Dual frequency cards: one credential for an estate that is half upgraded

Almost nobody replaces an entire reader estate at once. Budgets arrive in phases, buildings are refurbished one at a time, and the result is the same everywhere: a site running two generations of reader, and staff carrying two credentials.

A dual frequency card is the standard answer, and it is routinely misunderstood as a compromise. It is not. It is two complete systems in one piece of PVC, each performing exactly as it would alone.

The misunderstanding costs real money, because it sends people looking for a converter that does not exist, or it makes them reject the card on the assumption that both halves will be degraded. Neither is the case. What a dual frequency card does is remove a logistics problem: one credential per person instead of two, one issuing process instead of two, one thing to lose instead of two. What it does not do is make either system better than it was.

This guide is for whoever has to specify one: an integrator, a distributor, or a facilities team halfway through a migration.

01. What is actually inside

Two inlays, two chips, two antennas, one laminated body. That is the whole idea, and the diagram is worth a minute because the two antennas look nothing like each other.

The two do not talk to each other, and neither knows the other exists. There is no shared memory, no shared identifier and no bridge. If you want the same number on both halves, that has to be written into both, separately.

Why the antennas look so different

At 125 kHz the card is coupled to the reader magnetically and needs a large loop with relatively few thick turns to build enough inductance. At 13.56 MHz the wavelength is far shorter, the coupling is different, and the tuned circuit wants many fine turns in a smaller area. That is not a styling choice; it falls straight out of the physics, and it is the reason the two antennas can share a card at all. A loop tuned for one band is close to invisible at the other.

02. What each reader sees

This matters operationally more than it sounds. It means no software change on either system, no migration of user records, and no window where a credential works on one system and not the other. You issue the new card, and both estates accept it from day one.

It also means the rollout can be done by whoever issues credentials rather than by whoever runs the systems. There is no coordinated cutover, no maintenance window and no rollback plan, because nothing on either side changes. In a live hotel or a hospital that difference is often what decides whether the project happens this year or next.

03. What it is not

It is not a converter

It does not translate a 125 kHz credential into a 13.56 MHz one. Both halves have to be enrolled in their own system, with their own identifier. If your access platform expects one record per person and one credential number, you will be creating two records, or one record with two credentials attached, depending on what the platform supports.

It is not a security upgrade

A dual frequency card carries the weaknesses of both halves. If the low frequency chip is an EM4200 that can be cloned in ten seconds, it can still be cloned in ten seconds, and the door it opens is still open. Dual frequency solves a logistics problem, not a security one, and the chip guide is where the security question gets answered.

This is worth stating explicitly in a proposal, because the opposite assumption is common. Putting a DESFire EV3 half on the same card as an EM4200 half does not raise the security of the estate to DESFire level. The estate is exactly as secure as its weakest enrolled credential, and that is the old half, for as long as it remains enrolled.

It is not a way to avoid deciding

It is a bridge with a lifetime. It should end at a planned point, when the last old reader comes out and the low frequency half is no longer enrolled anywhere.

Write down when the bridge ends

A dual frequency programme with no end date is a permanent commitment to the weaker of the two technologies, bought at the price of the stronger one.

04. The pairings we see most

One note on the first row. EM4200 is read only: it has a fixed factory number and nothing can be written to it, so if your old system expects specific numbers rather than whatever the card happens to carry, T5577 is the low frequency half you want, because it can be programmed to present the number the old system is expecting. That single distinction decides a surprising number of dual frequency specifications, and it is easier to settle before the order than after.

05. What it costs, and what it costs in tolerance

The price is the second inlay plus a tighter manufacturing tolerance. The tolerance is the interesting part. Two antennas in one 0.76 mm body have to be positioned so that neither detunes the other, and that placement is fixed in the inlay layout rather than adjusted afterwards.

The practical consequences for you are two. First, the inlay area is more crowded, so anything pressed into the card, embossing, a punched slot, hot foil, needs checking against the layout earlier than usual. Second, a dual frequency card is a poor candidate for a very thin body: below about 0.60 mm there is simply less room to keep the two inlays apart.

A third consequence shows up in artwork rather than in engineering. A punched slot at the short edge, which hotel guests expect on a lanyard card, sits very close to the low frequency loop. On a single frequency card there is room to move the loop; on a dual frequency card there is much less. Send the slot position with the artwork rather than adding it later, and the layout can be chosen around it. Adding it after the inlay is fixed usually means a new inlay and a new lead time.

06. Testing one properly

A dual frequency card doubles the test matrix, and the half that gets skipped is always the old one, because everybody is focused on the new system.

• Test both halves, on their own readers, before the full run.
• Test on the oldest reader in the estate, not the newest.
• Test both halves on the same card, in sequence, at each door type.
• Test at the edge of range, not just flat against the reader.
• Test a card from more than one carton, because inlay placement is where batch variation shows.

The full protocol for this, and why cards can pass at the encoder and fail on a door, is in the compatibility guide. The point about cartons is not pedantry: inlay placement is the variable that moves between production batches, and it is exactly the variable a dual frequency card is most sensitive to. Keeping later batches identical to the approved one is a separate discipline, and it matters more here than on a plain card.

07. Other bodies

Dual frequency is not limited to cards. A key fob can carry two inlays, and so can a wristband, which is often the better answer for staff on a site with two reader generations. Larger bodies have more room, so the tolerance question is easier than it is on a thin card.

For staff specifically, a fob is usually the better body regardless of frequency. It survives being carried on a keyring for years, where a card carried loose in a pocket does not, and a credential that lasts is both cheaper and less disruptive than one reissued twice a year.

08. Where Kaway fits

We manufacture for the trade and do not sell to your customers. Dual frequency combinations of the two bands are a standard product on RFID and NFC cards, laminated, printed and encoded on one floor.

Send the two reader or lock models the card has to work with and we confirm the pairing in writing before anything goes into production. Minimum order is 500 units, standard production thirteen calendar days from artwork approval to dispatch, and quotes come back the same working day. Where the request is qualified we will send a free sample of the exact pairing so it can be tested on the real doors before the order is placed. The rest of the commercial detail sits on the FAQ.

09. Frequently asked questions

Do the two chips interfere with each other?

No, when the inlay layout is done properly. They operate decades apart in frequency and are placed so neither detunes the other. That placement is the manufacturing skill involved.

Can both halves carry the same number?

They can carry the same number if you write it into both, but they will always have different factory UIDs. Any system matching on UID has to be told about both.

Is a dual frequency card thicker?

Not at the standard 0.76 mm. It becomes difficult below about 0.60 mm, which is where the two inlays start competing for the same space.

Does the read range change?

Each half reads at its own normal range. In a well laid out card the presence of the second inlay is not something a user notices.

What happens when we finish the migration?

You order single frequency cards for the new system and stop enrolling the old half. That is the point the bridge was built for, and it is worth putting a date on it at the start.

Can a dual frequency card also be printed and numbered like a normal card?

Yes. Full colour print, sequential numbering, barcodes and QR codes all behave as they would on a single frequency card. The variable data guide covers how those are produced and what has to be supplied.

Can you encode both halves at the factory?

Often, depending on the two systems involved. Some platforms will not release the keys or the number ranges needed, in which case the card ships blank and is encoded on site. The encoding guide sets out which route applies.

Is a triple frequency card possible?

Three inlays in one 0.76 mm body is not something we would recommend. Two is already a tolerance exercise; three tends to mean one of the three underperforms, and the usual answer is a second credential for the outlying system.