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903MHz Transverter Club Project |
The objective is to purchase complete 903MHz transverter kits described as #903-144CK, from Down East Microwave, as shown on the DEM website at http://www.downeastmicrowave.com/Catalog.htm.
This kit will include a 144MHz to 903MHz transverter outputting either 10mW or approximately 10 watts and with a receive noise figure better (less) than 1.5dBNF. The transverter will not need a sequencer and will accept up to 10 w of drive from the IF radio (as per DEM documentation). The transverter will be complete with case and ALL hardware (if that is the kit you choose), but will be a KIT with full instructions, requiring assembly. VE3CVG will be available to assist with assembly.
We are considering a 1 day construction workshop at VE3XK's place, as he has an excellent facility for group kit building.
You may choose either a 144MHz or 28MHz IF - same price.
At this time it is our understanding that the IF and RF switching are included for this model, however there is some ambiguity with respect to the RF switching when the 10w module is installed (as we are ordering it). If RF and IF switching is included, the project is more attractive, since no costly external relays are required.
Participants are free to consider a kit without the 10w module. This would mean that their transverter has 10mW output which is still adequate for Ottawa area QSO's. The club 900MHz class C amps, which you may already have, can be used, as these will work fine for CW. If a participant goes this route, the cost of their transverter will drop by about $125 CDN.
Project contact - Rick (VE3CVG)
The only issues discovered to date revolve around whether we should purchase a 902MHz kit or a 903MHz kit.
This may seem obvious but .... if you buy a 902MHz unit, and assuming a 2m IF, 144.1MHz on the IF will correspond to 902.1MHz operating frequency, and you will probably be able to tune 902MHz to 906MHz. If you buy the 903MHz unit, 144.1MHz on the IF will correspond to 903.1MHz operating frequency, and you will be able to tune 903 to 907MHz.
The Canadian 900MHz band currently covers 902MHz to 928MHz and the generally accepted SSB/CW calling frequency is 903.1MHz. The FM calling frequency is 904.5MHz simplex. The repeater input frequencies are 907MHz to 910MHz and the repeater outputs are on 919MHz to 922MHz. Most of this is probably not cast in stone.
The first issue is that the band starts at 902MHz, and there are some digital modes, EME, and beacons operating in the 1MHz portion 902MHz to 903MHz. If you get the 903MHz unit and use an IF radio which will not operate below 144.0MHz, you will not be able to tune down to the band edge. You probably will not be missing much but this may be important to you .... so keep this in mind.
The second issue .... if you use the same IF radio for multiple bands, it is desirable (but not mandatory) that 144.1 MHz on the IF corresponds to the calling frequency on all the bands that the radio is used as the IF. For example, if the same IF radio is used for both the 33cm and 23cm band, then it would be "nice" if both 1296.100MHz and 903.1MHz both fell on 144.100MHz on the IF. This saves considerable dial spinning or memory channel activity when "running the bands" during a contest.
If your IF radio transmits and receives in the segment 143MHz to 144MHz, the entire matter may be a non-issue for you, because you can tune the operating frequency to 902.0MHz, even if you buy a 903MHz transverter.
A related third issue is that many IF radios for transverters can experience leak-through on their IF frequency. That means that if you are operating on 903.2MHz using your 903 transverter and there is another powerful station nearby operating on 144.200MHz you may mistake the signal on 144.200 to be on 903.2MHz. This should not happen because the coax cable between the transverter and the IF rig should provide adequate shielding, and also in theory the IF radio does not have a 2m antenna connected ..... but it DOES happen and it can be very confusing to everyone. Also beware of APRS stations operating on 144.39MHz. A 902 transverter may be slightly less likely to have interference because the calling frequency (and main operating area) corresponds to 145.1MHz. However, 2m FM repeaters may be a problem at that frequency.
Greetings All.
What a fine group. We should have some fun opening up the band in this area, and fun getting everyone's transverter going too..
As Rick has mentioned, I prefer the 902 to 906 MHz range for my transverter, as opposed to 903 to 907, putting 903.1 at 145.1 MHz on my IF rig. My reason is that I want to have access to the range 902 to 903. I believe that there may be (now or in future here) some interesting activity in this first MHz of the band. Please see the 'However' below.
