Using EMP-Hardened HF Ham Radio to Send/Receive E-Mail During Nationwide Outage- Part 1, by PrepperDoc

There are multiple possible scenarios that may result in a regional an/or national combined loss of Internet connectivity and cell/telephone service, during which you would probably wish to maintain communications to loved ones and others. EMP may destroy routers, cell towers, and power sources; solar coronal mass ejection (CME) may remove power from all communications systems; cyber warfare may have similar outcomes. Travel in some of these circumstances will be difficult, or dangerous to impossible.

Ham radio VHF/UHF repeaters may go down, due to power outages or EMP. Direct, point to point simplex VHF Ham radio will still work (even after an EMP, if hand-held radios were at all hardened or protected) over modest distances. Long range HF direct Ham radio communications will work (possibly after a delay of any EMP), presuming you had protection (if EMP) and have your own power. However, they will be of less usefulness if you haven’t established communications plans, frequencies, modes, and protocols with your loved ones. Without prior pre-arranged schedules, connecting directly with your intended recipient may take precious hours of transmissions, create immense interference to others, use precious power, and provide a very easy radio signature from your location.

It would be really nice to be able to reach people via asynchronous email, so that direct radio contact and simultaneous radio communications aren’t necessary. You’d prefer to connect to a server, digitally send your message, and have your intended recipient be able to do the same at times that are convenient to both of you. Such communications may allow you to set up direct communications (if desired), or pass crucial information or requests. If you are not familiar with Ham radio digital communications, this reference may help:[1].

The WINLINK system[2], which is available to all Ham radio operators, was designed over the last 20 years with this exact capability, and it currently serves ships at sea as well as anyone who has a communications need that requires radio contact. Their system is provided by volunteers and is free and reliable, though not without controversy, as some object to what they see as automated interference to their activities in the name of providing free email to “yachtsmen”. Critics do not recognize the catastrophic scenario benefit. WINLINK has the ability to do intelligent automated radio forwarding from server to server, completely independent of but similar to the Internet, and thus it provides a fairly comprehensive alternate communications system. Email attachments are allowed; in the event of national emergency, you might be able to attach encrypted material, which is not legal under current FCC regulations. This may not even be necessary, as the request/acknowledgment packet handshakes make it difficult for anyone but a very capable and well-funded foe to decipher your communications. Users specify to three “message pick up stations” (MPS) where their mail will be delivered and from which they can retrieve it. You might want to pick a couple within your geographic area and one that is totally out of your nation.


It is extremely likely that the WINLINK system will continue to operate in some form after most catastrophes. Their five central servers are distributed across multiple continents. Their volunteer RMS email-server high frequency Ham radio stations are located all over the world, and these stations function with different equipment of different vintages and manufacture. There is a very good chance that some of them will either be unaffected or have equipment that is impervious to the catastrophe, with some stations likely EMP-hardened. Since HF signals can easily span continents and oceans, you will have multiple options to make the necessary contacts. The flip side is that HF radio communications modems are relatively slow, compared to the broadband connections to which much of us are accustomed. Transfer speed is back to what you may remember from the old telephone modem days. However, for email, it works!

Getting Started

If you have (or can borrow for your initial learning curve) a newer, solid state HF Ham radio transceiver with digital frequency readout, you will have little trouble learning and using this system. After the initial setup of your equipment and software (follow the directions in the videos on the WINLINK site!), it will take you less than 30 minutes to have it all figured out. Many new solid-state Ham rigs include their own sound card that will work with RMS-EXPRESS and its embedded WINMOR software terminal node controller (TNC). However, If your rig doesn’t have a built-in sound card, you can a buy Signalink-USB, which works with any Windows computer that has a USB port. In either case, download the free RMS-EXPRESS software from their web site[3], carefully watch the videos on their web site to understand how to use the system and create a free account, and you should be good to go. You may want to do your configurations by going step-by-step through the videos, which lead you through the process. Note that you must USE your new account, via either TELNET or actual Ham radio contact, at least once every 400 days or it will lapse. You automatically get your own WINLINK email account, to which you can set size limitations so as not to overburden your downloading ability. The system resists spam wasting precious bandwidth by using “white lists” of email addresses allowed to send to you; until you send to THEM, they can’t send to you. Otherwise, it works just like any other email account and receives and sends regular Internet email.

