RMRL Cross Band Repeater

The Rocky Mountain Radio League's cross band repeater was built by Bob Schellhorn [N�TI], Glenn Casino [WN�EHE] and Bob Ragain [WB4ETT]. For some close up pictures of the interior of the machine click here.

Click HERE for the schematic.


  • Input Frequency 445.975 MHz.

  • Output Frequency 147.555 MHz

Repeater ID:

The repeater identifies itself with a Morse Code beacon every 8 minutes. Periodically a robot voice announces the identification and also notes the input and output frequencies of the repeater.


The cross band repeater has a GPS/APRS system on board. Go to the APRS Formats Page to see what this string looks like.

Every 60 seconds during normal flight an APRS position packet will be transmitted. During descent, when the payload approaches the ground, the APRS beacons increase in frequency to approximately once every 10 seconds.

Please, turn off any beacons you may have running on packet if you are listening to the receive frequency. They will only interfere with other stations in your area attempting to log the APRS data.

Do NOT attempt to DIGI through the cross band repeater. It is not a true packet station. There is NO mailbox, no digi, no gate associated with the callsign of the APRS packet data.

Often the signal from this payload is received by a station in the Denver area and retransmitted into the National APRS system. If that is the case, we may appear nationwide either via 30 meter gates (10.151 MHz LSB) or perhaps internet gates (www.aprs.net).

Signal Idiosyncrasies:

The Repeater uses vertically polarized antennae for both receive and transmit. However, the payload string is usually swinging back and forth, thus altering the polarity significantly. The balloon also tends to rotate spinning the antennae about their vertical axis. All this motion tends to create a signal that fluctuates quite a bit on both input and output. This fluctuation is most pronounced while the balloon is transitioning between "layers" of the atmosphere where different wind conditions exist. 

A circularly polarized antenna would offer the best opportunity for strong signal reception and transmission from a ground station. However, we have noted that most stations can make good contacts through this type of disturbance with standard vertically polarized antennae.

When the balloon bursts, or a payload is cut away from the balloon, the payloads tumble around quite a bit and the signal quality becomes extremely erratic. If you hear a relatively constant signal with periodic variations in strength and suddenly the signal starts fluctuating wildly, you are probably "witnessing" a burst or cut down event. Within a minute or two, the parachute will begin to provide enough drag to force the payload train into a more orderly vertical orientation. Signals will then more closely resemble those received during ascent. However, there is always much more fluctuation during descent. 

Voice Operations:

There are no CTCSS tone blocks on the repeater. Just transmit on 445.975 MHz and you should hear yourself coming back down on the output frequency of 147.555 MHz. Remember to use headphones or control the receive volume in order to eliminate feedback on your transmission.

Depending on conditions, the repeater may be operated under various limitations set by a net control operator.

The most common operating mode is a directed net where all stations are invited and encouraged to check in and participate. 

When you hear a break in the net, call net control and give your callsign, name, city and state of your location. If you live in a small town that the net control station might not recognize, you might instead check in and state your location as 25 miles south west of a well known city in your area. That way net control will be aware of your location. The net control operator will acknowledge stations checking in. He or she will attempt to facilitate long distance QSOs by making suggestions on who should try and contact whom.

If you hear a very distant station and wish to make a contact with them, do not hesitate to ask net control for permission to make the call. While net control will attempt to put together long distance QSOs, he or she may miss an excellent possibility that you are aware of. 

Try and defer to stations out on the border of the footprint. Granted, if you live in Denver and hear someone in Pierre, SD it's a long contact for you. But, someone else (say in Albuquerque, New Mexico) would be in a better position for a really long range QSO. See the Window of Opportunity section below for more info on how the footprint expands over time.

If traffic is minimal, a net control operator might open things up a bit allowing stations to freely use the repeater. However there is ALWAYS a net control station who may at any time step in and assume control of the frequency.

Why not just let the repeater be open at all times?

Two reasons. 

  1. We like to try and put together long range QSOs. A net control operator will be most aware of the geographical "condition" of the net, and may be the best facilitator of this type of contact.

  2. At times, the repeater is closed to all traffic with the exception of the tracking and recovery teams.

Occasionally, the only repeater coverage a recovery team has is the cross band repeater. In that event, the frequency is turned over to them to coordinate the recovery operation. This happens infrequently, as most of our flight land somewhere within repeater coverage of the front range of Colorado. But, should the balloon dash out too far to the east and outrun repeater coverage, the balloon is the recovery team's best means of coordination.

A typical EOSS balloon will ascend at a rate of approximately 1100 feet per minute to around 95,000 feet.