It is my opinion that the lowest part of the band should be essentially for weak signal work. What do we find in the current RAC bandplan? RTTY? Packet? !! The balance of the RAC plan seems rather detailed and complicated, especially for the foreseeable level of band activity. The ARRL plan on the other hand is pretty straightforward, although it has limitations that need to be addressed. Someone needs to get off their butt and do something about the RAC plan to harmonize to a greater degree with the US plan. OOPS!! That's me !! Darn.
For your perusal, the two plans are at the bottom of this message. Please note that in the US plan the primary weak signal calling frequency is 902.1, not 903.1 MHz.
I can understand Rick's preference to have all his transverters come out on 144.1 on his IF radio. Why though are we deciding on 903.1 rather than 902.1 as our prime weak signal calling frequency? The chance that Rochester might be listening and hear us on a regular basis is pretty thin, I think. During contests and tropo openings it would be easy to slip up and work them from 903.1 MHz at 145.1 on the IF. Anyhow, I hate to lose access to 902 to 903. 902.1 seems more pure to me for CW/SSB calling.
However ---- I also want (need) to be able to tune on a channel used by the Linx modules. The beacon is on 903.37. The next frequency available on the modules is 906.370. Channels above that are all above 907 MHz. My desire for simplicity in my life is .......! As usual.
I have to conclude that there is no simple answer for me. So, .... I have decided to buy crystals for both ranges. Thereby I can put off the absolute choice for the moment. I am hoping that I may be able to use a socket and switch crystals when I need to do so.
I would be interested to hear what others think about the choice between the 902 range versus the 903 range for our local net and weak signal activity.
ARRL Bandplan
- 902.0-903.0 Narrow-bandwidth, weak-signal communications
- 902.0-902.8 SSTV, FAX, ACSSB, experimental
- 902.1 Weak-signal calling frequency
- 902.8-903.0 Reserved for EME, CW expansion
- 903.1 Alternate calling frequency
- 903.0-906.0 Digital communications
- 906-909 FM repeater inputs
- 909-915 ATV
- 915-918 Digital communications
- 918-921 FM repeater outputs
- 921-927 ATV
- 927-928 FM simplex and links
Current RAC Bandplan
- 902.0 - 902.5 PACKET (<=2400 B, 25 kHz CH)
- 902.5 - 902.8 TTY, PACKET (<= 2400 B, <=2.5 kHz BW)
- 902.8 - 902.9 PACKET (<= 2.5 kHz BW), TTY, CW, EME
- 902.9 - 903.1 CW; EME
- 903.100 NATIONAL CW/SSB DX CALLING FREQUENCY
- 903.1 - 903.2 CW, SSB, EME
- 903.200 NATIONAL SSB CALLING FREQUENCY LOCAL
- 903.2 - 903.3 SSB, SSTV, FAX, PACKET (BW <=2.5 kHz) AM , AMTOR
- 903.3 - 903.32 PROPAGATION BEACON NETWORK
- 903.32 - 903.4 GENERAL PROPAGATION BEACONS
- 903.4 - 903.5 SSB, SSTV, ACSSB, FAX, PACKET (BW <=2.5 kHz), AM, AMTOR, EXPERIMENTAL (BW <= 2.5 kHz)
- 903.5 - 903.7 CROSSBAND LINEAR TRANSLATOR INPUTS
- 903.7 - 903.9 CROSSBAND LINEAR TRANSLATOR OUTPUTS
- 903.9 - 904.0 EXPERIMENTAL BEACONS
- 904.0 - 904.3 CONTROL AND AUXILIARY LINKS
- 904.3 - 904.5 FM SIMPLEX (25 kHz CHANNELING)
- 904.500 NATIONAL FM CALLING FREQUENCY
- 904.5 - 905.0 FM SIMPLEX (25 kHz CHANNELING)
- 905.0 - 907.0 HIGH RATE DATA (>=4800 B, DUPLEX)
- 907.0 - 910.0 FM REPEATER INPUTS (25 kHz CHANNELING)
- 910.0 - 916.0 FAST SCAN TV (SIMPLEX OR REPEATER OUTPUT, PAIRED WITH 922.0 928.0 AND 439.0 444.0 MHz)
- 916.0 - 916.5 PACKET (<= 2400 B, 25 kHz CHANNELING)
- 916.5 - 919.0 HIGH RATE DATA (>=4800 B , DUPLEX)
- 919.0 - 922.0 FM REPEATER OUTPUTS ( 25 kHz CHANNELING)
- 922.0 - 928.0 FAST SCAN TV SIMPLEX OR REPEATER INPUT, SPREAD SPECTRUM, EXPERIMENTAL MODES
73 again
VE3BYT
Gents, I spoke to Steve (N2CEI) at Down East Microwave Inc. this afternoon and asked our questions. Steve is one of the principles in DEMI. Here is what I learned:
- Does the 10w version of the transverter require an outboard relay? Answer - No outboard relays are required for the 10w version - it is complete except for antenna, IF radio and cable.
