20 meter yagi acts like a dipole on the new bands. No gain or much directivity but a dipole at 60 feet is a big improvement over the verticals that have been in use. The tuner is a LDG Electronics model RT-100 remote automatic tuner mounted in the shack. This is similiar to using the tuner in a transceiver except this has wider coverage. A conjugate match can be made anywhere along a transmission line. However, any time a tuner is located at other than the antenna feed point there is loss introduced in the form of coax loss due to swr and cable loss. This is an experiment to see how well the concept will actually work in practice.
Our installation consists of 160 feet of LMR 400 coax between the transmitter and the antenna feed point (100′ to the base of the tower and 60′ up the tower). If the tuner was moved to the base of the tower 100 feet of coax would be bypassed. For these calculations we use the KV5R.com web site. At 17 meters for example, total loss at 160 feet is 2.8dB (coax loss plus swr loss). For 25 watts out from the transmitter the antenna would receive 13 watts. Moving the tuner to the base of the tower would improve the loss to 1.2dB. The antenna would receive 19 watts. We ignored the loss in the 100 feet of coax from the transmitter to the tuner. That loss would be .5dB (or 3 watts in this example) with virtually no swr loss. Therefore the coax would deliver 22 watts to the input of the tuner and the antenna would receive 3 watts less.. With 1.2dB of loss the antenna was receiving 19 watts. Now it would receive 16 watts. In conclusion if we moved the tuner to the base of the tower the antenna would receive 3 watts more power or .5 dB (16 watts vs 13 watts). Is it worth moving the tuner to gain 3 watts (or .5 db)?
SWR Loss at 18.100 MHz
100′ LMR400 = 3 watts
Update: It seems to work on 17 meters. FT8 contacts with Europe have been made. For the next experiment it would be fun to try a better tuner, such as the MFJ 998RT, at the base of the tower. This tuner would have less loss plus allowing bypass mode and tuning a wider range. It is expensive and putting a up a second antenna might be less money.
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: 39⁰ N 35’ 40”, 104⁰ W 18’ 55.600000000000001”. 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.
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. Possibilit 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. 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.
Google Maps (maps.google.com) now has an updated aerial picture showing the Strasburg remote base. We’re official at last! Prominent in the picture is the shed and the solar panels. Faintly visible are the radials and the coax running to the vertical antenna. The tower was not up yet but the partially dug hole is visible.
- Is the beam pointing in the direction the rotor says it is? It was within 5 degrees which is good enough considering the antenna has a 30 degree beamwidth.
- Replace faulty power unit. Bit the bullet and bought a new Rig Runner 4005i to replace the one that had been damaged by a lightning surge in the summer. Moved the damaged one down the line to the radio and some peripherals. It still turns the power on and off; it just can’t read the voltage or current since the lightning surge.
- The Internet controlled interface to the solar controller can be reset over the Internet now. The Morningstar Sunsaver Duo and it’s remote, the EMC-1 sometimes locked up and couldn’t be read over the Internet. Installed are relays on the EMC-1 wiring to allow it to be reset remotely.
- Braided straps on the big vertical antenna should improve the rf path through the tuner to the ground radials. These straps replace the single 12 gauge wire we had been using. The tips of the straps are soldered to keep water from seeping into the connection.
5. Waterproof the tower legs sticking down into the concrete. Water in the legs from the summer rains was pumped out and expanding foam was squirted in. Water does not drain out the bottom like one would expect. On the last tower it took 10 years but the steel legs finally rusted through and had to be replaced. Hopefully this problem has been eliminated with the expanding foam sealant.
More loose ends: put up a sign on the east side targeting the easement, “Danger, 13,400 Volts”. Will that make some people keep their distance? Maybe.
checked and topped off battery fluid, labeled all equipment with i.p. Address and port number.