At this rate of ascent, 22 minutes into the flight the balloon will be at an altitude of 30,000 feet above sea level and the footprint will have a radius of approximately 205 miles. Remember, we launch at around 5,000 ASL.

Footprint at 30,000 ft. ASL

For all footprint shots
light green = good packet, excellent voice
red = boundary beyond which received signal is less than 0.4 uV

50 minutes into the flight the balloon will be at an altitude of 60,000 feet above sea level and the footprint will have a radius of 310 miles.

Footprint at 60,000 ft. ASL

From this altitude it will take approximately 32 minutes to reach an altitude of 95,000 feet above sea level (82 minutes into the flight). Most of our flights will ascend to that height. At that altitude the foot print of the cross band repeater will be approximately 399 miles in radius. 

Footprint at 95,000 ft. ASL
Propagation Software -
Radio Mobile
Map Overlay - MapBlast

You should be in no great hurry to make contacts while the balloon is below 80,000 feet. There will be ample opportunities to jump in and get net control's attention.

However, once the balloon rises above 80,000 feet the likelihood of a balloon burst becomes significantly greater. Therefore, as good operating practice, we suggest that only really distant stations check into the net and request contacts at this point. Remember, the footprint is constantly growing. A station at the extreme edge of the footprint may not even hear the balloon until, literally, the last minute of ascent. Offering deference to those distant stations would be appreciated. 

Here is an example of how a net control station can be very helpful. In the above map, Pierre, SD would check in sometime within the last few minutes of the flight. Then at the very last minute, Albuquerque, NM would check in (assuming they found a high/hot spot). Net control would, hopefully, recognize this excellent opportunity for a really long distance QSO and tell Albuquerque to call Pierre. It takes Net Control to put this together because Albuquerque never heard the repeater or Pierre's check in since that event happened just prior to Albuquerque's reception of the repeater's signal. Of course, if Net Control misses this opportunity, hopefully Pierre will see the possibilities and request the QSO. If closer in stations are keeping clear of the repeater during the last few minutes of ascent this contact is much more likely to happen.

Try and be aware of your distance to all the stations checking into the net. In the above example, Albuquerque might not check in. Perhaps you are located in Pueblo, CO. You might be the station with the best chance for the maximum distance QSO during a flight by calling Pierre. But, with a lot of Colorado stations checked in, the Net Control might not pick up on this fact. In that case, you should try to get permission to make the contact. Just be sure to allow air time for more distant stations to check in. It's all a judgment call on your part. If you can make a contact of over 400 miles, you should elevate your own priority in your calculations and go for it.

Once the balloon bursts and falls below 80,000 feet net control will once again accept any contact requests. We've had our chance at long distance QSOs and now it's time to just have some fun.

The rate of ascent is a relatively constant factor. However, descent is entirely different. The only brake on descent speed is the parachute. And the parachute works against the surrounding air. And, obviously, the atmosphere is much less dense at high altitude. Therefore, the balloon begins its descent at a very high rate of speed. As the balloon moves into denser air, it continually slows its descent rate. 

  • At 100,000 feet altitude the descent rate is around 12,000 feet per minute

  • At 60,000 feet around 4600 feet per minute

  • At 45,000 feet around 3200 feet per minute

And so, stations on the fringes of the footprint will rapidly lose the signal.

Also, since the Tracking and Recovery teams usually don't need the repeater until the last stages of the flight (below 45,000 feet) they may not need to commandeer the system until most of the distant stations have already fallen out of coverage.

Propagation models for each altitude based on the location:

  • Last Chance, Colorado

    • 39� 44.402' N

    • 103� 35.606' W

This is a generic location used as an example. Actual flights will reach max altitude somewhere else and usually there will be a propagation chart on the Flight Announcement page based on the prediction for that flight.

QSL Cards Exchanged between Contact Stations:

Balloon borne repeaters are an excellent opportunity to do some "DX" work in the VHF/UHF realm of amateur radio. 

You should try and exchange QSL cards with really distant stations. Who knows, you might even make it into the record books. The current record (as of 25/Feb/2004) as posted on the Amateur High Altitude Ballooning Mission Records page is 647 miles. What do you know, it's held by our arch-nemesis ANSR. :-) Here's a cut from that page.

Greatest Two-Way QSO Repeating/Transponding Great Circle Distance
Typical QSL card proof of standard minimum QSO (calls, signal reports and acknowledgements) required.
Coordinates of both stations required for great circle calculations.
(Modes: EBE Earth-Balloon-Earth, EBBE Earth-Balloon-Balloon-Earth, etc.)






































It should be still be possible to beat this one. In the example above regarding a hypothetical contact between Pierre, SD and Albuquerque, NM the distance between stations is approximately 725 statute miles. 