- Any thoughts about 902 vs 903? Answer - Either unit will work fine. They are identical in every way except the LO crystal. Filters are 20MHz wide so no re-tuning needed for either 902 or 903.
- Any thoughts about crystal switching? Answer - Not recommended because of built-in heater and LO cover, etc. It is possible to construct the unit designed for an outboard LO but this would be a deviation from the basic kit.
- Any chance of a deeper discount? Answer - At least 12.5% possibly more. Determined at time of order. Free shipping.
- Does discount apply to entire order - i.e. other parts, MMICs, crystals, etc? Answer - Yes discount applies to everything except parts identified in policy statement, as on the web pages.
- Availability? Answer - 3 to 4 weeks ARO for 8 units, +/- a week.
Please decide which unit you want and be prepared to discuss/let me know on the evening of March 1.
An order for 8 units was submitted to DEMI by Fax on Friday afternoon to get final firm pricing etc. Rick expects to talk to DEMI on Monday to confirm pricing and payment arrangements.
On Thursday March 10, I finally spoke with Sandra at Down East Microwave and after exchanging information we arrived a the firm price as expected. Unfortunately delivery is 4-5 weeks from now. A bank draft in US funds was forwarded to DEMI on March 11, 2005.
On Tuesday April 19th, I received an email from Sandra at Down East Microwave, indicating that our order would be shipped by April 20th. So now we wait anxiously. With luck we can get these built in time for the June contest, or sooner.
This morning I was contacted by the border brokers requiring some paper work, which I supplied. We will be charged brokerage of about $62USD and also will have to pay some duty because some DEMI parts (external to kits) were manufactured outside North America. Double and triple taxation at its finest. The really good news is that our stuff is in transit.
The transverters were delivered to VE3CVG's QTH on May 2. VE3CVG delivered the transverters to their owners on 3 May. The transverters look really great. Top quality. Working from the parts placement drawing will be a challenge.
VE3CVG: I've almost completed my 903-144 transverter but have some questions that I need help with before I power up:
- C30 and C33 are marked as optional but it is not explained why and it is not immediately obvious to me. I am building the 903MHz 10w version with common IF and common antenna out. PTT is dry switching to ground. SO .... do I install C30 and C33? Why are they shown as an option?
DEMI:
- C74, R41 and IC11 are installed when using the optional TX gain stage
- C30, R18 and IC5 are installed when using the optional RX gain stage
- C33 and L12 are installed if you will be keying the transverter through the coax (PTT - H on coax)
VE3CVG: L2 is supposed to be a small moulded body choke with colouring brown/red. DEMI have supplied a small bodied choke but it is brown/black ..... same colour code as the larger moulded choke L12. I am hoping that the small bodied choke is really .1uH, in spite of markings. Comments?
DEMI: The colours of the 0.10uH choke where marked incorrectly. L2 should be the smallest body choke in the bag, green in colour with brown/black markings.
VE3CVG: C21 18p does not seem to exist on the board pictorial. Where does it go?
DEMI: C21 is only used in the 28MHz version and should not have been listed in the 144MHz version.
My transverter is completed. It tunes up a couple of kHz low and output is 8w. I will revisit later to see if I can eke out another watt or 2 but am satisfied with it as it is. The Rx is very sensitive. -120dBm produces an S4 signal on FM.
Almost all readings are within spec and those that are off, are just slightly off - the manual says this can happen due to part variation.
You only need a watt meter/dummy load, frequency counter, digital (high impedance) multimeter, your IF radio, and a power supply to tune up the transverter. A signal generator helps with the RX side. DO NOT try to use a wall wart for this transverter, it needs a regulated 13.8VDC supply @3A as used for many radios.
First a tip on building the crystal/heater assembly. DO THIS before you mount the crystal for the first time. But you don't need to connect the heater until told to do so in the manual.
- set the crystal on your work area.
- take the heater, which looks like an old fashioned surge suppressor about 1/4" d.