Making It EMP-Hardened

Now let’s shift focus to the more important point of this article: getting older, EMP-resistant vacuum tube gear working well with the WINLINK system. The most vulnerable portion of your communications equipment is the part connected to long wires: the transceiver. It has an unavoidable connection to antennas, which may deliver thousands of volts and amperes for nanoseconds in the event of an EMP. Thus, we focus there primarily. The computer and other equipment is more easily protected. (We’ll discuss this later).

Although it is frequently claimed that you should not try digital Ham radio using an older vacuum tube transceiver, those are exactly the systems that will best survive the EMP scenario, and it turns out that once configured properly it really isn’t difficult at all to send and receive email via the WINLINK system using 40-50 year old vacuum tube single-sideband Ham radios. I use them routinely with 40+ year old Heathkit SB-102/101/100 and HW-101/100 style vacuum tube gear that is relatively immune to EMP with minor protection additions.[4] This article is designed to help you discover how to take advantage of these inexpensive, older and readily available Heathkit rigs, with their inherent hardening to EMP. Entire stations can often be obtained from eBay for $200-$300. The remainder of this article is predominately devoted to the review of each hurdle and how to overcome them.

Frequency Control

You must have a stable transmit/receive frequency. This can usually be achieved by letting your radio warm up for 20 minutes or so. You must be within 200 Hz of the correct frequency, and preferably within 100 Hz; otherwise, the automated RMS server station will not acknowledge your connection attempt. The “dial accuracy” of older vacuum tube gear cannot hope to meet that accuracy. There are at least three possible solutions to achieve this frequency accuracy:

  1. Easiest: Simply measure your transmit frequency using an accurate digital frequency counter. You can use FLDIGI or similar program to send a 1.5 kHz (upper side band) audio tone, and use a bit of wire as an antenna on your counter to measure your own transmit frequency, which should be adjusted to exactly the published “center frequency” of the RMS server you want to try to reach. You can even transmit into a dummy load for this purpose.
  2. Next easiest and quite slick: Purchase the DD-103 universal digital dial from Electronics Specialty Products.[5] Tap into the LMO output with a 15-20 picofarad capacitor to the cathode of V5A (first transmitter mixer), and route the signal to the DD-103 with some RG174 flexible coax. For EMP protection, I would recommend adding back-to-back signal diodes (1N914’s or anything similar) between center conductor and shield, to clip signals more than a volt or so. Use MOV protection as appropriate on the power supply voltages to the DD-103. Follow the instructions included with the product to accurately adjust its measurements.
  3. Least expensive but far more work: Build the Pacific Antenna DIGITAL DIAL from[6] kit, and use it to give your vacuum tube rig a digital dial. Beware, this kit is surface component mounted. You may wish to grind your soldering tip to 0.025” or so and obtain rosin core solder of that or more slender size. A “third-hand-held-magnifying glass” helps a lot. As above, a 15 pF capacitor from the cathode of V5A (first transmitter mixer) will give you plenty of the 5.0-5.5 MHz VFO signal for your Digital Dial input; use coaxial RG174 cable to get the signal to the Digital Dial. Just as with the DD-103 above, protect the DIGITAL DIAL from EMP by adding back-to-back 1N914 diodes between its input RF signal and ground as input clippers, by providing it with metal-oxide-varistor 20V clipping on its 12V power input, and by mounting it in a metal case. After adjusting your Heathkit’s crystal calibrator by beating against WWV (using a 2nd receiver), you can tune to exactly the bottom of a frequency band (e.g, 3.5, 7, or 14 MHz), memorize the VFO frequency within the DIGITAL DIAL, then choose the third option to subtract, and the counter will read just like a digital dial. The Heathkit HW- and SB- series used a reverse direction VFO that was 5.5 MHz at the bottom of a band and 5.0 at the top; the Digital Dial kit allows to subtract the current measurement from the memorized VFO frequency, making the reading correct.




[3]RMS-EXPRESS client software for Windows:

[4]See for example, and

[5]Digital Dial,

[6]Universal Digital Dial,