DO NOT exchange address information during a QSO made through the repeater. Time may be short and a lengthily exchange of addresses might cause others to miss their opportunity to make a contact. 

Try and determine if either or both stations have their address information current with the FCC database. That way, you can just confirm that info and know you have a good address. You can easily get their address by going to one of the call sign servers on the Web. I'd recommend the QRZ database (www.qrz.com) or Buckmaster's site.

If only one station is current with the FCC then, the other station should take it upon themselves to initiate the QSL card exchange by sending their card to the station with the good address, including their current address for the reply QSL card.

ONE EXCEPTION, you can exchange an email address ONLY if it is one that goes through a REALLY WELL KNOWN reflector such as the ARRL.NET or AMSAT.ORG sites. Those exchanges should go quickly as all the individual need know about you is your call sign and which reflector you use. Don't try and send a unique email address though as that will undoubtedly require lots of phonetics and bog down the net. 

I am going to suggest that EOSS act as a QSL bureau for future flights. If we do take on that responsibility, the exchange of cards may be facilitated. Look for announcements here (on this page) or on the flight announcement page for the availability of a Bureau service on future flights. This will depend on recruitment of a Bureau manager. If you would like that job, contact one of the officers of EOSS at their email address.

The Record Books

EOSS would really like to get into the record books with a long distance QSO through our repeater. To that end I've created an email list on YahooGroups to help in scheduling contacts through the repeater prior to a flight. Here's how it works.

First, join the group. It is open to all. And, notice, it's not group specific. ALL GROUPS are encouraged to use this announcement list to post their upcoming flight notices.

Subscribe to Balloon_Sked
Powered by groups.yahoo.com

Next, look at the footprint (above) and determine if you will be able to communicate through the repeater. 

If you can, then, send an email to the rest of the Balloon_Sked members letting them know you plan to be on the air and your location. In the subject of the message mention the flight name, your location and availability. Something like "EOSS-46, Parker, CO will be active". Also, you might visit the web site to see if anyone has left a message detailing their availability prior to your joining the list. EGroups archives all past messages so they should be easy to find. Easier still if you remember to follow that subject suggestion above, as it will make finding potential contacts easier when searching through past messages.

When you find someone planning to be active on the repeater who is especially distant from you, send them a direct email planning a QSO. 

This list was previously hosted by eGroups. All those addresses will continue to work, however if you wish to visit the web page, you will need to register on Yahoo and convert your eGroup accounts. It took me about 5 minutes ... no problem.

EOSS Special Event QSL Cards:

Occasionally EOSS will produce a QSL card for a particular flight.

Check the QSL page for information about any upcoming or recent flight's QSL information. A link to this page should appear on the Flight Announcement.

An example of one of these cards is linked to the flight recap for EOSS-45.

Whether or not EOSS will be generating a QSL card of our own, we always appreciate receiving cards from folks who use the cross band repeater. 

Regardless of which policy (outlined below) we intend to follow, if EOSS is planning to send out cards, we would appreciate it if folks send in their card along with a stamped self-addressed envelope to facilitate sending our card to you. This is especially important if your address is NOT current with the FCC.

The determination on how QSLing will be conducted for a particular flight will usually depend on the number of stations that check into the cross band repeater net. The policy of how we plan to send out QSL cards will be posted on the Flight Recap Page for that individual flight, once we know ourselves just how many folks will be expecting cards.

If a very limited number of stations check in, EOSS may foot the bill and send out QSL cards to all stations who check in. These cards will be sent to the address as listed in the current FCC database for a each amateur radio operator's callsign. We will wait approximately 30 days before sending out any cards. By doing so, we can allow for folks whose addresses are not up to date, time to submit their cards and return envelops to us in order to ensure they receive cards.

When a flight generates a large list of checked in stations, we encourage those stations to send a QSL card of their own to EOSS along with a self- addressed stamped return envelope to:

Edge of Space Sciences, Inc.
4633 W. Tufts Circle
Denver, Colorado  80236

Place "QSL REQUEST" in the upper left corner (above your return address) of the envelope you send. That way your request can be quickly segregated and forwarded on to the individual who is responsible for QSL cards for that flight.

If you are not an amateur radio operator, but have monitored one of our flights via a scanner and wish to receive an "SWL" card, follow the above procedure, mention some of the traffic you heard (so we can verify you actually heard the repeater) and we'll send you a card.

Ballistic Descent Rate

On a recent flight the repeater separated from the fight string. Running various simulations the closest descent rate prediction to actual landing location yielded a rate of 3000 fpm sea level descent speed.