- apply lots of heat to either wire and the solder will melt and the lead will come off (use needle nose or you will be branded for life)
- tin the centre of one side of the crystal - no big lumps but some extra solder
- set the heater unit on the tinned area of the crystal, with the remaining wire on the heater on the upper (outer) surface and extending over the end of the crystal opposite the connection wires and apply heat by laying your soldering iron on the heater.
- when it gets hot enough, the solder will melt and the heater will settle down onto the crystal can.
- keep it immobile and allow to cool off - and you have made your heated crystal.
- solder a piece of clipped tinned lead wire to a ground point on the board, very near the crystal, but so that it will NOT interfere with the can when it is placed over the oscillator. When the crystal is mounted as per the instructions, solder this wire onto the crystal can. This completes the dc circuit for the heater.
- ALWAYS turn off the power at the supply when working on this transverter, to be safe.
NOTE: this heater, when it is operating, AND the 9v regulator run very warm inside the oscillator can.
BEWARE - I wasn't getting much more than 5w out and it had me scratching my head for a minute or 2. The problem turned out to be that I was using some RG8 and a handful of adapters to connect to the N type antenna connector. I replaced that with a piece of LMR400 without adapters and the reading jumped to 8w.
Here is what worked well for me: With your IF radio connected and in RX and no signal coming in, but the transverter on, and in FM, you should hear the noise level coming from the transverter. I had about S8 or more of noise. Adjust R14 until the S meter just stops displaying an S meter reading. Now any signal that you hear, should be above the noise and should result in an S meter reading.
Well, we have 4 transverters built at this time, VE3XK, VA3KA, VA3NFA and VE3CVG. VE3BYT, VA3WK, VE3XZT, VE3ZRK have all started construction.
The transverters put out about 8w when powered by 12VDC and this goes up over 10w when powered by 13.8VDC. So it is quite voltage sensitive. In most cases, until the problem with the crystal oscillator frequency is resolved, some of the crystal heaters have been left unconnected. This is to be discussed with DEMI.
Ken and Rick have heard each other. Ken heard Rick's CW and Rick heard Ken give calls on USB. However at the time of the test, Rick's antenna was fixed, pointing at Rochester so it is way off the proper heading. Rick's antenna work scheduled for June 9 should solve this.
Friday evening June 10th, 2005 between 2100 and 2200hrs (local) we had some excitement on 903MHz in this area, for the first time in history, I think: Ken (VA3KA) and I (VE3CVG) completed a two way Q5 contact on 903.1MHz at a distance of over 60km. This was followed by a contact between Ken and Doug (VE3XK), and then a contact between Ken and Tom (VA3NFA).
For those of you who are not aware, Tom, Ken, Doug and I tried our 903 transverters during the contest. We all had great success and contacts were made with FN14, FN24, FN25, and FN15 with the VE3WCC rover team. Ken and I were also successful in working N2PA in FN12 and also Ken worked W2SZ in FN32. I think Ken worked more than that but I'm not sure which grids.
Ken was using a full size 903MHz looper (at 60' I believe), Tom was using a 903MHz cheap yagi on a short mast (for roving), and Doug and I used 9 element broad yagis (see my web pages). Doug's was at ground level, about 6 feet and mine was at 50'.
What excitement! You should have heard Tom when he hooked up with me for the first time in FN24. You should have heard me, for that matter. So ..... obviously these transverters work well and have very good sensitivity.
The problems that we encountered:
- All units need to have the oscillator drift resolved and the frequency needs to be set. I spoke with Steve at DEMI this afternoon. Here were his suggestions:
It is remotely possible that the crystals are off frequency but doubtful that they are all off.
Activate the crystal heater on all units. The heater is a thermistor with a positive coefficient. The resistance increases as the device approaches 50C. Set the oscillator by first peaking for voltage. This should be very close to correct freq (say within a couple of kHz). If unit does not oscillate in the correct area, do the series capacitance mod - cut the trace to the crystal and solder a cap in series (across the cut). The supplied cap is 10pF but Steve feels that is too large. Try 5pF instead. Note: that the voltage peak should not change much, if at all, between a cold crystal and a hot crystal.
- The rover seemed to drift down in frequency considerably during a contact. This should not happen if everything is working properly.
- Power output varies considerably with battery voltage. Yes - this is normal. These modules are quite resilient right up to 17v or more. Running at 15w should not hurt them and they will maintain linearity. If they will be run from 12v all the time (like a rover), the PA module can be re-biased to substantially increase power out.
Also note that the transverters should be adjusted to work with their respective transceivers, specially the noise gain.
This project is considered COMPLETE.